CC BY-NC-ND
0Accepted Manuscript
SnS2 nanosheets arrays sandwiched by N-doped carbon and TiO2 for highperformance Na-ion storage
Weina Ren, Haifeng Zhang, Dr. Cao Guan, Chuanwei Cheng, Prof.
PII: S2468-0257(17)30114-0
DOI: 10.1016/j.gee.2017.09.005
Reference: GEE 90
To appear in: Green Energy and Environment
Received Date: 30 June 2017
Revised Date: 25 September 2017
Accepted Date: 30 September 2017
Please cite this article as: W. Ren, H. Zhang, C. Guan, C. Cheng, SnS2 nanosheets arrays sandwiched by N-doped carbon and TiO2 for high-performance Na-ion storage, Green Energy & Environment (2017), doi: 10.1016/j.gee.2017.09.005.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
SnS2 nanosheets arrays sandwiched by N-doped carbon and TiO2 for high-performance Na-ion storage
Weina Rena, Haifeng Zhanga, Cao Guanb*, and Chuanwei Chengac*
[a] W. N. Ren, H. F. Zhang, Prof. C. W. Cheng
Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092, People's Republic of China. E-mail: cwchen g@ton gji.edu.cn
[b] Dr. C. Guan
Department of Materials Science and Engineering, National University of Singapore, 117574 Singapore.
[c] Prof. C. W. Cheng
The Institute of Dongguan-Tongji University, Dongguan, Guangdong, 523808, People's Republic of China.
Abstract
In this paper, SnS2 nanosheets arrays sandwiched by porous N-doped carbon and TiO2 (TiO2@SnS2@N-C) on flexible carbon cloth are prepared and tested as a free-standing anode for high-performance sodium ion batteries. The as-obtained TiO2@SnS2@N-C composite delivers a remarkable capacity performance (840 mA h g-1 at a current density of 200 mA g-1), excellent rate capabilityand long-cycling life stability (293 mA h g-1 at 1 A g- after 600 cycles). The excellent electrochemical performance can be attributed to the synergistic effect of each component of the unique hybrid structure, in which the SnS2 nanosheets with open framworks offer high capacity, while the porous N-doped carbon nanoplates arrays on flexible carbon cloth are able to improve the conductivity and the TiO2 passivation layer can keep the structure integrity of SnS2 nanosheets.
Keywords: Sandwich structure; SnS2 nanosheets; N-doped carbon; TiO2; sodium-ion battery
1. Introduction
In the era of rapid development of energy storage devices, Na-ion batteries (NIB) have attracted considerable research attention due to its advantages of low cost and nature abundance of sodium element.[1-5] Currently the non-graphitic carbon based materials,[5-8] titanium based intercalation materials,[9-12] metal alloy-based materials[13-16] and transition metal complexes[ 17-21] are extensively investigated as the anode materials of NIB. Among them, Sn-based materials stand out on account of their high reversible theoretical capacity (Sn: 847 mAh g"1, Sn02:1378 mAh g"1, SnS: 1022 mAh g"1, SnS2: 1136 mAh g"1) for Na-ion storage.[22, 23] Especially, SnS2 with a typical 2D structure consists of a layer of tin atoms sandwiched by two layers of hexagonally close packed sulfur atoms. [24, 25] Compared with other Sn based anodes like Sn, Sn02 and SnS, the SnS2is more attractive due to that SnS2 can store more Na+ via two-steps reaction of conversion and alloying mechanisms;[26, 27] the weaker Sn-S ionic bonds belong to SnS2 are more reversible than Sn-0 bonds; [22] and the larger interlayer spacing of SnS2 (c = 0.59 nm) could facilitate and accelerate the insertion/extraction of Na+ and adapt more easily to the volume changes in the host in conversion reaction. [28-31] However, the poor electrical conductivity, huge volume change (324%) and the dissolution of reaction intermediates (Na2S) during sodiation/desodiation of SnS2 anode would result in severely structural breakdown, electrical contact loss and electrode collapse.[32, 33]
To address these issues, a series of effective strategies have been developed. For instances, various low dimensional nanostructures with open frameworks have been developed for SIBs with improved performance.[26, 34, 35] In addition, the carbonaceous materials are often introduced as the conductive matrix to contruct carbon/SnS2 composites due to their excellent electrical conductivity and electrochemical stability.[36-38] Besides, deposition of a passivation layer at the electrode/electrolyte interface has also been widely adopted as an effective strategy to prevent the structure degradation and repeated formation of solid electrolyte interphase (SEI) films. [39-41] Although, much progress has been made in SnS2 based anodes, the development of SnS2 composite anode with superior rate capability and
cycling life are still required.
Herein, we report the design and construction of SnS2 nanosheets arrays sandwiched by porous N-doped carbon nanoplates skeleton and ultrathin TiO2 layer for the first time via a combination of hydrothermal and atomic layer deposition (ALD) technique. In this architecture, the SnS2 nanosheets arrays with rich porosity provide shortened and fast ion diffusion pathways, which can facilitate the sodium intercalation/deintercalation. The metal organic frameworks derived prorous N-doped carbon nanoplates arrays on carbon cloth as support is able to improve the electrical conductivity and buffer the volume change of SnS2, and the ultrathin TiO2 passivation layer can further avoid the formation of SEI film and keep the structure integrity of SnS2 nanosheets during the cycling process. As a consequence, this sandwiched structured composite material as a binder-free anode for sodium ion batteries yields excellent performance in terms of high capacity (840 mA h g-1 at a current density of 200 mA g-1), superior rate capability (462 mA h g-1 at 1 A g-1 and 152 mA h g-1 at 10 A g-1) and long cycling life (293 mA h g-1 at 1 A g-1 after 600 cycles). 2. Experimental 2.1. Samples preparation
2.1.1. Preparation of nanoplate-like porous N-doped carbon (N-C) arrays. The nanoplate-like porous N-C arrays were derived by a cobalt-based metal organic framework (Co-MOF) precursor. The precursor nanoplate arrays were synthesized on carbon cloth using a solution method. [42, 43] In a typical process: (I) The equal volume aqueous solution of 0.4 M 2-methylimidazole and 50 mM Co(NO3)2-6H2O were quickly mixed evenly under agitation. (II) One piece of clean carbon cloth (2X5 cm ) was immersed into the mixture solution with an angle of 60° and reacted for 4 hours at room temperature. (III) Taken out the sample and cleaned with deionized water, then dried at 80°C overnight. After that, the as-prepared sample was annealed in Ar at 800 °C for 2 h with a ramp rate of 1 °C min-1 to reduce the Co-MOF precursor to Co metal particles embedded in N-C nanoplate arrays. Then these Co metal particles were removed by soaking in the aqueous solution contain 3M FeCl3 and 3.6 mM HCl. After washed with deionized water repeatedly, and dried at 80°C
overnight, the plate-like porous N-C arrays were achieved and the mass loading on carbon cloth is ~1 mg cm"".
