Mechano‐Electrochemical Coupling Enabled by Triple‐Gradient Interface Engineered Garnet for Durable All‐Solid‐State Lithium Metal Batteries

All‐solid‐state lithium metal batteries are promising for next‐generation energy storage but remain limited by interfacial instability arising from coupled electrochemical and mechanical failures. Here, we propose a triple‐gradient interface engineering strategy to resolve this challenge by simultaneously regulating chemical functionality, mechanical compliance, and lithium‐ion transport across inorganic–organic interfaces. Garnet‐type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) is transformed into a hierarchical core–bridging–coordinating architecture through sequential adhesion, covalent bridging, and adaptive polymerization. A polydopamine‐derived adhesion layer enhances polymer affinity, a silane‐mediated bridging layer passivates surface Li 2 CO 3 and mitigates interfacial stress, and an outer poly(dioxolane) shell provides dynamic Li + coordination and stress buffering. The resulting triple‐gradient composite electrolyte exhibits a high ionic conductivity of 2.62 × 10 −4 S cm −1 at 60°C and a Li + transference number of 0.86. Symmetric Li‖Li cells cycle stably for over 2400 h, while full cells deliver excellent long‐term stability, demonstrating an effective mechano‐electrochemical regulation paradigm for durable solid‐state lithium metal batteries.