Operating Highly Stable LiCoO_2 Cathodes up to 4.6 V by Using an Effective Integration of Surface Engineering and Electrolyte Solutions Selection

摘要

The need for high power density cathodes for Li-ion batteries can be fulfilledby application of a high charging voltage above 4.5 V. As lithium cobalt oxide(LCO) remains a dominant commercial cathode material, tremendous effortsare invested to increase its charging potential toward 4.6 V. Yet, the longtermperformance of high voltage LCO cathodes still remains poor. Here,an integrated approach combining the application of an aluminum fluoridecoating and the use of electrolyte solutions comprising 1:1:8 mixtures ofdifluoroethylene:fluoroethylene carbonate:dimethyl carbonate and 1 m LiPF_6 isreported. This results in superior behavior of LCO cathodes charged at 4.6 Vwith high initial capacity of 223 mAh g~（?1）, excellent long-term performance, and78% capacity retention after 500 cycles. Impressive stability is also found at450 ℃ with an initial capacity of 220 mAh g~（?1） and around 84% capacity retentionafter 100 cycles. Systematic post-mortem analysis of LCO cathodes and Lianodes after prolonged cycling reveals two main degradation routes related tochanges at the surface of the cathodes and formation of passivation layers onthe anodes. This study demonstrates the importance of appropriate selectionof electrolyte solutions and development of effective coatings for improvedperformance of high voltage LCO-based Li batteries.