2.1.2. Preparation of SnS2@N-C core-shell nanoplate arrays.
SnS2 nanosheets were grown on N-C nanoplate arrays by a hydrothermal method. 0.43 g tin (IV) chloride pentahydrate (SnCl4 • 5H20) and 0.24 g thioacetamide (C9H5NS) were dissolved in 40 ml ethanol and stirred until clear, then one piece of the as prepared N-C@carbon cloth and the above solution was transferred to a 50 ml sealed Teflon-lined stainless steel autoclave. After keeping the temperature at 80 °C for 1 hour, the sample was taken out and washed with deionized water repeatedly, and dried at 60 °C overnight. The mass loading of SnS? is -0.6 mg cm"".
2.1.3. Preparation of Ti02@SnS2@N-C sandwiched nanoplate arrays.
TiO? film was coated on the SnS2 surface by using an ALD reactor of Picosun R-200 ALD system. [44, 45] The TiCU and H2O were used as the reactants. During the deposition process, sequential exposure to TiCU and H20 defines one TiC>2 cycle, and an amorphous film was deposited at 75 °C with a growth rate of - 0.8 A a cycle. The thickness of the TiC>2 layer can be effectively controlled by cycles' settings: 2 nm TiC>2 layer was deposited after about 25 cycles.
2.2 Material characterizations
The microscopic structure and morphology of the as-synthesized sandwiched arrays electrode material were recorded by field-emission scanning electron microscope (FE-SEM, FEI Sirion200), high-resolution transmission electron microscope (HR-TEM, JEM-2010F) and selected area diffraction patterns. The crystal structure was characterized by X-ray powder diffraction (XRD, Bruker D8-Advance) using Cu Ka radiation (k=0.15406 nm) over a 20 range of 10°~70°. To measure the surface area of electrode materials, nitrogen adsorption-desorption isotherms were measured on a Micromeritics ASAP 2020 at 77 K. The surface area was obtained using the Brunauer-Emmett-Teller (BET) method. The mass ratio of N to C in N-C was measured by nitrogen oxygen analyzer (LECO TC500) and carbon sulfur analyzer (LECO CS844).
2.3 Electrochemical Measurements
Electrochemical measurements of all the active materials were carried out by using CR2032 coin cells which were assembled in an Ar filled glove box (H20 and O < 0.1 ppm). SnS2@N-C and Ti02@SnS2@N-C nanoplate arrays on carbon cloth were directly used as binder-free anodes; sodium foil (I&K Scientific) and microporous glass fiber membrane (Whatman) were used as the cathode and separator respectively; 1 M solution of NaC104 in ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 by weight) with 5 vol% fluoroethylene carbonate (FEC) was employed as the electrolyte for the sodium ion battery. Each work electrode contains 1.6 mg cm"" active material. Before testing, the batteries were remained in place for 12 hours to ensure complete electrode wetting by the electrolyte. Galvanostatic charge-discharge at various current densities was tested in a multi-channel battery tester (Neware Technology Co., Ltd.) with cut off potentials of 0.01 V for discharge and 3.0 V for charge at room temperature (25 °C). Cyclic voltammetry (CV) measurements were performed on a CHI760D electrochemical workstation at different scan rates. Noting that the capacities were calculated based on the total mass of active material other than carbon cloth. 3. Results and Discussion 3.1. Synthesis and Characterizations
The overall synthetic strategy for the ternary Ti02@SnS2@N-C sandwiched arrays is schematically illustrated in Figure la. First, the triangular like Co-based MOF nanoplates arrays with a smooth and flat surface are vertically grown on carbon cloth by a solution route, as shown in Figure lb. Then, the Co-based MOF was treated by thermal treatment (The morphologies of the obtained Co-MOF are shown in Figure SI) and acid etching. After that, these nanoplates become small and thin due to the reduction reaction. TEM image in Figure lc of the porous N-C indicates that the carbon nanoplates are distributed with pores of 30-60 nm. These voids are beneficial to increase the specific surface area and also improve the loading surface of the active material. Finally, the SnS2 nanosheets were coated on the surface of porous N-C nanoplates by a hydrothermal method and subsequently a ultrathin Ti02 (~2 nm) layer was deposited on the surface of SnS2 via ALD. In view of the good shape preserving
property of ALD, the morphology doesn't change much after the treatment with ALD (See Figure S2a, b).
