Transport and electrochemical properties of the Li yCr xMn 2− xO 4 (0 < x < 0.5) cathode material

Abstract

In this paper structural, electrical, electrochemical and thermal (DSC) characterization of series of manganese spinel samples with manganese substituted to different degree ( x = 0–0.5) with chromium are presented. The conductivity and thermoelectric power measurements were performed in wide temperature range also versus oxygen partial pressure and for deintercalated samples. Electrochemical studies of these cathode materials were conducted in Li/Li +/Li y Cr x Mn 2− x O 4 type cells. Substitution of manganese with chromium causes disappearance of the phase transition characteristic of LiMn 2O 4 spinel. Studies of electrical properties reveal that Cr ions do not participate in charge transport at low temperatures. In the charge curves of Li/Li +/Li y Cr x Mn 2− x O 4 cells there are two visible plateaux, separated with distinct potential jump (∼0.5 V), which position on Li content perfectly matches the Mn 3+ content in the doped cathode material. The lower plateau is related to the Mn 3+ → Mn 4+ oxidation, while the next of higher voltage, of the dopant Cr 3+ → Cr 4+ oxidation. The schematic diagrams of relative Mn–Cr electronic levels alignment are proposed.