Mitigating storage-induced degradation of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode material by surface tuning with phosphate

Abstract

The Ni-rich LiNi0.8Co0.1Mn0.1O2 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 Li3PO4 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 Li3PO4 nanolayer that inhibits parasitic reactions at the electrode-electrolyte interface. Furthermore, Li3PO4 provides an effective barrier to H2O and CO2 infiltration into the particle agglomerates, thereby suppressing the loss of particle integrity.