The detailed structural and component information of the ternary sandwiched TiO2@SnS2@N-C arrays is shown in Figure 2. As shown in Figure 2a, overall 2D nanoplates are radially and vertically grown on the surface of each carbon fiber. The optical photos inset in Figure 2a indicate the flexibility of as-prepared samples. From a magnification view in Figure 2b, the thickness of individual ternary sandwiched nanoplate is between 260~300 nm, which is thicker than the N-C nanoplates (95~120 nm, Figure S3), indicating the thickness of SnS2 is about 75~95 nm. From a closer view, it can be seen that the surface of the nanoplates is evenly distributed with a dense honeycomb-like structure in Figure 2c. The energy dispersive X-ray (EDX) area scan (Figure S4) shows the atomic percentage of S and Sn is 65.8% : 34.2% ~ 2, identifying the active substance is SnS2. The TEM image of the TiO2@SnS2@N-C is shown in Figure 2d, the measured value of thickness of SnS2 shell is ~82 nm, which is consistent with the estimated values in SEM. Such a double-multiaperture structure consists of porous nanoplate N-C core and porous nanosheet SnS2 shell is beneficial to increase the specific surface area and improve the electron/ion transport in electrochemical reactions. In order to prevent the loss of active materials and protection of structural integrity, a TiO2 passivation layer is introduced. Figure 2e and 2f show the HR-TEM of SnS2 before and after the deposition TiO2. The lattice fringes of 6.1, 3.2, and 2.7 A respectively correspond to the (001), (100), and (101) planes of SnS2. After deposition of TiO2, the amorphous TiO2 layer is uniformly coated the outside of the multilayer structure, and the thickness is precisely controlled at about 2 nm by ALD. The selected area electron diffraction patterns (SAED) in Figure 2f is well-indexed as hexagonal SnS2 phase. The EDX elemental mapping (Figure 2g, h) images obtained from the TiO2@SnS2@N-C sample indicate that the uniform distribution of Sn, S, Ti and O elements within the 2D nanoplates. The phase purity and crystallinity of the as-prepared samples were further demonstrated by XRD. As shown in Figure 2i, both the binary SnS2@N-C and ternary TiO2@SnS2@N-C contain characteristic peaks of 2T-type layered hexagonal SnS2 (JCPDS 23-0677),
expect for the two peaks marked by "#" at 26° and 44° resulting from the N-doped carbon and carbon cloth substrate. Notably, the TiO2@SnS2@N-C exhibits the (001) diffraction at 20=14.5° with a d-spacing of 0.61 nm, which is in good agreement with the TEM observations. The increased interlayer spacing can promote the intercalation of Na+ and provides short diffusion paths for Na+ transport. Benefitting from the
porous nanostructures, the TiO2@SnS2@N-C with carbon textiles exhibits a high
specific surface area of ~19.3 m g- , as shown in Figure S5. The mass ratio of N to C in the N-C is estimated to be 1:18. 3.2. Electrochemical Performance
The sodium storage performances of as-deposited and SnS2@N-C on carbon cloth were evaluated directly without adding any conductive agent and binder. Noting that the capacity contribution from the carbon cloth can be ingored, as shown in Figure S6. voltammograms of the two electrodes, which were evaluated at a scan rate of 0.2 mV s-1 between 0.01 V and 3.0 V. During the initial sodiation processes, the SnS2@N-C show three reduction peaks at 1.7, 0.75 and 0.55 V and three corresponding oxidation peaks at 1.2, 0.75 and 0.4 V, respectively. The broad peak at 1.7 V can be attributed to the intercalation of Na+ into SnS2 layers:[46, 47]
xNa++SnS2+xe-^NaxSnS2 (1)
The peak at 0.75 V is due to the conversion reaction:[32]
NaxSnS2+(4-x)Na ^Sn+2Na2S (2)
And the peak at 0.55 V is assigned to the alloying reaction and the formation of SEI layer:[48, 49]
Sn+yNa+^NaySn (0<y<3.75) (3)
The new reduction peaks at ~0.2 V in the following four cycles are ascribed to the SEI layer. Similarly, the TiO2@SnS2@N-C also shows three pairs of reduction/oxidation peaks at 1.6 V/1.25 V, 0.65 V/0.75 V and 0.5 V/0.4 V, arising from the intercalation/extraction reaction, conversion reaction and alloying/dealloying reaction, respectively. Differently, by comparing the CV curves of TiO2@SnS2@N-C and SnS2@N-C, it is found that a sharper reduction peak at 1.6 V and a new oxidation
peaks at 2.0 V appeared after TiO2 coating. The reduction peak at 1.6 V may be due to the reduction of Ti4+ into Ti3+ during the cathodic scan, and the addition anodic peak at 2.0 V is attributed to the oxidation to TiO2.[50] The Ti4+/Ti3+ redox couple of 1.75 V/2.0 V in subsequent cycles indicate excellent reversibility of the TiO2 insertion host. The charge-discharge voltage-capacity curves of the two electrodes for the first five cycles at the current density of 200 mA g-1 and a potential window of 0.01~3 V are displayed in Figure 3c and 3d. In agreement with the CV curves, three voltage plateaus of the TiO2@SnS2@N-C at around 2~1.25 V, 1.25~0.55 V and 0.55~0.25 V can be observed in the discharge process of the first cycle. Similar electrochemical behavior is noticed for the SnS2@N-C electrodes. From these two graphs, we can get more information that the first discharge/charge capacity of the TiO2@SnS2@N-C is 1285/825 mA h g-1, while the SnS2@N-C is 1258/775 mA h g-1. The similar initial discharge capacity of two electrodes indicated that ultrathin TiO2 layer has little effect on electrode capacity, but the initial Coulombic efficiency (CE) is improved from 61.6% to 64.2% by TiO2 modification. In addition, the reversible capacitance of TiO2@SnS2@N-C maintained at 820 mA h g-1 in the second cycle, delivering almost 100% Coulombic efficiency, much higher than that of the SnS2@N-C binary counterpart (reversible capacity of 691 mA h g-1 with a CE of 89%). Compared to the obvious capacity attenuation of SnS2@N-C, the extremely close voltage profiles of TiO2@SnS2@N-C in subsequent cycles further confirm the higher Coulombic efficiency of sandwiched electrode. Moreover, the TiO2@SnS2@N-C sandwiched electrode exhibits superior rate performance. As shown in Figure 4a, the TiO2@SnS2@N-C electrode exhibits average discharge capacities of 840, 659, 462, 307, 210 and 152 mA h g-1 at different current densities. of 0.2, 0.5, 1.0, 2.0, 5.0 and 10.0 A g-1, respectively. After experiencing charging and discharging tests for such a large current density span, the discharge capacity of the ternary electrode could reach to 360 mA h g-1 when the current density is returned to 1 A g-1, while the capacity of the binary SnS2@N-C is only 260 mA h g-1. The discharging capacities of the SnS2@N-C electrode at varied current densities are 658, 462, 319, 227, 154 and 91 mA h g-1 respectively, always lower than that of the TiO2@SnS2@N-C electrode,
