Significantly Improved Sodium-Ion Storage Performance of CuS

Subscriber access provided by University of Newcastle, Australia

Article

Significantly improved sodium-ion storage performance of CuS nanosheets anchored into reduced graphene oxide with ether-based electrolyte Jinliang Li, Dong Yan, Ting Lu, Wei Qin, Yefeng Yao, and Likun Pan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b12529 • Publication Date (Web): 29 Dec 2016 Downloaded from http://pubs.acs.org on December 30, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Significantly Improved Sodium-Ion Storage Performance of CuS Nanosheets Anchored into Reduced Graphene Oxide with Ether-Based Electrolyte Jinliang Li,† Dong Yan,† Ting Lu,† Wei Qin, ‡* Yefeng Yao, † Likun Pan†* †

School of Physics and Materials Science, Engineering Research Center for

Nanophotonics & Advanced Instrument, Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai, 200062, China ‡

State Key Laboratory of Optoelectronic Materials and Technologies, Nanotechnology

Research Center, School of Materials Science & Engineering, Sun Yat-sen University, Guangzhou 510275, Guangdong, China

Co-authors: E-mail:

[email protected]

(Jinliang

Li);

[email protected]

(Dong

Yan);

[email protected] (Ting Lu); [email protected] (Yefeng Yao) ∗

Corresponding author:

E-mail: [email protected] (Likun Pan); [email protected] (Wei Qin) Tel.:+86 21 62234132; Fax: +86 21 62234321

1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 32

Abstract

Currently sodium-ion batteries (SIBs) as energy storage technology have attracted lots of interest due to their safe, cost-effective and non-poisonous advantages. However, many challenges are remained for development of SIBs with high specific capacity, high rate capability and long cycle life. Therefore, CuS as an important earth-abundant, low-cost semiconductor was applied as anode of SIBs with ether-based electrolyte instead of conventional ester-based electrolyte. By incorporating reduced graphene oxide (RGO) into CuS nanosheets and optimizing the cut-off voltage, it is found that the sodium-ion storage performance can be greatly enhanced using ether-based electrolyte. The CuS-RGO composites deliver an initial Coulombic efficiency of 94% and a maximum specific capacity of 392.9 mAh g−1 after 50 cycles at a current density of 100 mA g−1. And a specific capacity of 345 mAh g-1 is kept after 450 cycles at a current density of 1 A g-1. Such an excellent electrochemical performance is ascribed to the conductive network construction of CuS-RGO composites, the suppression of dissolved polysulfide intermediates by using ether-based electrolyte and the avoidance of conversion-type reaction by optimizing the cut-off voltage.

Keywords: CuS; reduced graphene oxide; ether-based electrolyte; cut-off voltage; sodium-ion batteries

2


Page 3 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction The investigation of sodium ion batteries (SIBs) has recently attracted considerable attention because they are regarded as a potential cost-effective alternative to lithium ion batteries (LIBs).1-3 However, the performance of SIBs is greatly hindered by the larger diameter of sodium ion than lithium ion.4-6 Thus one of the key issues in developing high performance SIBs is seeking for suitable electrode materials at present. It is generally believed that the widely used graphite electrode in LIBs is not suitable as electrode material of SIBs due to the larger diameter of sodium ion.7-8 However, it is found that by using ether-based electrolyte rather than conventionally used ester-based electrolyte, the co-insertion of solvent and sodium ion can be successfully realized in graphite electrode recently.9-10 Despite the above-mentioned progress, the graphite only delivers a specific capacity of ~150 mA g-1. Therefore, seeking for high performance electrode materials which surpass graphite is of great importance. Currently, due to the unique physical and chemical properties, metal sulphides have attracted particular interest,11-12 and they also represent a prospective category of alternatives for energy storage.13-15 To date, many metal sulfides have been applied in SIBs in previous literatures.16-18 Among various metal sulfides, copper sulphide (CuS, Cu2S) is one of cost-effective semiconductors with prospect for many novel applications such as sensors, photocatalysts, and bio-devices.19-21 Moreover, copper sulphide has been 3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 32

studied and demonstrated as a prospective anode material for LIBs, and also been successfully applied in SIBs.22-24 Kim et al.25 prepared Cu2S electrode by ball-milling for SIBs and the result turned out that the initial discharge capacity was 294 mAh g-1 and decreased to 220 mAh g-1 at 50 mA g-1 after 20 cycles. But this progress is unsatisfactory because of its low specific capacity and poor stability, which is ascribed to the failure structure and poor electrical conductivity of the Cu2S electrode. To solve these problems, constructing a well-conductive matrix of composite is one of effective

strategy,

which

can

relieve

the

volume

change

during

the

sodiation-desodiation process.26-28 As known, reduced graphene oxide (RGO) is an ideal matrix applied in energy storage because of its superior chemical stability, excellent electrical conductivity and high specific surface area.29-31 In this fashion, Ren et al.32 synthesized double sandwich-like CuS@RGO via hydrothermal process and found that the specific capacity and the cycling performance of LIBs were greatly improved. Furthermore, previous works also demonstrated that incorporating RGO to form composites could enhance the cycling stability effectively for SIBs.33-35 In addition, the electrolyte is one of significant factors for enhancing the electrochemical performances of SIBs. At present, conventional electrolytes for SIBs are based on ester-based solvents, due to their large electrochemical cut-off voltages and high dielectric constants.36 However, ester-based electrolyte is not suitable for some electrode materials of SIBs because they would induce side reaction with the anionic group.37 Therefore, for improving the specific capacity and cycle stability, 4


