Constructing Stable Sub/Surface Structure to Boost Superior Cyclabilities of Single-Crystalline Ni-Rich Cathode

Under prolonged high-voltage cycling, single-crystalline Ni-rich cathodes are prone to severe transition metal dissolution, irreversible phase transformations, and reduced structural stability, which significantly hinder their practical application. Hence, a dual-modification strategy is proposed and implemented for single-crystalline LiNi_0.90Co_0.05Mn_0.05O₂ (SCNCM90) cathodes by introducing Al/B gradient co-doping and an Al₅BO₉ surface coating to mitigate anisotropic structural changes. The subsurface Al/B gradient doping induces a lithium-rich vacancy disordered structure, which effectively suppresses the H2-H3 phase transition, while suppressing lattice strain and mechanical degradation. In parallel, the chemically stable Al₅BO₉ surface coating significantly mitigates harmful electrode-electrolyte interfacial reactions, thereby enhancing both structural and electrochemical stability under high-voltage conditions. Electrochemical tests reveal that the Al/B co-modified SCNCM90 electrode exhibits markedly improved performance, achieving 95.83% capacity retention after 200 cycles at 4.5 V and maintaining 89.6% retention at 1C after 1000 cycles in pouch-type full cells within 3-4.25 V. Moreover, the modified electrode demonstrates superior lithium-ion diffusion kinetics and enhanced thermodynamic stability during cycling. This effective dual-modification strategy offers a promising pathway to improve the structural robustness and electrochemical durability of single-crystalline Ni-rich cathodes, thus accelerating their adoption in next-generation high-energy lithium-ion batteries.