SnO2@C@VO2 Composite Hollow Nanospheres as an Anode

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Functional Nanostructured Materials (including low-D carbon) 2

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SnO@C@VO Composite Hollow Nanospheres as an Anode Material for Lithium-Ion Batteries Wenbin Guo, Yong Wang, Qingyuan Li, Dongxia Wang, Fanchao Zhang, Yiqing Yang, and Yang Yu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 16 Apr 2018 Downloaded from http://pubs.acs.org on April 16, 2018

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ACS Applied Materials & Interfaces

SnO2@C@VO2 Composite Hollow Nanospheres as an Anode Material for Lithium-Ion Batteries Wenbin Guo, Yong Wang*, Qingyuan Li, Dongxia Wang, Fanchao Zhang, Yiqing Yang, and Yang Yu Department of Chemistry, Capital Normal University, Beijing 100048, China KEYWORDS:

Nanostructures,

Transition

metal

oxide,

Composite

nanomaterials,

Electrochemical properties, Lithium-ion batteries

ABSTRACT: Porous SnO2@C@VO2 composite hollow nanospheres have been ingeniously constructed through the combination of layer-by-layer deposition and redox reaction. Moreover, to optimize the electrochemical properties, SnO2@C@VO2 composite hollow nanospheres with different contents of the external VO2 have been also studies. On the one hand, the elastic and conductive carbon as interlayer in the SnO2@C@VO2 composite can not only buffer the huge volume variation during repetitive cycling, but also effectively improve electronic conductivity and enhance the utilizing rate of SnO2 and VO2 with high theoretical capacity. On the other hand, hollow nanostructures of the composite can be consolidated by the multi-layered nanocomponents, resulting in outstanding cyclic stability. In virtue of the above synergetic contribution from individual components, SnO2@C@VO2 composite hollow nanospheres exhibit a large initial discharge capacity (1305.6 mAhg-1) and outstanding cyclic stability (765.1 mAhg-1

ACS Paragon Plus Environment

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after 100 cycles). This design of composite hollow nanospheres may be extended to the synthesis of other nanomaterials for electrochemical energy storage.


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INTRODUCTION Nowadays, electrochemical energy storage (EES) devices, such as supercapacitors and batteries, have been comprehensively studied in multifarious energy storage systems and identified as one of the most promising green energy sources.1,2 Observably, lithium ion batteries (LIBs) have been extensively applied for portable devices and electrical vehicles as rechargeable batteries with advantages of excellent cyclability and high capacity.3,4 Transition metal oxides (TMOs) as promising substitutes for graphite anode materials have caused increasingly wide attention due to their relatively high theoretical capacity.5-7 However, large volume variation of TMOs exists during the lithiation/delithiation process, which results in large irreversible capacity loss and pulverization of the material.8-13 Recently, some novel strategies, such as special nanostructures and carbon hybridization, have been developed to solve the problems.14-27 Reducing the TMOs size to the nanoscale has been seen as an important strategy to improve the electrochemical performance of materials. Particularly, TMOs hollow nanostructures, for example, hollow nanospheres,14-16 hollow nanometer boxes17,18 and hollow nano-spindles,19-22 have been widely studied for their hollow structures can effectively withstand cyclic changes in volume. Another effective strategy is to combine TMOs with the elastic and conductive material, such as amorphous carbon and graphene, which can not only offer a cushion effect to cope with the internal stress, but also improve the electrical conductivity during cycling.23-27 Therefore, a reasonable design of TMO@C composite hollow nanostructures with the aforementioned two structural characteristics is of great significance for both fundamental studies and practical application of anode materials in LIBs. However, the carbon material with low theoretical capacity (372 mAhg-1) in the TMO@C composites can decease the total theoretical capacity of the composite, which hinders further