Page 5 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ether-based electrolytes have been reported for SIBs, and they could availably improve the specific capacity and cycle stability.37-39 Unfortunately, up to now, few attentions have been concentrated on the synthesis CuS-RGO composite electrode material for sodium-ion storage based on ether-based solvents. In our work, CuS nanosheets anchored into RGO (CuS-RGO) composites were prepared by microwave-assisted process, which were used as anode materials for SIBs. The composite electrodes coupled with ether-based electrolyte exhibit high specific capacity, high initial Coulombic efficiency (CE), superior rate performance and excellent long-term cycle stability. 2. Experimental 2.1. Synthesis The preparation of graphene oxide (GO) has been described in our previous work using commercial graphite as starting material via a modified Hummer’s method.40 Typically, the synthetic route of CuS and CuS-RGO composites is described as following: 0.51 g thioacetamide and 1.25 g CuSO4·5H2O were first dissolved into 50 mL water under stirring, respectively. Afterwards, both of solutions were mixed. Subsequently, GO (0, 100, 200 and 400 mg) was added into the aforementioned mixed solution to form homogeneous dispersions under vigorous stirring for another 2 h. Subsequently, 20 mL of aforementioned dispersion was taken into 35 mL microwave tube and treated at 160 °C for 10 min with a maximum power of 100 W. The obtained samples synthesized using 0, 100, 200 and 400 mg GO in the precursor, 5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 32

labelled as CuS, CuS-RGO-1, CuS-RGO-2 and CuS-RGO-3 were separated by centrifugation, washed and finally dried at 80 °C for one day. 2.2. Characterization The samples were examined using field-emission scanning electron microscopy (FESEM, S-4800, Hitachi) and transmission electron microscopy (TEM, JEM-2010, JEOL). Thermogravimetric analysis (TGA, STA449F3, NETZSCH) was recorded from room temperature to 1000 °C in air. The crystal structure was measured by X-ray diffraction (XRD, DX-2700, Fangyuan). Brunauer-Emmett-Teller (BET) specific surface area was calculated from the nitrogen adsorption isotherm, which was obtained at 77K using ASAP 2010 Surface Area and Porosimetry System (Norcross, GA). 2.3. Electrochemical measurement The as-prepared samples as anode materials were used for SIBs to assess their electrochemical performance. 80 wt% as-prepared samples, 10 wt% Super-P and 10 wt% carboxyl methyl cellulose in deionized water were first mixed to form a uniform sizing. The as-prepared sizing was covered on Cu foil and subsequently dried overnight. The loadings of the active materials are 1.50, 1.61, 1.48, 1.61 mg for CuS, CuS-RGO-1, CuS-RGO-2 and CuS-RGO-3, respectively, and their thicknesses are ∼10 µm. CR2032 type coin cells were packaged in argon-filled MBRAUN glove box (MB-10-compact). The metallic sodium was used as the counter/reference electrodes, and Whatman glass fiber filter was used as the separator. 1 M CF3SO3Na solution in 6


Page 7 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


diethylene glycol dimethyl ether (NaFS/DMG) was used as the electrolyte and 1 M NaClO4 in ethylene carbonate and propylene carbonate (1: 1, w/w) with 5wt% fluoroethylene carbonate (NaClO4/FEP) was used for comparison. Unless otherwise specified, galvanostatic charge-discharge curve was recorded with a voltage of 0.4~2.6 V at a current density of 100 mA g-1 by using a Land2001A battery test system. Cyclic voltammetry (CV) curve was recorded using an AutoLab electrochemical workstation (EW, PGSTAT302N) at a scan rate of 0.2 mV s-1. The electrochemical impedance spectroscopy (EIS) test was recorded by the same EW with a frequency range of 10-1~105 Hz. 3. Results and discussion Under microwave process, GO is reduced to RGO, which has been confirmed in our previous work.41 The RGO mass percentages are 20.8%、26.7% and 34.0% for CuS-RGO-1, CuS-RGO-2 and CuS-RGO-3, respectively, derived from TGA measurement (Fig. S1). Fig. 1(a)-(d) show FESEM images of CuS, CuS-RGO-1, CuS-RGO-2 and CuS-RGO-3. Pure CuS is constituted by quasi-microsphere with the diameter of ~300 nm. As seen from Fig. 1(b)-(d), with the introduction of RGO, all of the CuS-RGO composites exhibit similar morphologies. It is clearly observed that CuS particles are transformed into nanosheets, and they are closely and homogeneously dispersed on the surface of RGO sheets. Some CuS nanosheets are anchored perpendicularly on the surface of RGO, as shown clearly in Fig. 1(c). This structure is helpful to improve the connection between CuS and electrolyte. Due to the 7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 32

microstructures of the composites, the CuS nanosheets can be easily accessible to electrolyte with the size decrease, which facilitates the reversibility of sodium-ion storage and shorten the sodium-ion diffusion pathway to ensure the full utilization of CuS-RGO composites.14 The RGO in the composites also undertakes a buffer layer, which can alleviate the volume change during sodiation-desodiation process.42-43 Furthermore, the conductive network is formed with the introduction of RGO, which is conduced to the enhanced electrical conductivity of the electrodes.42-43 All of these aspects are favourable to enhance the electrochemical performance of the composites. To investigate the detailed structure of the composites, low-magnification and high-magnification TEM images of CuS-RGO-2 were recorded, as shown in Fig. 1(e) and (f). It can be seen from Fig. 1(e) that CuS nanosheets are uniformly distributed on the surface of RGO, and some are anchored perpendicularly on the surface, which is in accordance with the FESEM results. In Fig. 1(f), as seen, CuS nanosheets are anchored onto the RGO closely. The inset of Fig. 1(f) shows an interplanar distance of 0.188 nm, which is indexed to the (110) plane of CuS. Moreover, the diffraction rings from SAED pattern of CuS-RGO-2 in Fig. S2 are well assigned to the (100), (102), (110) planes of CuS, indicating that CuS exhibits a high crystallinity in the composites.

