amorphous vpo4 c with the enhanced performances as an anode for lithium ion batteries

Accepted Manuscript Amorphous VPO4/C with the Enhanced Performances as an Anode for Lithium Ion Batteries Xihui Nan, Chaofeng Liu, Kan Wang, Wenda Ma, Changkun Zhang, Haoyu Fu, Zhuoyu Li, Guozhong Cao PII: S2352-8478(16)30106-X DOI: 10.1016/j.jmat.2016.10.001 Reference: JMAT 74 To appear in: Journal of Materiomics Received Date: October 2016 Revised Date: 26 October 2016 Accepted Date: 26 October 2016 Please cite this article as: Nan X, Liu C, Wang K, Ma W, Zhang C, Fu H, Li Z, Cao G, Amorphous VPO4/ C with the Enhanced Performances as an Anode for Lithium Ion Batteries, Journal of Materiomics (2016), doi: 10.1016/j.jmat.2016.10.001 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT Table of contents ACCEPTED MANUSCRIPT Amorphous VPO4/C with the Enhanced Performances as an Anode for Lithium Ion Batteries ǂ ǂ Xihui Nana , Chaofeng Liua , Kan Wanga, Wenda Maa, Changkun Zhanga, Haoyu Fua, Zhuoyu Lia, Guozhong Caoa,b* China RI PT a Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing, 100083, P.R b Department of Materials and Engineering, University of Washington, Seattle, WA 98195-2120, USA *Address correspondence to gzcao@u.washington.edu (G.Z Cao) SC Abstract M AN U Amorphous and crystalline VPO4/C were synthesized by a facile solution reaction method followed with controlled annealing The discharge capacities of amorphous VPO4/C at 0.1, 1.0, and 2.0 A g-1 achieved 730, 498, and 397 mAh g-1, respectively However, the discharge capacities of crystalline VPO4/C at the same rates were substantially lower and could only TE D reach 487, 319, and 237 mAh g-1, respectively Characterization and analyses of electrochemical properties and ionic diffusion suggested more reaction sites and open EP framework in the amorphous sample facilitated ion migration and lithium ion storage resulting in both high capacity and rate capability The results showed that the amorphization AC C could be an effective way towards electrodes for high energy density lithium-ion batteries Keywords: VPO4/C; amorphous; anode material; lithium ion battery Introduction With increasing concerns on environmental pollution and depletion of fossil fuels, clean ACCEPTED MANUSCRIPT sustainable energy has attracted much attention and efforts in both research and industrial communities Solar energy [1-3] and electrical energy storage [4-6] are among the most explored technologies Lithium ion batteries with high power and energy densities are RI PT becoming more and more popular in many fields, including applications in portable electronics and hybrid and full electric cars [7,8] Although lithium ion batteries have succeeded in commercialization and achieved the widespread applications, they could not SC meet the demand of the rapidly advanced electronic devices and electrical vehicles for high M AN U power and high energy densities [9,10] It is imperative to develop new alternative electrode materials with high capacity and rate performances [11-13] Crystalline materials were extensively exploited for lithium ion batteries in academia and industry [14-16] In terms of the insertion-type crystalline materials, the host structures have the strong metal−oxygen TE D bonds lithiated without bond cleavage; however, the storage and rate capacities of such materials are commonly low owing to the limited active sites in the host lattices [17,18] For example, lithium titanate (Li4Ti5O12) exhibits a zero-strain during the Li-ion EP insertion/extraction, but the reversible discharge capacity approximates 170 mAh/g in AC C practice [19,20] With regard to the conversion-type crystalline materials, the materials go through bond cleavage during the lithiation reactions, with the metal−oxygen bonds are broken and the metal ions are reduced to their metallic states [13] The storage capacity of such materials might be high but the cycling stability is less desirable [21] For example, well crystallized MnO anode delivers a reversible capacity of > 600 mAh/g, but suffers from the degradation with the cycles [22] The alloying-type materials possess high capacities; however, they undergoes unacceptable volume change during Li-ion insertion and extraction, ACCEPTED MANUSCRIPT leading to the exfoliation of the active material