demonstrating that the ALD TiO2 layer can effectively improve the rate capability. Figure S7a and 7b show the charge/discharge voltage profiles of two electrodes in the voltage window of 0.01-3.0 V at different current densities. The TiO2@SnS2@N-C electrode exhibits more stable profiles when the current density increased from 200 to 1000 mA g-1, which further indicates the enviable rate capability and high stability of the designed composite electrode. To further check the long-term cycling stability of the TiO2@SnS2@N-C electrode, the cycling test under high current density of 1 A g-1 was continued. After 600 cycles, as shown in Figure S7c, the capacity is remained at 293 mA h g-1, delivering a retention rate up to 81.4% of 37th cycle (360 mA h g-1), which is much higher than that of the SnS2@N-C in Figure S7d (173 mA h g-1; 66.5%). Furthermore, the morphology changes of the electrodes after cycling tests directly reflect the structural stability. Figure S8 present the SEM images of two electrodes after 600 cycles at 1 A g-1. For TiO2@SnS2@N-C, the structure of SnS2 nanosheets has a tendency to collapse, but the nanowall arrays structure remains intact; while a serious collapse and agglomeration phenomenon happens in the SnS2@N-C electrodes. All that suggesting the TiO2 passivation layer can prevent pulverization of SnS2 caused by the volume change during the long-time electrochemical reactions.
3.3. Mechanism Investigation
The mechanisms of the improved performance for TiO2@SnS2@N-C were furthered explained by electrochemical impedance spectrum (EIS) and CV measurements. First, EIS was employed to understand the difference in electrochemical behaviors between the TiO2@SnS2@N-C and SnS2@N-C. The impedance measurements of the two samples were carried out after 5 cycles at a scan rate of 0.2 mV s-1 between 0.01 V and 3.0 V. In Figure 4b, all the Nyquist plots were consisted of two semicircles at high and medium frequencies and straight sloping lines at low frequencies, corresponding to the resistance of SEI film (Rs), charge-transfer resistance (Rct) and the diffusion resistance of sodium ions in the active material.[51] As compared to the counterpart of SnS2@N-C, the TiO2@SnS2@N-C electrode demonstrates much lower Rct value, indicating superior electron/ionic conductivity for the TiO2@SnS2@N-C electrode. The kinetic parameters obtained from the equivalent circuit fitting are listed in Table
SI (Supporting Information). To explain the high-rate performance during sodiation-desodiation processes, a series of CV scans at different sweep rates from 0.2 to 1 mV s"1 were recorded to calculate the capacitive effect for both electrodes. As shown in Figure 4c and Figure S9, the intensity of anodic and cathodic peaks for both electrodes increases with the increased scan rate. The preterit researches verify that, the total charge storage mechanism can be separated into three components: the faradaic contribution from the battery process, the surface pseudocapacitance effect as well as the non-faradaic processes in the double layer capacitor. [52] All that can be calculated according to Equations (4) and (5):[53]
i = avb (4)
log i = b x log v + log a (5)
Where i is the current density, v is the scan rate, a and b are adjustable parameters. The b value is determined from the slope of the plot of log i vs log v. The charge storage mechanism can be revealed from the b values: when b = -0.5, it is dominated by diffusion-controlled process; when b= ~1, it is a feature of capacitive process. Figure 4d shows the linear relationship between logi vs logv plots at anodic peaks of two electrodes. After coating TiCh, the b value of sample improved from 0.79 to 0.54, confirming the TiO? (b-value > 0.87 [54]) coating can improve the capacitive property. The higher b value of the Ti02@SnS2@N-C electrode (0.79 vs. 0.54 of the SnS9@N-C electrode at the anodic peaks) indicates that the current of Ti02@SnS9@N-C is predominantly controlled by the capacitive process, leading to a fast Na+ insertion/extraction.
Table 1 shows the comparison of the electrochemical performance of our TiC>2@SnS2@N-C nanoplates arrays with SnS2-based materials for sodium ion batteries in recent literatures. Among the many electrodes, TiC>2@SnS2@N-C has the highest reversible capacity at 0.2 A g"1 and the highest capacity retention rate at high current density of 1 A g"1, while the much higher rate performance than most electrodes. Base on the above results, the improved performance of the TiC>2@SnS2@N-C sandwiched electrode can be attributed to the following reasons. First, the TiC>2 passivation layer can prevent pulverization of SnS2 caused by the volume change
during charging/discharging process, as well as protecting the SnS2 from corrosion and preventing the formation of SEI film over and again. Second, the porous N-doped carbon and honeycomb-like SnS2 nanosheet arrays structure with large surface area and rich porosity are beneficial to improve electrode/electrolyte contact and accelerate the ion/electron exchange. Moreover, the good conductivity and mechanical resilience of the N-doped carbon nanoplates would facilitate the electron/ion transportation. 4. Conclusions
In summary, we have designed a unique ternary composite electrode of SnS2 nanosheets arrays sandwiched by porous N-doped carbon and ultrathin TiO2 layer on flexible carbon cloth as a free-standing anode for Na ion batteries. The TiO2@SnS2@N-C sandwiched electrode demonstrated a high reversible capacity (840 mAh g-1 at 200 mA g-1), good rate performance (152 mA h g-1 at 10 A g-1) and long cycle-life (293 mAh g-1 at 1 A g-1 for 600 cycles). The excellent electrochemical performance could be attributed to unique structure design and synergistic effect of each component: the TiO2 layer can protect the SnS2 from corrosion and pulverization, meanwhile prevent the formation of SEI film over and again; the N-doped carbon nanoplates with good conductivity and mechanical resilience can facilitate the electron/ion transportation and morphology preservation; while the TiO2@SnS2@N-C sandwiched composite structure with large surface area can improve the reaction sites. This work provides a valuable reference for the electrode design and surface engineering towards high performance energy storage device.