8


Page 9 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 1 FESEM images of (a) CuS, (b) CuS-RGO-1, (c) CuS-RGO-2, (d) CuS-RGO-3 and (e) low-magnification and (f) high-magnification TEM images of CuS-RGO-2. The inset in (f) show corresponding lattice fringe of CuS-RGO-2.

9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 32

Fig. 2 (a) XRD patterns, (b) nitrogen adsorption-desorption isotherms and (c) corresponding pore size distribution curves of CuS, CuS-RGO-1, CuS-RGO-2, and CuS-RGO-3. 10


Page 11 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 2(a) shows the XRD patterns of CuS, CuS-RGO-1, CuS-RGO-2 and CuS-RGO-3. The CuS exhibits several diffraction peaks, indexed to hexagonal structure CuS (JCPDS 65-3561), which is consistent with the HRTEM results. Compared with pure CuS, the diffraction peak intensities of the composites obviously decrease and the half peak width becomes broadened, which is due to the decrease of the size of CuS nanosheets with the introduction of RGO in the composites.30 Besides, an additional diffraction peak around 26° can be observed for the composites, which can be indexed to the (002) crystal planes of graphite, resulting from the restacking of the graphene. The intensity of this peak increases with the increasing of RGO amount, indicating that more graphene layers restack in the composites. Nitrogen adsorption-desorption isotherms and pore size distribution curves of CuS, CuS-RGO-1, CuS-RGO-2, CuS-RGO-3 are displayed in Fig. 2(b) and (c). All of the samples show IV-type isotherm, which is highly indicative of their porous structures. The pore size distribution curves of CuS, CuS-RGO-1, CuS-RGO-2, CuS-RGO-3 illustrate that the pore of samples is mainly mesopores and macropores (IUPAC classification). Among the samples, CuS exhibits the smallest specific surface area of 4.63 m2 g-1. With the introduction of RGO, the specific surface area of the composite increases to 28.99, 31.40 and 33.66 m2 g-1 for CuS-RGO-1, CuS-RGO-2 and CuS-RGO-3, respectively. Larger specific surface area can provide better electrode-electrolyte contact and more sodium-ion diffusion pathways. Furthermore, during sodiation-desodiation process, larger specific surface area also offer more 11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 32

space to adapt the volume change. These result in better electrochemical performances of CuS-RGO composite electrodes.44 To obtain superior performance, the electrolytes and cut-off voltages were optimized for CuS-RGO-2 electrode at a current density of 100 mA·g-1. Fig. 3(a)-(d) display the charge-discharge curves using ester-based and ether-based electrolytes in different cut-off voltages. It can be observed that the batteries using NaFS/DGM possess smaller voltage polarization than those using NaClO4/FEP. Besides, all the charge-discharge curves exhibit similar properties and are constituted by several voltage plateaus, demonstrating that the sodiation process is proceeded via multiple steps for both electrolytes. Moreover, the electrolytes and cut-off voltages have different effects on the cycling performance and corresponding CE, as shown in Fig. 3(e)-(h). As seen, there is severe specific capacity fading after 50 galvanostatic charge-discharge cycles in the voltage of 0.005~3.0 V for both electrolytes. However, when the voltage is changed to 0.4~2.6 V, the cycling performance can be significantly improved when using NaFS/DGM electrolyte. No obvious specific capacity fading can be found from the 3rd cycle and a stable discharge capacity of 392.9 mAh g-1 after 50 cycles can be obtained. This results from the avoidance of conversion-type reaction, which happens below 0.4 V. In contrast, even when the voltage is 0.4~2.6 V, rapid specific capacity fading can still be observed (309.8 mAh g-1 at 2nd cycle and 68.3 mAh g-1 at 50th cycle, respectively) when using NaClO4/FEP electrolyte, further demonstrating that both the electrolytes and cut-off 12


Page 13 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


voltages play important roles in improving the electrochemical performance. This is consistent with previous report, which shows that the ester-based electrolyte can react with anionic group of metal sulfide.37 In addition, both of the CEs are below 70% initially when using NaClO4/FEP electrolyte and slowly increase to above 95% after 30 charge-discharge cycles, demonstrating that the sodiation process is not fully reversible. Surprisingly, the CE can reach as high as 94% in the first cycle when using NaFS/DGM electrolyte in the cut-off voltage of 0.4~2.6 V and increases quickly to more than 99.7% since the second cycle, indicating that the sodium ion can be fully extracted from the electrode. The high CE of CuS-RGO-2 is ascribed to the use of ether-based electrolyte and high cut-off voltage. The CE of CuS-RGO-2 electrode using NaFS/DGM electrolyte is higher than those using NaClO4/FEP electrolyte, which suggests that NaClO4/FEP electrolyte can react with the anionic group of intermediate products during charge-discharge cycling, leading to the decrease of active materials.37 As known, the initial irreversible capacity is mainly contributed by the discharge capacity in the voltage range of 0~0.5 V, which has been reported in previous literatures.9, 39, 45 It should be emphasized that the initial CE is important to evaluate the electrochemical performance of a battery and most of the values reported in the literatures are below 60%.37, 39 The EIS tests of CuS-RGO-2 electrode in the voltage of 0.4~2.6 V for both electrolytes were investigated to study the mechanism for this improvement, as shown in Fig. S3. It can be seen that the Rct value of CuS-RGO-2 using NaFS/DGM electrolyte before cycling is 45.5 Ω, which is much 13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 32