and rapid degradation in the capacity with the on-going cycles [23] For example, crystalline silicon (Si) has an ultrahigh theoretical capacity of ~4200 mAh/g when an alloying compound Li22Si4 is formed [24] The volume RI PT expansion leads to an inferior stability limiting its practical applications [25,26] Searching for anodes with high capacity and good cycling stability stimulates researchers to modify or tune the known materials through doping, composites, and nanostructures [27-29] In addition, SC controlling the crystallinity or fabricating amorphous materials have been demonstrated to be M AN U effective approaches to improve the lithium-ion insertion reversibility because more open channels and active sites created in the hosts enhance their rate and cycling performances [30-33] TE D Crystalline VPO4 (c-VPO4) is one of the promising anode materials for lithium ion batteries with orthorhombic structure [34] VPO4 consists of [VO6] octahedrons and [PO4] tetrahedrons, and the edge sharing [VO6] octahedrons arrays endow the material a short V-V EP distance, which is conducive to quick electron transfer Although the pristine VPO4 exhibits AC C low electronic conductivity that restrains the rate performance, it is possible to improve the electronic conductivity by applying carbon coating or forming composites as reported in other electrode materials [12,35] c-VPO4 presents a specific capacity of 550 mAh g-1, higher than many popular anodic materials, including Li4Ti5O12 [20], graphite and Li3VO4 [36] In the present investigation, amorphous VPO4 (a-VPO4/C) and c-VPO4/C were synthesized via a low-temperature solution reaction followed with a heating treatment, aiming at a good understanding of the impacts of crystallinity on the electrochemical performances of VPO4 ACCEPTED MANUSCRIPT because lower crystallinity can create more open framework for fast ion transportation in some electrode materials [22,37,38] The a-VPO4/C showed a large capacity, good cycling and rate performances in comparison with those of c-VPO4/C The relationship between RI PT disordered structure of a-VPO4/C with more active sites and open channels for lithium ions during charge and discharge process and the lithium ion insertion properties has been SC discussed M AN U Experimental Preparation of a-VPO4/C V2O5 (2 mmol) and H2C2O4 (6 mmol) were dissolved into 20 mL deionized water stirring for TE D h at 70 oC mmol of NH4H2PO4 and 0.8 g of glucose were added in order, stirring for 10 after each step and finally a homogeneous solution was formed 50 mL of n-propanol EP was added into the reaction system and kept stirring for further 10 The solution was transformed into a 100 mL beaker and dried at 70 °C for 12 h in an electric oven At last, the AC C prepared green powder was calcined at 750 oC for h in argon atmosphere Preparation of c-VPO4/C V2O5 (4 mmol) and H2C2O4 (12 mmol) were dissolved into 20 mL deionized water, stirring for h at 100 oC Then added mmol NH4H2PO4 and 1.6 g glucose in order, stirring for 10 after each step and finally a homogeneous solution was formed 50 mL of n-propanol was added into the reaction system and kept stirring for further 10 Finally, the solution ACCEPTED MANUSCRIPT was transformed to a 100 mL beaker and dried at 100 °C for 12 h in an electric oven On cooling to room temperature, the prepared green powder was preheated at 350 oC for h in RI PT air before it was calcined at 750 oC for h in argon atmosphere Materials characterizations The crystalline structure of the materials were studied by X-ray diffraction (XRD, X’pert3 SC powder, Netherlands) with a monochromatic Cu Kα radiation (λ= 1.5418 Å) The M AN U morphology of the prepared materials was characterized by a field emission scanning electron microscope (FE-SEM, SU8020, Japan), and its nanostructure was measured by a transmission electronic microscope (TEM, JEOL JEM-2010, Japan) at the accelerating voltage of 200 kV The Brunauer-Emmett-Teller (BET) surface area was analyzed by nitrogen adsorption TE D measurements using a Micromeritics surface area and porosity analyzer (ASAP 2020 HD88, USA) Raman spectra were collected by a Horiba JOBIN YVON system (LabRAM HR EP Evolution, France) and the excitation source was argon ion laser (532 nm) AC C Electrochemical measurements Electrochemical