《Tab.1 EIS fitting parameters of different carboxylic acids based 10%vanadium modified Li2Fe Si O4/C

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《不同羧酸对钒改性硅酸铁锂结构性能的影响（英文）》

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To examine possible chemical states of vanadium and iron presented in the composites，X-ray photoelectron spectroscopy（XPS）was employed.Figure6 gives typical XPS survey spectrum（A）and high resolution deconvoluted spectra of iron（Fe2p）and vanadium（V2p3/2）for the acetic acid based composite having the highest capacity retention.It is evident in Fig.6A that the composite consisted of V，Fe，Si，O，C and Li elements.To identify the diversify chemical states of iron and vanadium，a multi-peak fitting procedure was performed and the information based on previous studies[18-19]is provided in Fig.6（B，C）.The simultaneous presences of Fe0（707.8 e V），Fe2+（710.0e V）and Fe3+（711.8 e V）implied that the disproportionation reaction of Fe3+→Fe2+→Fe0might take place during the synthesis process.Noticed that the trivalent ions such as Fe3+and V3+from the raw materials of Fe（NO3）3and V2O3，respectively，were initially presented.The maximum reductions of Fe3+to Fe2+and V3+to V2+are desirable.However，the approximate 6.1%of Fe2+were reduced to metallic iron at the surface and further crystallized as impure phase as supported by the XRD data in Fig.1.The presences of multivalent vanadium ions including divalent（V2+），trivalent（V3+），quadrivalent（V4+）and pentavalent（V5+）ions were confirmed.Only 26.8%of V3+could be reduce d to V2+，while~33%oxidized to V4+and~6%to V5+.The XPS analysis results also suggested that although nearly 1/4 of the original V3+could be reduced to V2+，the V3+was the predominant form，which could be mainly responsible for the discharge capacity obtained being lower than that expected from 10%vanadium substitution.Future work will be conducted to optimize the preparation conditions.