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improvement of their electrochemical properties.8,23,28,29 More recently, in situ hybridization of two or more active materials has drawn much attention. Therefore, another attractive approach is proposed for acquiring anode materials with large capacity and long cycling life to synthesize TMO@C@TMO composite with multi-components.12,30-34 For example, Mai and Xiao et al. have reported that TiO2-C/MnO2 nanowire arrays possess outstanding performances as LIB anode materials.30 The group of Wang and Shu et al. has reported that the cube-like Fe3O4@(C– MnO2) core–double-shell composite exhibits improved electrochemical properties compared with α-Fe2O3 and Fe3O4–C.31 Bals and co-workers have reported the excellent Li storage capacity of the heterogeneous TiO2/V2O5/C nanotubes.32 Xu and co-workers have reported Fe3O4/VOx@C microboxes possess outstanding rate performance and cyclability for LIBs.33 Wang and Yu et al. have reported that TiO2@C@MnO2 multi-shelled hollow nanospheres exhibit excellent rate capability and cyclic stability.34 The above reports on TMO@C@TMO composites have demonstrated that composites with three layers possess effectively improved electrochemical properties. In a word, great efforts have been devoted to developing a novel method for the synthesis of TMO@C@TMO composite with large capacity and long cycling life. Among TMOs, tin dioxide (SnO2) has been considered as a potential anode material for LIBs because of its safe lithiation potential, natural abundance and relatively high theoretical capacity (782 mAhg-1).20,23,31 Moreover, VO2 (B) has also been regarded as a prospective electrode material due to its proper electrode voltage and special layered structure which can remain stable and thus achieve high capacity and long cycle life. 35-42 Herein, to combine the advantages of SnO2, VO2 and conductive carbon materials, we have successfully

designed

and

prepared

SnO2@C@VO2

composite

hollow

nanospheres


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(SnO2@C@VO2 CHNs) to adequately exert their electrochemical properties by using layer-bylayer

deposition

techniques.

Moreover,

to

optimize

the

electrochemical

properties,

SnO2@C@VO2 CHNs with different contents of the external VO2 have also been studies. In virtue of the synergetic contribution from individual components and the suitable content of VO2 (35 wt%), SnO2@C@VO2 CHNs exhibit a large initial discharge capacity (1305.6 mAhg-1) and outstanding cyclic stability (765.1 mAhg-1 after 100 cycles). RESULTS AND DISCUSSION The fabrication process of SnO2@C@VO2 CHNs is shown in the schematic illustration (Figure 1). Firstly, SiO2 nanospheres as hard-templates were coated by SnO2 nanoparticles to form SiO2@SnO2 nanospheres (Figure S1). Next, the polysaccharide can be uniformly deposited on the surface of SiO2@SnO2 core-shell nanospheres by using glucose as raw materials via the hydrothermal method.28,29 After heated at 500 oC for 4 h in Ar, the polysaccharide layer was carbonized. SiO2 templates were removed by using 0.6 wt % HF solution, which led to the formation of SnO2@C HNs (Figure S2). Finally, SnO2@C@VO2 CHNs were obtained by a relatively facile redox method. In the final reaction step, ammonium metavanadate could be reduced by carbon to form a granular VO2 which was uniformly deposited on the surface of the carbon layer.36,41,43,44 It is noted that the generation of carbon after the calcination treatment is important for the formation of VO2 due to the redox reaction between NH4VO3 and carbon. The reaction can be described as Equation (1)-(3): 2NHସ VOଷ → 2NHଷ +Hଶ O + Vଶ Oହ

(1)

2Vଶ Oହ + 2C → 4VOଶ + 2CO

(2)

2Vଶ Oହ + C → 4VOଶ + COଶ

(3)


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SEM and TEM images of SnO2@C@VO2 CHNs prepared with different quantities of NH4VO3 are shown in Figure 2. The samples of SnO2@C@VO2 CHNs prepared by adding 0.01, 0.03 and 0.05 g of NH4VO3 in the final reaction step are denoted as SnO2@C@VO2-1 (Figure 2a-d), SnO2@C@VO2-3 (Figure 2e-h) and SnO2@C@VO2-5 (Figure 2i-l), respectively. All samples of SnO2@C@VO2 CHNs present clear hollow spherical nanostructures with diameters ranging from 230 to 290 nm, and their shell thickness increases with the added quantities of NH4VO3. As shown in Figure 2, the shell thickness of SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5 is estimated to be ca 15, 30 and 60 nm, respectively. As shown in Figure 2a-c, when the amount of NH4VO3 is 0.01 g, the porous wall in SnO2@C@VO2-1 can easily be observed. When the amount of NH4VO3 is increased to 0.03 g, many nanoparticles can be observed on the surface of SnO2@C@VO2-3, which is apparently rougher than that of SnO2@C HNs precursor (Figure 2e-g). However, when the amount of NH4VO3 is further increased to 0.05 g, some impurities can be observed (Figure 2i-j). As shown in HRTEM images of Figure 2d, h and l, the clear lattice spacings of 0.26, 0.33 and 0.35 nm can be observed in SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5, respectively, which corresponds to (101), (110) plane of SnO2 and (110) plane of VO2 (B), indicating good crystallinity of the above three samples.15,20,41 The EDX spectra of the above samples in Figure S3 show the strong C, O, Sn and V peaks. It should be noted that a small amount of Si signal is detected in the above three spectra, which probably arises from a small amount of tin silicate formed during annealing. 19 EDX elemental mappings for vanadium, oxygen, tin and carbon under TEM observations demonstrate the welldistribution of V, O, Sn and C over all the SnO2@C@VO2 samples (Figure 3). Moreover, with the amount of NH4VO3 increased in the above three samples, color blocks of V mappings


