Charge Compensation Mechanism and Structural Change of Li-Rich Layered Oxide Li1.23Mn0.46Fe0.15Ni0.15O2 Electrode during Charging and Discharging

Abstract

We investigated changes in the valence and structure of positive electrodes composed of Li-rich layered manganese (Mn) oxides (Li1.23Mn0.46Fe0.15Ni0.15O2, LMFN) when they were charged and discharged. Hard X-ray photoemission spectroscopy (HAXPES) and 57Fe Mössbauer spectroscopy measurements indicated that charge compensation occurred through changes in the valences of the Mn, Fe, Ni, and oxide ions, from Mn4+, Fe3.2+, Ni3.4+, and O1.78− in the charged state to Mn3.6+, Fe3+, Ni2+, and O2− in the discharged state. Neutron diffraction (ND) measurements indicated the LMFN powder had a layered rock-salt structure. However, reconstruction of the transition metal and oxide ions in the lattice during charging indicated spinel phases made up 17% of the structure, the remaining 83% being layered rock-salt. The oxygen deficiency formed during charging recovered during discharging and the lost oxygen became implanted again in the lattice of the cathode. We believe that the elucidation of the charge compensation mechanism and structural changes during charging and discharging will be useful for designing materials with larger capacity and improved cycle performance.