Synthesis of Mg and Mn Doped LiCoO2 and Effects on High Voltage Cycling

Abstract

LiCo1-2xMgxMnxO2 (0 ≤ x ≤ 0.05) materials were prepared from Co1-2xMgxMnx(OH)2 (0 ≤ x ≤ 0.05) co-precipitated precursor materials by mixing precursor materials with stoichiometric amounts of Li2CO3 and heating to 900°C for 10 h. All precursor and lithiated materials were characterized by Scanning Electron Microscopy, X-ray Diffraction (XRD), Inductively Coupled Plasma – Optical Emissions Spectroscopy and electrochemical testing. In situ XRD was performed on LiCo1-2xMgxMnxO2 (x = 0, 0.02, 0.05) electrodes while cycling to study the effects of substitution on phase transitions and unit cell variations. Increasing Mg/Mn substitution in the material was found to slightly increase the 1st charge capacity, decrease the 1st discharge capacity and increase the 1st cycle irreversible capacity (3.6 V–4.7 V). Cells with even 1% Mg/Mn doping were shown to have markedly improved cycling performance, and results suggest that the improvements stem from suppressing the cell impedance growth, not from the suppression of the O3-O6-O1 phase transitions. Differences between LiCoO2 cells and LiCo0.9Mg0.05Mn0.05O2 cells become significant at 4.5 V and above, where the LiCoO2 cells underwent the O3-O6-O1 phase transitions and the LiCo0.9Mg0.05Mn0.05O2 cells appeared to undergo oxygen loss but not this series of phase transitions.