Ce & F multifunctional modification improves the electrochemical performance of LiCoO2 at 4.60 V

Abstract

Lithium cobalt oxide (LiCoO2) is proverbially employed as cathode materials of lithium-ion batteries attributed to the high theoretical capacity, and currently, it is developing towards higher cut-off voltages in the pursuit of higher energy density. However, it suffers from serious structural degradation and surface side reactions, in particular, at the voltage above 4.60 V, leading to rapid decay of the battery life. Taking into account the desirable oxygen buffering property and the fast ion mobility characteristic of cerium oxide fluoride, in this work, we prepared Ce & F co-modified LiCoO2 by using the precursors of Ce(NO3)3·6H2O and NH4F, and evaluated the electrochemical performance under voltages exceeding 4.60 V. The results indicated that the modified samples have multiphase heterostructure of surface CeO2−x and unique CeOF solid solution phase. At 3.0–4.60 V and 25 °C, the preferred sample LCO-0.5Ce-0.3F has a high initial discharge specific capacity of 221.9 mA h g−1 at 0.1 C, with the retention of 80.3% and 89.6% after 300 cycles at 1 and 5 C, comparing with the pristine LCO (56.4% and 22.6%). And at 3.0–4.65 V, its retention is 64.0% after 300 cycles at 1 C, versus 8.5% of the pristine LCO. Through structural characterizations and DFT calculations, it suggests that Ce4+ & F− co-doping suppresses the H3 to H1/3 irreversible phase transition, stabilizes the lattice structure, and reduces the redox activity of the lattice oxygen by modulating the Co 3d–O 2p energy band, consequently improving the electrochemical performance of LiCoO2 at high voltages.