Doped Li-Mn spinels: Physical/chemical characteristics and electrochemical performance in Li batteries

Several doped spinel-type Li−Mn oxides of formula Li1+xMyMn2-(x+y)O4+z, where Mn is partly replaced by Li, Cu, Zn, Ni, Co, Fe, Cr, Ga, Al, B, or Ti, were prepared by a solid-state reaction at 730 °C. These spinels were investigated by X-ray powder diffraction, thermal analysis, slow step voltammetry, and galvanostatic cycling at medium-high rates. Even substitutional levels as low as 0.05 atom/formula unit produce structural effects that are reflected in the electrochemical characteristics. The substituents may occupy either tetrahedral 8a sites or octahedral 16d sites. Examples of the first type of substitution are provided by Ga3+ and Zn2+, while octahedral sites are preferred by, e.g., Ni2+ and Cr3+. Cycling at practical rates produces capacities of ∼100 mA h/g for the best materials with limited capacity losses (3−6·10-2 mA h/g·cycle). The lower Mn3+ content with respect to undoped spinel explains the initially lower capacities.