Mechanically Adaptive Polyimide Interfaces for Stable High‐Voltage NCM–Sulfide All‐Solid‐State Batteries

(sNCM). The grafted PI layer establishes robust carboxylate-transition metal coordination bonds, effectively eliminating surface lithium residues and suppressing oxygen release. Owing to its viscoelastic nature, the PI coating reduces the surface modulus of sNCM by 26.6%, accommodating anisotropic volume changes and mitigating intragranular microcrack propagation. Most significantly, the PI interface functions as an electrochemically driven self-optimizing system during cycling, progressively decreasing total interfacial impedance by 38%. Consequently, the sNCM@PI0.05 cathode delivers 83.6% capacity retention after 400 cycles at 1C under a 4.3 V cutoff voltage, significantly outperforming unmodified sNCM (33.2% retention). It also maintains 90.2% of its initial capacity after 200 cycles at 4.5 V. This reactive polymer interphase design harmonizes chemical passivation and mechanical adaptability, providing a transformative strategy for durable, high-energy ASSBs.