electrochemical performance of LiNi0.8Co0.15Al0.05O2 cathode by reducing lithium residue with low-temperature fluorination treatment

LiNi0.8Co0.15Al0.05O2 is considered as a representative layer-structured cathode material. Decreasing residual lithium (LiOH and Li2CO3) on its surface is the main challenge to improve cycling performance for commercial application. In this study, a dry and low-temperature fluorination (350 degrees C) method was proposed to modify LiNi0.8Co0.15Al0.05O2 cathode. The effects of fluorine content on the microstructure, surface composition and electrochemical properties of the cathode were extensively studied. The results showed that fluorination had multi-functions: (i) decreasing the lithium residues and generating amorphous LiF coating layer on the particle surface, (ii) restraining the diffusion of metal ions conveyed in the electrolyte, particularly at high temperature, (iii) retarding the increase of charge transfer impedance, and (iv) maintaining the structural stability of electrode during extended cycles. Electrochemical test results indicated that the sample fluorinated with 1.0 mol% F exhibited excellent cycling performance with the capacity retention of 93.9% after 100 cycles at 1 C, showing dramatical improvement compared with that of the pristine cathode (86.2%). This designed low-temperature dry fluorination process is expected to be practically applicable in other nickel-rich cathodes.