The effect of 3d substitutions in the manganese sublattice on the electrical and electrochemical properties of manganese spinel

Abstract

Electrical conductivity and thermoelectric power (TEP) measurements accompanied by differential scanning calorimetry (DSC) and XRD studies of series of manganese spinel samples with manganese substituted with 3d metals LiM x Mn 2− x O 4 (M=Cr, Fe, Co, Ni, and Cu; x=0–0.5) are presented. Charge curves of Li/Li +/Li y M x Mn 2− x O 4 type cells and therein determined chemical diffusion coefficients of lithium are shown. In the charge curves of Li/Li +/Li y M x Mn 2− x O 4 cells, two visible plateaux separated with distinct potential jump (0.5–0.7 V) were observed. The lower plateau is related to the Mn 3+→Mn 4+ oxidation, while the next of higher voltage, of the M m+ dopant oxidation. Substitution of manganese causes disappearance of the phase transition characteristic of a stoichiometric spinel. The schematic diagrams of relative Mn–M electronic levels alignment are proposed. It was shown that substitution of manganese with copper and iron improves both electrical conductivity and chemical diffusion coefficient of lithium in the cathode materials.