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

To obtain positive electrode materials with higher energy densities ( W s), we performed systematic structural and electrochemical analyses for LiCo x Mn 2- x O 4 (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 Fd 3̅ m space group, whereas the samples with x ≥ 0.75 are in a mixture of the spinel-phase and Li 2 MnO 3 phase with the C 2/ m space group. The x -dependence of the discharge capacity ( Q dis ) indicated a broad maximum at x = 0.5, although the average operating voltage ( E ave ) monotonically increased with x . Thus, the W value obtained by Q dis × E ave reached the maximum (=627 mW h·g -1 ) at x = 0.5, which is greater than that for Li[Ni 1/2 Mn 3/2 ]O 4 . Furthermore, the change in the lattice volume (Δ V ) during charge and discharge reactions approached 0%, that is, zero-strain, at x = 1. Because Δ V for x = 0.5 was smaller than that for Li[Ni 1/2 Mn 3/2 ]O 4 , the x = 0.5 sample is found to be an alternative positive electrode material for Li[Ni 1/2 Mn 3/2 ]O 4 with a high W .