lower than that using NaClO4/FEP electrolyte (365 Ω), indicating that NaFS/DGM electrolyte can improve the electron transport in the battery. During the charge-discharge process, the battery using NaFS/DGM electrolyte exhibits the Rct value of 120.7 Ω, which is much lower than that using NaClO4/FEP electrolyte (1147.5 Ω), indicating that NaFS/DGM electrolyte can effectively suppress the generation of by-products and the cracking of active material. This clearly illustrates the superior electrochemical performance offered by the ether-based electrolyte for SIBs.

14


Page 15 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 3 Charge-discharge curves of CuS-RGO-2 electrode at a current density of 100 mA g-1 in (a) NaClO4/FEP, 0.005~3.0 V, (b) NaClO4/FEP, 0.4~2.6 V, (c) NaFS/DGM, 0.005~3.0 V and (d) NaFS/DGM, 0.4~2.6 V; (e) cycling performance and (f) corresponding CE of CuS-RGO-2 electrode using NaClO4/FEP electrolyte with different cut-off voltages; (g) cycling performance and (h) corresponding CE of CuS-RGO-2 electrode using NaFS/DGM electrolyte with different cut-off voltages. To further study the electrochemical performances of CuS-RGO-2 electrode in different electrolytes and cut-off voltages, the CV curves were performed, as shown in Fig. 4. As seen, in the first reduction scan for all the samples, the irreversible reaction occurs, which is mainly attributed to the decomposition of electrolyte to form SEI layer in the first sodiation process.9 Several anodic peaks can be observed in the first anodic scan, which indicates that sodium ions are extracted by several steps.9 Compared with the CV curves using NaClO4/FEP electrolyte, those using NaFS/DGM electrolyte exhibit significantly different characteristics. The CV curves using NaClO4/FEP electrolyte cannot achieve a good coincidence and the intensity of cathodic and anodic peaks decrease with the following scan, which is in accordance with the specific capacity fading. But for those using NaFS/DGM electrolyte, the CV curves overlap well after the first cycle scan. There are three cathodic peaks at about 2.0 V, 1.5 V and 0.75 V, corresponding to three anodic peaks at about 1.6 V, 1.8 V and 2.2 V, which agree with the voltage plateaus in Fig. 3(a)-(d), indicating that the sodiation process of CuS-RGO-2 as anode of SIBs is not just a simple one-step 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 32

conversion reaction. For those using NaClO4/FEP electrolyte, the cathodic peaks appear in the same position, but the anodic peak at about 1.8 V disappears, indicating that the reactions in SIBs are not exactly same by using different electrolytes. It is worth noting that the CV curves using NaFS/DGM electrolyte in a cut-off voltage of 0.005~3V exhibit a new reduction peak at ~0.4 V in first cycle compared with those in a cut-off voltage of 0.4~2.6 V, corresponding to the conversion-type reaction for SIBs. This conversion-type reaction can cause the huge volume change within the electrode, resulting in a poor cycling performance in SIBs.37

Fig. 4 CV curves of CuS-RGO-2 in (a) NaClO4/FEP, 0.005~3.0 V, (b) NaClO4/FEP, 0.4~2.6 V, (c) NaFS/DGM, 0.005~3.0 V and (d) NaFS/DGM, 0.4~2.6 V at a scan rate of 0.2 mV·s-1. 16


Page 17 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Furthermore, the morphology change of CuS-RGO-2 electrode was recorded before and after 50 cycles at the current density of 100 mA g-1 in 0.4~2.6 V using NaClO4/FEP and NaFS/DGM as electrolytes, as shown in Fig. 5. It can be seen that some particles fall from the surface of RGO in the electrode using NaClO4/FEP as electrolyte, while the electrode keeps integrity when using NaFS/DGM as electrolyte. The results suggest that NaClO4/FEP electrolyte can react with the anionic group of the intermediate during charge-discharge cycling, resulting in the breakdown of the electrode structure.39 Therefore, NaFS/DGM electrolyte is beneficial to the excellent long cycle characteristics.

Fig. 5 SEM images of CuS-RGO-2 electrode (a) before and after 50 cycles using (b) NaClO4/FEP and (c) NaFS/DGM electrolytes.

17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 32

Fig. 6 Ex-situ XRD patterns of CuS-RGO-2 in different insertion-extraction states during second charge-discharge cycle. To investigate the detailed sodium-ion insertion-extraction mechanism, the ex-situ XRD patterns of CuS-RGO-2 electrode using NaFS/DGM electrolyte in the cut-off voltage of 0.4~2.6 V during second charge-discharge cycle were recorded, as shown in Fig. 6. From these patterns, three strong peaks of Cu can be seen, which stem from the Cu collector. By comparing the XRD pattern of CuS-RGO-2 before cycling in Fig. 2(a), the diffraction peaks of Cu2S can be observed after discharge or charge, and the peaks of CuS disappear, which indicates that CuS is converted to Cu2S and this reaction is not reversible.46 During the discharge process, some weak diffraction peaks of Na2S appear and the peaks of Cu2S become weak and disappear finally. With the charge proceeding, the diffraction peaks of Cu2S appear again and the diffraction 18


Page 19 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


peaks of Na2S disappear, indicating that the electrode has a good cycling performance in SIBs. Some other diffraction peaks of Na2O are present for all the samples, which is ascribed to the metallic sodium oxidized in air atmosphere.