performances were evaluated with the standard CR2032 coin cells assembled in an argon filled glovebox with water and oxygen contents less than ppm The electrode slurry was mixed by active material, acetylene black, and Li-PAA (7:2:1, wt%) and coated on copper foil with a loading mass of 0.9-1.0 mg/cm2 The electrode was dried at 120 °C for 12 h in a vacuum oven The lithium foil was used as the counter electrode of the cells, and the separator was Celgard 2500 The electrolyte was M LiPF6 solution in ethylene ACCEPTED MANUSCRIPT carbonate (EC)/dimethyl carbonate (DMC) (EC/DMC = 1:1 in volume) The galvanostatic charging/discharging measurements were performed on a multichannel battery test system (LAND CT2001A, China) Electrochemical impedance spectroscopy (EIS) and cyclic RI PT voltammetry (CV) were carried out on a Solartron electrochemical workstation The frequencies of EIS measurement ranged from 100 kHz to 0.1 Hz All electrochemical SC measurements were carried out in the potential range of 0.01-3.00 V versus Li/Li+ M AN U Results and discussion Figure shows and compares the XRD patterns of c-VPO4/C and a-VPO4/C powder samples All the diffraction peaks of c-VPO4/C can be well indexed to the orthorhombic structure (reference code: 00-034-1336) with space group Cmcm (63) The XRD pattern of a-VPO4/C TE D is visibly different with a very high noisy to signal ratio, three weak diffraction peaks corresponding to the strong peaks of crystal structure are barely discerned, suggesting that EP a-VPO4/C has very low crystallinity or predominantly amorphous No diffraction peaks from graphite implies the remaining carbon with an amorphous state Figure S1a-d shows the SEM AC C photographs of two samples c-VPO4/C and a-VPO4/C possess similar morphologies a-VPO4/C composed of smaller particles than that of c-VPO4/C, attributable to the high temperature treatment process of c-VPO4/C Nitrogen sorption isotherms in Figure S1e-f are a little abnormal and reveal both samples are soft and underwent structural contraction induced by capillary force when liquid nitrogen condensed inside pores So it is impossible to use the classic model to estimate the specific surface area and pore size, the similarity of both isotherms does imply the similar microporous structure with similar surface Figure 2a and d ACCEPTED MANUSCRIPT revealed that a-VPO4/C and c-VPO4/C particles are both irregular, however, their corresponding electron diffraction patterns are different (Figure 2b and e) Diffraction spots and rings of (110) and (021) planes for c-VPO4/C displayed in Figure 2b, while there is no RI PT diffraction pattern for a-VPO4/C (Figure 2e) In addition, lattice fringes can be clearly observed in the HRTEM image of c-VPO4/C (Figure 2c) and its interplanar distance of 0.435 nm corresponds well to the d-spacing of (110) planes for orthorhombic VPO4, whereas there SC are no lattice fringes in a-VPO4/C (Figure 2f) These results are consistent with XRD patterns M AN U Energy dispersive X-ray spectroscopy (EDS) was used to collect the information of elements distribution in a-VPO4/C, and Figure 2g-l show its SEM photograph, energy spectrum and corresponding EDS mappings The energy spectrum (Figure 2h) exhibits the X-ray characteristic peaks of all elements contained in the sample a-VPO4/C, and the EDS TE D mappings demonstrate all the elements distributed homogeneously, suggesting that the AC C EP amorphous sample with the same compositions as that in crystalline VPO4/C Figure XRD patterns of a-VPO4/C and c-VPO4/C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C Figure (a) TEM image of c-VPO4/C; (b) electron diffraction pattern of c-VPO4/C; (c) HRTEM image of c-VPO4; (d) TEM image of a-VPO4/C; (e) electron diffraction pattern of a-VPO4/C; (f) HRTEM image of a-VPO4 (g) SEM photograph of a-VPO4/C and its corresponding (h) energy spectrum and EDS mapping of elements (i-l) Figure 3a-b shows the thermal gravitation (TG) analysis results of both a-VPO4/C and c-VPO4/C, carried out with a heating rate of 10 oC min-1 in O2 with a flow rate of 60 mL min-1 The subtle weight loss from 25 oC to 200 oC was due to the evaporation of adsorbed moisture ACCEPTED MANUSCRIPT The weight decrease from 350 oC to 500 oC is mainly due to the removal of carbon through oxidation The carbon contents in a-VPO4/C