Operating Highly Stable LiCoO₂ Cathodes up to 4.6 V by Using an Effective Integration of Surface Engineering and Electrolyte Solutions Selection

The need for high power density cathodes for Li-ion batteries can be fulfilled by application of a high charging voltage above 4.5 V. As lithium cobalt oxide (LCO) remains a dominant commercial cathode material, tremendous efforts are invested to increase its charging potential toward 4.6 V. Yet, the long-term performance of high voltage LCO cathodes still remains poor. Here, an integrated approach combining the application of an aluminum fluoride coating and the use of electrolyte solutions comprising 1:1:8 mixtures of difluoroethylene:fluoroethylene carbonate:dimethyl carbonate and 1 m LiPF₆ is reported. This results in superior behavior of LCO cathodes charged at 4.6 V with high initial capacity of 223 mAh g⁻¹, excellent long-term performance, and 78% capacity retention after 500 cycles. Impressive stability is also found at 450 °C with an initial capacity of 220 mAh g⁻¹ and around 84% capacity retention after 100 cycles. Systematic post-mortem analysis of LCO cathodes and Li anodes after prolonged cycling reveals two main degradation routes related to changes at the surface of the cathodes and formation of passivation layers on the anodes. This study demonstrates the importance of appropriate selection of electrolyte solutions and development of effective coatings for improved performance of high voltage LCO-based Li batteries.