Toward Positive Electrode Materials with High-Energy Density: Electrochemical and Structural Studies on LiCoxMn2-xO4 with 0 ≤x≤1

Abstract

To obtain positive electrode materials with higher energy densities (Ws), we performed systematic structural and electrochemical analyses for LiCoxMn2-xO4 (LCMO) with 0 ≤ x ≤ 1. X-ray diffraction measurements and Raman spectroscopy clarified that the samples with x ≤ 0.5 are in the single-phase of a spinel structure with the Fd3m space group, whereas the samples with x ≥ 0.75 are in a mixture of the spinel-phase and Li2MnO3 phase with the C2/m space group. The x-dependence of the discharge capacity (Qdis) indicated a broad maximum at x = 0.5, although the average operating voltage (Eave) monotonically increased with x. Thus, the W value obtained by Qdis × Eave reached the maximum (=627 mW h·g-1) at x = 0.5, which is greater than that for Li[Ni1/2Mn3/2]O4. Furthermore, the change in the lattice volume (V) during charge and discharge reactions approached 0%, that is, zero-strain, at x = 1. Because V for x = 0.5 was smaller than that for Li[Ni1/2Mn3/2]O4, the x = 0.5 sample is found to be an alternative positive electrode material for Li[Ni1/2Mn3/2]O4 with a high W.