and c-VPO4/C are 18 wt % and 15 wt %, respectively It is worth noting that a slight weight increase appeared at temperature exceeded RI PT 450 oC, which attributes to the oxidation of V3+ [39,40] Direct current four-probe method was adopted to measure the electrical conductivity of samples, which are 0.18 and 0.21 S cm-1 for crystalline and amorphous VPO4, suggesting that both samples have similar nominal SC electrical conductivity The value of a-VPO4/C is slightly higher than that of c-VPO4/C, it M AN U maybe attribute to the former with the higher carbon content of 18 wt% In order to distinguish the degree of graphitization of carbon, Raman spectroscopy was adopted to collect the information relating to D- and G-band of carbon, and the peak intensity ratios of the D and G bands, denoted as I(D)/I(G), were used to evaluate the degree Figure 3c-d show TE D Raman spectra of both samples and the peak fitting was performed with Gauss function for D and G bands and Lorentz function for I and D’’ bands The D-band located at ~1339 cm-1 originates from a double resonance process involving a phonon and a defect, which implies EP the disordered carbon The G-band located at ~1589 cm-1 stems from in-plane vibrations and AC C has E2g symmetry that presents the graphitization of carbon [41] The I band seen from ~1180-1290 cm-1 relates to the disorder in the graphitic lattice, sp2-sp3 bonds or the presence of polyenes, and the D’’ band sited at ~1500 cm-1 presents the amorphous carbon The values of I(D)/I(G) are 1.52 and 1.36 for a-VPO4/C and c-VPO4/C, respectively, implying a higher degree of graphitization in c-VPO4/C because of the longer time in the process of heating treatment M AN U SC RI PT ACCEPTED MANUSCRIPT Figure TG-DSC curves of a-VPO4/C (a) and c-VPO4/C (b), samples were treated with a heating rate of 10 oC min-1 under an O2 flow of 60 mL min-1 Raman spectra of a-VPO4/C (c) and c-VPO4/C (d), the peak TE D fitting distinguishes the effects from different sources EP Figure 4a shows and compares the rate performance of a-VPO4/C and c-VPO4/C a-VPO4/C delivered discharge specific capacities: 730, 666 and 586 mAh g-1, respectively, at 0.1, 0.2, AC C and 0.5 A g-1 , exceeding the theoretical capacity of VPO4 of 550 mAh g-1 [34] Discharge capacities of c-VPO4/C at the same rates of 0.1, 0.2, and 0.5 A g-1 can only reach 487, 451 and 393 mAh g-1, respectively At higher current densities of 0.8, 1.0, 1.5, 2.0 A g-1, the discharge specific capacities of a-VPO4/C are 536, 498, 441 and 397 mAh g-1, respectively The discharge capacity of c-VPO4/C at the rates of 0.8, 1.0, 1.5, 2.0 A g-1 are 348, 319, 279 and 237 mAh g-1, respectively Although the discharge capacities of a-VPO4/C at different rates are much higher than that of c-VPO4/C, both of a-VPO4/C and the c-VPO4/C ACCEPTED MANUSCRIPT demonstrate good rate performance Figure 4b shows the cycling performance of two samples at a current density of 0.2 A g-1 The discharge capacity of a-VPO4/C and c-VPO4/C in the first cycle are 1094.6 and 770.5 mAh g-1, respectively The discharge capacity for the second RI PT cycle of a-VPO4/C and c-VPO4/C are 771.0 and 527.8 mAh g-1, respectively The sharp drop of discharge capacities from first to second cycle suggests the formation of a SEI layer during the first charge and discharge cycle [42,43] The discharge capacities of a-VPO4/C are SC constantly much higher than that of c- VPO4/C regardless of the cycles and the rates at the M AN U same conditions The capacity retention of a-VPO4/C and c-VPO4/C cycled at 0.2 A g-1 for 50 times are 73.5 % and 73.4 %, respectively It shows that the disordered structure of the material has not undermined the cycle stability The increased discharge capacity and improved rate capability of a-VPO4/C maybe be attributed to the disordered atomic TE D arrangement that suggests a loose atom/ion stack and open channels for Li ion storage and migration [30,33,44] More importantly, amorphous state is a metastable state with a higher internal energy that may promote electrochemical reaction than that in crystalline materials, EP at the same time the metastable state would provide more active sites to improve the kinetics AC C of energy storage reaction Figure S2 shows second charge-discharge curves of a-VPO4/C and c-VPO4/C at different rates, from 