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

LiCo 1-2x Mg x Mn x O 2 (0 ≤ x ≤ 0.05) materials were prepared from Co 1-2x Mg x Mn x (OH) 2 (0 ≤ x ≤ 0.05) co-precipitated precursor materials by mixing precursor materials with stoichiometric amounts of Li 2 CO 3 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 1-2x Mg x Mn x O 2 (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 LiCoO 2 cells and LiCo 0.9 Mg 0.05 Mn 0.05 O 2 cells become significant at 4.5 V and above, where the LiCoO 2 cells underwent the O3-O6-O1 phase transitions and the LiCo 0.9 Mg 0.05 Mn 0.05 O 2 cells appeared to undergo oxygen loss but not this series of phase transitions.