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become more, indicating the increase of vanadium sources. ICP-MS was used to ascertain the chemical composition of SnO2@C@VO2 CHNs. The content of the VO2 in SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5 is 22, 35 and 44 wt %, respectively. To further understand the growth mechanism of SnO2@C@VO2 CHNs, controlled experiments were conducted. When SnO2@C HNs as the precursor were replaced by carbon spheres in the final step and the other steps were the same as those of SnO2@C@VO2 CHNs, C@VO2 spheres (C@VO2 Ss) could be obtained (experimental details see SI, Figure S4). As shown in Figure S4b-c, the surfaces of C@VO2 Ss are covered by nanoparticles, which makes the smooth surface of carbon spheres rough. Based on the above observation, it can be inferred that carbon can be used as the reducing agent to acquire VO2. XRD patterns of C@VO2 Ss, SnO2@C HNs and SnO2@C@VO2 CHNs are shown in Figure 4a. All the identified peaks of SnO2@C HNs can be indexed to tetragonal SnO2 (JCPDS file No. 41-1445, signal ◆).15,19,20 All the diffraction peaks of C@VO2 Ss can be assigned to VO2 (B) (JCPDS file No. 31-1438, signal*).35,36,41 The XRD pattern of SnO2@C@VO2 CHNs can be recognized as SnO2 (JCPDS file No. 41-1445, signal ◆) and VO2 (B) (JCPDS file No. 31-1438, signal*), indicating the combination of SnO2 and VO2 (B) in the composite. It is noted that the carbon layer is amorphous, and thus does not give rise to any strong diffraction peaks in the above three samples.23,41 To further investigate valence states of elements in the composites, XPS is used (Figure 4b-d). The full-survey-scan spectrum of SnO2@C@VO2-3 in Figure 4b displays four identified peaks of C 1s, Sn 3d, O 1S and V 2p. The Sn3d spectrum (Figure 4c) shows two obvious peaks of Sn3d3/2 and Sn3d5/2, which can be assigned to 492.6 and 486.8 eV, revealing the binding energy of Sn4+.20,28 As seen from Figure 4d, the V2p core level spectrum possesses two distinct peaks


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with binding energy at 524.9 and 517.4 eV, corresponding to V2p1/2 and V2p3/2, respectively. It is worth mentioning that the spin-orbital splitting binding energy of V2p1/2 and V2p3/2 is close to 7.5 eV, which matches with the electronic states of VO2.37,38,45,46 The XPS spectra of SnO2@C@VO2-1, SnO2@C@VO2-5 and C@VO2 Ss are shown in Figure S5. It is noted that the corresponding peaks of Sn 3d and V 2p in SnO2@C@VO2-1 and SnO2@C@VO2-5 are still similar to those of SnO2@C@VO2-3, and their binding energy of V2p3/2 and V2p1/2 is still close to 7.5 eV, revealing the existence of Sn4+ and V4+. The above results confirm that VO2 formed from NH4VO3 can be successfully adhered to the surface of the SnO2@C HNs precursor. The surface areas and porous structure of the above five samples have been investigated by N2 adsorption-desorption tests. The typical type-IV sorption isotherms and corresponding pore size distribution curves are displayed in Figure 5. The surface area and pore volume of SnO2@C@VO2-3 are 338.4 m-2g-1 and 0.20 cm-3g-1, respectively, which are evidently higher than those of the other samples (Table S1). The relatively high surface area and porous structure of SnO2@C@VO2 CHNs have advantages for electrolyte diffusion and provide plentiful active sites for redox reaction, resulting in the improvement of the lithium storage performance.19,23,41 The CVs of SnO2@C@VO2-3 are shown in Figure 6a. The CV scans consist of a plateau, which is in good agreement with the first discharge curve. During the first discharge, the intense reduction peak at 0.52 V can be assigned to undecomposed Li2O phase and the generation of a SEI layer on the surface of active materials.15,20,28,41 As seen from the second scan, the reduction peak of 0.9 V can be attributed to the conversion of SnO2 to Sn, while the reduction peak of 1.42 V can be related to intercalation of lithium into VO2 to form LixVO2. Moreover, the oxidic peak at about 0.64V may be ascribed to dealloy of LixSn alloy, and other oxidic peaks at 1.26 and 1.9 V correspond to the electrochemical reaction of LixVO2 to vanadium oxide as well as tin to tin


