(A) study on the improvements in electrochemical properties of Li-excess layered cathode via F anion doping and Li3PO4 coating

Abstract

As the demands of electric vehicle and energy storage system are increased, lithium-ion battery system get attention for energy storage device, and Li-excess layered cathode for lithium-ion battery has emerged as a strong candidate of new cathode material due to its high specific energy density. However, commercialization of Li-excess layered cathode is struggling due to layered to spinel phase transformation in bulk and transition metal (TM) dissolution on the surface by HF attack. These problems mitigates Li-ion diffusion during cycling. Herein, we devised a new method of doping and coating in one annealing treatment. We selected F$^-$ anion as doping material by PVDF in electrode, and Li$_3$PO$_4$ as coating material by PH$_3$ gas. The F$^-$ anion doping mitigates spinel transformation in the bulk due to its stronger binding energy with transition metal than that of oxygen, and Li$_3$PO$_4$ coating prevents transition metal dissolution on the surface due to HF scavenger property of Li3PO4. The F$^-$ anion doped and Li$_3$PO$_4$ layer coated LLC shows discharge capacity 223.9 mAh g$^{-1}$ after 100 cycle, 0.2 C.