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

Abstract

Single-crystalline Ni-rich LiNi_xMn_yCo_1-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.