磷酸钒锂/碳复合材料在锂离子电池中的电化学性能及电极反应动力学研究

Study on Electrochemical Performance and Electrode Reaction Kinetics of Lithium Vanadium Phosphate/Carbon Composites in Lithium-Ion Batteries

相比于溶胶-凝胶法制备的Li_(3)V_(2)(PO_(4))_(3)/C(LVP/C-S),采用水热超声辅助流变相法结合溶液沉积法制备的Li_(3)V_(2)(PO_(4))_(3)/C(LVP/C-R)复合正极材料具有更优异的电化学性能。通过XRD、SEM和Raman光谱仪等对合成材料进行表征。将合成材料作为锂离子电池正极组装半电池进行倍率和循环性能测试,同时通过循环伏安法、电化学阻抗以及恒流间歇滴定技术分析电极反应动力学。结果表明,水热超声辅助流变相法合成的Li_(3)V_(2)(PO_(4))_(3)(LVP-R)通过溶液沉积法包覆碳层后,晶面间距增大,粒径更小,导电性、振实密度增大,分散性明显提升。这有利于Li^(+)在正极材料中嵌入/脱出,以及缩短Li^(+)的扩散路径,从而促使锂离子电池的倍率性能、库仑效率和循环稳定性提高。LVP/C-R作为锂离子电池正极材料,在0.1 C电流密度下表现出较高的初始放电比容量(160.12 mA·h/g),且在1 C倍率下循环200圈后放电容量保持率为89.16%,远高于LVP/C-S。此外,相比于LVP/C-S和LVP-R,LVP/C-R在锂离子电池中具有更大的Li^(+)表观扩散系数且动力学性能更优。

Compared with the Li_(3)V_(2)(PO_(4))_(3)/C(LVP/C-S)prepared by sol-gel method,the Li_(3)V_(2)(PO_(4))_(3)/C(LVP/C-R)composite cathode material prepared by hydrothermal ultrasonic-assisted rheological phase method combined with solution deposition method has better electrochemical performance.The synthesized materials were characterized by XRD,SEM and Raman spectroscopy.The synthesized materials were used as cathodes of lithium-ion batteries to assemble half-cells for rate and cycling performance tests,while the electrode reaction kinetics were analyzed by cyclic voltammetry,electrochemical impedance,and galvanostatic intermittent titration technique.The results show that the Li_(3)V_(2)(PO_(4))_(3)(LVP-R)synthesized by hydrothermal ultrasonic-assisted rheological phase method is coated with a carbon layer by solution deposition,leading to an increase in the crystal plane spacing,a smaller particle size,an increase in the electrical conductivity and tap density,and a significant enhancement in the dispersion.This facilitates the insertion/extraction of Li^(+)in the cathode material and shortens the diffusion path of Li^(+),resulting in improved rate performance,coulombic efficiency and cycling stability of lithium-ion batteries.As the cathode material of lithium-ion batteries,LVP/C-R exhibits a high initial discharge specific capacity(160.12 mA·h/g)at a current density of 0.1 C,and the discharge capacity retention rate is 89.16%after 200 cycles at a current density of 1 C,which is much higher than that of LVP/C-S.In addition,LVP/C-R has a larger apparent Li^(+)-diffusion coefficient and better kinetic performance in lithium-ion batteries compared to LVP/C-S and LVP-R.