Acknowledgements
This work was financially supported by National Natural Science Foundation of China (Grant No. 51772213) and 973 Program (Grant No. 2013CB632701).
References
[1] H. Kim, H. Kim, Z. Ding, M.H. Lee, K. Lim, G. Yoon, K. Kang, Recent Progress in Electrode Materials for Sodium-Ion Batteries, Adv. Energy Mater. 6 (2016) 1600943.
[2] N. Yabuuchi, K. Kubota, M. Dahbi, S. Komaba, Research development on sodium-ion batteries, Chem. Rev. 114 (2014) 11636-11682.
[3] L. Wei, S. Fei, C. Bommier, H. Zhu, X. Ji, L. Hu, Na-Ion Battery Anodes:
Materials and Electrochemistry, Accounts Chem. Res. 49 (2016) 231-240.
[4] F. Bonaccorso, L. Colombo, G. Yu, M. Stoller, V. Tozzini, A.C. Ferrari, R.S. Ruoff, V. Pellegrini, 2D materials. Graphene, related two-dimensional crystals, and hybrid systems for energy conversion and storage, Science 347 (2015) 1246501.
[5] D. Kong, C. Cheng, Y. Wang, B. Liu, Z.X. Huang, H. Yang, Seed-assisted growth of a-Fe2O3 nanorod arrays on reduced graphene oxide: A superior anode for high-performance Li-ion and Na-ion batteries, J. Mater. Chem. A 4 (2016) 11800-11811.
[6] L. Fan, Q. Liu, S. Chen, Z. Xu, B. Lu, Soft Carbon as Anode for High-Performance Sodium-Based Dual Ion Full Battery, Adv. Energy Mater. (2017).
[7] J. Chen, S. Li, V. Kumar, P.S. Lee, Carbon Coated Bimetallic Sulfide Hollow Nanocubes as Advanced Sodium Ion Battery Anode, Adv. Energy Mater. (2017).
[8] M. Dahbi, M. Kiso, K. Kubota, T. Horiba, T. Chafik, K. Hida, T. Matsuyama, S. Komaba, Synthesis of hard carbon from argan shells for Na-ion batteries, J. Mater. Chem. A 5 (2017) 9917-9928.
[9] H. Li, H. Fei, X. Liu, J. Yang, M. Wei, In situ synthesis of Na2Ti7O15 nanotubes on a Ti net substrate as a high performance anode for Na-ion batteries, Chem. Commun. 51 (2015) 9298-9300.
[10] J. Xu, C. Ma, M. Balasubramanian, Y.S. Meng, Understanding NaDTiDOD as an ultra-low voltage anode material for a Na-ion battery, Chem. Commun. 50 (2014) 12564-12567.
[11] K. Cao, L. Jiao, W.K. Pang, H. Liu, T. Zhou, Z. Guo, Y. Wang, H. Yuan, Na2Ti6 O13 Nanorods with Dominant Large Interlayer Spacing Exposed Facet for High-Performance Na-Ion Batteries, Small 12 (2016) 2991-2997.
[12] H. Pan, X. Lu, X. Yu, Y.S. Hu, H. Li, X.Q. Yang, L. Chen, Sodium Storage and Transport Properties in Layered Na2Ti3O7 for Room-Temperature Sodium-Ion Batteries, Adv. Energy Mater. 3 (2013) 1186-1194.
[13] A. Darwiche, M. Toiron, M.T. Sougrati, B. Fraisse, L. Stievano, L. Monconduit, Performance and mechanism of FeSb2 as negative electrode for Na-ion batteries, J. Power Sources 280 (2015) 588-592.
[14] M. He, M. Walter, K.V. Kravchyk, R. Erni, R. Widmer, M.V. Kovalenko, Monodisperse SnSb nanocrystals for Li-ion and Na-ion battery anodes: synergy and dissonance between Sn and Sb, Nanoscale 7 (2015) 455-459.
[15] J. Liu, L. Yu, C. Wu, Y. Wen, K. Yin, F.-K. Chiang, R. Hu, J. Liu, L. Sun, L. Gu, New Nanoconfined Galvanic Replacement Synthesis of Hollow Sb@C Yolk-Shell Spheres Constituting a Stable Anode for High-Rate Li/Na-Ion Batteries, Nano Lett. 17 (2017) 2034-2042.
[16] M.-S. Balogun, Y. Luo, W. Qiu, P. Liu, Y. Tong, A review of carbon materials and their composites with alloy metals for sodium ion battery anodes, Carbon 98 (2016) 162-178.
[17] G. Longoni, R.L.P. Cabrera, S. Polizzi, M. D'Arienzo, CM. Mari, C. Yi, R. Ruffo, Shape-Controlled TiO2 Nanocrystals for Na-Ion Battery Electrodes: The Role of Different Exposed Crystal Facets on the Electrochemical Properties, Nano Lett. 12 (2017) 992-1000.
[18] Y. Liu, N. Zhang, C. Yu, L. Jiao, J. Chen, MnFe2O4@ C nanofibers as high-performance anode for sodium-ion batteries, Nano Lett. 16 (2016) 3321-3328.