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oxide (Figure 6a).23,41,47 Moreover, the subsequent cycles have better repeatability, showing the good reversible activity. It is noted that the above corresponding peaks can be also found in C@VO2 Ss, SnO2@C HNs, SnO2@C@VO2-1 and SnO2@C@VO2-5 (Figure S6). It is reported that the CV curves of single-component vanadium oxide with complex nanostructures display several distinct catholic peaks, while the CV curves of the composite of vanadium oxide and carbon only possess a broad cathodic peak, which can also be verified by the CV curves of C@VO2 Ss in our works (Figure S6a) and the previous literatures on VO2-C composite .40-42 Figure 6b-e displays the electrochemical performances of SnO2@C HNs, C@VO2 Ss SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5 used as anode materials. The first charge/discharge profiles at 0.1 Ag−1 in the range of 0.01–3.0 V are seen from Figure 6b. The first discharge capacities of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5 are 1028, 896.2, 1081.9, 1305.6 and 1159.2 mAhg-1, respectively, and their initial Coulombic efficiencies are 58.7%, 56.4%, 63.5%, 64% and 69.2%, respectively. It is noted that the initial discharge capacity of SnO2@C@VO2-3 in the range of 0.01-1.0 V is about 1200 mAh g-1. The irreversible capacity loss in the initial cycle can be ascribed to undecomposed Li2O phase and the formation of the solid electrolyte interface (SEI) film.8,23,31 The cycling performances of the samples at 0.1 Ag-1 are shown in Figure 6c. After 100 cycles, the reversible capacity of SnO2@C@VO2-3 still maintains 765.1 mAhg-1, which is much better than that of SnO2@C HNs (419 mAhg-1), C@VO2 Ss (415.2 mAhg-1) SnO2@C@VO2-1 (532.8 mAhg-1) and SnO2@C@VO2-5 (606.6 mAhg-1), respectively. It is noted that the capacity retention ratio of SnO2@C@VO2-3 after 100 cycles (versus the 2nd discharge capacity) is 84.8%, which is higher than that of SnO2@C HNs (59.6%) and C@VO2 spheres (67.9%). In Figure 6c, the Coulombic efficiency of SnO2@C@VO2-3 remains at more than 98% after the first cycle, indicating the


