Article pubs.acs.org/cm
A Chemically Coupled Antimony/Multilayer Graphene Hybrid as a High-Performance Anode for Sodium-Ion Batteries Lingyun Hu,† Xiaoshu Zhu,‡ Yichen Du,† Yafei Li,† Xiaosi Zhou,*,† and Jianchun Bao*,† †
Jiangsu Key Laboratory of Biofunctional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, P. R. China ‡ Center for Analysis and Testing, Nanjing Normal University, Nanjing 210023, P. R. China S Supporting Information *
ABSTRACT: Sodium-ion batteries have recently attracted considerable attention as a promising alternative to lithium-ion batteries owing to the natural abundance and low cost of sodium compared with lithium. Among all proposed anode materials for sodium-ion batteries, antimony is a desirable candidate due to its high theoretical capacity (660 mA h g−1). Herein, an antimony/multilayer graphene hybrid, in which antimony is homogeneously anchored on multilayer graphene, is produced by a confined vapor deposition method. The chemical bonding can realize robust and intimate contact between antimony and multilayer graphene, and the uniform distribution of antimony and the highly conductive and flexible multilayer graphene can not only improve sodium ion diffusion and electronic transport but also stabilize the solid electrolyte interphase upon the large volume changes of antimony during cycling. Consequently, the antimony/multilayer graphene hybrid shows a high reversible sodium storage capacity (452 mA h g−1 at a current density of 100 mA g−1), stable long-term cycling performance with 90% capacity retention after 200 cycles, and excellent rate capability (210 mA h g−1 under 5000 mA g−1). This facile synthesis approach and unique nanostructure can potentially be extended to other alloy materials for sodium-ion batteries.
1. INTRODUCTION Room temperature sodium-ion batteries (SIBs) have attracted increasing attention and been considered as a promising alternative to lithium-ion batteries (LIBs) due to the abundance of sodium sources and the even global distribution of such sources compared with lithium.1−7 In the light of the similarity between elemental lithium and sodium, a straightforward idea is to directly transform well-established electrode materials in LIBs into SIBs by replacing lithium with sodium.8−13 Unfortunately, the widely used graphite anode in LIBs was proven to only intercalate a very small amount of sodium, as Na ion possesses a much larger radius than does Li ion (1.02 vs 0.76 Å).14−16 This is a serious obstacle for commercial application of SIBs and requires development of novel anode materials to realize fast and reversible sodium ion uptake and release. Unremitting efforts have been devoted to new anode materials for high-performance SIBs, including carbonaceous materials,17−32 metal oxides and sulfides,33−38 and alloy-based materials.39−45 However, each class of such materials presents certain intrinsic limitations, such as a specific capacity typically less than 300 mA h g−1 related to carbonaceous electrodes and a high voltage plateau associated with conversion reaction or alloying reaction electrodes. Antimony (Sb) stands out as an attractive candidate because it can afford a high theoretical specific capacity of 660 mA h g−1 © XXXX American Chemical Society
to form the Na3Sb phase and a quite safe operating potential of ∼0.40 V vs Na+/Na.46−55 Nevertheless, the application of Sb in SIBs is hindered by the large volume expansion and contraction during sodiation/desodiation. This significant volume change (>300%) of Sb results in pulverization of active material and loss of electrical contact between active material and conductive additive/current collector, leading to capacity degradation.56−63 Similar to the well-known germanium anode in LIBs, the huge volume changes will also produce unstable, thick, and electrically insulating solid electrolyte interphase (SEI) layer on the active material surface, impeding the reaction kinetics and causing insufficient Coulombic efficiency and capacity decay.64−67 To circumvent this obstacle, Sb was usually mixed with carbonaceous materials to generate Sb−carbon composites. These composites were generally prepared by ball milling of Sb and carbon sources including carbon black, carbon nanotubes, and graphene oxide,41,46−49 during which Sb was transformed into Sb nanoparticles well-dispersed in the carbon matrix. As a result, the carbon matrix can increase the electrical conductivity of the as-prepared composites, and the nanosized Sb can shorten the diffusion length for sodium ions during the Received: October 6, 2015 Revised: November 17, 2015
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Figure 1. Schematic illustration of the preparation process for the Sb/MLG hybrid.
electrode materials with large volume changes and low electrical conductivities.
