Scholarly article on topic 'Review on recent progress of nanostructured anode materials for Li-ion batteries'

Review on recent progress of nanostructured anode materials for Li-ion batteries Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — Subrahmanyam Goriparti, Ermanno Miele, Francesco De Angelis, Enzo Di Fabrizio, Remo Proietti Zaccaria, et al.

Abstract This review highlights the recent research advances in active nanostructured anode materials for the next generation of Li-ion batteries (LIBs). In fact, in order to address both energy and power demands of secondary LIBs for future energy storage applications, it is required the development of innovative kinds of electrodes. Nanostructured materials based on carbon, metal/semiconductor, metal oxides and metal phosphides/nitrides/sulfides show a variety of admirable properties for LIBs applications such as high surface area, low diffusion distance, high electrical and ionic conductivity. Therefore, nanosized active materials are extremely promising for bridging the gap towards the realization of the next generation of LIBs with high reversible capacities, increased power capability, long cycling stability and free from safety concerns. In this review, anode materials are classified, depending on their electrochemical reaction with lithium, into three groups: intercalation/de-intercalation, alloy/de-alloy and conversion materials. Furthermore, the effect of nanoscale size and morphology on the electrochemical performance is presented. Synthesis of the nanostructures, lithium battery performance and electrode reaction mechanisms are also discussed. To conclude, the main aim of this review is to provide an organic outline of the wide range of recent research progresses and perspectives on nanosized active anode materials for future LIBs.

Academic research paper on topic "Review on recent progress of nanostructured anode materials for Li-ion batteries"

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Review on recent progress of nanostructured anode materials for Li-ion batteriesq

Subrahmanyam Goripartia,b, Ermanno Mielea,b, Francesco De Angelisa, Enzo Di Fabrizio' Remo Proietti Zaccariaa, Claudio Capiglia3, *

a Istituto Italiano di Tecnologia, Department of Nanostructures, Via Morego 30, Genova 1-16163, Italy b University of Genova, Genova 16145, Italy

c King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia HIGHLIGHTS

• Recent progress of nanosized active anode materials has been reviewed.

• Shape and size control of nanosized active materials.

• Improved specific capacity, cycle life and rate capability of active materials.

• Anodes with conductive matrices showing superior rate capability and cyclability.



Article history: Received 3 August 2013 Received in revised form 18 November 2013 Accepted 22 November 2013 Available online 22 January 2014

Keywords: Li-ion batteries Anode materials Nano-structures Rechargeable batteries


This review highlights the recent research advances in active nanostructured anode materials for the next generation of Li-ion batteries (LIBs). In fact, in order to address both energy and power demands of secondary LIBs for future energy storage applications, it is required the development of innovative kinds of electrodes. Nanostructured materials based on carbon, metal/semiconductor, metal oxides and metal phosphides/nitrides/sulfides show a variety of admirable properties for LIBs applications such as high surface area, low diffusion distance, high electrical and ionic conductivity. Therefore, nanosized active materials are extremely promising for bridging the gap towards the realization of the next generation of LIBs with high reversible capacities, increased power capability, long cycling stability and free from safety concerns. In this review, anode materials are classified, depending on their electrochemical reaction with lithium, into three groups: intercalation/de-intercalation, alloy/de-alloy and conversion materials. Furthermore, the effect of nanoscale size and morphology on the electrochemical performance is presented. Synthesis of the nanostructures, lithium battery performance and electrode reaction mechanisms are also discussed. To conclude, the main aim of this review is to provide an organic outline of the wide range of recent research progresses and perspectives on nanosized active anode materials for future LIBs.

© 2013 The Authors. Published by Elsevier B.V. All rights reserved.

1. Introduction

The research community is currently engaging in profuse efforts to achieve effective energy storage strategies which are the key for the exploitation of alternative energy and thus for the replacement of fossil fuels and traditional energy sources [1]. In this regard, rechargeable Li-ion batteries (LIBs) play a significant role due to

q This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Corresponding author. E-mail addresses:, (C. Capiglia).

their high gravimetric and volumetric energy, high power density, long cycle life and low self-discharge property [2—9]. Furthermore, they have proved to be the most efficient energy storage strategy for a wide range of portable devices like cellular phones, laptops and digital electronics [10—16]. However, the employment of Li-ion batteries in hybrid electric vehicles (HEV), plug in hybrid electric vehicles (PHEV) and pure electric vehicles (PEV), needs from two to five times more energy density than the present lithium batteries technology can offer (150 Wh/kg) [17]. The increase of the energy density of lithium batteries can be achieved by either using high voltage cathode active materials as electrodes or by developing high capacity anode and cathode electrode materials. One of the main hindrances to design high voltage cathode in LIBs is

0378-7753/$ - see front matter © 2013 The Authors. Published by Elsevier B.V. All rights reserved. http://dx.doi.Org/10.1016/j.jpowsour.2013.11.103

represented by the electrolyte decomposition that occurs at more than 4.2 V vs. Li/Li+ [18—27]. Hence, the development of electrolyte with wider electrochemical window stability is also essential in the realization of the next generation of devices that will operate at higher cell potential with appropriate Li-ion conductivity. In this sense, remarkable research is still under progress to improve the performance of LIBs by using inorganic and organic based materials [2—9,28—35].

The common concept of present LIBs relies, at the cathode side, on transition metals oxides or phosphates active material (LiCoO2, LiMn2O4, LiCo1/3Mn1/3Ni1/3O2, LiFePO4, etc.), while graphite is commonly used as anode active material. Cathode and anode are separated by a membrane made of polypropylene/polyethylene filled with electrolyte which contains lithium salts (i.e. LiPF6) in alkyl organic carbonates such as ethylene, propylene, dimethyl carbonates at different ratio. The separator prevents the electrical contact between the electrodes and, at the same time, it allows the diffusion of Li-ions from cathode to anode during the charging and the reverse discharging process. The latter is defined as the flow of Li-ions from the anode to the cathode allowing the conversion of chemical energy into electrical energy. For example, the chemical reactions occurring in a typical LIB based on LiCoO2 cathode are as follows;

Anode: C + xLi + xe_ 4 LixC6

Cathode: LiCoO2 4 Li1 _ xCoO2 + xLi + xe_

Active materials, in order to be considered suitable candidates for LIBs, should fulfil the requirements of reversible capacity, good ionic and electrical conductivity, long cycle life, high rate of lithium diffusion into active material and conclusively low cost and eco-compatibility.

The state-of-the-art for cathode materials is represented by LiCoO2, LiMn2O4, and LiFePO4 [33—38], while graphite is definitely the most used anode [2—5] owing to its excellent features, such as flat and low working potential vs. lithium, low cost and good cycle life. However, graphite allows the intercalation (see Fig. 1) of only one Li-ion with six carbon atoms, with a resulting stoichiometry of LiC6 and thus an equivalent reversible capacity of 372 mAh g_1. In addition, the diffusion rate of lithium into carbon materials is

between 10_12 and 10_6 cm2 s_1 (for graphite it is between 10_9 and 10_7 cm2 s_1), which results in batteries with low power density [39,40]. Hence, there is an urgency to replace graphite anodes to materials with higher capacity, energy and power density. Even though lithium metal holds one of the highest capacity among anode materials (3860 mAh g_1), safety issues prevent the use of lithium as anode material in secondary batteries. In fact, dendrites formation on the lithium metal can cause short circuit between anode and cathode [14,41,42].

Therefore, the path leading to LIBs with improved energy and power density has, as major challenge, the selection of suitable anode materials which can provide high capacity and ease diffusion of Li-ions into the anode, along with good cycling life and free from safety concerns (see Fig. 2).

Many efforts have been done in the investigation of both carbon and non-carbon materials for high performances and high capacity anode in LIBs. A short list must include: carbon nanotubes (1100 mAh g_1) [43], carbon nanofibers (450 mAh g_1) [44], gra-phene (960 mAh g_1) [45], porous carbon (800—1100 mAh g_1) [46], SiO (1600 mAh g_1) [47], silicon (4200 mAh g_1) [48], germanium (1600 mAh g_1) [49], tin (994 mAh g_1) [50] and transition metal oxides (500—1000 mAh g_1) [51—53]. Furthermore, metal sulphides, phosphides and nitrides [54—56] might be also considered for anodes purposes, in fact they possess specific capacity higher than 500 mAh g_1. However, high volume expansion, poor electron transport, capacity fading, and low coulombic efficiency as well, are the main limitations that have to be overcame before they can be used as effective anodes. In this sense, promising results and a bright perspective is offered by nanostructuring the above listed materials. Nano-size and tailored morphology represent the key feature capable of leading these innovative materials from being theoretically relevant to an effective technological breakthrough [57—60]. The expected advantages from using nanotechnology in LIBs can be listed as follow [56,61—64]:

i) Realization of active materials with high surface to volume ratio, therefore intensification of the presence of active sites for lithium storage. This would result in a considerable increase of the specific capacity. Furthermore, the high surface area would imply a high contact area with the electrolyte, hence leading to high lithium-ion flux across the electrode/ electrolyte interface.

ii) Considering that some of the electrochemical reactions are hard to be triggered in bulk materials, shifting the anode research to the nanoscale would result in removing these limitations (for example $MnO2) [65].

Fig. 1. Schematic representation of lithium insertion/de-insertion mechanism for current rechargeable lithium battery.

Fig. 2. Schematic illustration of active anode materials for the next generation of lithium batteries. Potential vs. Li/Li+ and the corresponding capacity density are shown.

iii) Improved lithium diffusion due to the reduction of its path length, hence batteries with enhanced power capability.

iv) Higher electron transfer rates.

In the next sections we will discuss the state of the art of anode materials for LIBs, with particular emphasis on the recent nano-technology research outcomes and outstanding results. For sake of simplicity, we will classify the discussed innovative anode materials in three main groups, depending on their Li-ion battery performances and reaction mechanism (see Table 1):

1) Intercalation/de-intercalation materials, such as carbon based materials, porous carbon, carbon nanotubes, graphene, TiO2, Li4Ti5O12, etc;

2) Alloy/de-alloy materials such as Si, Ge, Sn, Al, Bi, SnO2, etc;

3) Conversion materials like transition metal oxides (MnxOy, NiO, FexOy, CuO, Cu2O, MoO2 etc.), metal sulphides, metal phosphides and metal nitrides (MxXy; here X = S, P, N).

2. Insertion/de-insertion materials

2.1. Carbon based materials

Carbon-based materials with various consistencies and morphologies have been recognized as appropriate anode materials for LIBs due to their features, such as ease of availability, stability in thermal, chemical and electrochemical environment, low cost, and good lithium intercalation and de-intercalation reversibility [2— 5,66]. These characteristics are quite important especially when considering that charged electrode materials, either delithiated cathodes or lithiated anodes, have the tendency to violently react with non-aqueous electrolytes at elevated temperatures. However, also at room temperature, side reactions can occur [66—69]. In particular, the lithium salt LiPF6 has the tendency of reacting with moisture resulting in the formation of HF. The produced HF would, in turn, cause the dissolution of any transition metal in the

electrodes and/or the surface erosion of the active materials, therefore leading to capacity decay upon charge—discharge cycling. The final result is the slow degradation of both the active electrode material and the electrolyte as well as the formation of a thick passive layer on the electrode surface during cycling. In particular, when it comes to anode, this layer is known as Solid Electrolyte Interface (SEI). In this regard, the use of carbon coating on the active materials can provide a way to mitigate the mentioned drawbacks. In fact, carbon shows an electrochemical activity towards the electrolyte only at very low potentials, and without any oxidation up to the cutoff voltage of the battery. Furthermore, high resistance to HF corrosion can be expected owing to the very good chemical stability of carbon. Finally, carbon coating can also prevent the surface oxidation of active materials in air, especially at the nano-scale level. In fact, nanostructured active materials present a high surface area which enhances the surface oxidation. For these reasons the carbon coating has the capability to greatly retard any surface degradation during storage and to strongly reduce the capacity fading upon charge—discharge cycling.

Some studies reporting the role of carbon coating on anode active materials for Li-ion batteries are here listed. For example, Zhang et al. directly observed the difference in the SEI formation between carbon coated and non-coated graphite anode [68]. The SEI film for carbon coated natural graphite spheres was found to be quite compact with a thickness from 60 nm to 150 nm, much thinner than the SEI film found on uncoated graphite spheres, showing thickness from 450 nm to 980 nm. The conclusion was that carbon coating can reduce the decomposition of the electrolyte and it can lead to the formation of a thin SEI on the electrode surface. Furthermore, it has been proved that after carbon coating the graphite surface, any direct contact of graphite with the electrolyte is prevented, therefore the decomposition of propylene carbonate is greatly reduced and the intercalation of electrolyte species (organic carbonates) into graphene layer is prevented [69,70]. The role of carbon coating on different kinds of active materials other than graphite has also been studied. For example, He et al. investigated the effect of carbon coating on

Table 1

Most common anode materials used for lithium ion batteries.

Active anode material

Insertion/de-insertion materials

A. Carbonaceous

a. Hard carbons


c. Graphene

B. Titanium oxides

a. LiTi4O5

b. TiO2

Theoretical capacity (mAh g_1) [Reference]

200-600 [83-85] 1116 [91-94] 780/1116 [45]


330 [121]

Alloy/de-alloy materials

a. Silicon

b. Germanium

c. Tin

d. Antimony

e. Tin oxide

f. SiO

Conversion materials

a. Metal oxides(Fe2O3, Fe3O4, CoO , Co3O4, MnxOy, Cu2O/CuO, NiO, Cr2O3, RuO2, MoO2/MoO3 etc.)

b. Metal phoshides/sulfides/nitrides (MXy; M = Fe, Mn, Ni, Cu,

Co etc. and X = P, S, N)

4212[156] 1624 [191,192] 993 [61] 660 [150] 790 [52] 1600 [47]

500-1200 [51-53, 56]

500-1800 [54-56]


Common issues

> Good working potential

> Low cost

> Good safety

► Low coulombic efficiency High voltage hysteresis High irreversible capacity

> Extreme safety

> Good cycle life

> Low cost

> High power capability

> Very low capacity

► Low energy density

> Higher specific capacities

> High energy density

> Good safety

♦{♦ Large irreversible capacity <♦ Huge capacity fading <♦ Poor cycling

> High capacity

> High energy

> Low cost

> Environmentally compatibility

> High specific capacity

> Low operation potential and Low polarization than counter oxides

> Low coulumbic efficiency

> Unstable SEI formation Large potential hysteresis

> Poor cycle life

> Poor capacity retention Short cycle life

High cost of production

Li4Ti5O12 finding that it reduces the decomposition of the electrolyte when compared to uncoated Li4Ti5O12 [71] (for further information on LTO see section 2.2.1). Similarly, carbon coating of Silicon and Germanium was shown to improve the lithium-ion battery performance [72,73] (for further information on Si and Ge see sections 3.1 and 3.3, respectively). The importance of carbon coating on silicon surface has been examined in details by using FT-IR and X-ray photoelectronic spectroscopy [67]. In this study the authors observed that the absence of native oxide layer on silicon surface was prevented by carbon coating. In addition, the formation of silicon and carbon fluorides (CFx and SiFx) into SEI was not found, meaning that the involvement of active materials (i.e. Silicon) into the SEI formation can be reduced/prevented through carbon coating. However, in this study the authors also reported about the formation of siloxane species in SEI for carbon coated silicon electrodes, otherwise absent when uncoated silicon electrodes where considered. Further examples on the role of carbon coating on anode active materials will be described in the next sections.