Fig. 7 (a) Cycling performance of CuS, CuS-RGO-1, CuS-RGO-2, CuS-RGO-3 and RGO at a current density of 100 mA g-1; (b) rate performance of CuS-RGO-2 and (c) long cycling performance of CuS-RGO-2 at 1 A g-1. Fig. 7(a) shows the cycling performances of CuS, CuS-RGO-1, CuS-RGO-2, CuS-RGO-3 and RGO samples measured using NaFS/DGM as electrolyte in a voltage of 0.4~2.6 V at a current density of 100 mA g-1. As seen clearly, the initial discharge specific capacity is 471.5 mAh g-1 for RGO electrode, while the corresponding initial reversible specific capacity is only 189.4 mAh g-1. With the proceeding of charge-discharge cycles, the specific capacity decreases to 119.3 mAh g-1 after 50 cycles. Compared with RGO electrode, CuS, Cu-RGO-1 and CuS-RGO-2 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 32

electrodes exhibit higher initial reversible specific capacities, and their values are 400.0, 494.2 and 509.1 mAh g-1, respectively. The specific capacities of CuS and CuS-RGO composite electrodes decrease in initial a few cycles and keep stable in the following cycles. The specific capacities are remained at 311.8, 381.7 and 392.9 mAh g-1 for CuS, CuS-RGO-1 and CuS-RGO-2 electrodes after 50 galvanostatic charge-discharge cycles, with capacity conservation of 78.0%, 77.6% and 77.2%, respectively. The enhanced specific capacity is ascribed to the suppression of dissolved polysulfide intermediates in the ether-based electrolyte, which is helpful to maintain the integrity of electrode.38 Furthermore, another reason is that RGO can reduce the size of CuS, which is beneficial to the sodium-ion diffusion. For CuS-RGO-2 electrode, assuming that the reversible specific capacity of RGO is stable in composite, the specific capacity of CuS in CuS-RGO-2 electrode is 492.5 mAh g-1 (higher than that of pure CuS) after 50 galvanostatic charge-discharge cycles. Therefore, the contribution of CuS to the specific capacity of CuS-RGO-2 is about 92%. However, as the RGO content is further increased, CuS-RGO-3 shows an initial reversible specific capacity of 435.2 mAh g-1, and it is remained at 328.9 mAh g-1 after 50 cycles, with a capacity conservation of 75.6%, which is lower than those of CuS-RGO-1 and CuS-RGO-2. This is mainly due to excessive RGO with lower specific capacity can contribute to the decrease of the specific capacity in the composite. Moreover, as seen from Fig. S4, all of samples exhibit similar initial CEs, which are 93.1%, 93.8%, 94.5% and 85.9% for CuS, CuS-RGO-1, CuS-RGO-2 and 20


Page 21 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CuS-RGO-3 electrodes, respectively. With the cycle proceeding, the CEs of all the samples increase to ~100% after the second cycle, demonstrating that they have a good reversibility of sodiation and desodiation. It is worth noting that CEs are slightly larger than 100% during the cycling, which is ascribed to the co-intercalation of solvent molecules when using ether-based electrolyte in SIBs.9, 47 The rate capability of CuS-RGO-2 was also investigated, as shown in Fig. 7(b), and the corresponding CE is shown in Fig. S5. As seen, the CuS-RGO-2 electrode exhibits reversible capacities of 509.1, 383.3 and 370.2 mAh g-1 at the current densities of 100, 250 and 500 mA g-1, respectively. Although the specific capacity of CuS-RGO-2 electrode decreases in initial a few cycles at the current density of 100 mA g-1, it keeps stable in subsequent cycles at the current densities of 250 and 500 mA g-1. Even at a current density of 1 A g-1, the specific capacity can still achieve a value of 359.5 mAh g-1 and is remained at 359.3 mAh g-1 after 10 cycles. Moreover, the specific capacity can be recovered to 368.4 and 381.5 mAh g-1 when the current density returns to 500 and 100 mA g-1, indicating that the sample possesses a high reversibility of electrochemical reaction. The initial CE is 94.6%, increases to 97.8% in following cycle and achieves ~99.2% after 10 cycles, further demonstrating that the CuS-RGO-2 electrode possesses an excellent reversibility of sodiation and desodiation. The rate charge-discharge curves at the current density of 100, 250, 500 and 1000 mA g-1 (in 10th cycle for each current density in Fig. 7(b)) are shown in Fig. S6(a). It can be seen that all the curves are similar. Compared with the initial several 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 32

charge-discharge curves in Fig. 3(d), the curves in Fig. S6(a) exhibit a decrease of voltage polarization, which contribute to the improvement of the rate performance. The decrease of voltage polarization is due to the fact that CuS is converted to Cu2S in the initial a few cycles, and Cu2S is stable in subsequent cycles. Moreover, long cycling stability of CuS-RGO-2 electrode was tested at 1 A g-1 in Fig. 7(c), and the corresponding charge-discharge curves are shown in Fig. S6(b). As seen, all of the curves at different cycles are similar, and they exhibit quite low voltage polarization, indicating that the electrode has good cycle stability. From Fig. 7(c), it is observed that CuS-RGO-2 exhibits a high specific capacity and superior cycle stability even at a high current density of 1 A g-1, and a capacity of 345.7 mAh g-1 is maintained after 450 cycles. Such superior cycle stability at high current density indicates that the excellent structure stability of CuS-RGO-2 during the repeated sodiation-desodiation process. 4. Conclusions CuS and CuS-RGO composites were prepared by microwave-assisted reduction. It is found that the CuS nanosheets are uniformly distributed and tightly anchored onto the surface of RGO nanosheets. Such composite electrodes were studied as anode materials for SIBs, which exhibit a significant improvement of sodium-ion storage capacity compared with CuS electrode. By optimizing the content of RGO, the CuS-RGO-2 electrode achieves a maximum specific capacity of 392.9 mAh g-1 at a current density of 100 mA g-1 after 50 cycles and also remains a high CE and rate 22


