Bulk/Interfacial‐Mediated Dynamic Phase Stabilization Restricting Mn Dissolution in 5 V‐Class LiNi _0.5 Mn _1.5 O ₄ Cathodes at 45 °C

Abstract High‐voltage spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) is a promising lithium‐ion battery cathode due to its low cost and environmental compatibility. However, high‐voltage operation triggers phase transition and transition metal dissolution, causing irreversible active material loss. Dissolved metals further migrate to the anode, inducing harmful crosstalk that accelerates failure. These degradation mechanisms fundamentally limit high‐energy, safe battery development. Here, a bulk/interfacial strategy involving an architected doping gradient and near‐surface reconstruction is proposed from the structure/function relation of LNMO. Specifically, uniform incorporation of Co stabilizes the 16 c /16 d sites strategically, facilitating solid‐solution reactions while preserving structural stability at elevated temperatures. Simultaneously, surface‐gradient Na and near‐surface B slightly‐doping to in situ derivation a Na 2 B 4 O 7 coating—a fast‐ion conductor that functions as a preferential sacrificial scavenger. This dual‐functional structure enables rapid Li + conduction while inhibiting electrolyte decomposition and HF attack. Notably, the crosstalk effect related to Mn‐ion migration is effectively restricted during harsh 45 °C/4.95 V cycling. Consequently, the modified cathode (NCB‐LNMO) retains an ultrathin, dense, and homogeneous cathode electrolyte interfaces (CEI)/solid electrolyte interphas (SEI) architecture, achieving an exceptional capacity retention of 94.5% after 300 cycles at 45 °C. This study highlights that the bulk/interface engineering establishes a blueprint for LNMO‐based LIBs with enhanced cycle life and safety metrics.