One-Step Synthesis of LiCo 1-1.5x Y x PO 4 @C Cathode Material for High-Energy Lithium-ion Batteries.

Intrinsically low ion conductivity and unstable cathode electrolyte interface are two important factors affecting the performances of LiCoPO 4 cathode material. Herein, a series of LiCo 1-1.5x Y x PO 4 @C (x = 0, 0.01, 0.02, 0.03) cathode material is synthesized by a one-step method. The influence of Y substitution amount is optimized and discussed. The structure and morphology of LiCo 1-1.5x Y x PO 4 @C cathode material does not lead to obvious changes with Y substitution. However, the Li/Co antisite defect is minimized and the ionic and electronic conductivities of LiCo 1-1.5x Y x PO 4 @C cathode material are enhanced by Y substitution. The LiCo 0.97 Y 0.02 PO 4 @C cathode delivers a discharge capacity of 148 mAh g -1 at 0.1 C and 96 mAh g -1 at 1 C, with a capacity retention of 75% after 80 cycles at 0.1 C. Its good electrochemical performances are attributed to the following factors. (1) The uniform 5 nm carbon layer stabilizes the interface and suppresses the side reactions with the electrolyte. (2) With Y substitution, the Li/Co antisite defect is decreased and the electronic and ionic conductivity are also improved. In conclusion, our work reveals the effects of aliovalent substitution and carbon coating in LiCo 1-1.5x Y x PO 4 @C electrodes to improve their electrochemical performances, and provides a method for the further development of high voltage cathode material for high-energy lithium-ion batteries.