Synthesis of Mg and Mn Doped LiCoO2and Effects on High Voltage Cycling

Abstract

LiCo_1-2xMg_xMn_xO₂ (0 ≤ x ≤ 0.05) materials were prepared from Co_1-2xMg_xMn_x(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 LiCo_1-2xMg_xMn_xO₂ (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 1^st charge capacity, decrease the 1^st discharge capacity and increase the 1^st 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 LiCo_0.9Mg_0.05Mn_0.05O₂ cells become significant at 4.5 V and above, where the LiCoO₂ cells underwent the O3-O6-O1 phase transitions and the LiCo_0.9Mg_0.05Mn_0.05O₂ cells appeared to undergo oxygen loss but not this series of phase transitions.