Enhanced electrochemical performances and thermal stability of LiNi1/3Co1/3Mn1/3O2 by surface modification with YF3

Layered LiNi1/3Co1/3Mn1/3O2 cathode materials were prepared using a sol-gel method and subsequently surface-modified with YF3 layer by a wet chemical process. In comparison with pristine LiNi1/3Co1/3Mn1/3O2, LiNi1/3Co1/3Mn1/3O2@YF3 exhibited higher rate capability, better cyclability and better thermal stability. After 100 cycles at 5 C and 25 °C, LiNi1/3Co1/3Mn1/3O2@YF3 showed 93% capacity retention compared with 74% for pristine LiNi1/3Co1/3Mn1/3O2. Electrochemical measurements demonstrated that the improved electrochemical performances of YF3-coated LiNi1/3Co1/3Mn1/3O2 might be attributed to smaller charge-transfer resistance, higher lithium diffusion rate, more stable electrolyte/electrode interfacial structure, and lower activation energy. Kelvin probe force microscopy measurements revealed that the LiNi1/3Co1/3Mn1/3O2@YF3 cathode possessed a lower surface potential and work function than those of the pristine one, which help to facilitate electron transport and suppress reactions between the electrolyte and cathode during the charge/discharge processes. In a certain way, the reported results clarified the possible mechanism of the enhanced performances of cathode materials with surface modification in terms of interfacial effect.