Study on the effect of Ni and Mn doping on the structural evolution of LiCoO2 under 4.6 V high-voltage cycling

Abstract

The superior tap density (4.1 g cm−3) and high theoretical specific capacity (274 mA h·g−1) of LiCoO2 make it still the first choice of cathode for batteries in next-generation portable electronic devices. However, the structural instability in the deeply delithiated state severely restricts the reversible capacity of LiCoO2 for practical applications. Owing to the recently popular Ni and Mn elements in ternary cathodes, we explored the effects of Ni–Mn co-doping and each individual dopant on the electrochemical behavior and structural evolution of LiCoO2 at a high upper cut-off voltage of 4.6 V by the means of in-situ XRD and GITT measurements. LiMn0.05Co0.95O2 shows the best cycle stability at 4.6 V with a capacity retention of 55% after 100 cycles. The doping suppresses various two-phase transitions, especially, the O3/H1-3 phase transition at ∼4.55 V, leading to better cycling stability of LiCoO2 at 4.6 V. Due to the significant stabilizing effect on the structure, Mn seems to be an ideal choice for the modification of high-voltage LiCoO2 in the future.