[19] B. Anasori, M.R. Lukatskaya, Y. Gogotsi, 2D metal carbides and nitrides (MXenes) for energy storage, Nat. Rev. Mater. 2 (2017) 16098.
[20] H. Geng, J. Yang, Z. Dai, Y. Zhang, Y. Zheng, H. Yu, H. Wang, Z. Luo, Y. Guo, Y. Zhang, Co9S8/MoS2 Yolk–Shell Spheres for Advanced Li/Na Storage, Small 13 (2017) 1603490.
[21] Z. Li, L. Zhang, X. Ge, C. Li, S. Dong, C. Wang, L. Yin, Core-Shell Structured CoP/FeP Porous Microcubes Interconnected by Reduced Graphene Oxide as High Performance Anodes for Sodium Ion Batteries, Nano Energy 32 (2017) 494-502.
[22] T. Zhou, W.K. Pang, C. Zhang, J. Yang, Z. Chen, H.K. Liu, Z. Guo, Enhanced sodium-ion battery performance by structural phase transition from two-dimensional hexagonal-SnS2 to orthorhombic-SnS, ACS Nano 8 (2014) 8323-8333.
[23] B. Zhang, G. Rousse, D. Foix, R. Dugas, D.A.D. Corte, J.M. Tarascon, Microsized Sn as Advanced Anodes in Glyme-Based Electrolyte for Na-Ion Batteries, Adv. Mater. 28 (2016) 9824-9830.
[24] C. Ma, J. Xu, J. Alvarado, B. Qu, J. Somerville, J.Y. Lee, Y.S. Meng, Investigating the energy storage mechanism of SnS2-rGO composite anode for advanced Na-ion batteries, Chem. Mat. 27 (2015) 5633-5640.
[25] P. Zhou, X. Wang, W. Guan, D. Zhang, L. Fang, Y. Jiang, SnS2 Nanowall Arrays toward High-Performance Sodium Storage, ACS Appl. Mat. Interfaces 9 (2017) 6979-6987.
[26] W. Sun, X. Rui, D. Yang, Z. Sun, B. Li, W. Zhang, Y. Zong, S. Madhavi, S. Dou, Q. Yan, Two-dimensional tin disulfide nanosheets for enhanced sodium storage, ACS nano 9(2015)11371-11381.
[27] Z. Li, J. Ding, D. Mitlin, Tin and tin compounds for sodium ion battery anodes: phase transformations and performance, Accounts Chem. Res. 48 (2015) 1657-1665.
[28] Y. Zhang, J. Lu, S. Shen, H. Xu, Q. Wang, Ultralarge single crystal SnS rectangular nanosheets, Chem. Commun. 47 (2011) 5226-5228.
[29] Z. Deng, D. Cao, J. He, S. Lin, S.M. Lindsay, Y. Liu, Solution synthesis of ultrathin single-crystalline SnS nanoribbons for photodetectors via phase transition and surface processing, ACS nano 6 (2012) 6197-6207.
[30] Y. Liu, H. Kang, L. Jiao, C. Chen, K. Cao, Y. Wang, H. Yuan, Exfoliated-SnS2 restacked on graphene as a high-capacity, high-rate, and long-cycle life anode for sodium ion batteries, Nanoscale 7 (2015) 1325-1332.
[31] B. Qu, C. Ma, G. Ji, C. Xu, J. Xu, Y.S. Meng, T. Wang, J.Y. Lee, Layered SnS2D Reduced Graphene Oxide Composite-A High-Capacity, High-Rate, and Long-Cycle Life Sodium-Ion Battery Anode Material, Adv. Mater. 26 (2014) 3854-3859.
[32] J. Wang, C. Luo, J. Mao, Y. Zhu, X. Fan, T. Gao, A C. Mignerey, C. Wang, Solid-state fabrication of SnS2/C nanospheres for high-performance sodium ion battery anode, ACS Appl. Mat. Interfaces 7 (2015) 11476-11481.
[33] S.H. Choi, Y.C. Kang, Aerosol-assisted rapid synthesis of SnS-C composite microspheres as anode material for Na-ion batteries, Nano Res. 8 (2015) 1595-1603.
[34] D. Guan, J. Li, X. Gao, Y. Xie, C. Yuan, Growth characteristics and influencing
factors of 3D hierarchical flower-like SnS2 nanostructures and their superior lithium-ion intercalation performance, J. Alloy. Compd. 658 (2016) 190-197.
[35] X.Y. Yu, L. Yu, X.W.D. Lou, Metal sulfide hollow nanostructures for electrochemical energy storage, Adv. Energy Mater. 6 (2016) 1501333.
[36] Y. Jiang, Y. Feng, B. Xi, S. Kai, K. Mi, J. Feng, J. Zhang, S. Xiong, Ultrasmall SnS2 nanoparticles anchored on well-distributed nitrogen-doped graphene sheets for Li-ion and Na-ion batteries, J. Mater. Chem. A 4 (2016) 10719-10726.
[37] Q. Lian, G. Zhou, X. Zeng, C. Wu, Y. Wei, C. Cui, W. Wei, L. Chen, C. Li, Carbon coated SnS/SnO2 heterostructures wrapping on CNFs as an improved-performance anode for Li-ion batteries: lithiation-induced structural optimization upon cycling, ACS Appl. Mat. Interfaces 8 (2016) 30256-30263.
[38] D. Chao, C. Zhu, P. Yang, X. Xia, J. Liu, J. Wang, X. Fan, S.V. Savilov, J. Lin, H.J. Fan, Array of nanosheets render ultrafast and high-capacity Na-ion storage by tunable pseudocapacitance, Nat. Commun. 7 (2016) 12122.
[39] W. Ren, W. Zhou, H. Zhang, C. Cheng, ALD TiO2 coated flower-like MoS2 nanosheets on carbon cloth as sodium ion battery anode with enhanced cycling stability and rate capability, ACS Appl. Mat. Interfaces 9 (2017) 487-495.