Page 23 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


capability. And a capacity of 345 mAh g-1 is retained after 450 cycles even at a current density of 1 A g-1. Furthermore, these results also show that the ether-based electrolyte is helpful to enhance the sodium-ion storage capacity in CuS-RGO composite. The novel strategy in this work should be promising to develop low-cost SIBs for prospective energy storage applications.

Supporting Information: Text giving the TGA curves, SAED patterns and CE of the samples. This material is available free of charge via the Internet at http://pubs.acs.org. Corresponding Author ∗

E-mail: [email protected] (Likun Pan); [email protected] (Wei Qin)

Tel.:+86 21 62234132; fax: +86 21 21 62234321 Notes The authors declare no competing financial interest. Acknowledgements Financial support from the Basic Research Project of Shanghai Science and Technology Committee (No. 14JC1491000) is gratefully acknowledged.

References:

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1.

Page 24 of 32

Kim, S.-W.; Seo, D.-H.; Ma, X.; Ceder, G.; Kang, K., Electrode Materials for

Rechargeable Sodium-Ion Batteries: Potential Alternatives to Current Lithium-Ion Batteries. Adv. Energy Mater. 2012, 2 (7), 710-721. 2.

Kundu, D.; Talaie, E.; Duffort, V.; Nazar, L. F., The Emerging Chemistry of

Sodium Ion Batteries for Electrochemical Energy Storage. Angew. Chem. Int. Edit. 2015, 54 (11), 3431-3448. 3.

Nam, K. W.; Kim, S.; Yang, E.; Jung, Y.; Levi, E.; Aurbach, D.; Choi, J. W.,

Critical Role of Crystal Water for a Layered Cathode Material in Sodium Ion Batteries. Chem. Mater. 2015, 27 (10), 3721-3725. 4.

Dall’Agnese, Y.; Taberna, P.-L.; Gogotsi, Y.; Simon, P., Two-Dimensional

Vanadium Carbide (MXene) as Positive Electrode for Sodium-Ion Capacitors. J. Phys. Chem. Lett. 2015, 6 (12), 2305-2309. 5.

Xiong, X.; Luo, W.; Hu, X.; Chen, C.; Qie, L.; Hou, D.; Huang, Y., Flexible

Membranes of MoS2/C Nanofibers by Electrospinning as Binder-Free Anodes for High-Performance Sodium-Ion Batteries. Sci. Rep. 2015, 5, 9254. 6.

Ge, Y.; Jiang, H.; Zhu, J.; Lu, Y.; Chen, C.; Hu, Y.; Qiu, Y.; Zhang, X., High

Cyclability of Carbon-Coated TiO2 Nanoparticles as Anode for Sodium-Ion Batteries. Electrochim. Acta 2015, 157, 142-148. 7.

Ding, C.; Nohira, T.; Hagiwara, R.; Fukunaga, A.; Sakai, S.; Nitta, K.,

Electrochemical Performance of Hard Carbon Negative Electrodes for Ionic

24


Page 25 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Liquid-Based Sodium Ion Batteries over a Wide Temperature Range. Electrochim. Acta 2015, 176, 344-349. 8.

Liu, X.; Zhang, K.; Lei, K.; Li, F.; Tao, Z.; Chen, J., Facile Synthesis and

Electrochemical Sodium Storage of CoS2 Micro/Nano-Structures. Nano Res. 2016, 9 (1), 198-206. 9.

Kim, H.; Hong, J.; Park, Y.-U.; Kim, J.; Hwang, I.; Kang, K., Sodium Storage

Behavior in Natural Graphite using Ether-Based Electrolyte Systems. Adv. Funct. Mater. 2015, 25 (4), 534-541. 10. Zhu, Z.; Cheng, F.; Hu, Z.; Niu, Z.; Chen, J., Highly Stable and Ultrafast Electrode Reaction of Graphite for Sodium Ion Batteries. J. Power Sources 2015, 293, 626-634. 11. Wang, J.; Luo, C.; Gao, T.; Langrock, A.; Mignerey, A. C.; Wang, C., An Advanced MoS2/Carbon Anode for High-Performance Sodium-Ion Batteries. Small 2015, 11 (4), 473-481. 12. Zhu, C.; Kopold, P.; Li, W.; van Aken, P. A.; Maier, J.; Yu, Y., A General Strategy to Fabricate Carbon-Coated 3D Porous Interconnected Metal Sulfides: Case Study of SnS/C Nanocomposite for High-Performance Lithium and Sodium Ion Batteries. Adv. Sci. 2015, 2 (12), 201500200. 13. Choi, S. H.; Ko, Y. N.; Lee, J. K.; Kang, Y. C., 3D MoS2-Graphene Microspheres Consisting of Multiple Nanospheres with Superior Sodium Ion Storage Properties. Adv. Funct. Mater. 2015, 25 (12), 1780-1788. 25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 32