The variety of carbon based materials used as active anode in LIBs are classified into two categories, according to the degree of crystallinity and carbon atoms stacking [3,74]: i) SOFT carbon (graphitizable carbons) where crystallites are stacked almost in the same direction and ii) HARD carbon (non-graphitizable carbons) where crystallites have disordered orientation. In particular, the former is quite popular in the battery community. In fact, it shows an appropriate reversible capacity (i.e. 350—370 mAh g_1), long cycling life and good coulombic efficiency (more than 90%) [2,37,55,69,75,76]. The reaction mechanism between lithium and graphite, following an intercalation/de-intercalation process, has been extensively studied with various analytical techniques [77,78]. Among the types of commercially available graphite is worth mentioning Mesocarbon Microbead (MCMB), Mesophase-pitch-based carbon fibre (MCF), vapour grown carbon fibre (VGCF) and Massive Artificial Graphite (MAG). Despite their massive production and the relative low cost of the industrial processes, these classes of carbon materials have, as major issue, a low specific capacity (i.e.372 mAh g_1), especially for applications such as HEV, PHEV or PEV. Hence, the use of graphitic carbon as anode is still limited to low power devices like mobile phones and laptops. Therefore, further advances in anode materials for lithium batteries are necessary to the development of competitive performance electric vehicles, smart electric grid systems and, in general, of portable high power consuming devices. One of the possible scenario involves the use of carbon base materials showing high capacity [37,79]. Presently, the research activity is strongly focused on porous carbon, carbon nanotubes (CNTs), nanofibers and graphene, as the most promising carbon based anode materials. The size reduction and the unique shape of these structures introduce novel properties that can substantially improve the energy storage capacity in LIBs [37,42—45,73,80]. For example, carbon nanorings (CNRs) with 20 nm outer diameters and 3.5 nm wall thickness, have shown outstanding performances as anode active materials: high lithium uptake and larger capacity, i.e. more than 1200 mAh g_1, and over a hundreds of cycles at the current density of 0.4 A g_1. Even at the higher current rates of 45 A g_1, it has been observed a capacity as high as 500 mAh g_1. The larger specific capacity and the high rate capability have been rationalized as due to the reduction of the diffusion distance and to the increase of the number of storage sites for Li-ions [81]. These advantages are paradigmatic results of the developing of nanosized carbon based materials.

2.1.1. Hard carbon

Even though soft carbons represent the state of art for anode materials in LIBs, some limitations, such as their low capacity and

the high voltage hysteresis during the delithiation process, might hinder their use as anode materials for the next generation of LIBs [12,82]. On the other hand, hard carbons have high reversible capacity (more than 500 mAh g_1) in the potential range 0—1.5 V vs. Li/Li+, therefore they represent a valid alternative to soft carbons. Hard carbons were developed in 1991 by Kureha Corporation (Japan) and used as the negative electrode materials in the first built lithium-ion secondary battery, but they were subsequently dismissed from the electronic industry. Hard carbon have random alignment of graphene sheets which provides many voids to accommodate lithium, however the manner in which lithium diffusion occurs inside hard carbons makes lithium diffusion very slow, namely very poor rate capacity. Nevertheless, a number of automakers and battery companies have been focussing on the development of hard carbon for use in Electric Vehicles, mainly motivated by its high reversible capacity. Recently, anode capacity between 200 and 600 mAh g_1 has been reported [83—85]. This high capacity is associated to the material porous nature, number of graphene sheets and surface area [86]. However, hard carbons present two main drawbacks, namely low initial coulombic efficiency and low tap density. In order to overcome these problematics, a number of strategies has been pursuing, for example by means of surface oxidation, fluorination or by using metal coating or a thin layer of soft carbon [83,87]. In particular, the latter resulted in better lithium battery performance by improving both the coulombic efficiency and the lithium storage capacity. Further progress in this direction has been obtained through a systematic investigation of the effects of the temperature during the carbon coating process [87]. However, both the capacity and the cycling life of hard carbons still need to be improved. Haung et al. have synthesized porous structures of hard carbons and observed improved capacity, i.e. more than 400 mAh g_1 [88]. Interesting results have been observed with micron size hard carbon synthesized from potato starch. In fact, the results demonstrated reversible capacity of almost 530 mAh g_1 with good cycling life and rate capability [89]. Similarly, nano-porous hard carbons were synthesized from pyrolyzed sucrose and their electrochemical performances for LIBs were evaluated (see Fig. 3). These nanoporous materials exhibited remarkable capacity close to 500 mAh g_1 along with a good cycling life and rate capability. High rate capability has been demonstrated to be related to the fast lithium diffusion ~4.11 x 10_5 cm2 s_1 for hierarchical nanoporous hard carbon [84].

2.1.2. Carbon nanotubes

CNTs are characterized by highly ordered carbon nano-structures, realized through a self-assembly unidirectional growth process [37,90]. CNTs can be classified in single (SWCNTs) and multiwall carbon nanotubes (MWCNTs) depending on the thickness and on the number of coaxial layers. Since their discovery in 1991, both SWCNTs and MWCNTs were extensively investigated both as anode materials and as composites. In particular, when used together with other active anode materials, they exhibited better output than non CNT composite due to their superior electronic conductivity, good mechanical and thermal stability, adsorption and transport properties [37,90]. The maximum theoretical value obtained for the reversible capacity of CNTs has been estimated to be 1116 mAh g_1 for SWCNTs in LiC2 stoichiometry [91 —94]. This is by far the highest capacity among carbon based active materials, and it has been attributed to the intercalation of lithium into stable sites located on the surface of pseudo graphitic layers and inside the central tube as well. However, to experimentally confirm the maximum theoretical predictions associated to CNTs/lithium is a major challenge. The research activity in CNTs as anodes is intense: several attempts were made with a variety of synthesis protocol and pre-treatments such as acid treatment and

Fig. 3. SEM and TEM images of porous hard carbon-1 (a, c) and porous hard carbon-2 (b, d), respectively; (e) typical plot of their discharge capacities vs. number of cycles at various current rates. (From Ref. [84].)

ball milling surface modification [37,91]. Recently, Di Leo et al. reported that purified SWCNTs, produced by laser vaporization procedure, yield indeed the best lithium battery performance in terms of high capacity, i.e. more than 1050 mAh g_1 [95]. However, the achievement of high coulombic efficiency with CNTs remains challenging because of the presence of large structure defects and high voltage hysteresis. In order to overcome these issues, research has been focused on the morphological features of CNTs, such as wall thickness, tube diameter, porosity and shape (bamboo-like, quadrangular cross section, etc.) [96,97]. Particularly interesting is the approach that Oktaviano et al. have reported. In this work, chemically drilled MWCNTs have been synthesized by solid state reaction [98]. The process is summarized in Fig. 4. Cobalt oxide nanoparticles were wired onto the CNTs surface and an oxidation process was performed. Finally, the removal of oxide particles led to 4 nm size holes on the MWCNTs surface. The lithium battery performances of these structures were evaluated and they showed higher capacity, better cycling life and higher coulombic efficiency than pristine MWCNTs.

In order to improve the lithium storage capacity and the cycling life in batteries, CNTs conjugated with a variety of nanostructured materials (Si, Ge, Sn, Sn-Sb) or metal oxides (MxOy; M = Fe, Mn, Ni, Mo, Mo, Cu, Cr) have been synthesized [37,55,73,99-102]. These

hybrid systems result in CNTs with enhanced electrical conductivity and reduced volume changes during the charging and discharging processes. For example, Fan et al. reported that the uniform coating of Fe3O4 onto aligned CNTs by magnetron sputtering leads to a capacity over 800 mAh g_1 with 100 charge— discharge cycles along with good rate capability [103]. Similarly, Mahanthy's research group prepared MoS2/MWCNTs composite. The electrochemical studies of this hybrid material showed a stable capacity of 1030 mAh g^1 at the 60th cycle [104].

Even though we have shown a number of interesting and promising results where CNT played a fundamental role, from the battery industry point of view the CNT technology is not yet considered mature enough. In fact, open issues regarding CNT mass production and cost presently hinder their use in LIBs applications.

2.1.3. Graphene

Graphene consists in a honey comb network of sp2 carbons bonded into two dimensional sheets with nanometre thickness (single-atom thickness). Since the introduction of the term gra-phene in 1987, this material has drawn much attention because of its admirable properties and versatility in a number of fields such as chemical, physical, biological and engineering sciences [45,105]. Among its astonishing properties, we can recall good electrical


Fig. 4. (a) Schematic representation of the synthesis protocol for drilling multiwalled carbon nanotubes; (b) Charge—discharge profile of MWCNTs, purified MWCNTs and nano-drilled MWCNTs at the 20th cycle and current density 25 mA g_1. (From Ref. [98].)

conductivity, relevant mechanical strength, high values of charge mobility and high surface area which make graphene a suitable electrode material for LIBs [45,73,106,107]. However, the theoretical lithium storage studies of graphene are quite controversial. In fact, even though the amount of lithium adsorbed by a single layer of graphene is low compared to graphite (372 mAh g-1) [108], when a number of graphene sheets is considered together this value overtakes the graphite performance leading either to 780 mAh g_1 or to 1116 mAh g_1 [45,109,110]. These two values are associated to two different descriptions of the interaction between lithium and graphene. In particular, the former assumes absorption of Li-ions on both faces of graphene (Li2C6stoichiometry), while the latter assumes Li trapped at the benzene ring in a covalent bond (LiC2stoichiometry).

Interestingly, the experimental research activity about graphene as anode material for LIBs is quite rich. Pan et al. prepared disordered graphene sheets by various methods: hydrazine reduction process, low-temperature pyrolysis and electron beam irradiation [110]. Electrochemical measurements demonstrated that graphene sheets exhibit high gravimetric capacity in the range 790—1050 mAh g_1 due to the presence of additional active sites for lithium storage such as edges and other defects. However, the drawback of the disordered structure is the poor electronic conductivity. Similarly, to achieve high capacity from graphene anode in LIBs, Lian et al. proposed high quality graphite with few graphene layers (~4) and with a surface area over 490 m2 g_1. Electrochemical studies have shown large reversible capacities close to 1200 mAh g_1 at the initial cycles, with values around 848 mAh g_1 even at the 40th cycle [111]. Recently, Wang et al. reported in-situ fabrication of doped hierarchically porous graphene (DHPG)electrodes for LIBs with ultrafast and long cycling capability [112]. As shown in Fig. 5, low and high magnification SEM and TEM images indicated that hollow graphene assemblies can contains small nanoscale pores. The electrochemical performance of DHPG electrodes exhibited high lithium storage with long cycling capability, around 3000 cycles, at a current density of 5 A g_1. These promising results are attributed to the synergetic effects of the hierarchically porous structure, good conductive network and hetero-atom doping, which facilitate the mass transport and the speeding up the electrochemical reactions. Among the graphene class of materials, nanoribbons synthesized from MWCNTs hold promising potential in lithium storage capability. In particular, Fahlman's research group obtained both reduced and

oxided graphene nanoribbons, the latter with increased lithium uptake and stable capacity of 800 mAh g_1 [113].

Presently, the LIBs research activity suggests, as suitable anode candidates, the use of various hybrid graphene/metals or semiconductors and graphene/metal oxides/phosphides [103,114—116]. For example, it is well known that SnO2 possess good anode properties, however its volume changes, while cycling, represents the major drawback for a good reversible capacity. This issue was faced by considering a graphene—SnO2 particles composite. In fact, graphene can insert SnO2 nanoparticles, therefore supporting the electrical conductivity to SnO2. In particular, it was recently proposed a hybrid system formed by 2—3 nm SnO2 particles/nitrogen doped graphene (1220 mAh g_1 gravimetric capacity over 100 cycles) [117]. Similarly, silicon composite with carbon nanocables and reduced graphene oxide sheets showed excellent Li-ion battery performance by reaching a capacity value of 1600 mAh g_1 over 100 charge—discharge cycles along with high coulombic efficiency [118]. An alternative approach considered Fe3O4 nanorods implanted onto graphene. This nanorod/graphene hybrid system showed a capacity retention of 867 mAh g_1 with only 5% loss from its initial capacity [119].

2.2. Titanium based oxides

Titanium based oxides have drawn significant attention in the lithium battery community because they allow the designing of operational devices with minor safety concerns. Moreover, this class of active materials shows other interesting features such as inexpensiveness, low toxicity, low volume change (2—3%) on both lithium insertion and de-insertion, along with an excellent cycling life [120—123]. However, it shows also low theoretical capacity, in the range 175—330 mAh g_1, and low electronic conductivity.

The electrochemical performance and the lithium insertion/ removal capacity of titanium based oxides mainly depend on their structure, morphology and size. In particular, it has been found that nanostructured titanium oxides lead to better capacity, longer cycling life and higher rate capability than the bulk materials [60,123,124]. Hence, a lot of efforts have been spent in the development of anode materials based on nanostructured titanium oxides. To date, titanium dioxide with various allotropic forms and spinel Li4Ti5O12 have been extensively studied for anode purposes [120—122,125,126].

(vck aumhrr t>*k number

Fig. 5. (a, b) SEM, (c) TEM and (d) HRTEM images of doped hierarchically porous graphene (DHPG) electrodes; (e) Corresponding Electrochemical performance of DHPG electrodes. (From Ref. [112].)

2.2.1. Spinel Li4Ti5OI2 (LTO)

Spinel Li4Ti5O12 is considered the most appropriate titanium based oxide material for lithium storage purposes because it exhibits excellent Li-ion reversibility at the high operating potential of 1.55 V vs. Li/Li+. Lithium insertion/extraction in LTO occurs by the lithiation of spinel Li4Ti5O12 yielding rock salt type Li7Ti5O12. During the insertion process, the spinel symmetry and its structure remain almost unaltered [120,127,128]. The high operating potential guarantees safety conditions, in fact the formation of the solid electrolyte interface (SEI) is mitigated and the development of dendrites, typical issue in carbon based anodes, is avoided [129]. However, the low theoretical capacity of 175 mAh g-1 and the low electronic conductivity ~ 10-13 S cm-1 limit the full capacity at high charge—discharge rates and reduce the Li-ion diffusion [130]. To overcome these issues two approaches have been followed: the first one is to enhance the electronic conductivity of LTO by surface treatments [131,132], the second one consists in enhancing the Li-ion diffusion by downsizing the LTO to the nanoscale. Nano-crystalline LTO, with particle sizes between 20 and 50 nm, has been synthesized by simple combustion method in short time period (less than 1 min) [133]. An experimental discharge capacity, i.e. 170 mAh g-1, very close to the maximum theoretical value, was measured at 0.5C rate, while stable capacities of 140 and 70 mAh g-1 were observed at higher charge—discharge rates of 10C and 100C, respectively. The doping of low conductivity materials, such as LTO, is one of the prominent techniques to enhance their electrical conductivity. In this regard, Shen et al. implemented a methodology for direct growing of LTO nanowires on titanium foil and they further showed an improvement in the conductivity of LTO nanowires by introducing Ti+3 ions through hydrogenation. The results were confirmed through XPS technique [134]. These nanowires containing Ti foil were directly used as electrodes without any conductive additives and binders, and they exhibited brilliant rate performance by reaching a capacity value close to the theoretical one, i.e. 173 mAh g-1 at 0.2C rate with good cycle life. Moreover, this value became 121 mAh g-1 at 30C (see Fig. 6). These nice results are related to the enhancement of the electron conductivity in hydrogenated LTO with respect to the pristine one. Furthermore, Xia's research group reported binary nanocomposites of Li4Ti5O12—Li2Ti3O7 for overcoming the LTO sudden voltage drop at the end of the charge—discharge process. These composites, having dimensions of few hundreds of nanometres, show a lamellar-like morphology formed by interconnected nanograins of ~20 nm size. The composites exhibited superb electrochemical

performance, in terms of capacity and cycling life. Finally, their voltage profile could be altered by monitoring the composite ratio, therefore fulfilling the request of a smooth voltage output in order to prevent overcharging and over discharging [130].