[40] K. Wang, X. Li, J. Chen, Surface and Interface Engineering of Electrode Materials for Lithium-Ion Batteries, Adv. Mater. 27 (2015) 527-545.
[41] A. Lahiri, M. Olschewski, R. Gustus, N. Borisenko, F. Endres, Surface modification of battery electrodes via electroless deposition with improved performance for Na-ion batteries, Phys. Chem. Chem. Phys. 18 (2016) 14782-14786.
[42] C. Guan, W. Zhao, Y. Hu, Z. Lai, X. Li, S. Sun, H. Zhang, A.K. Cheetham, J. Wang, Cobalt oxide and N-doped carbon nanosheets derived from a single two-dimensional metal-organic framework precursor and their application in flexible asymmetric supercapacitors, Nanoscale Horiz. 2 (2017) 99-105.
[43] C. Guan, X. Liu, W. Ren, X. Li, C. Cheng, J. Wang, Rational Design of Metal-Organic Framework Derived Hollow NiCo2O4 Arrays for Flexible Supercapacitor and Electrocatalysis, Adv. Energy Mater. 7 (2017) 1602391.
[44] H. Zhang, D. Zhang, X. Qin, C. Cheng, Three-Dimensional CdS-Sensitized Sea Urchin Like TiO2-Ordered Arrays as Efficient Photoelectrochemical Anodes, J. Phys. Chem. C 119 (2015) 27875-27881.
[45] H. Zhang, W. Ren, C. Cheng, Three-dimensional SnO2@ TiO2 double-shell nanotubes on carbon cloth as a flexible anode for lithium-ion batteries, Nanotechnology 26 (2015) 274002.
[46] Y. Jiang, M. Wei, J. Feng, Y. Ma, S. Xiong, Enhancing the cycling stability of Na-ion batteries by bonding SnS2 ultrafine nanocrystals on amino-functionalized graphene hybrid nanosheets, Energy Environ. Sci. 9 (2016) 1430-1438.
[47] Y. Liu, Y. Yang, X. Wang, Y. Dong, Y. Tang, Z. Yu, Z. Zhao, J. Qiu, Flexible Paper-like Free-Standing Electrodes by Anchoring Ultrafine SnS2 Nanocrystals on Graphene Nanoribbons for High-Performance Sodium Ion Batteries, ACS Appl. Mat. Interfaces 9 (2017) 15484-15491.
[48] H. Li, M. Zhou, W. Li, K. Wang, S. Cheng, K. Jiang, Layered SnS2 cross-linked by carbon nanotubes as a high performance anode for sodium ion batteries, RSC Adv.
6 (2016) 35197-35202.
[49] X. Xie, D. Su, S. Chen, J. Zhang, S. Dou, G. Wang, SnS2 Nanoplatelet@Graphene Nanocomposites as High-Capacity Anode Materials for Sodium-Ion Batteries, Chem.-Asian J. 9 (2014) 1611-1617.
[50] L. Wu, D. Bresser, D. Buchholz, G.A. Gifin, C.R. Castro, A. Ochel, S. Passerini, Unfolding the mechanism of sodium insertion in anatase TiO2 nanoparticles, Adv. Energy Mater. 5 (2015) 1401142.
[51] Y. Zhang, P. Zhu, L. Huang, J. Xie, S. Zhang, G. Cao, X. Zhao, Few-Layered SnS2 on Few-Layered Reduced Graphene Oxide as Na-Ion Battery Anode with Ultralong Cycle Life and Superior Rate Capability, Adv. Funct. Mater. 25 (2015) 481-489.
[52] J. Wang, J. Polleux, J. Lim, B. Dunn, Pseudocapacitive Contributions to Electrochemical Energy Storage in TiO2 (Anatase) Nanoparticles, J. Phys. Chem. C 111 (2007) 14925-14931.
[53] Z. Hu, L. Wang, K. Zhang, J. Wang, F. Cheng, Z. Tao, J. Chen, MoS2 nanoflowers with expanded interlayers as high-performance anodes for sodium-ion batteries, Angew. Chem. Int. Ed. 126 (2014) 13008-13012.
[54] H. Xiong, M.D. Slater, M. Balasubramanian, C.S. Johnson, T. Rajh, Amorphous TiO2 Nanotube Anode for Rechargeable Sodium Ion Batteries, J. Phys. Chem. Lett. 2 (2011) 2560-2565.
[55] W. Xu, K. Zhao, L. Zhang, Z. Xie, Z. Cai, Y. Wang, SnS2@Graphene nanosheet arrays grown on carbon cloth as freestanding binder-free flexible anodes for advanced sodium batteries, J. Alloy. Compd. 654 (2016) 357-362.
[56] X. Zhang, J. Xiang, C. Mu, F. Wen, S. Yuan, J. Zhao, D. Xu, C. Su, Z. Liu, SnS2 nanoflakes anchored graphene obtained by liquid phase exfoliation and MoS2 nanosheet composites as lithium and sodium battery anodes, Electrochim. Acta 227 (2017) 203-209.
Graphical abstract
Free-standing hierarchical TiO2@SnS2@N-C heterostructure arrays were fabricated through a convenient process, which possess highly electrochemical performance as Na-ion battery anode.
Figure captions:
Figure 1. (a) Schematic illustration of synthesis of the TiO2@SnS2@N-C arrays; SEM and TEM of (b) Cobalt-based MOF; (c) porous N-C; and (d) TiO2@SnS2@N-C.
Figure 2. (a-c) SEM images of the TiO2@SnS2@N-C arrays; (d) TEM image of the TiO2@SnS2@N-C; (e, f) HR-TEM image of the SnS2@N-C and the TiO2@SnS2@N-C; (g, h) elemental mapping images of Sn, S, Ti and O components; (i) XRD patterns of porous N-C, SnS2@N-C and TiO2@SnS2@N-C.
