Since the significance of Li-ion batteries (LIBs) has been dramatically increased nowadays, numerous investigations have focused on the enhancement of the electrochemical performances of active materials in LIBs. Among them, many researchers have concentrated on the Li and Mn-rich layered oxides for the cathode active materials in LIBs due to their intrinsic high specific capacity and energy density. However, their superior performances suffer from drastic degradations (e.g. voltage fading, capacity loss, and large voltage hysteresis, etc.) during cycling. Herein, we proposed an ultra-simple 1 step LiF coating method for NMC-LLC system (Li_1.2Mn_0.54Ni_0.13Co_0.13O₂), enhancing their performances, especially the capacity retention.

During the post-heating, the LiF layer was formed through the reaction between Li residues on the surface of as-synthesized LLC active material particles and fluorine inside PVDF binder molecules. Since the Li residues, such as Li₂O, Li₂CO_3, and LiOH, can induce the continuous formation of corrosive HF molecules, the passivating layer can prevent the autocatalytic HF-attack, as well as other vigorous side reactions (e.g. TM migration, TM dissolution, and electrolyte decomposition, etc.) at the interface between the electrode and electrolyte, the inferior cyclability of LLC was certainly increased. Our LiF-coated LLC samples exhibited the high capacity retentions 95.9% after 100 cycles at 0.2 C and 92.5% after 150 cycles at 1 C. XPS and HAADF-STEM measurements were conducted to manifest the successful formation of LiF layer above the surface of LLC active material particles via the treatment introduced in this paper.