Ultrahigh-Nickel Cathodes with B/Al Codoped Gradient Interface for High-Energy All-Solid-State Lithium Batteries

Ultrahigh-nickel layered oxide cathodes (LiNi x Co y Mn 1– x – y O 2, NCM, x ≥ 0.9) offer exceptionally high energy density essential for next-generation and safe all-solid-state batteries (ASSBs). However, severe interfacial side reactions (e.g., electrolyte decomposition) and structural degradation (involving oxygen loss and phase transition) at the cathode–solid electrolyte interface remain critical obstacles. Herein, we introduce a novel gradient cation-disordered layer (∼5 nm) engineered at the surface of single-crystal LiNi 0.92 Co 0.06 Mn 0.02 O 2 (SNCM) through synergistic codoping with boron (B) and aluminum (Al). The B-induced cation-disordered structural protective layer effectively reduces side reactions between highly active Ni/lattice oxygen and the SSE. Specifically, near-surface Al dopants play a dual role: enhancing interfacial Li + kinetics and critically stabilizing lattice oxygen, collaborating with the disordered structure to suppress interface structure degradation. Consequently, the modified SNCM delivers a high initial discharge capacity of 236.0 mAh g –1 (1C, 60 °C, 4.5 V cutoff) with 91% initial Coulombic efficiency and retains 86% capacity after 200 cycles. Notably, at room temperature and a high rate of 5C, the cell maintains 94% capacity retention over 500 cycles. Our findings demonstrate a novel surface engineering strategy, constructing a gradient cation-disordered layer via codoping, that effectively mitigates interfacial degradation (side reactions and structural instability), thereby enabling highly stable and long-cycle-life ultrahigh-nickel cathodes for practical ASSBs.