2.2.2. Titanium dioxide (TiO2, titania)

Titanium dioxide (titania) is a very promising material for anode applications in the LIBs field, in fact it is suitable for mass production and it is also cost effective. In addition, titania shows excellent safety and stability characteristics at the operative potential of 1.5 V vs. Li/Li+. Moreover, TiO2 has admirable advantages such as high electro-activity, strong oxidation capability, good chemical stability, high abundance and structural diversity [120,121,135]. These features make titania a good candidate as anode material in LIBs, especially for HEV applications. Titania can host 1 mol of lithium per 1 mol of TiO2 with a theoretical maximum capacity of 330 mAh g-1 and LiTiO2 stoichiometry (almost double than LTO). However, the exploitation of the entire capacity is a major experimental challenge. The lithium intercalation/de-intercalation process in titania typically depends on its crystallinity, particle size, structure and surface area [136—138]. Titania has several allotropic forms, the most well-known are rutile (tetragonal, P42/mnm), anatase (tetragonal, I41/amd) and brookite (orthorhombic, Pbca) [139,140]. Even though anatase titania has been considered the most electroactive form, other allotropes such as rutile and brookites are also widely studied for anode purposes [136,141,142].

Regarding the rutile form of TiO2, it has been shown that decreasing its particle size to 15 nm allows a larger capacity of 378 mAh g-1 at first discharge and subsequent stable capacity of 200 mAh g-1 (0.6 Li per one molecule of rutile TiO2) over 20 cycles, at the current density of 0.05 A g-1. With particle size of 300 nm, the initial and the 20th cycle capacities of 110 and 50 mAh g-1 were observed, respectively [142]. The improvement of the capacity and the Li-ion uptake are related to the nanosize characteristic and to the high surface area. Similarly, it was reported that 6 nm particle size of TiO2 anatase maintains high capacity at more than 200 mAh g-1 over 20 cycles at the current density of 0.1 A g-1. Furthermore, at the current rate of 10 A g-1, the capacity of 125 mAh g-1 was attained. When moving to higher particle sizes of TiO2, such as 15 nm and 30 nm, lower capacities of 80 and 71 mAh g-1 were found, respectively [143]. In particular, the reduction in the particle size facilitates the lithium intercalation/ de-intercalation and the electron collection at the anode by enhancing the Li-ions diffusion and shortening the charge path

Fig. 6. (a) Schematic representation of the fabrication of hydrogenated-LTO (H-LTO); (b) Electrochemical performance of H-LTO and LTO nanowires. (From Ref. [134].)

length, respectively. In this regard, Lee's research group synthesized anatase TiO2 microspheres by solvothermal process. These TiO2 microspheres are formed by the combination of ultra-fine 6— 8 nmTiO2 nanocrystals with 4—6 nm pore size microstructures. The optimal performances of TiO2 microspheres, such as high lithium storage capability, high number of charging—discharging cycles and high tap density were explained with their spherical morphology [123]. This last characteristic was in fact tuned to improve the capacity, the rate capability as well as the cycling life of titania based anodes [135,141]. For example, Gentili et al. synthesized, by means of hydrothermal route, nanotube of anatase TiO2 with wall thickness of 2—3 nm, an external diameter of 8—10 nm and length in the range 100—300 nm [144]. These nanotubes exhibited maximum capacity at around 300 mAh g_1 with lithium uptake roughly 0.98 Li for unit formula of titania. Along with high capacity, these titania nanotubes showed high rate capability and good cycling life with a capacity around 250 mAh g_1 over 100 charge—discharge cycles. Similarly, Brown et al. have synthesized mesoporous TiO2—B microspheres, with 12 nm pore size [145]. This porous titania has proved to be a good anode material at different current densities. Interestingly, a lithium storage capacity of ~120 mAh g_1 was attained at the high current rate of 60C. This improved rate performance was related to the fast kinetics from the pseudocapacitive electrochemical behaviour of microspheres of TiO2—B.

Further development of TiO2 in terms of power density and cycling life can be reached by combining titania nanostructures with conductive matrices such as carbon, CNTs and graphene

[146,147]. For example, as shown in Fig. 7, Wang et al. fabricated an hybrid composite of titania and graphene by hydrothermal procedure. The obtained structure consisted of 10 nm diameter TiO2 nanotube, with length from few hundreds to thousands of nanometres, built on a graphene layer [148]. The obtained specific capacity of this composite was more than 300 mAh g_1 in the potential range from 1.0 to 3.0 V vs. Li/Li+. The stability of these hybrid composites was proved over few thousands of charge— discharge cycles, from low to high currents, namely from 10 mA g_1—8000 mA g_1, along with very good columbic efficiency. This promising results were possible due to the nanotube smor-phology and to the electronic interactions between the hybrid components.

3. Alloy/de-alloy materials

The next generation of LIBs is expected to fulfil the power demand of high energy consuming devices, to power electric vehicles and HEVs and to be used in stationary applications. Hence, the specific capacity is the fundamental parameter to be considered in novel anode active materials. Materials which can satisfy the requirement of high capacity are, for example, silicon, germanium, silicon monoxide and tin oxide which react with lithium according to an alloy/de-alloy mechanism. Their specific theoretical capacity ranges from 783 mAh g_1 for tin oxide up to 4211 mAh g_1 for silicon [149—151]. Even though these alloy based materials can provide larger specific capacity than graphite (372 mAh g_1) and

Fig. 7. Schematic illustration of (a) TiO2 nanotube/graphene (TG) composite; (b) electron transport through graphene and ion diffusion in the tubular TiO2; (c) Initial discharge capacities of TG composite electrodes at various current densities from 10 to 8000 mA g_1; (d) Cycling stability of TG composite at current densities from 100 to 4000 mA g_ (voltage range: 1.0-3.0 V). (From Ref. [148].)

LTO (175 mAh g-1), the major drawbacks are the poor cycling life due to the high volume expansion/contraction and the larger irreversible capacity at the initial cycles. In order to overcome these issues, various approaches have been followed: the downsizing from micro to nanoscale particle and the fabrication of composites with both lithium active and inactive material, are the most promising. In the latter case the lithium active/inactive material serves as a conductive buffer matrix between the alloy materials and lithium source [152]. Nanostructured alloy materials with different morphologies like nanowires and nanotubes have been considered as an implementable path to achieve high capacity with a good rate capability and long cycling life [153,154].

3.1. Silicon (Si)

Silicon has both the highest gravimetric capacity (4200 mAh g-1, Li22Si5) and volumetric capacity (9786 mAh cm-3) among the anode material candidates [155—159]. In addition, the discharge (lithiation) potential of silicon is almost close to graphite i.e. 0.4 V vs. Li/Li+. Finally, Si is the 2nd most abundant element on earth, hence inexpensive and eco-friendly. It is then easily understood why silicon and its derivatives are considered the most promising and interesting materials for the realization of the future generation of LIBs, which justifies the strong academic and industrial interest for their development as anode active materials. The electrochemical lithiation of Si electrodes has been deeply investigated by many groups. It has been clarified that the high specific capacity value is due to the formation of intermetallic Li—Si binary compounds such as Li12Si7, Li7Si3, Li13Si4, Li22Si5 [156]. However, some issues prevent the employment of Si as anode in LIBs. Firstly, the large volume modification (~400%) during the charge/ discharge process causes poor cycling life and irreversible capacity. Secondly, the formation of Si compounds at the solid electrolyte interface inhibits the alloy/de-alloy process. In order to understand the exact reason of poor cycling stability of Si as anode in LIBs, many in-situ investigations with different experimental techniques such as XRD, NMR, TEM have been performed [160—164]. These studies evidenced that the electrical contact between the active material and both the conductive carbon and current collector undergoes a drop due to the large volume expansion/contraction of the Si anode, leading to an irreversibility of lithium insertion/extraction. Eventually, these volume changes result in shorter cycling life and capacity fading.

To overcome these issues, a lot of efforts were focused on nanostructured Si, especially on their morphology aspect. For example nanowires, nanotubes and nanospheres were considered due to their capability of providing the necessary free volume for accommodating the Si expansion during the alloying/de-alloying process. In particular, Si nanowires (Si NWs) and nanotubes have shown a reversible capacity over 2000 mAh g-1 with good cycling stability. The best results were obtained by the direct growth of Si NWs on the metallic current collectors, following a vapour—liquid— solid approach. Such technique gives better accommodation to the large volume changes and all the nanowires participate to the lithium alloy process because of the direct contact with the current collector [165]. This anode fabrication approach led to remarkable electrochemical performances. In fact, the observed charge— discharge capacity was 3500 mAh g-1 over 20 cycles at 0.2C rate, while at the higher current rate of 1C the capacity value was set at 2100 mAh g-1. This impressive lithium storage results were possible due to the good electronic contact between the current collector and the Si NWs, to an efficient charge transport mechanism and to the small diameter of Si NWs, which allows better accommodation of the volume change without any initiation of fractures. Similarly, Yao et al. reported about composite nanofibers

formed by Si, lithium and highly electrical conductive materials such as TiC/C, fabricated by low pressure chemical vapour deposition [166]. These synthesized silicon composite nanofibers showed high specific capacity around 2800 mAh g-1 at 0.2C current rate, with an excellent cycling life, over 100 charge—discharge cycles. When a higher 2C current rate was considered, a specific capacity close to 1500 mAh g-1 was observed.

Despite the mentioned nanostructures showed superior electrochemical properties, their fabrication is not cost-effective, and thus this emerging technology is still not applicable at an industrial level. In order to move from an experimental proof-of-concept device towards the realization of effective anodes for LIBs, research groups are seeking for alternative fabrication methods such as the promising hydrothermal and solvothermal techniques. For example, Chan et al. introduced a new method to grow carbon coated Si NWs in solution. The main point was the carbon coating of Si NWs by means of their mixing with conductive matrices such as MWCNTs and with amorphous carbon [167]. The synthesized carbon coated Si NWs, showed stable reversible capacity of 1500 mAh g-1 and about 100 charge—discharge cycles at the current rate 0.2C.

Similar approaches have been exploited to fabricate carbon coated Si NWs. An example is offered by the metal catalytic etching of silicon wafer in HF aqueous solution followed by carbon coating. The prepared carbon coated silicon nanowires exhibited reversible capacity around 1326 mAh g-1 [168]. Further improvements in the performances of Si NWs as anode were made by Ge et al. [48] with direct etching of boron-doped silicon wafers. The obtained porous Si NWs exhibited superior electrochemical performance and long cycling life. In fact, even after 250 cycles, the reported reversible capacities were 2000,1600 and 1100 mAh g-1 at 2, 4 and 8 A g-1 current density, respectively. This impressive performance was possible due to the high porosity of silicon nanowires and to the improvement of the electronic conductivity through boron doping.

In other works, Si nanotubes demonstrated even larger reversible capacity up to 2500 mAhg-1 [156,169]. For example, Songet al. fabricated sealed tubular shape silicon nanostructures by chemical vapour deposition in a ZnO assisted approach [170]. These kinds of nanotubes are capable to accommodate the Si volume change during the lithiation/delithiation process, they show high initial coulombic efficiency together with discharging/charging capacities around 3860 and 3360 mAh g-1, respectively. Interestingly, these high capacities are very close to the theoretical ones which indicates that all Si nanotubes are connected to the current collector and are fully reacting with lithium. In addition, electrochemical measurements evidenced stable capacities from 2600 to 1490 mAh g-1 at high current rate regimes from 0.2C to 2C. Similarly, carbon coated Si nanotubes were fabricated by Cho et al. with the use of alumina as template [171]. These carbon coated nano-tubes showed the impressive capability to deliver large reversible charge capacity of 3247 mAh g-1 and high coulombic efficiency, close to 89%. In the perspective to introduce Si nanotubes as anodes into the commercial market, they have been tested by using standard cathode electrode, i.e. LiCoO2. Li-ion technology, based on these materials, exhibited 10 times larger capacity than commercially available graphite based lithium cells, even after 200 cycles. This exceptional behaviour has been attributed to three main aspects: i) availability of free volume in the nanotubes for accommodating lithium, ii) amorphous phase dominance vs. the crystalline form during cycling, iii) carbon coating. Recently, Wu et al. developed stable Si double walled nanotubes surrounded by ion permeable silicon oxide shell as anode for advanced LIBs (as shown in Fig. 8) [172]. The thin layer of SiOx on the Si nanotube allows the diffusion of Li-ions but, at the same time, it prevents direct contact with the electrolyte. These hybrid nanotubes showed outstanding stable anode performance with a cycling life over 6000

Fig. 8. (a, b) SEM and (c) TEM images of double-walled Si—SiOx nanotube (DWSiNTs); (d) Electrochemical charging—discharging cycling performance of DWSiNTs electrodes. (From Ref. [172].)

cycles, with a specific capacity retention close to 88% and with a superior coulombic efficiency.

3.2. Silicon monoxide (SiO)

SiO is considered an alternative choice to silicon, as anode candidate, due to its high theoretical capacity (>1600 mAh g-1). In

addition, lithium oxygen co-ordination implies minimal volume change and, at the same time, lower activation energy [173—176]. The electrochemical reactions happening during the charge— discharge process determine the conversion of SiO into Si and lithium oxides and, possibly, the formation of Si—Li or, alternatively, the direct formation of Si—Li alloy and lithium silicates. The mechanism can be schematized as follows:

SiO + xLi 4 Si + LixO xLi + Si 4 LixSi (or)

xLi + SiO 4 Lix—ySiz + LixSiOz

Solid SiO is thermodynamically unstable at all temperatures. Therefore, it can be transformed into Si and SiO2 in a temperature triggered disproportionation reaction [177,178]. As previously pointed out about silicon, also SiO undergoes consistent changes in the volume during the lithiation and de-lithiation processes. Moreover, both the electrical conductivity and the lithium insertion/de-insertion rates remain quite poor [179,180]. To solve these problems and to improve the reversible capacity as well as the cycle retention, different approaches have been tested. The most promising are carbon coating, electrochemical reduction of SiO with lithium and, finally, the size reduction of SiO [181,182]. Among these solutions, particle size reduction combined with carbon coating is an effective way to overcome the above issues by shortening the diffusion distance of Li-ions and thus to enhance the ionic and the electrical conductivities.

In 2002 it was demonstrated the effect of both the oxygen concentration and particle size on the cycling life and on the reversible capacity of SiOx [47]. The lithium battery analysis performance was carried out by changing the oxygen concentration of SiO, such as SiO0.8, SiO and SiO1.1, along with the particle size, such as 30 and 50 nm. It was observed that SiO0.8 with 50 nm particle size shows the high capacity of 1700 mAh g_1 at initial cycles accompanied by large capacity fading over cycling. However, when SiO11 was considered, a stable capacity over cycling of750 mAh g_1 was found. The conclusion was that lower oxygen contents in SiOx allow for higher specific capacity associated to poorer cycling life. In addition, also the particle size was found to affect the anode performance. In particular, 30 nm SiOx particle size showed better capacity retention with high reversible capacity compared to larger particles.

Finally, it is interesting to notice that in order to understand the electrochemical reaction mechanisms between SiO and lithium, various analytical techniques have been employed, such as X-ray, photoelectron spectroscopy, NMR, high resolution TEM and electrochemical dilatometry [183—188]. In particular, 29Si Magic Angle Spinning (MAS) NMR, 7Li MAS NMR and HRTEM experiments were carried out at various discharge/charge potentials of SiO electrode with lithium. From these results it has been suggested that Si—Li alloy, along with LiOx and Li—Si—O ternary, were the intermediate products of reversible electrochemical reactions [187]. Hence, further investigations on SiO electrode for LIBs are still required.

Recently Liu et al. [173,189] published an interesting work about SiO composites containing highly conductive intermetallic compounds, such as Sn—Co—C and Sn—Fe—C, which have the advantages of good cycleability and high tap density. However, they also present the major drawback of low reversible capacity which make their performance not better than graphite. Hence, the authors realized a composite by combining these intermetallic materials with an anode showing high theoretical capacity, such as SiO. This led to new kinds of hybrid materials which are expected to overcome the volume expansion problem of SiO and to achieve high capacity with good cycling stability. Therein, tin acts as active phase with lithium while the transition metal (i.e. Cobalt or Iron) serves as a tin alloying buffer layer, inactive to lithium. These composites exhibited stable capacity of 700—900 mAh g_1 over a large number of charge—discharge cycles.

