非水体系中钒酸锂/聚吡咯复合正极材料的制备及性能研究

Electrochemical performance of LiV3O8/PPy composite materials synthesized by the non-water system

摘要:

采用乙醇作为介质,FeCl₃为氧化剂,对甲苯磺酸钠为掺杂剂,通过吡咯单体在钒酸锂表面的氧化聚合制备出了钒酸锂/聚吡咯(LiV₃O₈/PPy)复合材料。采用X-射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)对复合材料的结构与形貌进行表征。用恒流充放电测试、循环伏安(CV)和交流阻抗(EIS)等研究了聚吡咯包覆量对材料电化学性能的影响。结果表明：在钒酸锂表面均匀地包覆了一层厚度约10nm的聚吡咯,但并没有改变钒酸锂的晶型结构。当聚吡咯包覆量为6% 时,复合材料的电化学性能最好,在0.1C充放电倍率下,首次放电比容量为274mAh/g,循环100次后样品的放电比容量为239.4mAh/g,容量保持率为87.4%,而未包覆PPy的LiV₃O₈,其首次放电比容量为227.4mAh/g,循环100次后样品的放电比容量为160.1mAh/g,容量保持率仅为70.4%。LiV₃O₈/PPy复合正极材料的电化学性能得到了明显提高。

Abstract:

LiV₃O₈/polypyrrole (PPy) composite materials were prepared by an oxidative polymerization of pyrrole monomer on the surface of LiV₃O₈ using ethanol as medium, FeCl₃ as oxidant, benzene sulfonic acid sodium salt as dopant. The crystal structures and microstructures of LiV₃O₈/PPy were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The electrochemical properties of the composites were investigated with galvanostatic charge–discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that 10nm pyrrole was uniformly polymerized around the LiV₃O₈, and the PPy-coating did not alter the crystal structure of the LiV₃O₈. LiV₃O₈/PPy composite material containing 6% PPy (LVP6) exhibits perfect electrochemical properties, its first discharge capacity reaches a high specific discharge capacity of 274 mAh/g and maintains a stable capacity of 239.4 mAh/g within 100 cycles at the charge–discharge rate of 0.1 C and in the voltage range of 1.8～4.0 V, the capacity retention is 87.4%. But the pure LiV₃O₈ shows that the first discharge capacity is 227.4 mAh/g and the discharge capacity is 160.1 mAh/g after 100 cycles, the capacity retention is only about 70.4%. LiV₃O₈/PPy composite materials show better cycling performance than the pure LiV₃O₈.