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excellent reversibility. Moreover, when tested at a high current density of 0.5 Ag-1, SnO2@C@VO2-3 delivers a reversible capacity of 597.4 mAhg-1 and 424.1 mAhg-1 after 100 and 600 cycles (Figure 6d), respectively. As we all know, the rate property is an important factor in evaluating the quality of lithium electrode materials. Figure 6e displays the rate performance of the five samples at various current rates from 0.1 to 5.0 Ag-1. As expected, with the current rate increased, discharge capacity decreases gradually. The reversible capacity of SnO2@C@VO2-3 is 756.9, 630, 483.4, 425.8 and 367.5 mAhg-1 when tested at 0.2, 0.5, 1.0, 2.0 and 5.0 Ag-1. More importantly, when the current density returns to 0.1 Ag-1 from 1 Ag-1, the discharge capacity can be recovered, confirming the superior rate performance and cycling stability. Compared with SnO2@C HNs and C@VO2 Ss, the SnO2@C@VO2 CHNs composite has obvious advantages. Electrochemical properties of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO23 and SnO2@C@VO2-5 are also evaluated by the EIS of the corresponding electrodes after 10 cycles. The EIS curves can be acquired in the frequency range of 0.01-10 kHz at 5 mv s-1 (Figure 6f). The graph contains a semicircle at the high frequency and a sloping line at the low frequency, which is ascribed to the charge transfer impedance and mass transfer of lithium ion, respectively.8,15,40,41 The components of the equivalent circuit are displayed in the inset of Figure 6f. The parameters of Re, Rct, Rf, W and CPE are presented as internal resistance, charge transfer resistance, uncompensated resistance, Warburg impedance and constant phase element.40,41 The charge transfer resistance (Rct) of SnO2@C@VO2-3 is about 30.8 Ω, which is much lower than that of C@VO2 Ss (57.3 Ω), SnO2@C@VO2-1 (55.5 Ω) and SnO2@C@VO2-5 (35.7 Ω), respectively. The enlargement of EIS curves is shown in the Figure S7. It is noted that the charge transfer resistance of SnO2@C HNs (26.4 Ω) is still low perhaps for its higher electrical


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conductivity.8,28 The relatively low charge transfer resistance can accelerate ion transport between electrolytes and active materials, and enhance the utilizing rate of SnO2 and VO2 with high theoretical capacity, resulting in the excellent electrochemical performance. 8,40,47 The excellent electrochemical performances of SnO2@C@VO2 CHNs are comparable or even superior to those of SnO2/C, C@VO2, TMO, TMO@C and other TMO@C@TMO anode materials in previous reports (Table S2). The improved performance of SnO2@C@VO2 CHNs can be mainly ascribed to the following factors. (a) The high specific surface areas provide plentiful active sites between electrolyte and active materials, and shorten the transmission distance of lithium ion (Figure 5a).21,47 (b) Hollow nanostructures of SnO2 internal layer and nanoporous structures of VO2 external layer built from loose nanoparticles make them possess plentiful cavity, which provides more space to cope with the volume change of SnO2 and VO2 during the repeated cycling, and prevents the accumulation and pulverization of the material (Figure 5b).20,28 (c) The low charge transmission resistance can improve charge transport capability and enhance the utilizing rate of SnO2 and VO2 with high theoretical capacity (Figure 6f).39,41 (d) The special structure with three layered shells of SnO2, C and VO2 can be in favor of the stability of the hollow nanostructure, and thus effectively prevent the collapse of the composite material during the cycling (Figure 7). Without the reinforcing VO2 external layer, some broken hollow nanospheres can be obviously observed in the SnO2@C HNs sample after 100 cycles (black and white arrows of Figure S8). Owing to the existence of the reinforcing VO2 external layer, the hollow nanostructures of the SnO2@C@VO2-3 composite can be still sustained even after 100 cycles (Figure 7), which indicates that the hollow composite structure of SnO2@C@VO2-3 has outstanding stability. Moreover, V element in EDS mappings of SnO2@C@VO2-3 after 100 cycles can be still detected on the SnO2@C@VO2 composite (Figure


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S9), indicating that the VO2 layer is stable for repeated cycling. (e) It is noted that the electrochemical performance of SnO2@C@VO2 CHNs can also be related to the content of VO2 in the composite. On the one hand, when the content of VO2 is low (SnO2@C@VO2-1), it can be seen that a small amount of VO2 nanoparticles deposit on the surfaces of the flexible and conductive carbon layers (Figure 2c), which offer a cushion effect to cope with the partial stress of the volume change for VO2 and maintain the sufficient contact with VO2. However, the content of VO2 in SnO2@C@VO2-1 is too low, resulting in the low initial discharge capacity. On the other hand, when the content of VO2 is too high (SnO2@C@VO2-5), some VO2 nanoparticles can’t be in good contact with the C layer, which leads to low electronic conductivity due to the thick coating of VO2 (Figure 6f). Therefore, SnO2@C@VO2-3 with suitable content of VO2 exhibits higher initial discharge capacity and more outstanding cycling stability compared to SnO2@C@VO2-1 and SnO2@C@VO2-5 (Figure 6b-e). CONCLUSIONS In this study, we have reported for the first time the preparation of SnO2@C@VO2 CHNs with excellent electrochemical properties. The electrochemical investigation indicates that this SnO2@C@VO2 composite is a very potential anode material because of its large specific capacity, high surface area, high electrical conductivity, and outstanding structural stability. Moreover, controlled experiments with different amounts of NH4VO3 have been conducted. It is found that the optimum amount of NH4VO3 is 0.03 g. It is mentioned that the outstanding structural stability of composite hollow nanospheres plays a role in accommodating the volume expand and preventing the self-agglomerations of pulverized.