Na-ion insertion/extraction processes, thus leading to the significantly enhanced electrochemical performance of Sb. In addition to the Sb−carbon composites formed by ball milling, Wang et al.51 and Cao et al.52 successively and independently reported that, by a single-nozzle electrospinning and subsequent carbonization, Sb nanoparticle−carbon composites could deliver a high charge capacity of 405 mA h g−1 at the current density of 100 mA g−1 and 631 mA h g−1 at the current density of 40 mA g−1. A common drawback of these Sb/carbon hybrid materials is the poor structural stability, which originates from the weak interaction between active component and carbon matrix. As a result, electrodes prepared with these hybrid materials typically suffer from relatively low cycling stability and power densities, which are unsatisfactory for practical applications. To make better utilization of the active material Sb, construction of chemically bonded structures could partly overcome the abovementioned limitation of hybrid materials. However, fabrication of strongly coupled structures is generally challenging and complicated, and the particle size should be carefully controlled to maximize the electrochemical performance. Herein, we report an Sb/multilayer graphene (denoted as Sb/MLG) hybrid, in which Sb is uniformly anchored on the MLG surface, as a desirable anode for SIBs. Different from the previous Sb−carbon composites fabricated by ball milling/ electrospinning techniques, the Sb/MLG hybrid is synthesized by a confined vapor deposition method, in which Sb particles and freeze-dried graphene oxide (denoted as FGO) are separately located at the lower and upper parts of a singlehead sealed glass tube. Therefore, Sb vapor will continuously generate and easily diffuse into the empty spaces of in situ formed MLG during heat treatment under argon flow, enabling a uniform deposition of Sb on MLG due to the strong chemical bonding between Sb and GO. This chemical bonding can facilitate robust and intimate contact between Sb and MLG, and the uniform distribution of Sb and the highly conductive and flexible MLG can not only enhance sodium ion diffusion and electronic transport but also stabilize the SEI layer upon the huge volume changes of Sb during cycling. As a result, the Sb/MLG hybrid shows superior electrochemical performance when evaluated as a sodium-ion battery anode, with a high initial charge capacity of 452 mA h g−1 at a current density of 100 mA g−1 and good cycling stability (90% capacity retention after 200 cycles) as well as excellent rate capability (210 mA h g−1 under 5000 mA g−1). Moreover, the confined vapor deposition approach may be applied to other high-capacity
2. EXPERIMENTAL SECTION 2.1. Synthesis of the Sb/MLG Hybrid. Typically, 100 mg of Sb and 5 mL of graphene oxide aqueous suspension (10 mg mL−1, produced from a modified Hummers method68) were loaded in a single-head sealed glass tube in sequence. The glass tube was frozen with liquid nitrogen and then freeze-dried for 2 days. After that, the glass tube was placed on two crucibles in a tube furnace, heated to 600 °C, and kept at that temperature for 6 h under argon atmosphere with a heating rate of 5 °C min−1 to deposit Sb on MLG. After cooling to room temperature, the glass tube was taken out from the furnace and cut from the bottom to remove the excess Sb, and finally the Sb/MLG hybrid was collected from the upper part of the glass tube. In a control experiment, the Sb−MLG mixture was prepared by hand-grinding Sb and MLG with a weight ratio of 4:6 in a mortar for 30 min. MLG was fabricated by a similar method to that of Sb/MLG except for the use of Sb. 2.2. Materials Characterization. X-ray diffraction (XRD) patterns were obtained on a Rigaku D/max 2500/PC diffractometer using Cu Kα radiation. Raman spectra were recorded on a Labram HR800 with a laser wavelength of 514.5 nm. X-ray photoelectron spectroscopy (XPS) measurements were carried out on an ESCALab250Xi electron spectrometer from VG Scientific using 300 W Al Kα radiation. Scanning electron microscopy (SEM) was performed on a JEOL JSM-7600F scanning electron microscope operated at 10 kV. