Constructing a Highly Salt‐Dissociated Interface Via a Salt‐Rich Polyurea Coating for Advanced LiNi _0.9 Co _0.05 Mn _0.05 O ₂ Cathode

Abstract Nickel‐rich ternary cathode materials possess high energy density but suffer from severe chemical and mechanical degradation in both surface and bulk regions. Herein, the construction of a salt‐rich polymer coating layer, composed of a polyurea matrix and lithium bis(fluorosulfonyl)imide on the LiNi 0.9 Co 0.05 Mn 0.05 O 2 surface, is reported via in situ thermally initiated polymerization. This coating mitigates interfacial side reactions at the source by capturing salt anions while simultaneously establishing a fast lithium‐ion transport interface through a unique coupling effect between the polymer and lithium salt. Moreover, the flexible polymer layer accommodates lattice volume changes during cycling, effectively relieving mechanical stress and suppressing microcrack formation. The coating exhibits high reliability and remains functional during long‐term electrochemical cycling. Hence, the salt‐rich polyurea‐modified cathode demonstrates significantly enhanced electrochemical performance with 97.8% capacity retention after 200 cycles. This modified cathode maintains stability under harsh conditions such as high temperature and high voltage, while also being compatible with polymer solid electrolytes for long‐cycling solid‐state batteries. This work expands coating material options and introduces an innovative salt‐rich coating design, advancing the development of stable nickel‐rich cathodes for next‐generation energy storage applications.