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

Ultrahigh-nickel layered oxide cathodes (LiNi_<i>x</i>Co_<i>y</i>Mn_{1-<i>x</i>-<i>y</i>}O₂, 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_0.92Co_0.06Mn_0.02O₂ (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.