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) observations were conducted on a JEOL JEM-2100F transmission electron microscope operated at 200 kV. Scanning transmission electron microscopy (STEM) meaurement as well as elemental mapping analysis were carried out on the JEOL JEM-2100F transmission electron microscope equipped with a Thermo Fisher Scientific energy-dispersive X-ray spectrometer. Thermogravimetric analysis (TGA) was determined on a NETZSCH STA 449 F3 in air atmosphere with a heating rate of 10 °C min−1 from room temperature to 800 °C. 2.3. Electrochemical Measurements. Electrochemical experiments were perfomed using CR2032 coin cells. The working electrodes were prepared by mixing Sb/MLG, Sb−MLG mixture, MLG, or Sb with Super-P carbon black and carboxymethyl cellulose sodium with a weight ratio of 80:10:10 in water using a mortar and pestle. The resulting slurry was coated onto pure Cu foil (99.9%, Goodfellow) and then dried in a vacuum oven at 40 °C for 12 h. The mass loading of active material is 1.0−1.5 mg cm−2. The electrolyte solution for all tests was 1 M NaClO4 in ethylene carbonate/diethyl carbonate/fluoroethylene carbonate (FEC) (1:1:0.1 v/v/v). Glass fiber (GF/D) from Whatman and sodium metal were used as separators and counter electrodes, respectively. The coin cells were assembled in an argon-filled glovebox (H2O, O2 < 0.1 ppm, MBraun, Germany). B
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Chemistry of Materials Galvanostatic charge−discharge tests of the batteries were carried out on a Land CT2001A multichannel battery testing system at various current densities in the fixed voltage window between 0.01 and 2 V vs Na+/Na at room temperature. 2.4. DFT Calculations. The spin polarized DFT computations used an all-electron method within a generalized gradient approximation (GGA) for the exchange-correlation term, as implemented in the DMol3 code.69,70 The double numerical plus polarization (DNP) basis set and PBE functional71 were employed in all computations. Self-consistent field (SCF) calculations were performed with a convergence criterion of 10−6 a.u. on the total energy and electronic computations. The Brillouin zone was sampled with a 6 × 6 × 1 Γ centered k points setting in geometry optimizations.
3. RESULTS AND DISCUSSION Figure 1 schematically illustrates the fabrication process of the Sb/MLG hybrid. The Sb/MLG hybrid is produced by a confined vapor deposition method. Sb and graphene oxide aqueous solution were successively loaded into a single-head sealed glass tube, followed by freeze-drying. Afterward, the glass tube was heated to 600 °C and kept at that temperature for 6 h under argon atmosphere, during which Sb vapor continuously generated and gradually deposited on the MLG surface owing to the strong chemical bonding formed between Sb and GO. After the bottom of the glass tube was cut off to remove the unevaporated Sb, the Sb/MLG hybrid was collected from the upper part of the glass tube. The photographs of the synthetic process and the as-obtained Sb/MLG hybrid are demonstrated in Figure S1 (Supporting Information). Figure 2a displays the XRD patterns for the hand-grinded Sb−MLG mixture and Sb/MLG hybrid. The XRD pattern of the Sb−MLG mixture shows highly crystalline Sb, with characteristic graphitic peak of MLG at 26.3°. By contrast, the Sb peaks in the XRD pattern of Sb/MLG hybrid are significantly weakened while the graphitic peak is greatly enhanced, implying the deposited Sb particles in the hybrid are probably nanometer-sized.43,72 The