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

Abstract LiCoO 2 is a historic lithium-ion battery cathode that continues to be used today because of its high energy density. However, the practical capacity of LiCoO 2 is limited owing to the harmful phase transition at high voltages, which prevents the realization of its theoretical capacity. Here, we treat LiCoO 2 particles with a molten salt of MgF 2 –LiF as a reaction accelerator to facilitate the diffusion and doping of magnesium into bulk LiCoO 2 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 LiCoO 2 was charged up to 4.7 V. The modified LiCoO 2 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 LiCoO 2 cathodes.