An investigation of V_2O_5/polypyrrole composite cathode materials for lithium-ion batteries synthesized by sol-gel

摘要

A lamellar compound of V_2O_5 was prepared by a simple sol-gel method using H_2O_2 and V_2O_5 as starting materials. The composites of V_2O_5/PPy (polypyrrole) were synthesized by in situ polymerization, and characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrum, and X-ray diffraction (XRD). The electrochemical properties of the composites were investigated with galvanostatic charge-discharge test, cyclic voltammetry and A.C impedance techniques. The results show that pyrrole was uniformly polymerized around the V_2O_5, and the V_2O_5/PPy composite possessed excellent electrochemical performance. The specific discharge capacity of the 2.5% mass percent PPy composites (271.8 mAhg~(-1)) was higher than that of pure V_2O_5 (247.6 mAh g~(-1)) at 0.1 C rate and it has the voltage limits of 1.8-4.0 V. Furthermore, the specific discharge capacity remained at 225.4mAhg"1 after 50 cycles. The chemical diffusion coefficient D_(Li)~+ values were calculated, depending on x-values in Li_(x+1.1) V_2O_5. The values of D_(Li)+ range from 2.18 × 10~~(12) cm~2 s~(-1) to 4.5 × 10~(-14) cm~2 s~(-1) for V_2O_5/PPy composite, and it decreased as the amount of intercalated Li~+ increased.