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METHODS Preparation of SiO2@SnO2 nanospheres. Uniform SiO2 nanospheres were successfully fabricated by using a Stöber method.48 Then, sodium stannate trihydrate (0.13 g, Na2SnO3·3H2O) and urea (0.90 g) were dissolved in a mixture of ethanol (9 mL) and deionized water (15 mL). Finally, colloidal SiO2 templates (4 mL, 0.12 g) were added to the above suspension and stirred for 30 min.28,29 The mixture was transferred to a 50 mL Teflon autoclave at 170 oC for 36 h, and then the samples were centrifuged and washed with deionized water several times and dried at 80 o

C. Preparation of SnO2@C hollow nanospheres (SnO2@C HNs). SnO2@C hollow

nanospheres were synthesized in the previously reported references.28,29 The obtained SiO2@SnO2 nanospheres (0.15 g) were firstly dispersed in a solution of glucose (3 g), ethanol (15 mL) and water (28 mL). The mixture was transferred into a 50mL Teflon autoclave heated at 200 oC for 2 h, and then the product was obtained by centrifugation. Finally, the sample was annealed at 500 oC for 4 h in Ar, and the SiO2 cores could be etched in a 0.6 wt% HF solution for 1 h. Synthesis of SnO2@C@VO2 composite hollow nanospheres (SnO2@C@VO2 CHNs). SnO2@C hollow nanospheres (0.05 g) were dispersed in deionized water (20 mL) by ultrasound for 20 min, and urea (0.7 g) and different quantities of NH4VO3 were also dissolved into water (5 ml) and heated to 80 °C in a water bath. Then, the above two solutions were mixed and stirred for 2 h at 80 °C. Finally, the suspension was transferred to a 50 mL Teflon autoclave and treated for 12 h at 190 °C. After naturally cooling to room temperature, a black precipitate was collected. Characterizations. The crystal structures were investigated by X-ray diffraction (XRD, Bruker D8 ADVANCE). Microstructures were observed by field emission scanning electron


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microscopy (FESEM, Hitachi S-4800) and transmission electron microscopy (TEM, Hitachi 250). The valence state was measured by X-ray photoelectron spectroscopy (XPS, ESCALAB 250), The Brunauere-Emmette-Teller (BET, Quantachrome NOVA 1000e) surface areas and porosities of the products were determined by N2 as the adsorbate gas. The content of V element was investigated by Inductively coupled plasma-mass spectrometry (ICP-MS, Agilent 7500). Electrochemical Measurements. The working anodes were composed of the active material (70 %), acetylene black (20 %) and polyvinylidene fluoride (PVDF) (10 %). Li foil and Cu foil were selected as the counter electrode and current collector, respectively. The LiPF6 (1 M) as electrolyte consists of dimethyl carbonate, ethylene methyl carbonate and ethylene carbonate (1:1:1 by volume). Packaged in glove box among argon atmosphere, charge-discharge characteristic of coin cells was studied by LAND CT2001A battery tester. Cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS) was implemented on a Bio-Logic SP-200 electrochemical workstation. ASSOCIATED CONTENT Supporting Information The following files are available free of charge on the ACS Publications website at DOI: 10.1021/ Additional figures including SEM/TEM/STEM images, EDS spectra, XPS spectrum, CV curves, Enlargement of Nyquist plot and comparison of electrochemical properties of SnO2@C@MnO2 HHHNs with SnO2/C, C@VO2, TMO, TMO@C, and other TMO@C@TMO anode materials for LIBs (PDF) AUTHOR INFORMATION Corresponding Author


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Figures

Figure 1. The synthesis process of SnO2@C@VO2 CHNs.