Further achievements regarding SiO anodes have been reached with the synthesis of three-dimensional porous SiO. The realization

of 3-D porous structures of SiO has been accomplished by depositing silver nanoparticles on SiO, followed by chemical etching in hydrofluoric acid solution. The best performances in terms of lithium reversibility and cycleability were observed with the carbon coating of the 3-D porous SiO, where the carbon source was acetylene gas [190]. Carbon coated 3-D porous SiO represents an effective way to achieve improved electrochemical conductivity and low volume expansion during the cycling process. In fact, carbon coated porous SiO have shown an excellent capacity around 1490 mAh g_1 over 50 charge—discharge cycles at 0.1C. A good response was also observed at the larger current rates of 3C and 5C with stable capacities of 1100 and 920 mAh g_1, respectively [190]. Recently, structurally and kinetically stable hierarchical SiOx (0.9 < x < 1) nanoconifers were reported by Song's group for applications as anode material in LIBs [174]. Columnar-shape SiOx nanoconifers were directly self-assembled on metallic NiSix nano-wires by means of chemical vapour deposition technique (see Fig. 9). These SiOx nanoconifers revealed stable charge—discharge performance over a hundred of charge—discharge cycles with specific capacity close to the theoretical one, along with good coulombic efficiency and high rate capability compared to bulk SiOx. This exciting result is due to the high conductivity of the metallic NiSix core, which assists the efficient charge transport pathway from/to SiOx phase.

3.3. Germanium (Ge)

Germanium is an extensively studied active anode material owing to its high lithium storage capability (1623 mAh g_1) with Li22Ge5 as equivalent stoichiometry and reversible alloy/de-alloy reactions [150,191]. Even though Ge is considerably more expensive and shows lower capacity than silicon, it has desirable advantages such as high intrinsic electrical conductivity (104 times higher than silicon), higher capacity than graphite anode and a narrow band gap (0.67 eV). Furthermore, it has been reported that the lithium diffusion into Ge is 15 and 400 times faster than in Si at 360 °C and at room temperature, respectively. This ensures higher rate capability and more efficient charge transport than in silicon and graphite as well [150,192]. Ge high power capability is then extremely important in advanced high power density applications such as electric vehicles. However, as discussed for silicon, the practical usage of Ge as active electrode in LIBs is hindered by the dramatic volume change (~300%) during lithium insertion/de-insertion [150,193]. Ge nanostructures, such as nanoparticles [194], nanowires [192] and nanotubes [171,195] can effectively sustain the volume change with better efficiency than bulk and microstructures. Noticeably, improvements have been observed with hybrid composite of Ge nanoparticles using conductive matrices, obtained through simple preparation routes, for example solid state pyrolysis [196].

For example, Ge nanoparticles, with diameter between 5 nm and 20 nm, were encapsulated inside carbon nanospheres with diameters in the range from 50 to 70 nm [196]. The role of the carbon nanospheres is to act as structural buffer and electro-active material during the lithium insertion and de-insertion process and to avoid direct contact with the electrolyte. This last aspect prevents Ge from the formation of SEI. These obtained composites exhibited highly reversible lithium storage along with high rate capability.

Similar behaviour has been observed in Ge nanoparticles deposited on SWCNTs by CVD [197]. Crystalline Ge nanoparticles, with an average size of 60 nm, were deposited on SWCNTs and coated with a thin layer of titanium for better rate capability. The major advantage of using CNTs is the increase of the conductivity between Ge and the current collector together with the increase

Fig. 9. (a) TEM image of SiOx nanoconifer on NiSix nanowires (NWs) (inset: SEM image ofSiOJNiSix NW); (b) scanning TEM-HAADF images and EDX elemental colour map of single SiOx/NiSix NW; (c) electrochemical cycling stability along with coulombic efficiency and specific capacity vs. charge/discharge cycle numbers of SiOx/NiSix NWs (inset: galvanostatic charge—discharge curves in the range of 0.01 and 1.2 V); (d) cycling performance of SiOx/NiSix NWs at different current rates. (From Ref. [174].) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

of the lithium diffusion which, in turn, means accommodation of Ge volume expansion while cycling. This hybrid Ge nano composite showed excellent anode capacity around 980 mAh g_1 vs. lithium metal and 800 mAh g_1 with LiFePO4 as cathode. Similarly, comparable high reversible capacities, along with excellent cycling life and high rate capability, were achieved by combining Ge nanoparticles with MWCNTs and reduced graphene oxide [49,198].

Nanostructured germanium nanowires and nanotubes have been investigated as well. For example, Yuan et al. proposed alkanethiol-passivated Ge NWs as anode in LIB [199]. Firstly, Ge NWs were synthesized through gold-seeded growth process. Secondly, HF solution was used to attain H-terminated Ge NWs which, in turn, underwent surface passivation of thiol by using dodeca-nthiol. The electrochemical performances of thiol-passivated Ge NWs showed remarkable results such as high reversible specific capacity of 1130 mAh g_1 along with a good cycling life at 0.1C. These structures were also proved to possess high power capability with a reversible capacity of 550 mAh g_1 at the higher current rate of 11C. For a better understanding of the passivation effect of Ge NWs in LIBs, comparison experiments with Ge nanoparticles and unpassivated Ge NWs were also carried out. Both electrochemical

and microscopy techniques confirmed that the surface passivation of Ge NWs leads to better structure integrity.

Similarly, hybrid metal/Ge nanostructures have also been fabricated and tested. For example, Wang et al. synthesized three dimensional Cu—Ge core—shell nanowires by direct RF-sputtering of Ge layer on previously prepared Cu nanowires [200]. These nanowires delivered large reversible capacity of 1419 mAh g_1 even after 40 cycles. They also attained a brilliant rate capability with capacities of 850 and 734 mAh g_1 at the current rates of 40C and 60C, respectively. These exciting results can be rationalized by considering that Cu nanowires act as good electrical contact between substrate and Ge, thereby facilitating electron transfer and charge collection by shortening the lithium diffusion length.

Finally, nanoscale germanium oxides were also studied as novel anode material for LIBs. Very recently, Seng et al. improved germanium dioxide (GeO2) electrochemical performance by using Ge with a conductive carbon coating [201]. GeO2/Ge/C was prepared in a three steps process, starting with the synthesis of GeO2 from hydrolysis of GeCl4 and followed by carbon coating with acetylene gas, resulting in GeO2/C. The last step was the reduction of GeO2/C to GeO2/Ge/C through high temperature ~650 ° C. The

Fig. 10. (a) Schematic representation of the lithium reaction mechanism in Ge, GeO2— C and GeO2/Ge/C; (b) Cycling performance of all samples for 50 cycles at 1C rate; (c) rate performance of all samples from 0.1 to 10C. (From Ref. [201].)

analysis of the lithium battery performance was carried out for materials such as GeO2/Ge/C, GeO2/C, nano GeO2 and bulkGeO2. The GeO2/Ge/C composite showed high capacities of 1860 and 1680 mAh g-1, with good cycling stability, at the current rates of 1C and 10C, respectively (see Fig. 10). Such a notable Li battery performance was related to the carbon coating of Ge, in particular it was found that carbon enhances the reversibility of the conversion reaction of GeO2 with lithium.

3.4. Tin oxide (SnO2)

Tin oxide was firstly developed by Fuji Photo film corporation and it received significant attention as anode in Li-ion batteries due to the high theoretical capacity and low work potential, i.e. 0.6 V vs. Li/Li+ [12,51,52,127]. The electrochemical lithium alloying reactions

can be summarized in a first partially irreversible step, where SnO2 is reduced into Sn and lithium oxides (SnO2 + 4Li 4 Sn + 2Li2O), which is followed by the reversible Sn—lithium alloying/de-alloying reaction (Sn + 4.4Li+ 4 Li44Sn). This overall electrochemical process involves 8.4Li for one SnO2 formula unit. The corresponding theoretical capacity is 1491 mAh g-1 but it is reduced to 783 mAh g-1 when the second highly reversible step is reached. Hence, 783 mAh g-1 is commonly considered as the actual theoretical capacity. Furthermore, severe electrode degradation is observed because of the consistent volume change (>200%) upon cycling. Therefore, a lot of attention has been paid to improve the cycling stability of SnO2 and to reduce the irreversible capacity caused by volume change [51,127].

Porous nanostructures, nanocomposites, and hollow nano-structured SnO2 have been proposed to overcome the above specified issues [51,202,203]. In particular, it was shown that porosity in nanostructured SnO2 is capable of balancing the volume changes during the lithium insertion/de-insertion. In fact, the pores act as buffer for the large volume changes. In this regard, Yin et al. prepared SnO2 mesoporous spheres in the range 100—300 nm from tin sulphate, by cost-effective and easy solution method [204]. The prepared SnO2 spheres showed notable lithium battery performance with capacities of 761 and 480 mAh g-1 after 50 charge— discharge cycles at current densities of 200 mA g-1 and 2000 mA g-1, respectively. Similar results were observed with mesoporous SnO2 using silica as template and, when compared to SnO2 nanowires, it was found the former providing better electrochemical response than the latter. In particular, the mesoporous SnO2 exhibited a reversible capacity of 800 mAh g-1, with capacity retention of 98%, even after 50 cycles at 0.2C current rate [202]. Responsible of this improved performance is the porosity of SnO2, which allows the flooding of the electrolyte among the particles together with the buffering role for volume changes during the charge—discharge cycles.

Due to the significant importance of carbon in the lithium batteries field, further developments were obtained by using composite carbon based materials such as carbon coated SnO2, SnO2/ nanofibers, SnO2/carbon nanoparticles, SnO2/CNTs and SnO2/gra-phene [203,205—207]. In this regard, carbon free and carbon coated SnO2 hollow microspheres, prepared through cost-effective hydrothermal route where glucose was used as carbon source, were proposed [203]. The results showed better performance for the carbon-coated SnO2, in terms of storage capacity, columbic efficiency and cycling life. This achievement was explained in terms of electrochemical oxidation of Sn, leading to SnO in carbon coated SnO2. In fact, the electrochemical oxidation of Sn was not observed in carbon free SnO2. Similarly, Jiang et al. proposed the use of gra-phene, as support for porous SnO2, to enhance the lithium storage capacity and the cycling life. This hybrid composite was prepared by using electrostatic spray deposition technique and it was found to possess very good characteristics for lithium battery purposes [208]. The proper assembly of SnO2 on graphene is considered highly beneficial for lithium battery performance because it enhances the electrical conductivity and, at the same time, it can provide mechanical support of the active nanoparticles (i.e. SnO2) during charging and discharging process. The electrochemical outcome of this hybrid system were large stable capacities of 551 and 507 mAh g-1, up to the 100th cycle, at current densities of 200 and 800 mA g-1, respectively. Similar results were observed with hierarchical carbon encapsulated in tin embedded in graphene nanosheet composites. The synthesis protocol of this hybrid composite undergoes three main steps: i) assembly of SnO2 on gra-phene, ii) reduction of SnO2 into Sn nanoparticles, iii) carbon coating of the composite via CVD procedure. The final structure was directly used as anode in LIBs [209].

In addition to these examples, various morphological structures of SnO2 have been widely investigated such as nanowires, nano-tubes, nanorod, nanoboxes and nanosheets, just to name a few [210—215]. For example, Ye et al. reported the effect of the size of SnO2 nanotubes on the anode performance [211 ]. Different lengths of SnO2 were synthesized through an hydrothermal process by using pre-fabricated mesostructured silica nanorods as sacrificial

template. Short size SnO2 nanotubes showed better electrochemical behaviour in terms of capacity and cycling life. The measured discharge capacity was 468 mAh g-1 after 30 cycles (see Fig. 11). This prominent outcome is thought to be related to the hollow characteristic of the nanotubes, that alleviate the volume changes and the mechanical stress during the cycling process.

4. Conversion materials

In this section we will provide an overview on the transition metal compounds such as oxides, phosphides, sulphides and nitrides (MxNy; M = Fe, Co, Cu, Mn, Ni and N = O, P, S and N) when utilized as anodes in LIBs. The electrochemical reaction mechanism involving these compounds together with lithium, implies the reduction (oxidation) of the transition metal along with the composition (decomposition) of lithium compounds (LixNy; here N = O, P, S and N). Anodes based on these compounds exhibit high reversible capacities (500—1000 mAh g-1) owing to the participation of a high number of electrons in the conversion reactions [56,127,216]. The electrochemical conversions reactions can be described as follows:

MxNy + zLi+ + ze N = O, P, S and N)

LizNy + xM (Here M = Fe, Co, Cu, Mn, Ni &

Fig. 11. (a, b) SEM and (c, d) TEM images of short and long SnO2 nanotubes, respectively; (e) plot of the first charge/discharge cycle of short SnO2 nanotube electrodes; f) Cycling performance of various SnO2 samples at a current density of 100 mA g_1. (From Ref. [211].)

4.1. Iron oxide

Iron based oxides have been extensively studied for rechargeable lithium batteries because of their low cost, non-toxicity and high natural abundance. Iron oxides, both haematite (a-Fe2O3) and magnetite (Fe3O4), are capable of participating in reversible conversion reactions with lithium, providing a theoretical capacity of 1007 and 926 mAh g-1, respectively [217]. However, iron oxides tend to exhibit poor cycling performance due to low electrical conductivity, low diffusion of Li-ions, high volume expansion and iron aggregation during charging and discharging. Therefore, to overcome the above identified limits, many recent investigations have been focused on developing new methods for the preparation of iron oxide nanomaterials as well as for modifying their size, shape and porosity [218—222]. Other studies have been focused on methods to stabilize their structure and to improve the electrochemical kinetics and power capability, mainly by carbon coating or by carbon based composites of a-Fe2O3 and Fe3O4 [223—225].

For example, Wang et al. reported a-Fe2O3 hollow spheres as anode in LIBs [226]. Hollow spheres of a-Fe2O3 have been synthesized by a facile quasiemulsion template method. In particular, water and glycerol were used for this purpose, in fact their mixing leads to the formation of quesiemulsion droplets, which served as soft template for the formation of a-Fe2O3 hollow spheres. The electrochemical reaction of a-Fe2O3 hollow spheres with lithium was studied in the potential window of 0.005—3 V vs. Li/Li+. The results revealed high lithium reversibility accompanied by a storage capacity higher than 700 mAh g-1 for about one hundred of charge—discharge cycles. These investigations on a-Fe2O3 hollow spheres suggested that the morphology of the nanosized Fe2O3 plays a significant role in the reactivity with lithium. Similarly, Wu et al. have studied the size and morphology effect of a-Fe2O3 nanorods in the range from 300 to 500 nm length with and without porosity [227]. Liu et al. prepared haematite a-Fe2O3 nanotubes with outer diameter ranging from 200 to 300 nm by using ZnO as sacrificial template. Next, they proceeded with carbon coating using glucose as carbon source [219]. The prepared a-Fe2O3 nano-tubes showed good lithium insertion and de-insertion reversibility with a capacity close to 750 mAh g-1 over 150 charge—discharge

cycles. The set current rate was 0.2C in the potential range 0.005— 3 V vs. Li/Li+ [219]. Similarly, carbon-decorated crystalline Fe3O4 nanowires were synthesized by Muraliganth et al. through microwave-assisted hydrothermal approach, using PEG-400 as soft template and polysaccharide as carbon source [228]. The resulted carbon decorated Fe3O4 nanowires, with diameter ranging from 20 nm to 50 nm and length of several micrometres, showed excellent electrochemical stability with a good reversible capacity of 830 mAh g_1 without any capacity damage over 50 cycles. These results are attributed to the positive role played by carbon in realizing a fast and highly reversible conversion reaction of iron oxides with lithium, which provides good electronic conductivity, enhanced lithium permeability and electrochemical stability. Recently, Xu et al. prepared spindle-like porous a-Fe2O3 from an iron-based metal organic structure, formed by nanoparticles with dimensions around 20 nm [229]. These novel a-Fe2O3 structures showed great enhancement of lithium storage with a reversible capacity of 911 mAh g_1 at 0.2C current rate for more than 50 charge—discharge cycles. In addition, the capacity of 424 mAh g_1 was achieved at the higher current rate of 10C. These promising results indicate that both size and morphology strongly affect both rate and lithium storage capability of iron oxides.

