Significant improvement of high voltage cycling behavior AlF3-coated LiCoO2 cathode

To improve the capacity retention of LiCoO2 at 4.5 V cut-off cycling, the AlF3 as new coating material was introduced. The AlF3-coated LiCoO2 showed no large difference in the bulk structure and a uniform AlF3-coating layer whose thickness is of about 10 nm covers LiCoO2 particles, as confirmed by transmission electron microscopy. The AlF3-coated LiCoO2 delivered the similar initial discharge capacity to pristine LiCoO2 to 4.5 V versus Li. Surprisingly, the capacity retention and rate capability were greatly enhanced comparing to the pristine LiCoO2. Ac-impedance results showed that the AlF3-coated LiCoO2 has stable charge transfer resistance (Rct) on cycling. Reduced Co dissolution was also seen for the AlF3-coated LiCoO2.