Improving the Structural Stability of Li-Rich Layered Cathode Materials by Constructing an Antisite Defect Nanolayer through Polyanion Doping

To mitigate the gradual phase transition and improve the structural stability of Li-rich layered cathode materials, an antisite defect nanolayer (transition-metal ions replacing Li+ in a Li slab) with a thickness of approximately 2 nm was induced on the surface of Li-1.16(Ni0.25Mn0.75)(0.84)O-2 by doping with boracic polyanions. It is found that the 2 and 3 mol% BO33- doped samples show excellent cycling stability with capacity retentions of 91.2 and 93.7%, respectively, after 300 cycles at 0.5 C. More importantly, the BO33- doping restrains the decay of discharge voltage upon cycling and has the prospect to overcome the fatal drawback of Li-rich layered oxides. The results demonstrate that the BO33- doping contributes to the generation of an antisite defect nanolayer on the surface, which hinders the formation of Li-ion vacancies and the continued migration of more transition-metal ions to the Li slab in a deep charging state. The antisite defect nanolayer clearly improves surface structural stability and inhibits the appearance of the amorphous domain in the bulk, which are favorable to maintain the facile lithium-diffusion pathways during cycling and improve the capacity retention and rate capability.