An investigation of V2O5/polypyrrole composite cathode materials for lithium-ion batteries synthesized by sol-gel

A lamellar compound of V2O5 was prepared by a simple sol-gel method using H2O2 and V2O5 as starting materials. The composites of V2O5/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 V2O5, and the V2O5/PPy composite possessed excellent electrochemical performance. The specific discharge capacity of the 2.5% mass percent PPy composites (271.8 mAh g(-1)) was higher than that of pure V2O5 (247.6 mAh g(-1)) at 0.1C rate and it has the voltage limits of 1.8-4.0 V. Furthermore, the specific discharge capacity remained at 225.4 mAh g(-1) after 50 cycles. The chemical diffusion coefficient DLi+ values were calculated, depending on x-values in Lix+1.1 V2O5. The values of DLi+ range from 2.18 x 10(-12) cm(2) s(-1) to 4.5 x 10(-14) cm(2) s(-1) for V2O5/PPy composite, and it decreased as the amount of intercalated Li+ increased. (c) 2012 Elsevier B.V. All rights reserved.