Mitigating storage-induced degradation of Ni-rich LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode material by surface tuning with phosphate

The Ni-rich LiNi _0.8 Co _0.1 Mn _0.1 O ₂ layered oxide (NCM811) is attracting considerable attention as a high-capacity cathode material for rechargeable Li-ion batteries. However, due to its inherent structural/chemical/electrochemical instability, NCM811 with high Ni content suffers from significant performance degradation upon storage even in ambient atmospheres as well as during charge–discharge cycling. Herein, we demonstrate a simple but effective surface-tuning approach to mitigate storage-induced degradation of NCM811, which is based on the conversion of undesirable Li residues to a protective Li ₃ PO ₄ nanolayer via phosphate treatment. The accelerated storage stability test shows that phosphate-modified NCM811 exhibits remarkably improved electrochemical performance (capacity, cycle life, and rate capability) over the pristine one after being stored under harsh environmental conditions. A combined analytical study indicates that surface tuning through phosphate treatment enhances the storage stability of NCM811 by eliminating impurity-forming Li residues and producing a Li ₃ PO ₄ nanolayer that inhibits parasitic reactions at the electrode–electrolyte interface. Furthermore, Li ₃ PO ₄ provides an effective barrier to H ₂ O and CO ₂ infiltration into the particle agglomerates, thereby suppressing the loss of particle integrity.