Sohn et al., through an aerosol-assisted process, followed by vapour coating, synthesized nanocomposites of Fe3O4 cores and porous carbon—silicate layers. Carbon was chosen for its characteristic of increasing the electrical conductivity, hence to mitigate the aggregation of iron oxides particles and to reduce the mechanical stress during cycling [230]. These nanocomposites showed quite stable capacity around 900 mAh g_1 with a coulombic efficiency close to 100% over 50 charge—discharge cycles. Very recently, nanoparticulate Fe2O3 tubes have been obtained from microporous organic nanotubes (MONT) used as template [220]. The prepared porous Fe2O3 nanotubes (FNT, see Fig. 12) exhibited excellent electrochemical performances with large capacities such as 918 and 882 mAh g_1 at current densities of 500 and 1000 mA g_1, respectively. These results indicate that low cost iron based oxides with highly conductive carbon composites can be a valid alternative to graphite anodes.

4.2. Cobalt oxides

In this section we will consider the recent advances on the research related to cobalt oxides materials (Co3O4 and CoO) used as anode for LIBs. Co3O4 and CoO show theoretical capacities of 890 and 715 mAh g~\ respectively [231,232]. Similarly to other kinds of materials, a number of different forms of cobalt oxides have been studied. Porous nanostructures, nanosheets, nanocubes, nanowires and nanotubes have been prepared by various synthetic routes such as wet chemical, solid-state, hydrothermal and microwave, therefore allowing the tailoring of their electrochemical performance [233—237]. For example, Guan et al. developed a template free method for the preparation of pure phase CoO octahedral nanocages by simply utilizing NH3 as a coordination etching agent [238]. Therein, uniform size of the octahedral nanocages, with edge length of 100—200 nm, were obtained. In the test as anode material, they exhibited excellent cycling performance along with a good rate capability and enhanced lithium storage capacity, as seen in Fig. 13. Even at the high current rate of 5C, these octahedral nanocages were able to deliver a reversible capacity of 474 mAh g_1. Their large capacity and the high rate capability were possible owing to the existing huge voids which can accommodate the large volume changes. Recently, Wang et al. reportedmesocrystalCo3O4nanoplatessyn-thesized by solid state crystal reconstruction from Co(OH)2 nanosheets [225]. The obtained porous Co3O4nanoplates showed

Fig. 12. (a, b) TEM images of Fe2O3 nanotubes (FNTs) from MONTs template; Li-ion battery performance of FNTs, (c) discharge capacity vs. number of cycles of FNTs (red) and commercial Fe2O3 nanoparticles (black). The coulombic efficiency of FNT is also included (violet); (d) galvanostatic charge—discharge curves; (e) cycling performance of FNT at different current rates. (From Ref. [220].) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

superior electrochemical performance with low initial irreversible capacity along with stable cycling performance. Discharge capacity of 1015 mAh g_1 was observed even after 30 cycles at the current rate of 0.2C. This amazing output was attributed to the 2-dimensional nature of the nanoplates together with their porosity that facilitates the accommodation of volume expansion during the charge/discharge process.

Further composites of cobalt oxides have been studied to buffer the volume changes and to prevent the detachment and the agglomeration of cobalt oxides during the lithium insertion/ extraction process. As previously described, especially carbon based composites are intensively studied due to their desirable properties. For example, ultra-fine CoO nanoparticles with size ~ 5 nm, densely anchored on graphene nanosheets, were fabricated by

Fig. 13. (a) Galvanostatic first charge—discharge curves and (b) cycling performance for three CoO samples at the current rate of 0.2C. (From Ref. [238].)

Haung et al. [239]. The resulted CoO/graphene composites exhibited excellent lithium storage for a long charge—discharge cycling with 100% coulombic efficiency. Stable capacity of 1015 mAh g-1 was maintained for 520 charge—discharge cycles. In fact, transmission electron microscopy analysis showed that the original morphology of CoO nanocomposites was preserved during such amount of cycles. This impressive result indicates that composites of CoO, with an electrically conductive network, can lead to high structural stability and enable long cycling life. A different morphology was introduced by Peng et al. who reported about

quantum dots of CoO/graphene composites and their high lithium storage capacity [240]. Similarly, Wu et al. prepared 10—20 nm Co3O4 particles size anchored on graphene nanosheets in basic aqueous solution starting from Co+2 inorganic salt and graphene [241]. This Co3O4/graphene nanocomposites displayed superior electrochemical performance with high reversible capacity, good cycling life and good rate capability.

Various other metal oxides, showing a conversion reaction mechanism with lithium, have also been studied. For example NiO, MnOx, CuOx, MoOx, CrOx were extensively investigated as anode

Fig. 14. TEM and HRTEM images of CoxP nanostructures, (a, d) Co2P rods; (b, e) CoP hollow spheres; (c, f) fine CoP nanoparticles. (From Ref. [259].)

materials for LIBs and they showed miscellaneous physico-chemical properties and a large reversible capacity around 500 mAh g"1 [242—249].

4.3. Metal phosphides (MPx)

Metal phosphides have also been deeply studied as anodes for rechargeable lithium batteries [55,58,250—255]. They can react with lithium, both in a conversion reaction schema and in an intercalation/de-intercalation reaction, depending on the nature of the transition metal and on phosphorous bonding stability upon electrochemical environment. It is possible to divide MPx into two groups. The first one involves the lithium insertion/extraction without breaking the metal—phosphorous bond, known as insertion/de-insertion mechanism:

MxPy + zLi+ + ze

4 LizMx—zPy

The second group involves a conversion reaction mechanism. In such electrochemical reactions the bonds between metal and phosphorous are broken, resulting in nanosized metal particles and Li-phosphides:

MxPy + zLi+ + ze" 4 LizPy + xM

Copper, cobalt, iron, nickel and tin based phosphides are usually considered to belong to the second group, i.e. conversion mechanism. Nevertheless, some reports showed that MPx could

participate to the insertion as well as the conversion mechanism with respective to potential vs. Li/Li+ [59,256]. Metal phosphides can deliver high capacities between 500 and 1800 mAh g"1. In addition, MPx as anode, show an high degree of electrons delo-calization, which leads to low formal oxidation state and strong covalent bond of M—Phosphorous. Another advantage is the lower insertion potential of MPx than their oxide counterparts. However, MPx usually have low electrical conductivity and high volume changes upon charge—discharge cycling. The use of MPx as anodes deserves further exploration to overcome these drawbacks. For example, cubic Ni2P crystals and lithiated NiP2, were prepared through the milling of a mixture of nickel powder and red phosphorus. Furthermore, Li—Ni—P ternary active composites were also synthesized. Both Ni2P and LI—Ni—P showed reversible lithium reactions in electrochemical environment. Especially the ternary composites exhibited a high reversible capacity of 600 mAh g"1 by conversion process [257]. Another approach was followed by Lu et al., who prepared carbon decorated hierarchical nanostructures of NiP2 spheres with an uniform size of 5—10 nm. The synthesis was based on an organic-phase mixture of nickel acetylacetonate, trioctylphosphine, tri-n-octylamine, and oleyl-amine, together with oleyamine as surfactant [258]. By introducing the carbon decoration into Ni2P, it was possible to enhance the capacity retention of lithium and to improve the structural stability by suppressing the aggregation and the pulverization of Ni2P particles. The electrochemical performance of these small size Ni2P spheres resulted in a capacity of 365 mAh g"1 at the current rate of 0.5C with a good reversible lithium charge—

Fig. 15. (a) Cyclic voltammograms of the first three cycles of CoP hollow particles in the potential range of 0.005—3.0 V vs. Li/Li+ at the scan rate of 0.5 mV s"1; (b) galvanostatic charge/discharge profiles for hollow CoP nanoparticles at the current density of 0.2C; (c, d) comparison of cycling performances of CoP hollow and solid particles at 0.2C and at different current rates. (From Ref. [259].)

discharge capability. In order to improve the lithium storage capacity with high cycling stability, the same research group synthesized carbon composites of mono phase Ni5P4 by solution chemistry. In fact, an increase of the phosphorus concentration within nickel lead to a high theoretical capacity while the carbon coating was introduced to generally enhance the lithium battery performance [256]. The carbon shell on the surface of Ni5P4 was achieved by thermal calcination at high temperatures. The gal-vanostatic charge—discharge measurements of Ni5P4/C as anode showed a specific capacity of 644 mAh g"1 after 50 cycles at the current rate 0.1C. Even at the higher current rate of 3C, it has been shown a noticeable capacity of 357 mAh g"1. This interesting improvement is due to the high crystallinity of Ni5P4 combined with the amorphous carbon shell.

Similar lithium performance was reported with copper and cobalt phosphides as well. Yang et al. prepared CoxP particles with carbon layer coating of various morphologies such as nanorods, spheres, and hollow structures in solution phase with oleylamine (see Figs. 14 and 15) [259]. In particular, the electrochemical investigations of CoP hollow nanoparticles, coated with a carbon layer, showed higher capacity retention together with stable cycling and good rate capability than Co2P nanorods and spheres. Their hollow peculiarity allows indeed an efficient lithium conversion reaction and, at the same time, it accommodates the volume changes during the charge—discharge process, thus leading to enhanced specific capacities and stability. Similarly, Trizio et al., reported size controlled hexagonal-like morphology of Cu3P nanostructures for LIBs [260]. Furthermore, Villevielle et al. prepared Cu3P nanorods from vaporized phosphorus and copper nanorods. This novel active electrode, i.e. the nanostructured Cu3P, was also tested for LIBs applications [251].

4.4. Metal sulphides (MSx) and nitrides (MNx)

Other kinds of materials, which have been thoroughly investigated for anode applications in the LIBs field, are the transition metal sulphides (MSx) and nitrides (MNx). Iron, molybdenum, tin, antimony, nickel, cobalt and tungsten have attracted major interest due to their high lithium storage capability and structural advantages during the lithium insertion/de-insertion process [56,127,261—265]. As anticipated in the previous sections, MSx and MNx reaction mechanisms with lithium involve the reduction to metal and, respectively, the formation of lithium—sulphur and lithium—nitride, through conversion reaction. For instance, Wang et al. reported phase controlled polyhedron CoSx prepared by solid state reaction. The synthesis procedure was based on a high temperature Co—sulphur powders reaction in presence of potassium halide (KX). Therein, KX served as reaction agent [266]. In particular, CoS2 and CoS were the most promising composites exhibiting superior reversible lithium insertion and extraction reaction, hence resulting in capacities of 929 and 835 mAh g"1, respectively. In another approach, Paolella et al. prepared nanoplates of Fe3S4 using sulphur and thiosulfate, octadecylamine, iron salt and 3-methyl catechol [263]. Therein, 3-methyl catechol acted as phase control agent and growth moderator as well. Furthermore, cyclic voltam-mograms of Fe3S4 electrode showed good reversible lithiation/de-lithiation process [267]. Similarly, composites of conductive matrices of carbon and graphene were also reported. For example, ultra-thin carbon coated FeS (C@FeS) nanosheets were prepared by surfactant assisted solution method [268]. Here the carbon coating served to avoid the dissolving of lithium sulphides (LixS), intermediate product of the metal sulphide formation during cycling, into the organic electrolyte inside LIBs. Owing to this advantage

Fig. 16. (a) Cyclic voltammetries of the C@FeS nanosheets electrode from potential window between 0 and 3 V vs. Li/Li+ at the scan rate of 0.5 mV s"1; (b) galvanostatic chargedischarge voltage curves of C@FeS nanosheets electrode at the current density of 0.1 A g"1 for the 1st and 2nd cycles; (c, d) cycling performance of C@FeS nanosheets, nanoplates and nanoparticles at various current densities. (From Ref. [268].)

provided by the carbon coating, 2-dimensional C@FeS nano-structures exhibited very interesting LIBs performance (see Fig. 16), with stable 100 cycles capacity of 615 mAh g_1 at the current rate of 0.16C and voltage between 0.01 and 3.0 V vs. Li/Li+. Interestingly, even at the current rate of 10C, it resulted in a reversible capacity of 235 mAh g-1. A similar electrochemical behaviour was also observed for graphene wrapped CoS nanoparticles [269]. These impressive results indicate that metal sulphides can represent a valid alternative as materials anode in future LIBs.

Besides metal sulphides, also metal nitrides have emerged as promising anodes for LIBs. Among them, Cu3N, VN, Co3N, CrN, Fe3N, Mn4N and Ni3N have especially been studied [56,127,270273]. Gillot et al. prepared Ni3N by various synthetic routes, such as ammonolysis of nickel salts, or nickel particles, and thermal decomposition of nickelamide in the presence of ammonia [274]. In particular, Ni3N from nickelamide showed the best electrochemical performances, with the largest capacity (1200 mAh g-1). Moreover, Ni3N exhibited also a good rate capability, with a reversible capacity of 500 mAh g_1 sustained in 10cycles at the current rate of 1Li per hour (see Fig. 17). Similarly, large discharge capacity (1200 mAh g-1) was achieved with Cr3N thin films by Sun et al. [275]. Nanopowder of Cu3N has been reported in a conversion reactions with Li3N and Cu particles, and the obtained first cycle discharge capacity was 675 mAh g_1 [272]. Das et al. prepared nanoflakes of CoN films by RF magnetron sputtering [273]. The galvanostatic charge-discharge measurements with lithium metal in the range 0.005-3 V vs. Li/Li+ showed an initial capacity close to 760 mAh g_1, however it was also observed a huge irreversibility in the first cycle due to SEI formation. Interestingly, upon cycling, the capacity increased consistently up to 960 mAh g-1, value observed after 80 cycles. From this result was deduced that the CoN electrode takes a certain number of cycles to reach a stable configuration.

Along with the above specified anode nanostructures, an important research field involves the use of conversion-alloy based materials, having the characteristic of undergoing reversible conversion reaction followed by reversible alloy reaction with lithium. It has been reported that lithium can form alloys with several metals such as Al, Si, Sn, Sb, In, Zn, Pb, Bi, Ag, Pt, Au, Cd, As, Ga and Ge [61,150,276-279]. However, few of them, together with their corresponding compounds such as intermetallic, oxide or phosphide, were studied in the anode perspective for lithium batteries [51,56,278]. These anodes can react with lithium, first through conversion, then through alloy reactions at a potential that depends on the selected material. In particular, metal oxides like SiO, SnO, GeOx have already been discussed in the present review. Intermetallic compounds based on Sn, Sb, Bi, Si, such as ZnxSb, SnSb, InSb, MnSb, AgxSb, and AlSb, have been extensively studied [142,278-282]. The main advantage of intermetallic compounds is the reaction capability with lithium provided by the metal elements, which leads to highly reversible capacities. However, some reports showed that these intermetallic compounds can instead activate an intercalation reaction with lithium (Li + MSb / LiMSb, therein M = Mn, Cu, etc.) [283,284], therefore lower capacities than under conversion alloy conditions are obtained. In order to clarify this aspect, further investigations, both in-situ and ex-situ, are required.

5. Summary

In summary, this extended overview showed the amount of research efforts towards the development of novel active anode materials for LIBs. A bright perspective is offered by nanoscience and nanotechnology. Novel techniques and deep insight on material science have offered the opportunity to design and synthesize

Specific Capacity (mAh/g)

5 2.5 Ü

® 1 R cn 1.0 ro

0 50 100 150 200 250 300 Specific Capacity (mAh/g)

Specific capacity (mAh/g)

Fig. 17. Galvanostatic charge—discharge voltage vs. capacity curves of Ni3N prepared by (a) ammonolysis of Ni(NH3)6Br2; (b) from nickel nanoparticles with ammonia at 260 °C; (c) from decomposition of nickelamide at 150 °C for 70 h. The cells are at the rate of 1 Li per 20 h (C/20). The insets describe the capacity evolution for each cycle. (From Ref. [274].)

appropriate nanostructured anode materials for the next generation of LIBs. Uniquely tailored physico-chemical properties of nanostructures allow achieving high lithium storage, high Li-ion flux at the electrode/electrolyte interface, lower diffusion length for both Li-ions and electrons, and minimal anode volume change during the charging/discharging process. These exquisite features, when combined together, can lead to high energy density and high power density devices.

