Anisotropic expansion and high rate discharge performance of V-doped MnO2 for Li/MnO2 primary battery

Abstract

V-doped MnO2 (VHEMD) has been prepared by thermally treating the mixture of electrolyzed manganese dioxide (EMD) and V2O5 powder and characterized using cyclic voltammetry (CV), constant current discharge, electrochemical impedance spectroscopy (EIS) and X-ray diffraction technique. CV results showed that VHEMD has a much higher reduction peak current than that of only thermally treated electrolyzed manganese dioxide (HEMD), though both have a similar reduction potential. Constant current discharge measurements showed VHEMD exhibits an improved high rate discharge performance. VHEMD reaches a maximum discharge capacity of 202 mAh g-1 at a high rate (2 mA cm-2), which is considerably higher than that of HEMD (155 mAh g-1), although both HEMD and VHEMD have similar discharge capacity at a low rate (0.1 mA cm-2). EIS results demonstrated that both Li+ insertion resistance (Rct) and Li+ diffusion impedance (W) in VHEMD were always lower than those of HEMD at any depth of discharge (DOD). XRD results confirmed that V-doping leads to an anisotropic expansion of MnO2 lattice, with a axis slightly elongated by 0.74% and c axis slightly shortened by 0.17%. The improved crystal structure after V-doping can be attributed to the faster kinetics of both Li+ insertion and diffusion in VHEMD.