0.1 to A g-1, in the potential window of 0.01 to 3.00 V versus Li/Li+ There is no potential plateau in charge-discharge curves of both a-VPO4/C and c-VPO4/C samples, indicating that the change of Gibbs free energy in transformation of crystal structure is continuous during charge-discharge process [18] In addition, discharge capacities of the two materials showed similar decreasing pattern with the increase of the current densities The characters of redox reaction in Figure 4c reveal the electrochemical ACCEPTED MANUSCRIPT process in the cathodic and anodic conditions In the cathodic scan, a broad peak sited at 1.05 V and a sharp peak closed to 0.1 V stand for the reduction reaction of VPO4 and the formation of metallic phases V and Li3PO4 Upon the charge process, three broad anodic RI PT peaks at 0.66, 1.03 and 1.95 V appear, implying the reversible oxidation reaction to transform metallic V and Li3PO4 to VPO4 The reaction can be described as the following [34], VPOସ + 3Liା + 3eି ↔ V + Liଷ POସ (1) SC These characters of conversion reaction can also elucidate the sloping charge/discharge M AN U curves, the phase transition accompanies with the decomposition of host materials and the inserted Li ions react to form new phase rather than enter the host lattice in the charge process In the other word, there does not exist the equivalent sites for Li ions, leading to a continuous AC C EP TE D change in Gibbs free energy and the sloping potential curves [18] EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT Figure (a) Rate performance of a-VPO4/C and c-VPO4/C; (b)cycling performance of a-VPO4/C and c-VPO4/C at a current density of 0.2 A g-1; (c) The second cycle CV curves of a-VPO4/C and c-VPO4/C; (d) AC C Nyquist plots of a-VPO4/C and c-VPO4/C; The relationship curve between Z’ and ω-1/2 in low frequencies calculated from EIS data for (e) a-VPO4/C and (f) c-VPO4/C, respectively Table The value of Rs(Ω), Rct(Ω) and DLi+ of samples a-VPO4/C and c-VPO4/C Sample ID Rs(Ω) Rct(Ω) DLi+ a-VPO4/C 1.5 100.7 7.49×10-15 c-VPO4/C 1.6 73.6 6.58×10-15 ACCEPTED MANUSCRIPT EIS measurement was carried out at 2.1 V in a frequency range from 100 kHz to 0.1 Hz for evaluating the characters of electrons and ions transportation in both materials Rs shown in Figure 4c represents the combined ohmic resistance of electrolyte, separator and metal RI PT electrodes in the battery, corresponding to the first intercept of the semicircle at Z’ axis at high frequency Rct is the charge transfer resistance, it depends on the distance between the two intercepts of the semicircle on Z’ axis The fitting results of the Nyquist plots are shown SC in Table The Rs value of a-VPO4/C and b-VPO4/C are 1.5 and 1.6 Ω, respectively, M AN U indicating that the combined ohmic resistances of the two samples are roughly the same because the same components were used to assemble the batteries The charge transfer resistance, Rct, of a-VPO4/C is 100.7 Ω, however, the corresponding value of c-VPO4/C is 73.6 Ω The results show that the value of Rct increased when the sample possesses low TE D crystallinity When edge-sharing [VO6] octahedra lined up along c-axis in c-VPO4/C, electron transfer is relatively easy, and a good electron transfer would decrease the Rct value Although lower crystallinity induces higher charge transfer resistance, specific capacities and rate EP capabilities were not found to deteriorate, which suggests the lithium ion insertion and AC C extraction reaction/process is not controlled or limited by electron transfer process It is known that ion diffusion would dominate the reaction when electronic conductivity exceeds a threshold [22] The lithium ion diffusion coefficients (DLi+) of the two samples are calculated using the data obtained from EIS analyses according to the following equations [45], DLi+ = R2 T2 2A2 n4 F4 C2 σ2ω Z' =Re +Rct +σω ω-1/2 (2) (3) R is the gas constant, T is the absolute temperature, F is the Faraday constant, n is the number ACCEPTED MANUSCRIPT of electrons transferred per molecule, A is the active surface area of the electrode (0.50 cm2), C0 is the concentration of lithium ions in the electrolyte (1×10−3 mol cm−3), DLi+ is the apparent ion diffusion coefficient, and σω is the Warburg factor that relates to Z’ and can be RI PT obtained from the slope