In this review, three categories of LIB anode materials were described depending on their reaction mechanism with lithium.

Firstly, the intercalation/de-intercalation group, which includes carbonaceous and titanium oxides materials, was illustrated. The storage capacity, that occurs through an intercalation path, is closely associated to the surface area, morphology, crys-tallinity and its orientation. Soft carbons are commonly well accepted and used in the battery industry. It was seen that Soft Carbon is quite a mature technology, while Hard Carbon may present an interesting alternative solution especially for applications requiring high capacity such as in the Electric Vehicle sector. Titanium Oxide anodes are currently under development with already some utilization in the batteries industry because, unless their poor energy density, the high reversible capacity, the high power density and the associated safety make these materials very good candidates for application in high power batteries for application in Hybrid Electric Vehicles and system that required High Power. Graphene was also extensively reviewed. In particular, it was seen that their electrical properties make this materials especially suitable for hybrid graphene/metal anodes (example graphene with SnO2 and Fe2O3). CNTs were overview for their very interesting academic results, although production cost might hinder their application as anode active material in the battery industry for the next future.

In a second category, alloying materials such as Si, Ge, SiO, SnO2 were described. These materials can provide larger capacities and high energy density compared to the previous group, by reacting with lithium in an alloy/de-alloy electrochemical mechanism. However, this process implies large volume expansion which results into substantial capacity loss upon cycling. The reduction from bulk dimensions to the nanoscale, along with the realization of complex structures by the combination with conductive matrices, has been proposed to overcome the above specified issues and to improve the overall anode performance. Silicon and SnO2 and their composite with carbon are the most promising materials for applications in future lithium batteries, however an inexpensive way for their mass production as anode materials is still necessary. On the other hand Ge, although interesting for its electrochemical properties and excellent experimental laboratory results, suffers of the drawback of being the fiftieth ranks element in terms of abundance in the Earth's crust. Therefore, it seems not to be a good option for lithium battery technology mass application.

In the third group, materials reacting with lithium in a conversion reaction fashion were described. In particular, metal oxides/ phosphides/nitrides/sulphides were considered. However, these materials are still far away from the large commercial lithium battery market, due to poor capacity retention and large potential hysteresis. Therefore, a variety of nanostructured forms of these materials have also been investigated to address the above identified problems.

Finally, from this review we can conclude that nanotechnology is definitely a formidable approach for engineering the next generation of anode materials for lithium batteries. In order to utilize the described materials as effective anodes in commercial LIBs, especially for electric vehicle applications, more research work is however required. In fact, it is necessary to achieve both higher energy and higher power density together with the developing of inexpensive fabrication processes for large scale synthesis of nanosized materials. Furthermore, the investigation of the mechanisms ruling the interaction between lithium and the nanosized forms of the described materials along with the electron transport properties at the electrode/electrolyte interface are of crucial importance for the designing of the next generation of anode active materials engineered by nanotechnology.


[1] C. Capiglia, Symposium on "Welfare Future Challenges Converging to Get over the Ditch", 11th Nov., 2011. Osaka, Japan,

[2] R. Marom, S.F. Amalraj, N. Leifer, D. Jacob, D. Aurbach, J. Mater. Chem. 21 (2011) 9938—9954.

[3] G.P. Gholam Abbas Nazri, Lithium Batteries: Science and Technology, 2003 ed., Springer, 2003.

[4] G. Girishkumar, B. McCloskey, A.C. Luntz, S. Swanson, W. Wilcke, J. Phys. Chem. Lett. 1 (2010) 2193—2203.

[5] B. Scrosati, J. Garche, J. Power Sources 195 (2010) 2419—2430.

[6] M. Armand, J.M. Tarascon, Nature 451 (2008) 652—657.

[7] T.-H. Kim, J.-S. Park, S.K. Chang, S. Choi, J.H. Ryu, H.-K. Song, Adv. Energy Mater. 2 (2012) 860—872.

[8] J.B. Goodenough, K.-S. Park, J. Am. Chem. Soc. 135 (2013) 1167—1176.

[9] V. Etacheri, R. Marom, R. Elazari, G. Salitra, D. Aurbach, Energy Environ. Sci. 4 (2011) 3243—3262.

[10] M. Winter, R.J. Brodd, Chem. Rev. 104 (2004) 4245—4270.

[11] F. Cheng, J. Liang, Z. Tao,J. Chen, Adv. Mater. 23 (2011) 1695—1715.

[12] H. Li, Z. Wang, L. Chen, X. Huang, Adv. Mater. 21 (2009) 4593—4607.

[13] J.B. Goodenough, Y. Kim, Chem. Mater. 22 (2009) 587—603.

[14] J.M. Tarascon, M. Armand, Nature 414 (2001) 359—367.

[15] B. Xu, D. Qian, Z. Wang, Y.S. Meng, Mater. Sci. Eng.: R: Rep. 73 (2012) 51—65.

[16] J. Li, J. Klee Barillas, C. Guenther, M.A. Danzer, J. Power Sources 230 (2013) 244—250.

[17] M.M. Thackeray, C. Wolverton, E.D. Isaacs, Energy Environ. Sci. 5 (2012) 7854—7863.

[18] A. Manthiram, J. Phys. Chem. Lett. 2 (2011) 176—184.

[19] Li Yanga, Boris Ravdelb, B.L. Lucht, Electrochem. Solid-State Lett. 13 (2010) A95—A97.

[20] A.v. Cresce, K. Xu, J. Electrochem. Soc. 158 (2011) A337—A342.

[21] R. Dedryvère, D. Foix, S. Franger, S. Patoux, L. Daniel, D. Gonbeau, J. Phys. Chem. C 114 (2010) 10999—11008.

[22] K.T. Lee, S. Jeong, J. Cho, Acc. Chem. Res. 5 (2012) 1161—1170.

[23] C. Capiglia, Y. Saito, H. Kageyama, P. Mustarelli, T. Iwamoto, T. Tabuchi, H. Tukamoto, J. Power Sources 81—82 (1999) 859—862.

[24] C. Capiglia, Y. Saito, H. Yamamoto, H. Kageyama, P. Mustarelli, Electrochim. Acta 45 (2000) 1341 — 1345.

[25] C. Capiglia, Y. Saito, H. Kataoka, T. Kodama, E. Quartarone, P. Mustarelli, Solid State Ionics 131 (2000) 291—299.

[26] C. Capiglia, J. Yang, N. Imanishi, A. Hirano, Y. Takeda, O. Yamamoto, Solid State Ionics 154—155 (2002) 7—14.

[27] C. Capiglia, J. Yang, N. Imanishi, A. Hirano, Y. Takeda, O. Yamamoto, J. Power Sources 119—121 (2003) 826—832.

[28] L. Hu, Z. Zhang, K. Amine, J. Power Sources 236 (2013) 175—180.

[29] X.-G. Sun, C. Liao, N. Shao, J.R. Bell, B. Guo, H. Luo, D.-E. Jiang, S. Dai, J. Power Sources 237 (2013) 5—12.

[30] E. Quartarone, P. Mustarelli, Chem. Soc. Rev. 40 (2011) 2525—2540.

[31] K. Xu, Chem. Rev. 104 (2004) 4303—4418.

[32] R. Borup, J. Meyers, B. Pivovar, Y.S. Kim, R. Mukundan, N. Garland, D. Myers, M. Wilson, F. Garzon, D. Wood, P. Zelenay, K. More, K. Stroh, T. Zawodzinski, J. Boncella, J.E. McGrath, M. Inaba, K. Miyatake, M. Hori, K. Ota, Z. Ogumi, S. Miyata, A. Nishikata, Z. Siroma, Y. Uchimoto, K. Yasuda, K.-i. Kimijima, N. Iwashita, Chem. Rev. 107 (2007) 3904—3951.

[33] Y. Liang, Z. Tao, J. Chen, Adv. Energy Mater. 2 (2012) 742—769.

[34] Z. Song, H. Zhou, Energy Environ. Sci. 6 (2013) 2280—2301.

[35] S. Goriparti, M.N.K. Harish, S. Sampath, Chem. Commun. 49 (2013) 7234.

[36] Z. Gong, Y. Yang, Energy Environ. Sci. 4 (2011) 3223—3242.

[37] C.-C. Li, Y.-W. Wang, J. Power Sources 227 (2013) 204—210.

[38] M.S. Whittingham, Chem. Rev. 104 (2004) 4271—4302.

[39] K. Persson, V.A. Sethuraman, L.J. Hardwick, Y. Hinuma, Y.S. Meng, A. van der Ven, V. Srinivasan, R. Kostecki, G. Ceder, J. Phys. Chem. Lett. 1 (2010) 1176— 1180.

[40] N.A. Kaskhedikar, J. Maier, Adv. Mater. 21 (2009) 2664—2680.

[41] J. Liu, Adv. Funct. Mater. 23 (2013) 924—928.

[42] F. Orsini, A. du Pasquier, B. Beaudouin, J.M. Tarascon, M. Trentin, N. Langenhuizen, E. de Beer, P. Notten, J. Power Sources 81 —82 (1999) 918—921.

[43] B.J. Landi, M.J. Ganter, C.D. Cress, R.A. DiLeo, R.P. Raffaelle, Energy Environ. Sci. 2 (2009) 638—654.

[44] C. Kim, K.S. Yang, M. Kojima, K. Yoshida, Y.J. Kim, Y.A. Kim, M. Endo, Adv. Funct. Mater. 16 (2006) 2393—2397.

[45] J. Hou, Y. Shao, M.W. Ellis, R.B. Moore, B. Yi, Phys. Chem. Chem. Phys. 13 (2011) 15384—15402.

[46] H. Zhou, S. Zhu, M. Hibino, I. Honma, M. Ichihara, Adv. Mater. 15 (2003) 2107—2111.

[47] J. Yang, Y. Takeda, N. Imanishi, C. Capiglia, J.Y. Xie, O. Yamamoto, Solid State Ionics 152—153 (2002) 125—129.

[48] M. Ge, J. Rong, X. Fang, C. Zhou, Nano Lett. 12 (2012) 2318—2323.

[49] I.-S. Hwang, J.-C. Kim, S.-D. Seo, S. Lee, J.-H. Lee, D.-W. Kim, Chem. Commun. 48 (2012) 7061—7063.

[50] K. Zhuo, M.-G. Jeong, C.-H. Chung, J. Power Sources 244 (2013) 601—605.

[51] J. Jiang, Y. Li, J. Liu, X. Huang, C. Yuan, X.W. Lou, Adv. Mater. 24 (2012) 5166— 5180.

Z. Wang, L Zhou, X.W. Lou, Adv. Mater. 24 (2012) 1903—1911.

P.P. Prosini, M. Carewska, S. Loreti, C. Minarini, S. Passerini, Int. J. Inorg.

Mater. 2 (2000) 365—370.

C.-H. Lai, M.-Y. Lu, L.-J. Chen, J. Mater. Chem. 22 (2012) 19—30. S. Boyanov, K. Annou, C. Villevieille, M. Pelosi, D. Zitoun, L Monconduit, Ionics 14 (2008) 183—190.

L Ji, Z. Lin, M. Alcoutlabi, X. Zhang, Energy Environ. Sci. 4 (2011) 2682—2699. Q. Sun, X.-Q. Zhang, F. Han, W.-C. Li, A.-H. Lu, J. Mater. Chem. 22 (2012) 17049—17054.

J. Chen, X.-h. Xia, J.-p. Tu, Q.-q. Xiong, Y.-X. Yu, X.-l. Wang, C.-d. Gu, J. Mater. Chem. 22 (2012) 15056—15061.

A. Ueda, M. Nagao, A. Inoue, A. Hayashi, Y. Seino, T. Ota, M. Tatsumisago, J. Power Sources 244 (2013) 597—600.

H. Hwang, H. Kim, J. Cho, Nano Lett. 11 (2011) 4826—4830.

P.G. Bruce, B. Scrosati, J.-M. Tarascon, Angew. Chem. Int. Ed. 47 (2008) 2930—

Y. Wang, H. Li, P. He, E. Hosono, H. Zhou, Nanoscale 2 (2010) 1294—1305. Nahong Zhao, Lijun Fu, Lichun Yang, Tao Zhang, Gaojun Wang, Y. Wu, a.T.v. Ree, Pure Appl. Chem. 80 (2008) 2283—2295.

L Qiao, X. Sun, Z. Yang, X. Wang, Q. Wang, D. He, Carbon 54 (2013) 29—35.

F. Jiao, P.G. Bruce, Adv. Mater. 19 (2007) 657—660.

H. Li, H. Zhou, Chem. Commun. 48 (2012) 1201—1217.

Y.C. Yen, S.C. Chao, H.C. Wu, N.L Wu, J. Electrochem. Soc. 156 (2009) A95—

H.L. Zhang, S.H. Liu, F. Li, S. Bai, C. Liu, J. Tan, H.M. Cheng, Carbon 44 (2006) 2212—2218.

M. Yashio, H. Wang, K. Fukuda, T. Umeno, T. Abe, Z. Ogumi, J. Mater. Chem. 14(2004) 1754—1758.

LJ. Fu, H. Liu, C. Li, Y.P. Wu, E. Rahm, R. Holze, H.Q. Wu, Solid State Sci. 8 (2006) 113—128.

Y.B. He, F. Ning, B. Li, Q.S. Song, W. Lv, H. Du, D. Zhai, F. Su, Q.H. Yang, F. Kang, J. Power Sources 202 (2012) 253—261.

S.H. Ng, J. Wang, D. Wexler, K. Konstantinov, Z.P. Guo, H.K. Liu, Angew. Chem. 118 (2006) 7050—7053.

G. Cui, L. Gu, L. Zhi, N. Kaskhedikar, P.A. Aken, K. Mullen, J. Maier, Adv. Mater. 20 (2008) 3079—3083.

T.-H. Park, J.-S. Yeo, M.-H. Seo, J. Miyawaki, I. Mochida, S.-H. Yoon, Electro-chim. Acta 93 (2013) 236—240.

O. Haik, S. Ganin, G. Gershinsky, E. Zinigrad, B. Markovsky, D. Aurbach,

I. Halalay, J. Electrochem. Soc. 158 (2011) A913—A923.

H. Wang, M. Yoshio, T. Abe, Z. Ogumi, J. Electrochem. Soc. 149 (2002) A499— A503.

H. Nakagawa, Y. Domi, T. Doi, M. Ochida, S. Tsubouchi, T. Yamanaka, T. Abe, Z. Ogumi, J. Power Sources 236 (2013) 138—144.

S. Tsubouchi, Y. Domi, T. Doi, M. Ochida, H. Nakagawa, T. Yamanaka, T. Abe, Z. Ogumi, J. Electrochem. Soc. 160 (2013) A575—A580. H. Zheng, Q. Qu, L Zhang, G. Liu, V.S. Battaglia, RSC Adv. 2 (2012) 4904— 4912.

S.L. Candelaria, Y. Shao, W. Zhou, X. Li, J. Xiao, J.-G. Zhang, Y. Wang, J. Liu, J. Li,

G. Cao, Nano Energy 1 (2012) 195—220.

J. Sun, H. Liu, X. Chen, D.G. Evans, W. Yang, X. Duan, Adv. Mater. 25 (2013) 1124.

J. Ni, Y. Huang, L. Gao, J. Power Sources 223 (2013) 306—311.

H. Fujimoto, K. Tokumitsu, A. Mabuchi, N. Chinnasamy, T. Kasuh, J. Power Sources 195 (2010) 7452—7456.

J. Yang, X.-y. Zhou, J. Li, Y.-l. Zou, J.-j. Tang, Mater. Chem. Phys. 135 (2012) 445—450.

C.A. Bridges, X.-G. Sun, J. Zhao, M.P. Paranthaman, S. Dai, J. Phys. Chem. C 116 (2012) 7701—7711.

