Structure and electrochemical characteristics of LiMn0.7M0.3O2 (M = Ti, V, Zn, Mo, Co, Mg, Cr)

A series of compounds LiMn0.7M0.3O2 (M=Ti,V, Zn, Mg, Mo, Co, Cr) with different doping elements were synthesized. It was found that the ionic size of the doping elements is not a discriminating factor in the structure of LiMn0.7M0.3O2 compounds. The LiMn0.7M0.3O2 (M=Cr, Zn, Mg,V) forms in the hexagonal structure, while the LiMn0.7M0.3O2 (M=Co, Ti, Mo) shows an orthorhombic structure. The LiMn0.7M0.3O2 compounds have less crystal distortion compared with o(orthorhombic)-LiMnO2. All substituted materials cycled between 4.4 and 2 V in Li cells show higher stability of capacity compared with the standard o-LiMnO2. AC impedance analysis results show that the charge transfer process and lithium ion diffusion process for doped LiMnO2 compounds are better than that for un-substituted compounds. (C) 2002 Elsevier Science B.V. All rights reserved.