Figure 2. FESEM, TEM and HRTEM images of SnO2@C@VO2 CHNs with various amounts of NH4VO3: (a-d) 0.01g, (e-h) 0.03g and (i-l) 0.05g.


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Figure 3. EDS mappings of C, O, Sn and V from SnO2@C@VO2 CHNs with various amounts of NH4VO3: (a-f) 0.01g, (g-l) 0.03g and (m-r) 0.05g.


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Figure 4. (a) XRD patterns of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-3; (b) XPS fullsurvey-scan spectrum, (c) Sn 3d spectrum and (d) V 2p spectrum of SnO2@C@VO2-3.

Figure 5. (a) N2 adsorption-desorption isotherms and (b) corresponding BJH pore-size distribution curses of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5.


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Figure 6. (a) Cyclic voltammogram curves of the SnO2@C@VO2-3 electrode, (b) first chargedischarge curves at 0.1 A g-1, cyclic performances at (c) 0.1 A g-1 and (d) 0.5 A g-1, (e) rate capability of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5, (f) Nyquist plots of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5, the inset shows the equivalent circuit. The Coulombic efficiency for SnO2@C@VO2-3 at 0.1 A g-1 is provided in the (c).


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Figure 7. (a) SEM and (b) TEM images of SnO2@C@VO2 CHNs after 100 cycles.


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Figure 1. The synthesis process of SnO2@C@VO2 CHNs. 153x35mm (300 x 300 DPI)



Figure 1. The synthesis process of SnO2@C@VO2 CHNs. 153x35mm (300 x 300 DPI)


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Figure 2. FESEM, TEM and HRTEM images of SnO2@C@VO2 CHNs with various amounts of NH4VO3: (a-d) 0.01g, (e-h) 0.03g and (i-l) 0.05g. 162x123mm (300 x 300 DPI)



Figure 3. EDS mappings of C, O, Sn and V from SnO2@C@VO2 CHNs with various amounts of NH4VO3: (af) 0.01g, (g-l) 0.03g and (m-r) 0.05g. 162x81mm (300 x 300 DPI)


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Figure 3. EDS mappings of C, O, Sn and V from SnO2@C@VO2 CHNs with various amounts of NH4VO3: (af) 0.01g, (g-l) 0.03g and (m-r) 0.05g. 162x81mm (300 x 300 DPI)



Figure 4. (a) XRD patterns of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-3; (b) XPS full-survey-scan spectrum, (c) Sn 3d spectrum and (d) V 2p spectrum of SnO2@C@VO2-3. 140x103mm (300 x 300 DPI)


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Figure 5. (a) N2 adsorption-desorption isotherms and (b) corresponding BJH pore-size distribution curses of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5. 140x52mm (300 x 300 DPI)



Figure 5. (a) N2 adsorption-desorption isotherms and (b) corresponding BJH pore-size distribution curses of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5. 140x52mm (300 x 300 DPI)


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Figure 6. (a) Cyclic voltammogram curves of the SnO2@C@VO2-3 electrode, (b) first charge-discharge curves at 0.1 A g-1, cyclic performances at (c) 0.1 A g-1 and (d) 0.5 A g-1, (e) rate capability of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5, (f) Nyquist plots of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5, the inset shows the equivalent circuit. The Coulombic efficiency for SnO2@C@VO2-3 at 0.1 A g-1 is provided in the (c). 140x153mm (300 x 300 DPI)



Figure 6. (a) Cyclic voltammogram curves of the SnO2@C@VO2-3 electrode, (b) first charge-discharge curves at 0.1 A g-1, cyclic performances at (c) 0.1 A g-1 and (d) 0.5 A g-1, (e) rate capability of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5, (f) Nyquist plots of SnO2@C HNs, C@VO2 Ss, SnO2@C@VO2-1, SnO2@C@VO2-3 and SnO2@C@VO2-5, the inset shows the equivalent circuit. The Coulombic efficiency for SnO2@C@VO2-3 at 0.1 A g-1 is provided in the (c). 140x153mm (300 x 300 DPI)


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Figure 7. (a) SEM and (b) TEM images of SnO2@C@VO2 CHNs after 100 cycles. 81x39mm (300 x 300 DPI)



Table of Contents Graphic 34x14mm (300 x 300 DPI)


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SnO2@C@VO2 Composite Hollow Nanospheres as an Anode

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