Controlling lithium cobalt oxide phase transition using molten fluoride salt for improved lithium-ion batteries

LiCoO₂ is a historic lithium-ion battery cathode that continues to be used today because of its high energy density. However, the practical capacity of LiCoO₂ is limited owing to the harmful phase transition at high voltages, which prevents the realization of its theoretical capacity. Here, we treat LiCoO₂ particles with a molten salt of MgF₂-LiF as a reaction accelerator to facilitate the diffusion and doping of magnesium into bulk LiCoO₂ and to form a stable coating layer on the particle surface. Ex situ X-ray diffraction analysis confirms the inhibition of the harmful phase transition and the emergence of a different phase as the modified LiCoO₂ was charged up to 4.7 V. The modified LiCoO₂ shows high electrochemical performance during high-voltage operation. This technology provides a guideline for the suppressing fundamental degradation associated with phase transition and achieving ultra-high energy density LiCoO₂ cathodes.

Mayumi Mikami, Jo Saito, Teruaki Ochiai, Masahiro Takahashi, Tatsuyoshi Takahashi, Yohei Momma, Kazutaka Kuriki, Rihito Wada, Kazune Yokomizo, Genki Kobayashi, Shinichi Komaba, Shunpei Yamazaki