14. Qin, W.; Li, D.; Zhang, X.; Yan, D.; Hu, B.; Pan, L., ZnS Nanoparticles Embedded in Reduced Graphene Oxide as High Performance Anode Material of Sodium-Ion Batteries. Electrochim. Acta 2016, 191, 435-443. 15. Liu, Y.; Zhang, N.; Kang, H.; Shang, M.; Jiao, L.; Chen, J., WS2 Nanowires as a High-Performance Anode for Sodium-Ion Batteries. Chem. Eur. J. 2015, 21 (33), 11878-11884. 16. Wang, T.; Hu, P.; Zhang, C.; Du, H.; Zhang, Z.; Wang, X.; Chen, S.; Xiong, J.; Cui, G., Nickel Disulfide-Graphene Nanosheets Composites with Improved Electrochemical Performance for Sodium Ion Battery. ACS Appl. Mater. Interfaces 2016, 8 (12), 7811-7817. 17. Sun, R.; Wei, Q.; Li, Q.; Luo, W.; An, Q.; Sheng, J.; Wang, D.; Chen, W.; Mai, L., Vanadium Sulfide on Reduced Graphene Oxide Layer as a Promising Anode for Sodium Ion Battery. ACS Appl. Mater. Interfaces 2015, 7 (37), 20902-20908. 18. Sun, W.; Rui, X.; Zhang, D.; Jiang, Y.; Sun, Z.; Liu, H.; Dou, S., Bismuth Sulfide: a High-Capacity Anode for Sodium-Ion Batteries. J. Power Sources 2016, 309, 135-140. 19. Mahanthappa, M.; Yellappa, S.; Kottam, N.; Vusa, C. S. R., Sensitive Determination of Caffeine by Copper Sulphide Nanoparticles Modified Carbon Paste Electrode. Sensor. Actuat. A-Phys. 2016, 248, 104-113. 20. Saranya, M.; Ramachandran, R.; Kollu, P.; Jeong, S. K.; Grace, A. N., A Template-Free Facile Approach for the Synthesis of CuS-rGO Nanocomposites 26


Page 27 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


towards Enhanced Photocatalytic Reduction of Organic Contaminants and Textile Effluents. RSC Adv. 2015, 5 (21), 15831-15840. 21. Zha, Z.; Zhang, S.; Deng, Z.; Li, Y.; Li, C.; Dai, Z., Enzyme-Responsive Copper Sulphide Nanoparticles for Combined Photoacoustic Imaging, Tumor-Selective Chemotherapy and Photothermal Therapy. Chem. Commun. 2013, 49 (33), 3455-3457. 22. Tao, H.-C.; Yang, X.-L.; Zhang, L.-L.; Ni, S.-B., One-Pot Facile Synthesis of CuS/Graphene Gomposite as Anode Materials for Lithium Ion Batteries. J. Phys. Chem. Solids 2014, 75 (11), 1205-1209. 23. Feng, C.; Zhang, L.; Yang, M.; Song, X.; Zhao, H.; Jia, Z.; Sun, K.; Liu, G., One-Pot Synthesis of Copper Sulfide Nanowires/Reduced Graphene Oxide Nanocomposites with Excellent Lithium-Storage Properties as Anode Materials for Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2015, 7 (29), 15726-15734. 24. Zhou, M.; Peng, N.; Liu, Z.; Xi, Y.; He, H.; Xia, Y.; Liu, Z.; Okada, S., Synthesis of Sub-10 nm Copper Sulphide Rods as High-Performance Anode for Long-Cycle Life Li-ion Batteries. J. Power Sources 2016, 306, 408-412. 25. Kim, J.-S.; Kim, D.-Y.; Cho, G.-B.; Nam, T.-H.; Kim, K.-W.; Ryu, H.-S.; Ahn, J.-H.; Ahn, H.-J., The Electrochemical Properties of Copper Sulfide as Cathode Material for Rechargeable Sodium Cell at Room Temperature. J. Power Sources 2009, 189 (1), 864-868.

27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 32

26. David, L.; Bhandavat, R.; Singh, G., MoS2/Graphene Composite Paper for Sodium-Ion Battery Electrodes. ACS Nano 2014, 8 (2), 1759-1770. 27. Hariharan, S.; Saravanan, K.; Ramar, V.; Balaya, P., A Rationally Designed Dual Role Anode Material for Lithium-Ion and Sodium-Ion Batteries: Case Study of Eco-Friendly Fe3O4. Phys. Chem. Chem. Phys. 2013, 15 (8), 2945-2953. 28. Wu, L.; Hu, X.; Qian, J.; Pei, F.; Wu, F.; Mao, R.; Ai, X.; Yang, H.; Cao, Y., Sb-C Nanofibers with Long Cycle Life as an Anode Material for High-Performance Sodium-Ion Batteries. Energy Environ. Sci. 2014, 7 (1), 323-328. 29. Nithya, C.; Gopukumar, S., RGO/nano Sb Composite: a High Performance Anode Material for Na+ Ion Batteries and Evidence for the Formation of Nanoribbons from the Nano rGO Sheet during Galvanostatic Cycling. J. Mater. Chem. A 2014, 2 (27), 10516-10525. 30. Zhang, Z.-J.; Wang, Y.-X.; Chou, S.-L.; Li, H.-J.; Liu, H.-K.; Wang, J.-Z., Rapid Synthesis of α-Fe2O3/rGO Nanocomposites by Microwave Autoclave as Superior Anodes for Sodium-Ion Batteries. J. Power Sources 2015, 280, 107-113. 31. Zheng, M.; Qiu, D.; Zhao, B.; Ma, L.; Wang, X.; Lin, Z.; Pan, L.; Zheng, Y.; Shi, Y., Mesoporous Iron Oxide Directly Anchored on a Graphene Matrix for Lithium-Ion Battery Anodes with Enhanced Strain Accommodation. RSC Adv. 2013, 3 (3), 699-703.