structure of Sb−MLG mixture and Sb/MLG hybrid is further examined by the Raman spectra (Figure 2b). Compared to the Sb−MLG mixture, the broader D band in the Sb/MLG shows an increase of amorphous structure, indicating that there may be a strong interaction between Sb and MLG. The interaction between Sb and MLG was further investigated by XPS and ab initio simulation. Usually, GO-converted graphene sheets are decorated with an oxygen-containing functional group, and Sb particles are covered with a thin layer of Sb-based oxides owing to surface oxidation. These are verified by the appearance of CO (286.4 eV), OCO (289.2 eV), and Sb3+ 3d3/2 (540.1 eV) characteristic peaks in the XPS spectra of the Sb−MLG mixture (Figure 2c,e). Notably, the characteristic peaks of CO and Sb 3d in the XPS spectrum of the Sb/MLG hybrid shift to 285.9 and 539.6 eV, respectively (Figure 2d,f). It could be reflective of the formation of SbOC bonding between the vapor-deposited Sb and oxygen-containing functional groups of MLG, which causes lower electron density at the Sb and C sites and thus weakens the CO bonds and the binding force between Sb nuclei and its electrons in the hybrid. In order to prove the rationality of XPS fitting, we take the Sb 3d XPS spectrum of the Sb/MLG hybrid as an example and demonstrate the fitting process in Figure S2 (Supporting Information). To further reveal the existence of SbO bonding, ab initio simulation was carried out (Figure 5a). Since GO has ample O sites on the surface, which are the key to anchoring metal atoms and improving the metalGO
Figure 2. (a) XRD patterns of the Sb−MLG mixture and Sb/MLG hybrid and standard XRD pattern of Sb (JCPDS card No. 35-0732). (b) Raman spectra of the Sb−MLG mixture and Sb/MLG hybrid. (c, d) High-resolution C 1s XPS spectra of the Sb−MLG mixture and Sb/ MLG hybrid. (e, f) High-resolution Sb 3d XPS spectra of the Sb− MLG mixture and Sb/MLG hybrid.
binding to avoid the formation of large metal particles, GO can serve as the promising substrate to covalently anchor metal atoms.73 For simplicity, we used the repeat unit of GO as the modeling molecule to calculate the binding energy to reveal the interaction between Sb and GO. This simulation can provide a qualitative explanation of the generation of chemically bonded Sb/MLG hybrid structure. The result is shown in Figure 5a. Our computations demonstrate that the Sb atom can form strong chemical bonds with epoxy and hydroxyl groups of GO with a binding energy as high as 3.22 eV. This chemical bonding enables MLG to strongly couple with the vapordeposited Sb and consequently helps stabilize Sb and NaxSb intermediates during battery cycling. To study the morphology of the as-formed Sb/MLG hybrid, we carried out SEM and TEM characterizations. SEM images (Figure 3a,b) illustrate that the obtained hybrid material shows a sheet-like structure with no evident particles exposed on the outer surface. The TEM image (Figure 3c) demonstrates that Sb is homogeneously distributed on the MLG surface. By contrast, the TEM image and elemental mapping images of the Sb−MLG mixture in Figures S3 and S4 (Supporting Information) shows that large Sb nanoparticles are isolated from graphene sheets. The ring-like mode in the selected-area electron diffraction (SAED) pattern (Figure 3d) confirms the existence of polycrystalline Sb, which can be identified as a hexagonal Sb (JCPDS card No. 35-0732) by the XRD measurement. The HRTEM images (Figure 3e,f) show some Sb nanocrystals deposited on amorphous multilayer graphene, in accordance with the XRD results. As can be observed, the C
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Figure 3. (a) SEM image, (b) high-magnification SEM image, (c) TEM image, (d) SAED pattern, (e, f) HRTEM images, (g) STEM image, and corresponding (h) C and (i) Sb elemental mapping images of the Sb/MLG hybrid.