Figure 3. The CV curves of (a) TiO2@SnS2@N-C, (b) SnS2@N-C at a scanning rate of 0.2 mV s-1 in the first 5 cycles; the charge-discharge profiles of (c) TiO2@SnS2@N-C, (d) SnS2@N-C in the first 2 cycles.
Figure 4. (a) The rate performance of the TiO2@SnS2@N-C and the SnS2@N-C at various current densities of 0.2, 0.5, 1, 2, 5 and 10 A g-1; and the cycling performances of the TiO2@SnS2@N-C and SnS2@N-C at 1 A g-1 after the rate test; (b) Impedance plots and equivalent circuit (inset) used for the EIS analysis of the TiO2@SnS2@N-C and the SnS2@N-C; (c) CV curves at different scan rate of the TiO2@SnS2@N-C; (d) Relationship between logarithm anodic peak current and logarithm scan rates.
Table 1. A comparison of the electrochemical performance of our TiO2@SnS2@N-C nanoplates arrays with Sn-based materials for sodium ion batteries in recent literatures.
(a) Co-based MOF Porous N-C Ti02@SnS2@N-C
Figure 1. Schematic illustration of synthesis of the TiO2@SnS2@N-C arrays: SEM and TEM of (a) Cobalt-based MOF; (b) porous N-C; and (c) TiO2@SnS2@N-C.
Figure 2. (a-c) SEM images of the TiO2@SnS2@N-C arrays; Inset of Figure 2a show the optical photos of the samples. (d) TEM image of the TiO2@SnS2@N-C; (e, f) HR-TEM image of the SnS2@N-C and the TiO2@SnS2@N-C; (g, h) elemental mapping images of Sn, S, Ti and O components; (i) XRD patterns of porous N-C, SnS2@N-C and TiO2@SnS2@N-C.
0.5 1.0 1.5 2.0 2.5 Potential (V vs. Na+/Na)
0.5 1.0 1.5 2.0 2.5 Potential (V vs. Na+/Na)
2.5-1 > 2.0
I i.<H
0.5-| 0.0
Ti02@SnS2@N-C I
— 1st
—2nd
— 3rd
—4th
— 5th
0 200 400 600 800 1000 1200 1400
Capacity (mA h/g)
200 400 600 800 1000 1200 1400 Capacity (mA h/g)
Figure 3. The CV curves of (a) TiO2@SnS2@N-C, (b) SnSi@N-C at a scanning rate of 0.2 mV s-1 in the first 5 cycles; the charge-discharge profiles of (c) TiO2@SnS2@N-C, (d) SnS2@N-C in the first 5 cycles.
Cycle number Cycle number
Z'/Ohm Potential (V vs. Na+/Na) log (v, mV s"1)
Figure 4. (a) The rate performance of the TiO2@SnS2@N-C and the SnS2@N-C at various current densities of 0.2, 0.5, 1, 2, 5 and 10 A g-1; and the cycling performances of the TiO2@SnS2@N-C and SnS2@N-C at 1 A g-1 after the rate test; (b) Impedance plots and equivalent circuit (inset) used for the EIS analysis of the TiO2@SnS2@N-C and the SnS2@N-C; (c) CV curves at different scan rate of the TiO2@SnS2@N-C; (d) Relationship between logarithm anodic peak current and logarithm scan rates.
ACCEPTED MANUSCRIPT
Table 1. A comparison of the electrochemical performance of our TiO2@SnS2@N-C nanoplates arrays with SnS2-based materials for sodium ion batteries in recent literatures.
Electrode description Voltage range Reversible capacity Rate performance Cycling stability Ref.
2D SnS2 nanosheet 0.005-3 V 733 mA h g- at 0.1 A g-1 432 mA h g-1 at 2 A g-1 88.2% after 50 cycles at 0.1 A g-1 [26]
SnS2-rGO 0.01-2.5 V 630 mA h g- at 0.2 A g-1 544 mA h g-1 at 2 A g-1 79.3% after 400 cycles at 1 A g-1 [31]
SnS2 nanowall array 0.01-2.5 V 576 mA h g- at 0.5 A g-1 370 mA h g-1 at 5 A g-1 88.5% after 100 cycles at 0.5 A g-1 [25]
SnS2/Graphene 0.01-2.5 V 650 mA h g- at 0.2 A g-1 326 mA h g-1 at 4 A g-1 93.8% after 300 cycles at 0.2 A g-1 [30]
SnS2/C nanospheres 0.005-2.5 V 660 mA h g-1 at 0.05 A g-1 360 mA h g-1 at 1 A g-1 86.3% after 100 cycles at 0.05 A g-1 [32]
SnS2/N-doped graphene 0.01-3 V 630 mA h g- at 0.2 A g-1 148 mA h g-1 at 10 A g-1 71.4% after 100 cycles at 0.2 A g-1 [36]
Few-layered SnS2-rGO 0.005-3 V 582 mA h g- at 0.2 A g-1 452 mA h g-1 at 6.4 A g-1 51% after 1000 cycles at 0.2 A g-1 [51]
SnS2@Graphene nanosheet 0.01-1 V 633 mA h g- at 0.2 A g-1 348 mA h g-1 at 3 A g-1 59.7% after 200 cycles at 1.2 A g-1 [55]
Graphene@ MoS2@SnS2 0.01-3 V 145 mA h g-1 at 0.32 A g-1 NA 68.9% after 100 cycles at 0.08 A g-1 [56]
SnS2@N-C 0.01-3 V 658 mA h g- at 0.2 A g-1 319 mA h g-1 at 1 A g-1 91 mA h g-1 at 10 A g-1 66.5% after 564 cycles at 1 A g-1 This work
TiO2@SnS2 @N-C 0.01-3 V 840 mA h g- at 0.2 A g-1 462 mA h g-1 at 1 A g-1 152 mA h g-1 at 10 A g-1 81.4% after 564 cycles at 1 A g-1 This work