of the fitting line of EIS data at low frequencies in Figure 4e and f The lithium ion diffusion coefficients of the two samples are listed in Table DLi+ of a-VPO4/C is 7.45 ×10-15 cm2 s-1 that is slightly higher than or similar to that of c-VPO4/C of SC 6.58×10-15 cm2 s-1 The amorphous sample possesses a loose atom stack that benefits the M AN U faster lithium ion diffusion in the electrochemical reaction, which guarantees the complete reaction at various current densities and renders it with an excellent rate capability, revealing the promising applications in the high-performance batteries in the future market TE D Conclusions a-VPO4/C and c-VPO4/C were synthesized by a simple solution method The study showed EP that a-VPO4/C possesses higher lithium ion storage capacity and better rate capability than that in c-VPO4/C sample, likely due to the loose packing of constituent ions and higher AC C energy state in amorphous material At current densities of 0.1, 1.0, and 2.0 A g-1, a-VPO4/C achieved the respective of discharge capacities of 730, 498, and 397 mAh g-1, however, at the same current densities, c-VPO4/C delivered the specific capacities of 487, 319, and 237 mAh g-1, respectively Amorphous VPO4 demonstrated 50% enhancement in lithium ion storage capacity at a low rate and 67% enhancement at a high rate, indicating also a better kinetics or higher power density In addition, a-VPO4/C exhibited the similar cycle stability with c-VPO4/C when they were cycled ACCEPTED MANUSCRIPT Acknowledgements This study was supported by the “Thousands Talents” program for pioneer researcher China ǂ Xihui Nan and Chaofeng Liu equally contribute to this work References RI PT Author contributions AC C EP TE D M AN U SC [1] Q Zhang, E Uchaker, S.L Candelaria, G Cao Nanomaterials for energy conversion and storage Chem Soc Rev 42 (2013) 3127-3171 [2] J Seo, J.H Noh, S.I Seok Rational Strategies for Efficient Perovskite 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Li batteries reacting through conversion reaction Electrochim Acta 61 (2012) 13-18 [43] S Laruelle, S Grugeon, P Poizot, M Dollé, L Dupont, J M Tarascon On the Origin of the Extra Electrochemical Capacity Displayed by MO/Li Cells at Low Potential J Electrochem Soc 149 (2002) A627-A634 [44] Y Fang, L Xiao, J Qian, X Ai, H Yang, Y Cao Mesoporous Amorphous FePO4 Nanospheres as High-Performance Cathode Material for Sodium-Ion Batteries Nano Lett 14 (2014) 3539-3543 [45] S L Chou, J Z Wang, H K Liu, S X Dou Rapid Synthesis of Li4Ti5O12 Microspheres as Anode Materials and Its Binder Effect for Lithium-Ion Battery J Phys Chem C 115 (2011) 16220-16227 ACCEPTED MANUSCRIPT Supporting information Amorphous VPO4/C with the Enhanced Performances as an Anode for Lithium Ion Batteries EP TE D M AN U SC RI PT Xihui Nan, Chaofeng Liu, Kan Wang, Wenda Ma, Changkun Zhang, Haoyu Fu, Zhuoyu Li, Guozhong Cao * AC C Figure S1 (a),(b) SEM photograph of a-VPO4/C; (c),(d) SEM photograph of c-VPO4/C; Nitrogen sorption isotherms of a-VPO4/C (e) and c-VPO4/C (f) Figure S2 The second charge-discharge curves of a-VPO4/C (c) and c-VPO4/C (d) at rates from 0.1 A g-1 to 2.0 A g-1 RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC Guozhong Cao is Boeing-Steiner Professor of materials science and engineering, professor of chemical engineering, and adjunct professor of mechanical engineering at the University of Washington, and also a professor at Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences and Dalian University of Technology His current research is focused on chemical processing of nanomaterials for energy related applications including solar cells, rechargeable batteries, supercapacitors, and hydrogen storage  ...ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT Table of contents ACCEPTED MANUSCRIPT Amorphous VPO4/ C with the Enhanced Performances as an Anode for Lithium Ion Batteries ǂ ǂ Xihui Nana , Chaofeng... M AN U SC RI PT ACCEPTED MANUSCRIPT Figure (a) Rate performance of a -VPO4/ C and c -VPO4/ C; (b)cycling performance of a -VPO4/ C and c -VPO4/ C at a current density of 0.2 A g-1; (c) The second cycle... Effect for Lithium- Ion Battery J Phys Chem C 115 (2011) 16220-16227 ACCEPTED MANUSCRIPT Supporting information Amorphous VPO4/ C with the Enhanced Performances as an Anode for Lithium Ion Batteries