estimated interlayer spacing of 0.34 and 0.23 nm in Figure 3e,f corresponds to the (002) plane of MLG and (104) plane of Sb, respectively. Energy dispersive X-ray spectrometry (EDX) elemental mapping (Figure 3g−i) demonstrates that carbon and Sb are homogeneously combined with each other in the hybrid, ensuring a high electronic conductivity for the entire hybrid. Moreover, the stable three-dimensional framework of Sb/MLG (Figure 3a) could offer excess active sites for Na storage without remarkable volume change, thus improving the storage capacity and cycling performance of the Sb/MLG hybrid electrode. Figure 4a shows the first three cyclic voltammetry (CV) curves of the Sb/MLG hybrid electrode from 0.01 to 2 V vs Na+/Na at a scanning rate of 0.1 mV s−1. A pronounced peak at 0.37 V during the first cathodic scan corresponds to the Nainsertion process of Sb to form NaxSb as well as the reduction of electrolyte to produce the SEI film. In the following cathodic scans, two new peaks at 0.66 and 0.52 V occurred and could be attributed to the initial and further sodiation of Sb, respectively. Starting from the second cathodic scan, the intensities of three peaks gradually stabilize, suggesting gradually stabilized sodiation kinetic. During all three anodic scans, a strong broad peak at 0.88 V is detected, corresponding to the desodiation of different NaxSb alloys. It is worth noting that the anodic peak current becomes steady from the first scan to the third scan, indicating that the desodiation kinetic is gradually stabilized as well. Figure 4b shows the charge/discharge profiles for the Sb/MLG hybrid electrode under a constant current density of 100 mA g−1. Except for the first discharge profile which is different from others because of the formation of the
Figure 4. (a) CV curves of the first three cycles of the Sb/MLG hybrid electrode. (b) Galvanostatic charge−discharge profiles of different cycles for the Sb/MLG hybrid electrode. (c) Cycling performance of the MLG, Sb, Sb−MLG mixture, and Sb/MLG hybrid electrodes. (d) Rate capability of the MLG, Sb, Sb−MLG mixture, and Sb/MLG hybrid electrodes.
SEI layer, the discharge profiles comprise a sloping region from 1.5 to 0.73 V and two successive plateaus from 0.73 to 0.36 V followed by a sloping region down to 0 V. Correspondingly, the charge profiles consist of a sloping region from 0.01 to 0.71 V and two inclined plateaus from 0.71 to 0.95 V followed by a sloping region up to 2 V. The two pairs of plateaus between D
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material for SIBs, the initial cycle CE is only 44.6% (Supporting Information, Figures S5b and S6).27 In addition to exhibiting the high specific capacity and stable cycling performance, the Sb/MLG hybrid shows a high rate capability as well. As displayed in Figure 4d, the Sb/MLG hybrid electrode delivers reversible capacities of 448, 456, 428, 382, 318, and 210 mA h g−1 at the current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A g−1, respectively. It is worth noting that the Sb/MLG hybrid electrode exhibits much higher capacities than does the MLG, Sb, or Sb−MLG mixture electrode under all applied current densities, which is consistent with the cycling performance (Figure 4c). The significant rate capability can be attributed to the superior conductive matrix of MLG, which is well preserved during the nondestructive vapor deposition process. As illustrated by the SEM and TEM images and elemental mapping (Figures 3 and 4), the vapor-deposited Sb is uniformly combined with MLG, allowing for fast and efficient electron transportation during Na ion insertion−extraction processes. Furthermore, the capacity increase demonstrated in Figure 4d might be resulted from the gradually decreased interface resistances, including SEI resistance and charge transfer resistance, during the initial few cycles.43 Electrochemical impedance spectroscopy (EIS) measurements were performed to achieve further insight into the stable cyclability of the Sb/MLG hybrid. The Nyquist plots for the Sb/MLG hybrid measured before cycling and after different cycles are shown in Figure 5b. The Nyquist plot consists of a
