Stabilizing Single-Crystalline Ni-Rich Cathode via Epitaxial Entropy-Assisted Surface.

Single-crystalline Ni-rich LiNixMnyCo1-x-yO2 (SNCM, x ≥ 0.8) materials are regarded as next-generation cathodes for lithium-ion batteries. However, SNCM cathodes show readily low structural stability due to surface reconstruction and irreversible strain evolution during cycling at high voltages. Here, we demonstrate that Y2O3 material incorporated into SNCM cathodes forms an epitaxial entropy-assisted surface layer, which acts as a highly compatible region to facilitate Li-ion transmission, suppress interface reaction and transition metal dissolution. Meanwhile, soluble Al ions are uniformly distributed in the SNCM lattice and combine with the surface Y-O bond, forming a pillaring effect to restrain irreversible strain evolution, eventually prevent the formation of gliding and nanocracks during high-voltage cycling. As a result, the SNCM cathode with a Y2O3 surface and Al doping shows a high specific discharge capacity of 210.5 mAh·g-1 at 1 C within 2.75-4.4 V and a capacity retention of 86.6% after 100 cycles. This study offers a new insight into the design of a strain-retardant method for obtaining single-crystalline Ni-rich cathode materials with high performance.