Study On Electrochemical Performance And Regulation Of Structure And Morphology For Vanadium-based Oxides Anode Materials

Vanadium based oxide（VO）anode materials possess promising application prospects owing to the advantages of high discharge specific capacity and rich resources.However,large volume change and low conductivity hinder their development and applications.In this work,Vanadium based oxides（VOs）with different valences of vanadium,their morphology and structure regulations and electrochemical performances were investigated.To solve the main problems affecting their electrochemical performance,the idears to improve conductivity,stabilize structure and enhance electrochemical kinetics of VO anodes were adopted.In particular,the strategies such as construction of special morphology,carbon coating and element doping were employed.The modification mechanisms were proposed and discussed with the help of various characterization methods combined with theoretical calculation.In order to enhance the charge-discharge performance of V₂O₃ anode material,the cotton-like three-dimensional porous structure design combined with carbon coating or inclusion of carbon nanotube were employed.Due to the large specific area,high pseudocapacitance ratio and excellent conductivity,enhanced electrochemical reaction kinetics were obtained.High charge-discharge specific capacity and superior rate capability of the modified cotton like V₂O₃/C and V₂O₃/CNT were shown.Both of them deliver a specific capacity of approximately 300 m Ah/g.In order to improve the coulombic efficiency of V₂O₃ material,the structural stability was subsequently improved by pre-embedding lithium.At the same time,through porous lamellar structure design and B doping,the electrochemical properties of VO anodes were significantly enhanced.The electrochemical properties of Li_xV₂O₄/C with the porous lamellar structure prepared by hydrothermal method were improved,which benefits from the synergistic of lithium pre-embedding,the coexistence of different valence states of vanadium and porous lamellar structure.B doping to Li₃VO₄ prepared by sol-gel method greatly enhanced the electrochemical kinetics of B-doped by improving conductivity,stabilizing structure and enlarging interplanar spacing of Li₃VO₄.Thus,enhaned cyclic stability and superior rate capability of Li_xV₂O₄/C and B-doped Li₃VO₄ were obtained.The specific capacity of VO anodes prepared by preembedding lithium was low,despite excellent cyclic stability and high coulombic efficiency of Li_xV₂O₄ and Li₃VO₄.In order to obtain VO anodes with excellent comprehensive performance,iron ions were doped into VO.Iron ion can offord multiple electrons in electrochemical reactions and it is rich in resources.Thus,Fe VO₄ possesses high capacity and low cost.To solve the problems of low conductivity and large volume change affecting electrochemical performance of Fe VO₄,modification methods of W doping,carbon coated and carbon cloth loading were adopted.The methods enhanced the conductivity and alleviate the stress caused by volume change.The electrochemical reaction kinetics and structure stability were improved.The W-reinforced Fe VO₄ and the Fe VO₄ with three-dimensional network structure supported by carbon cloth were synthesized by sol-gel method and hydrothermal method,respectively.When they were used as anode for LIB and alkali metal ion battery respectively,their discharge specific capacity,cyclic stability and rate capability displayed greatly improved.