0.36 and 0.95 V indicate two steps of sodium alloying and dealloying reactions with Sb to produce NaxSb and Na3Sb, which are in good agreement with the previous reports.49,52 On the basis of the previous results, the two pairs of redox bands can be attributed to the following reactions: Sb + x Na + + x e− ↔ NaxSb
(1)
NaxSb + (3 − x)Na + + (3 − x) ↔ Na3Sb
(2)
Figure 4c shows the cycling performance of the Sb/MLG hybrid electrode under 100 mA g−1 for 200 cycles between 0.01 and 2 V vs Na+/Na. The initial charge and discharge capacities are 452 and 593 mA h g−1, respectively, on the basis of the total mass of the Sb/MLG hybrid. For comparison, the cycling performance of the Sb, MLG, and the Sb−MLG mixture electrodes under the same current density are also displayed in Figure 4c with the charge−discharge profiles of those materials presented in Figure S5 (Supporting Information). Besides, the Coulombic efficiencies of these materials are shown in Figure S6 (Supporting Information). The Sb electrode possesses a charge capacity of 506 mA h g−1 in the first cycle (Supporting Information, Figure S5a); however, it decreases to less than 19 mA h g−1 after 20 cycles (Figure 4c). Compared to pristine Sb, the Sb−MLG mixture fabricated via hand-grinding exhibits an improved cycling stability with a charge capacity of 312 mA h g−1 at the 20th cycle (Figure 4c and Supporting Information Figure S6). Given the weight ratio between Sb and MLG is 4:6 in the mixture and MLG can afford a stable charge capacity of 198 mA h g−1 (Figure 4c and Supporting Information Figure S6), a reversible capacity of 483 mA h g−1 can be reached for Sb. However, its cycling performance is still unsatisfactory with a decrease in charge capacity to 282 mA h g−1 at the 200th cycle (Figure 4c and Supporting Information Figure S6). For the Sb/MLG hybrid with the same Sb content (∼40 wt % as determined by TGA in Supporting Information Figure S7), the charge (discharge) capacity gradually stabilizes from 452 (593) mA h g−1 in the first cycle to 445 (457) mA h g−1 at the 20th cycle then maintains 405 (406) mA h g−1 (∼660 mA h g−1 for Sb) even after 200 cycles. The apparent discharge capacity decay in the initial cycles is mainly ascribed to the reductive decomposition of the electrolyte and the formation of SEI film and irreversible reactions between sodium ions and the residual oxygen-containing functional groups of MLG. It is worth mentioning that the electrochemical performance demonstrated in Figure 4c is evaluated in the electrolyte with FEC additive, which is adopted to enhance the stability of SEI film. The Sb electrode displays an initial Coulombic efficiency (CE) of 77.5%. As to the Sb−MLG mixture electrode, the initial CE decreases to 61.8%, probably owing to the significantly decreased electrical conductivity by loosening contact between Sb and MLG. By contrast, the initial CE of the Sb/MLG hybrid electrode is as high as 76.2%. Moreover, the CE of the Sb/ MLG hybrid electrode exceeds 90% after the first cycle and maintains an average CE of >99% for up to 200 cycles after the second cycle. We note that the initial CE of the Sb/MLG hybrid electrode is much higher than most of the values reported for the Sb-based anode materials in the literature (Supporting Information, Table S1).50−52,57,63 This is probably due to the fact that MLG is well coated by Sb and the Sb layer could effectively mitigate the reaction between MLG and electrolyte to produce the SEI film, thus improving the first CE of the Sb/MLG hybrid electrode. It is reported that MLG has a high specific surface area, and when MLG is used as an anode
Figure 5. (a) Top (upper) and side (lower) views of the most stable Sb−GO structure. Color scheme: Sb, purple; C, gray; H, white; O, red. (b) Nyquist plots of the Sb/MLG cell before cycling and after 30 and 100 cycles with the inset displaying the equivalent circuit used for data fitting.
