Stable 4.5 V LiCoO₂ cathode material enabled by surface manganese oxides nanoshell

Charging the LiCoO₂ (LCO) cathode to a higher voltage, for example 4.5 V compared to the commonly used 4.2 V, is now intensively pursued so as to achieve a higher specific capacity. However, it suffers severe surface structural degradation and detrimental interfacial side reactions between cathode and electrolyte, which lead to the fast capacity fading during long-term cycling. Here, a surface coating strategy was developed for the protection of 4.5 V LCO by constructing a manganese oxides (MOs) nanoshell around LCO particles, which was achieved through a solution-based coating process with success in controlling the growth kinetics of the coating species. We found that the introduction of the MOs nanoshell is highly effective in alleviating the organic electrolyte decomposition at the cathode surface, thus ensuring a much more stable LiF-rich cathode-electrolyte interface and an obvious lower interfacial resistance during electrochemical cycling. Meanwhile, this protection layer can effectively improve the structural stability of the cathode by hindering the cracks formation and structural degradation of LCO particles. Therefore, the MOs modified LCO exhibited excellent rate performance and a high discharge capacity retention of 81.5% after 100 cycles at 1 C compared with the untreated LCO (55.2%), as well as the improved thermal stability and cyclability at the elevated temperature. It is expected that this discovery and fundamental understanding of the surface chemistry regulation strategy provide promising insights into improving the reversibility and stability of LCO cathode at the cut-off voltage of 4.5 V.