28


Page 29 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


32. Ren, Y.; Wei, H.; Yang, B.; Wang, J.; Ding, J., “Double-Sandwich-like” CuS@Reduced Graphene Oxide as an Anode in Lithium Ion Batteries with Enhanced Electrochemical Performance. Electrochim. Acta 2014, 145, 193-200. 33. Qin, W.; Chen, T. Q.; Pan, L. K.; Niu, L. Y.; Hu, B. W.; Li, D. S.; Li, J. L.; Sun, Z., MoS2-Reduced Graphene Oxide Composites via Microwave Assisted Synthesis for Sodium Ion battery Anode with Improved Capacity and Cycling Performance. Electrochim. Acta 2015, 153 (0), 55-61. 34. He, G.; Li, L.; Manthiram, A., VO2/rGO Nanorods as a Potential Anode for Sodium- and Lithium-ion Batteries. J. Mater. Chem. A 2015, 3 (28), 14750-14758. 35. Jian, Z.; Zhao, B.; Liu, P.; Li, F.; Zheng, M.; Chen, M.; Shi, Y.; Zhou, H., Fe2O3 Nanocrystals Anchored onto Graphene Nanosheets as the Anode Material for Low-Cost Sodium-Ion Batteries. Chem. Commun. 2014, 50 (10), 1215-1217. 36. Slater, M. D.; Kim, D.; Lee, E.; Johnson, C. S., Sodium-Ion Batteries. Adv. Funct. Mater. 2013, 23 (8), 947-958. 37. Hu, Z.; Zhu, Z.; Cheng, F.; Zhang, K.; Wang, J.; Chen, C.; Chen, J., Pyrite FeS2 for High-Rate and Long-Life Rechargeable Sodium Batteries. Energy Environ. Sci. 2015, 8 (4), 1309-1316. 38. Su, D.; Kretschmer, K.; Wang, G., Improved Electrochemical Performance of Na-Ion Batteries in Ether-Based Electrolytes: A Case Study of ZnS Nanospheres. Adv. Energy Mater. 2015, 6 (2), 1501785.

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 32

39. Zhang, K.; Hu, Z.; Liu, X.; Tao, Z.; Chen, J., FeSe2 Microspheres as a High-Performance Anode Material for Na-Ion Batteries. Adv. Mater. 2015, 27 (21), 3305-3309. 40. Li, J. L.; Liu, X. J.; Pan, L. K.; Qin, W.; Chen, T. Q.; Sun, Z., MoS2-Reduced Graphene Oxide Composites Synthesized via Microwave-Assisted Method for Visible-Light Photocatalytic Degradation of Methylene Blue. RSC Adv. 2014, 4, 9647-9651. 41. Li, J. L.; Liu, X. J.; Hou, X.; Qin, W.; Sun, Z.; Pan, L., Novel Reduced Graphene Oxide Wrapped Bi2.38Mo0.81O6 Microspheres for Highly Efficient Visible Light Photocatalysis. J. Colloid Interf. Sci. 2015, 458, 235-240. 42. Qu, B.; Ma, C.; Ji, G.; Xu, C.; Xu, J.; Meng, Y. S.; Wang, T.; Lee, J. Y., Layered SnS2-Reduced Graphene Oxide Composite-a High-Capacity, High-Rate, and Long-Cycle Life Sodium-Ion Battery Anode Material. Adv. Mater. 2014, 26 (23), 3854-3859. 43. Peng, S.; Han, X.; Li, L.; Zhu, Z.; Cheng, F.; Srinivansan, M.; Adams, S.; Ramakrishna, S., Unique Cobalt Sulfide/Reduced Graphene Oxide Composite as an Anode for Sodium-Ion Batteries with Superior Rate Capability and Long Cycling Stability. Small 2016, 12 (10), 1359-1368. 44. Qin, W.; Chen, T.; Hu, B.; Sun, Z.; Pan, L., GeO2 Decorated Reduced Graphene Oxide as Anode Material of Sodium Ion Battery. Electrochim. Acta 2015, 173, 193-199. 30


Page 31 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


45. Wang, L.; Zhang, K.; Hu, Z.; Duan, W.; Cheng, F.; Chen, J., Porous CuO Nanowires as the Anode of Rechargeable Na-Ion Batteries. Nano Res. 2014, 7 (2), 199-208. 46. Yuan, D.; Huang, G.; Zhang, F.; Yin, D.; Wang, L., Facile Synthesis of CuS/rGO Composite with Enhanced Electrochemical Lithium-Storage Properties through Microwave-Assisted Hydrothermal Method. Electrochim. Acta 2016, 203, 238-245. 47. Jache, B.; Adelhelm, P., Use of Graphite as a Highly Reversible Electrode with Superior Cycle Life for Sodium-Ion Batteries by Making Use of Co-Intercalation Phenomena. Angew. Chem. Int. Edit. 2014, 53 (38), 10169-10173.

31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 32

Table of Contents (ToC) Graphic

32


Significantly Improved Sodium-Ion Storage Performance of CuS

Recommend Documents