semicircle with a large diameter at medium frequencies and a straight line at low frequencies. The semicircle is attributed to Na+ crossing the SEI layer and charge transfer between electrolyte and electrode, and the straight line corresponds to Na+ diffusion inside the electrode material.43 A corresponding equivalent circuit is proposed and demonstrated in the inset in Figure 5b. Re, Rf, Rct, and CPE represent electrolyte resistance, SEI film resistance, charge-transfer resistance, and constant phase element, respectively. The kinetic parameters acquired from the equivalent circuit fitting are listed in Table S2 (Supporting Information). The values of Rf of the Sb/MLG hybrid electrode before cycling and after 30 and 100 cycles are 104.7, 54.5, and 53.8 Ω, respectively. In the case of chargetransfer resistance Rct, the values before cycling and after 30 and 100 cycles are 11.1, 8.0, and 7.6 Ω, respectively. The results suggest that the unstable SEI film formed before cycling becomes stabilized and the charge-transfer resistance decreases with the gradual infiltration of the electrolyte into the composite. These also reveal the formation of a stable interface E
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between the Sb/MLG hybrid electrode and electrolyte as well as the presence of activation process, both of which lead to the stable cycling performance of Sb/MLG after the initial few cycles. The generation of the stable interface between Sb/MLG and the electrolyte could be ascribed to the outstanding mechanical properties of the MLG network. It is reported that graphene foams repeatedly underwent sodiation/desodiation without creating any obvious deformation.27 The robust MLG network can act as a strong framework for the hybrid and alleviate the sodium ion insertion/extraction induced stress, thus maintaining the electrode integrity and stabilizing the SEI layer during cycling.27,43 As verified by the STEM image and the corresponding EDX elemental mapping of the cycled Sb/ MLG hybrid electrode material (Supporting Information, Figure S8), the structural integrity of the electrode material is well maintained without obvious cracks even after 200 cycles. The STEM image (Supporting Information, Figure S8a) shows that the loosely packed sheets can be observed on the cycle electrode material. The EDX elemental mapping in Figure S8c−f (Supporting Information) presents that both Sb and MLG are still inextricable, suggesting the robust structure of the Sb/MLG hybrid.
AUTHOR INFORMATION
Corresponding Authors
*(X.Z.) E-mail:
[email protected]. Telephone/Fax: +8625-85891027. *(J.B.) E-mail:
[email protected]. Telephone/Fax: +86-25-85891936. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
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REFERENCES
This work was supported by the National Natural Science Foundation of China (Grant Nos. 21503112, 51577094, and 21471081), the Natural Science Foundation of Jiangsu Province of China (BK20140915 and BK20150045), the Scientific Research Foundation for Advanced Talents of Nanjing Normal University (2014103XGQ0073), the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the Program of Jiangsu Collaborative Innovation Center of Biomedical Functional Materials.
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4. CONCLUSIONS In summary, we have successfully developed an Sb/MLG hybrid nanostructure anode for sodium-ion batteries through a facile confined vapor deposition method. The MLG strongly couples the Sb nanoparticles via chemical bonding, which can not only increase the electrical conductivity but also allow the MLG to serve as a conductive matrix to maintain electrical contact with Sb during the large volume expansion and help stabilize the SEI layer. This considerably enhances the sodium storage properties in comparison with a Sb−MLG mixture anode, delivering an initial charge capacity of 452 mA h g−1 with capacity retention of 90% relative to the first cycle after 200 cycles and superior rate capability of 210 mA h g−1 under 5000 mA g−1. Considering the simple and general method as well as the strong chemical bonding, we believe that the confine vapor deposition strategy will open new avenues to integrate advantages of both high-capacity alloy materials and graphene for high-performance sodium-ion batteries.
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.5b03920. Photographs of the synthetic process and the as-formed Sb/MLG hybrid; XPS fitting process for the Sb 3d peak of the Sb/MLG hybrid; TEM image, SEM image, and corresponding C, O, and Sb elemental mapping images of the Sb−MLG mixture; galvanostatic charge−discharge profiles of the Sb, MLG, and the Sb−MLG mixture electrodes; Coulombic efficiencies of the Sb, MLG, Sb− MLG mixture, and Sb/MLG hybrid electrodes; TGA and DTA curves of the Sb/MLG hybrid; STEM image, EDX spectrum, and EDX elemental mapping images of the cycled Sb/MLG hybrid electrode material; comparison of the reported Sb-based anode materials for sodium-ion batteries; and the resistances gained from the fitting experimental data in Figure 5b (PDF) F
DOI: 10.1021/acs.chemmater.5b03920 Chem. Mater. XXXX, XXX, XXX−XXX
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