Y. Liu, J.S. Xue, T. Zheng, J.R. Dahn, Carbon 34 (1996) 193—200.

J. Wang, J.-L. Liu, Y.-G. Wang, C.-X. Wang, Y.-Y. Xia, Electrochim. Acta 74

(2012) 1—7.

J. Hu, H. Li, X. Huang, Solid State Ionics 176 (2005) 1151—1159. W. Li, M. Chen, C. Wang, Mater. Lett. 65 (2011) 3368—3370. Y. Yu, C. Cui, W. Qian, Q. Xie, C. Zheng, C. Kong, F. Wei, Asia-Pacific J. Chem. Eng. 8 (2013) 234—245.

V. Meunier, J. Kephart, C. Roland, J. Bernholc, Phys. Rev. Lett. 88 (2002) 075506.

C.M. Schauerman, M.J. Ganter, G. Gaustad, C.W. Babbitt, R.P. Raffaelle,

B.J. Landi, J. Mater. Chem. 22 (2012) 12008—12015.

K. Nishidate, M. Hasegawa, Phys. Rev. B 71 (2005) 245418.

J. Zhao, A. Buldum, J. Han, J. Ping Lu, Phys. Rev. Lett. 85 (2000) 1706—1709.

R.A. DiLeo, A. Castiglia, M.J. Ganter, R.E. Rogers, C.D. Cress, R.P. Raffaelle,

B.J. Landi, ACS Nano 4 (2010) 6121—6131.

R. Lv, L. Zou, X. Gui, F. Kang, Y. Zhu, H. Zhu, J. Wei, J. Gu, K. Wang, D. Wu, Chem. Commun. (2008) 2046—2048.

J. Zhou, H. Song, B. Fu, B. Wu, X. Chen, J. Mater. Chem. 20 (2010) 2794— 2800.

H.S. Oktaviano, K. Yamada, K. Waki, J. Mater. Chem. 22 (2012) 25167—25173.

C. de las Casas, W. Li, J. Power Sources 208 (2012) 74—85.

Y. Gu, F. Wu, Y. Wang, Adv. Funct. Mater. 23 (2013) 893—899.

L. Xue, G. Xu, Y. Li, S. Li, K. Fu, Q. Shi, X. Zhang, ACS Appl. Mater. Interfaces 5

(2012) 21—25.

T.H. Yoon, Y.J. Park, Solid State Ionics 225 (2012) 498—501.

Y. Wu, Y. Wei, J. Wang, K. Jiang, S. Fan, Nano Lett. 13 (2013) 818—823.

[ 104] K. Bindumadhavan, S.K. Srivastava, S. Mahanty, Chem. Commun. 49 (2013) 1823—1825.

105] X. Huang, X. Qi, F. Boey, H. Zhang, Chem. Soc. Rev. 41 (2012) 666—686.

106] M. Liang, L Zhi, J. Mater. Chem. 19 (2009) 5871—5878.

107] D.A.C. Brownson, D.K. Kampouris, C.E. Banks, J. Power Sources 196 (2011) 4873—4885.

108] Y. Liu, V.l. Artyukhov, M. Liu, A.R. Harutyunyan, B.I. Yakobson, J. Phys. Chem. Lett. 4 (2013) 1737—1742.

109] H.J. Hwang, J. Koo, M. Park, N. Park, Y. Kwon, H. Lee, J. Phys. Chem. C 117 (2013) 6919—6923.

110] D. Pan, S. Wang, B. Zhao, M. Wu, H. Zhang, Y. Wang, Z. Jiao, Chem. Mater. 21 (2009) 3136—3142.

111] P. Lian, X. Zhu, S. Liang, Z. Li, W. Yang, H. Wang, Electrochim. Acta 55 (2010) 3909—3914.

112] Z.-L Wang, D. Xu, H.-G. Wang, Z. Wu, X.-B. Zhang, ACS Nano 7 (2013) 2422— 2430.

113] T. Bhardwaj, A. Antic, B. Pavan, V. Barone, B.D. Fahlman, J. Am. Chem. Soc. 132 (2010) 12556—12558.

114] V.H. Pham, K.-H. Kim, D.-W. Jung, K. Singh, E.-S. Oh, J.S. Chung, J. Power Sources 244 (2013) 280—286.

115] X. Li, H. Song, H. Wang, Y. Zhang, K. Du, H. Li, J. Huang, J. Appl. Electrochem. 42 (2012) 1065—1070.

116] H. Xia, D. Zhu, Y. Fu, X. Wang, Electrochim. Acta 83 (2012) 166—174.

117] B.P. Vinayan, S. Ramaprabhu, J. Mater. Chem. A 1 (2013) 3865—3871.

118] B. Wang, X. Li, X. Zhang, B. Luo, M. Jin, M. Liang, S.A. Dayeh, S.T. Picraux, L Zhi, ACS Nano 7 (2013) 1437—1445.

119] A. Hu, X. Chen, Y. Tang, Q. Tang, L. Yang, S. Zhang, Electrochem. Commun. 28 (2013) 139—142.

120] M. Wagemaker, F.M. Mulder, Acc. Chem. Res. 46 (2013) 1206—1215.

121] Z. Chen, I. Belharouak, Y.K. Sun, K. Amine, Adv. Funct. Mater. 23 (2013) 959— 969.

122] Z. Hong, M. Wei, J. Mater. Chem. A 1 (2013) 4403—4414.

123] A. Moretti, G.-T. Kim, D. Bresser, K. Renger, E. Paillard, R. Marassi, M. Winter, S. Passerini, J. Power Sources 221 (2013) 419—426.

124] Y. Ren, Z. Liu, F. Pourpoint, A.R. Armstrong, C.P. Grey, P.G. Bruce, Angew. Chem. Int. Ed. 51 (2012) 2164—2167.

125] Y. Ma, G. Ji, B. Ding, J.Y. Lee, J. Mater. Chem. 22 (2012) 24380—24385.

126] L Shen, C. Yuan, H. Luo, X. Zhang, K. Xu, Y. Xia, J. Mater. Chem. 20 (2010) 6998—7004.

127] X. Li, C. Wang, J. Mater. Chem. A 1 (2013) 165—182.

128] S.K. Martha, O. Haik, V. Borgel, E. Zinigrad, I. Exnar, T. Drezen, J.H. Miners, D. Aurbach, J. Electrochem. Soc. 158 (2011) A790—A797.

129] A. Mahmoud, J.M. Amarilla, K. Lasri, I. Saadoune, Electrochim. Acta 93 (2013) 163—172.

130] G.-N. Zhu, L. Chen, Y.-G. Wang, C.-X. Wang, R.-C. Che, Y.-Y. Xia, Adv. Funct. Mater. 23 (2013) 640—647.

131] J. Wang, X.-M. Liu, H. Yang, X.-d. Shen, J. Alloys Compd. 509 (2011) 712—718.

132] J.-Y. Lin, C.-C. Hsu, H.-P. Ho, S.-h. Wu, Electrochim. Acta 87 (2013) 126—132.

133] A.S. Prakash, P. Manikandan, K. Ramesha, M. Sathiya, J.M. Tarascon, A.K. Shukla, Chem. Mater. 22 (2010) 2857—2863.

134] L Shen, E. Uchaker, X. Zhang, G. Cao, Adv. Mater. 24 (2012) 6502—6506.

135] X. Meng, M.N. Banis, D. Geng, X. Li, Y. Zhang, R. Li, H. Abou-Rachid, X. Sun, Appl. Surf. Sci. 266 (2013) 132—140.

136] D. Deng, M.G. Kim, J.Y. Lee, J. Cho, Energy Environ. Sci. 2 (2009) 818—837.

137] J.W. Kang, D.H. Kim, V. Mathew, J.S. Lim, J.H. Gim, J. Kim, J. Electrochem. Soc. 158 (2011) A59—A62.

138] D. Bresser, E. Paillard, E. Binetti, S. Krueger, M. Striccoli, M. Winter, S. Passerini, J. Power Sources 206 (2012) 301—309.

139] D. Dambournet, I. Belharouak, K. Amine, Chem. Mater. 22 (2009) 1173— 1179.

140] X. Su, Q. Wu, X. Zhan, J. Wu, S. Wei, Z. Guo, J. Mater. Sci. 47 (2012) 2519— 2534.

141] A.R. Armstrong, G. Armstrong, J. Canales, R Garcia, P.G. Bruce, Adv. Mater. 17 (2005) 862—865.

142] C. Jiang, I. Honma, T. Kudo, H. Zhou, Electrochem. Solid-State Lett. 10 (2007) A127—A129.

143] A.K. Rai, L.T. Anh, J. Gim, V. Mathew, J. Kang, B.J. Paul, J. Song, J. Kim, Electrochim. Acta 90 (2013) 112—118.

144] V. Gentili, S. Brutti, L.J. Hardwick, A.R. Armstrong, S. Panero, P.G. Bruce, Chem. Mater. 24 (2012) 4468—4476.

145] H. Liu, Z. Bi, X.-G. Sun, R.R. Unocic, M.P. Paranthaman, S. Dai, G.M. Brown, Adv. Mater. 23 (2011) 3450—3454.

146] W. Xu, Z. Wang, Z. Guo, Y. Liu, N. Zhou, B. Niu, Z. Shi, H. Zhang, J. Power Sources 232 (2013) 193—198.

147] S.-J. Park, Y.-J. Kim, H. Lee, J. Power Sources 196 (2011) 5133—5137.

148] J. Wang, Y. Zhou, B. Xiong, Y. Zhao, X. Huang, Z. Shao, Electrochim. Acta 88 (2013) 847—857.

149] A.L.M. Reddy, S.R. Gowda, M.M. Shaijumon, P.M. Ajayan, Adv. Mater. 24 (2012) 5045—5064.

150] C.-M. Park, J.-H. Kim, H. Kim, H.-J. Sohn, Chem. Soc. Rev. 39 (2010) 3115— 3141.

151] W.-J. Zhang, J. Power Sources 196 (2011) 13—24.

152] U. Kasavajjula, C. Wang, A.J. Appleby, J. Power Sources 163 (2007) 1003— 1039.

[ 153] H. Zhang, P.V. Braun, Nano Lett. 12 (2012) 2778—2783.

161 162

180 181

J. Gu, S.M. Collins, A.I. Carim, X. Hao, B.M. Bartlett, S. Maldonado, Nano Lett. 12 (2012)4617-4623.

H. Wu, Y. Cui, Nano Today 7 (2012) 414-429.

J.R. Szczech, S.Jin, Energy Environ. Sci. 4 (2011) 56-72.

R. Teki, M.K. Datta, R. Krishnan, T.C. Parker, T.-M. Lu, P.N. Kumta, N. Koratkar,

Small 5 (2009) 2236-2242.

A. Magasinski, P. Dixon, B. Hertzberg, A. Kvit, J. Ayala, G. Yushin, Nat. Mater. 9 (2010) 353-358.

R. Chandrasekaran, A. Magasinki, G. Yushin, T.F. Fuller, J. Electrochem. Soc. 157 (2010) A1139-A1151.

B. Key, R. Bhattacharyya, M. Morcrette, V. Seznec, J.-M. Tarascon, C.P. Grey, J. Am. Chem. Soc. 131 (2009) 9239-9249.

T.D. Hatchard, J.R. Dahn, J. Electrochem. Soc. 151 (2004) A838-A842. S. Misra, N. Liu, J. Nelson, S.S. Hong, Y. Cui, M.F. Toney, ACS Nano 6 (2012) 5465-5473.

M.T. McDowell, S.W. Lee, J.T. Harris, B.A. Korgel, C. Wang, W.D. Nix, Y. Cui, Nano Lett. 13 (2013) 758-764.

M. Yoshio, H. Wang, K. Fukuda, T. Umeno, N. Dimov, Z. Ogumi, J. Electrochem. Soc. 149 (2002) A1598-A1603.

C.K. Chan, H. Peng, G. Liu, K. McIlwrath, X.F. Zhang, R.A. Huggins, Y. Cui, Nat. Nano 3 (2008) 31-35.

Y. Yao, K. Huo, L. Hu, N. Liu, J.J. Cha, M.T. McDowell, P.K. Chu, Y. Cui, ACS Nano 5 (2011) 8346-8351.

C.K. Chan, R.N. Patel, M.J. O'Connell, B.A. Korgel, Y. Cui, ACS Nano 4 (2010) 1443-1450.

R. Huang, X. Fan, W. Shen, J. Zhu, Appl. Phys. Lett. 95 (2009) 133113-133119. Z. Wen, G. Lu, S. Mao, H. Kim, S. Cui, K. Yu, X. Huang, P.T. Hurley, O. Mao, J. Chen, Electrochem. Commun. 29 (2013) 67-70.

T. Song, J. Xia, J.-H. Lee, D.H. Lee, M.-S. Kwon, J.-M. Choi, J. Wu, S.K. Doo, H. Chang, W.I. Park, D.S. Zang, H. Kim, Y. Huang, K.-C. Hwang, J.A. Rogers, U. Paik, Nano Lett. 10 (2010) 1710-1716.

M.-H. Park, M.G. Kim, J. Joo, K. Kim, J. Kim, S. Ahn, Y. Cui, J. Cho, Nano Lett. 9

(2009) 3844-3847.

H. Wu, G. Chan, J.W. Choi, I. Ryu, Y. Yao, M.T. McDowell, S.W. Lee, A. Jackson, Y. Yang, L. Hu, Y. Cui, Nat. Nano 7 (2012) 310-315. S.W. Hwang, J.K. Lee, W.Y. Yoon, J. Power Sources 244 (2013) 620-624. K. Song, S. Yoo, K. Kang, H. Heo, Y.-M. Kang, M.-H. Jo, J. Power Sources 229 (2013) 229-233.

B. Liu, A. Abouimrane, Y. Ren, M. Balasubramanian, D. Wang, Z.Z. Fang, K. Amine, Chem. Mater. 24 (2012) 4653-4661.

Y. Yamada, Y. Iriyama, T. Abe, Z. Ogumi, J. Electrochem. Soc. 157 (2010) A26-A30.

Y. Hwa, C.-M. Park, H.-J. Sohn, Meeting Abstracts, MA2012-02, 2012, p. 913.

C.-M. Park, W. Choi, Y. Hwa, J.-H. Kim, G. Jeong, H.-J. Sohn, J. Mater. Chem. 20

(2010) 4854-4860.

M. Zhou, M.L. Gordin, S. Chen, T. Xu, J. Song, D. Lv, D. Wang, Electrochem. Commun. 28 (2013) 79-82.

G. Jeong, J.-H. Kim, Y.-U. Kim, Y.-J. Kim, J. Mater. Chem. 22 (2012) 79998004.

J.-H. Kim, H.-J. Sohn, H. Kim, G. Jeong, W. Choi, J. Power Sources 170 (2007) 456-459.

T. Tabuchi, H. Yasuda, M. Yamachi, J. Power Sources 146 (2005) 507-509. J.Wang, H. Zhao, J. He, C. Wang, J. Wang, J. Power Sources 196 (2011)4811-4815.

M. Yamada, K. Uchitomi, A. Ueda, K. Matsumoto, T. Ohzuku, J. Power Sources 225 (2013) 221-225.

M. Miyachi, H. Yamamoto, H. Kawai, J. Electrochem. Soc. 154 (2007) A376-A380.

M. Miyachi, H. Yamamoto, H. Kawai, T. Ohta, M. Shirakata, J. Electrochem. Soc. 152 (2005) A2089-A2091.

J.-H. Kim, C.-M. Park, H. Kim, Y.-J. Kim, H.-J. Sohn, J. Electroanal. Chem. 661

(2011) 245-249.

T. Kim, S. Park, S.M. Oh, J. Electrochem. Soc. 154 (2007) A1112-A1117.

B. Liu, A. Abouimrane, D.E. Brown, X. Zhang, Y. Ren, Z.Z. Fang, K. Amine, J. Mater. Chem. A 1 (2013) 4376-4382.

J.-I. Lee, S. Park, Nano Energy 2 (2013) 146-152.

N.G. Rudawski, B.R. Yates, M.R. Holzworth, K.S. Jones, R.G. Elliman, A.A. Volinsky, J. Power Sources 223 (2013) 336-340. A.M. Chockla, K.C. Klavetter, C.B. Mullins, B.A. Korgel, ACS Appl. Mater. Interfaces 4 (2012) 4658-4664.

X.H. Liu, S. Huang, S.T. Picraux, J. Li, T. Zhu, J.Y. Huang, Nano Lett. 11 (2011) 3991-3997.

C.H. Kim, H.S. Im, Y.J. Cho, C.S. Jung, D.M. Jang, Y. Myung, H.S. Kim, S.H. Back, Y.R. Lim, C.-W. Lee, J. Park, M.S. Song, W.-I. Cho, J. Phys. Chem. C 116 (2012) 26190-26196.

M.-H. Park, Y. Cho, K. Kim, J. Kim, M. Liu, J. Cho, Angew. Chem. Int. Ed. 50 (2011) 9647-9650.

G. Cui, L. Gu, L. Zhi, N. Kaskhedikar, P.A. van Aken, K. Müllen, J. Maier, Adv. Mater. 20 (2008) 3079-3083.

R.A. DiLeo, S. Frisco, M.J. Ganter, R.E. Rogers, R.P. Raffaelle, B.J. Landi, J. Phys. Chem. C 115 (2011) 22609-22614.

A.M. Chockla, M.G. Panthani, V.C. Holmberg, C.M. Hessel, D.K. Reid, T.D. Bogart, J.T. Harris, C.B. Mullins, B.A. Korgel, J. Phys. Chem. C 116 (2012) 11917-11923.

F.-W. Yuan, H.-J. Yang, H.-Y. Tuan, ACS Nano 6 (2012) 9932-9942.

[202 [203

[207 [208

[211 [212

[213 [214

[217 [218

[229 [230

[236 [237

[239 [240

[243 [244

J. Wang, N. Du, H. Zhang, J. Yu, D. Yang, J. Mater. Chem. 22 (2012) 1511— 1515.

K.H. Seng, M.-h. Park, Z.P. Guo, H.K. Liu, J. Cho, Nano Lett. 13 (2013) 1230— 1236.

H. Kim, J. Cho, J. Mater. Chem. 18 (2008) 771—775.

Z. Yang, G. Du, Z. Guo, X. Yu, S. Li, Z. Chen, P. Zhang, H. Liu, Nanoscale 2

(2010) 1011 — 1017.

X. Yin, L. Chen, C. Li, Q. Hao, S. Liu, Q. Li, E. Zhang, T. Wang, Electrochim. Acta 56 (2011) 2358—2363.

X.W. Guo, X.P. Fang, Y. Sun, L.Y. Shen, Z.X. Wang, L.Q. Chen, J. Power Sources 226 (2013) 75—81.

L. Noerochim, J.-Z. Wang, S.-L. Chou, H.-J. Li, H.-K. Liu, Electrochim. Acta 56 (2010) 314—320.

R. Ravikumar, S. Gopukumar, Phys. Chem. Chem. Phys. 15 (2013) 3712—3717. Y. Jiang, T. Yuan, W. Sun, M. Yan, ACS Appl. Mater. Interfaces 4 (2012) 6216— 6220.

D. Wang, X. Li, J. Yang, J. Wang, D. Geng, R. Li, M. Cai, T.-K. Sham, X. Sun, Phys. Chem. Chem. Phys. 15 (2013) 3535—3542.

M.-S. Park, G.-X. Wang, Y.-M. Kang, D. Wexler, S.-X. Dou, H.-K. Liu, Angew. Chem. 119 (2007) 764—767.

J. Ye, H. Zhang, R. Yang, X. Li, L. Qi, Small 6 (2010) 296—306.

J. Liu, Y. Li, X. Huang, R. Ding, Y. Hu, J. Jiang, L. Liao, J. Mater. Chem. 19 (2009)


Y. Wang, H. C. Zeng, J. Y. Lee, Adv. Mater. 18 (2006) 645—649.

Z. Wang, D. Luan, F.Y.C. Boey, X.W. Lou, J. Am. Chem. Soc. 133 (2011) 4738—

J.S. Chen, M.F. Ng, H.B. Wu, L. Zhang, X.W. Lou, CrystEngComm 14 (2012)


P. Poizot, S. Laruelle, S. Grugeon, J.-M. Tarascon, J. Electrochem. Soc. 149 (2002) A1212—A1217.

J.-S. Xu, Y.-J. Zhu, ACS Appl. Mater. Interfaces 4 (2012) 4752—4757. B. Koo, H. Xiong, M.D. Slater, V.B. Prakapenka, M. Balasubramanian, P. Podsiadlo, C.S. Johnson, T. Rajh, E.V. Shevchenko, Nano Lett. 12 (2012) 2429—2435.

J. Liu, Y. Li, H. Fan, Z. Zhu, J. Jiang, R. Ding, Y. Hu, X. Huang, Chem. Mater. 22 (2009) 212—217.

N. Kang, J.H. Park, J. Choi, J. Jin, J. Chun, I.G. Jung, J. Jeong, J.-G. Park, S.M. Lee,

H.J. Kim, S.U. Son, Angew. Chem. Int. Ed. 51 (2012) 6626—6630.

X.-H. Ma, X.-Y. Feng, C. Song, B.-K. Zou, C.-X. Ding, Y. Yu, C.-H. Chen, Elec-trochim. Acta 93 (2013) 131—136.

S. Mitra, P. Poizot, A. Finke, J.M. Tarascon, Adv. Funct. Mater. 16 (2006) 2281—2287.

X. Zhu, W. Wu, Z. Liu, L. Li, J. Hu, H. Dai, L. Ding, K. Zhou, C. Wang, X. Song, Electrochim. Acta 95 (2013) 24—28.

J.-K. Hwang, H.-S. Lim, Y.-K. Sun, K.-D. Suh, J. Power Sources 244 (2013) 538— 543.

I.T. Kim, A. Magasinski, K. Jacob, G. Yushin, R. Tannenbaum, Carbon 52 (2013) 56—64.

B. Wang, J.S. Chen, H.B. Wu, Z. Wang, X.W. Lou, J. Am. Chem. Soc. 133 (2011) 17146—17148.

C. Wu, P. Yin, X. Zhu, C. OuYang, Y. Xie, J. Phys. Chem. B 110 (2006) 17806— 17812.

T. Muraliganth, A. Vadivel Murugan, A. Manthiram, Chem. Commun. (2009) 7360—7362.

X. Xu, R. Cao, S. Jeong, J. Cho, Nano Lett. 12 (2012) 4988—4991.

H. Sohn, Z. Chen, Y.S. Jung, Q. Xiao, M. Cai, H. Wang, Y. Lu, J. Mater. Chem. A 1

(2013) 4539—4545.

D. Barreca, M. Cruz-Yusta, A. Gasparotto, C. Maccato, J. Morales, A. Pozza, C. Sada, L. Sanchez, E. Tondello, J. Phys. Chem. C 114 (2010) 10054— 10060.

L. Zhang, P. Hu, X. Zhao, R. Tian, R. Zou, D. Xia, J. Mater. Chem. 21 (2011) 18279—18283.

L. Fei, Q. Lin, B. Yuan, M. Naeemi, Y. Xu, Y. Li, S. Deng, H. Luo, Mater. Lett. 98 (2013) 59—62.

W. Yuan, D. Xie, Z. Dong, Q. Su, J. Zhang, G. Du, B. Xu, Mater. Lett. 97 (2013) 129—132.

F. Wang, C. Lu, Y. Qin, C. Liang, M. Zhao, S. Yang, Z. Sun, X. Song, J. Power Sources 235 (2013) 67—73.

C.C. Li, Q.H. Li, L.B. Chen, T.H. Wang, J. Mater. Chem. 21 (2011) 11867—11872.

G. Binotto, D. Larcher, A.S. Prakash, R. Herrera Urbina, M.S. Hegde, J.M. Tarascon, Chem. Mater. 19 (2007) 3032—3040.

H. Guan, X. Wang, H. Li, C. Zhi, T. Zhai, Y. Bando, D. Golberg, Chem. Commun. 48 (2012) 4878—4880.

Y. Sun, X. Hu, W. Luo, Y. Huang, J. Phys. Chem. C 116 (2012) 20794—20799. C. Peng, B. Chen, Y. Qin, S. Yang, C. Li, Y. Zuo, S. Liu, J. Yang, ACS Nano 6 (2012) 1074—1081.

Z.-S. Wu, W. Ren, L. Wen, L. Gao, J. Zhao, Z. Chen, G. Zhou, F. Li, H.-M. Cheng, ACS Nano 4 (2010) 3187—3194.

A. Paolella, R. Brescia, M. Prato, M. Povia, S. Marras, L. De Trizio, A. Falqui, L. Manna, C. George, ACS Appl. Mater. Interfaces 5 (2013) 2745—2751. J. Li, S. Xiong, X. Li, Y. Qian, Nanoscale 5 (2013) 2045—2054. V. Aravindan, P. Suresh Kumar, J. Sundaramurthy, W.C. Ling, S. Ramakrishna, S. Madhavi, J. Power Sources 227 (2013) 284—290.

A. Bhaskar, M. Deepa, T. Narasinga Rao, ACS Appl. Mater. Interfaces 5 (2013) 2555—2566.

[246] H. Liu, X. Du, X. Xing, G. Wang, S.Z. Qiao, Chem. Commun. 48 (2012) 865867.

[247] B. Laik, P. Poizot, J.-M. Tarascon, J. Electrochem. Soc. 149 (2002) A251-A255.

[248] S. Grugeon, S. Laruelle, R. Herrera-Urbina, L. Dupont, P. Poizot, J.-M. Tarascon, J. Electrochem. Soc. 148 (2001) A285-A292.

[249] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.M. Tarascon, Nature 407 (2000) 496-499.

[250] V. Pralong, D.C.S. Souza, K.T. Leung, L.F. Nazar, Electrochem. Commun. 4 (2002) 516-520.

[251] C. Villevieille, F. Robert, P.L. Taberna, L. Bazin, P. Simon, L. Monconduit, J. Mater. Chem. 18 (2008) 5956-5960.

[252] S. Boyanov, D. Zitoun, M. Ménétrier, J.C. Jumas, M. Womes, L. Monconduit, J. Phys. Chem. C 113 (2009) 21441-21452.

[253] L. Li, Y. Peng, H. Yang, Electrochim. Acta 95 (2013) 230-236.

[254] M.G. Kim, J. Cho, Adv. Funct. Mater. 19 (2009) 1497-1514.

[255] M.C. Stan, R. Klopsch, A. Bhaskar, J. Li, S. Passerini, M. Winter, Adv. Energy Mater. 3 (2013) 231-238.

[256] Y. Lu, J.-P. Tu, Q.-Q. Xiong, J.-Y. Xiang, Y.-J. Mai, J. Zhang, Y.-Q. Qiao, X.-L. Wang, C.-D. Gu, S.X. Mao, Adv. Funct. Mater. 22 (2012) 3927-3935.

[257] A. Hayashi, A. Inoue, M. Tatsumisago, J. Power Sources 189 (2009) 669-671.

[258] Y. Lu, J.P. Tu, J.Y. Xiang, X.L. Wang, J. Zhang, Y.J. Mai, S.X. Mao, J. Phys. Chem. C 115 (2011) 23760-23767.

[259] D. Yang, J. Zhu, X. Rui, H. Tan, R. Cai, H.E. Hoster, D.Y.W. Yu, H.H. Hng, Q. Yan, ACS Appl. Mater. Interfaces 5 (2013) 1093-1099.

[260] L. De Trizio, A. Figuerola, L. Manna, A. Genovese, C. George, R. Brescia, Z. Saghi, R. Simonutti, M. Van Huis, A. Falqui, ACS Nano 6 (2011) 32-41.

[261] K. Aso, A. Hayashi, M. Tatsumisago, Electrochim. Acta 83 (2012) 448-453.

[262] H. Senoh, H. Kageyama, T. Takeuchi, K. Nakanishi, T. Ohta, H. Sakaebe, M. Yao, T. Sakai, K. Yasuda, J. Power Sources 196 (2011) 5631-5636.

[263] A. Paolella, C. George, M. Povia, Y. Zhang, R. Krahne, M. Gich, A. Genovese, A. Falqui, M. Longobardi, P. Guardia, T. Pellegrino, L. Manna, Chem. Mater. 23 (2011) 3762-3768.

[264] Q. Sun, W.-J. Li, Z.-W. Fu, Solid State Sci. 12 (2010) 397—403.

[265] J. Cabana, C.M. Ionica-Bousquet, C.P. Grey, M.R. Palacin, Electrochem. Commun. 12 (2010) 315—318.

[266] Y. Wang, J. Wu, Y. Tang, X. Lü, C. Yang, M. Qin, F. Huang, X. Li, X. Zhang, ACS Appl. Mater. Interfaces 4 (2012) 4246—4250.

[267] N.H. Idris, M.M. Rahman, S.-L. Chou, J.-Z. Wang, D. Wexler, H.-K. Liu, Elec-trochim. Acta 58 (2011) 456—462.

[268] C. Xu, Y. Zeng, X. Rui, N. Xiao, J. Zhu, W. Zhang, J. Chen, W. Liu, H. Tan, H.H. Hng, Q. Yan, ACS Nano 6 (2012) 4713—4721.

[269] Y. Gu, Y. Xu, Y. Wang, ACS Appl. Mater. Interfaces 5 (2013) 801—806.

[270] Z.-W. Fu, Y. Wang, X.-L. Yue, S.-L. Zhao, Q.-Z. Qin, J. Phys. Chem. B 108 (2004) 2236—2244.

[271] Q. Sun, Z.-W. Fu, Electrochim. Acta 54 (2008) 403—409.

[272] N. Pereira, L. Dupont, J.M. Tarascon, L.C. Klein, G.G. Amatucci, J. Electrochem. Soc. 150 (2003) A1273—A1280.

[273] B. Das, M.V. Reddy, P. Malar, T. Osipowicz, G.V. Subba Rao, B.V.R. Chowdari, Solid State Ionics 180 (2009) 1061—1068.

[274] F. Gillot, J. Oro-Sole, M.R. Palacin, J. Mater. Chem. 21 (2011) 9997—10002.

[275] Q. Sun, Z.-W. Fu, Electrochem. Solid-State Lett. 10 (2007) A189—A193.

[276] J.O. Besenhard, J. Yang, M. Winter, J. Power Sources 68 (1997) 87—90.

[277] M.S. Whittingham, Dalton Trans. (2008) 5424—5431.

[278] M. Winter, J.O. Besenhard, Electrochim. Acta 45 (1999) 31—50.

[279] J. Wang, I.D. Raistrick, R.A. Huggins, J. Electrochem. Soc. 113 (1986) 457—460.

[280] C.M. Park, H.J. Sohn, Adv. Mater. 22 (2010) 47.

[281] K.C. Hewitt, L.Y. Beaulieu, J.R. Dahn, J. Electrochem. Soc. 148 (2001) A402— A410.

[282] J. Yang, Y. Takeda, C. Capiglia, X.D. Liu, N. Imanishi, O. Yamamoto, J. Power Sources 119—121 (2003) 56—59.

[283] C.M. Ionica, P.E. Lippens, J.O. Fourcade, J.C. Jumas, J. Power Sources 146 (2005) 478—481.

[284] D. Larcher, L.Y. Beaulieu, D.D. MacNeil, J.R. Dahn, J. Electrochem. Soc. 147 (2000) 1658—1662.