Phase‐Changeable Dynamic Conformal Electrode/electrolyte Interlayer enabling Pressure‐Independent Solid‐State Lithium Metal Batteries

Abstract Lithium‐metal‐based solid‐state batteries (Li‐SSBs) are one of the most promising energy storage devices due to their high energy densities. However, under insufficient pressure constraints (<MPa‐level), Li‐SSBs usually exhibit poor electrochemical performances owing to the continuous interfacial degradation between the solid‐state electrolyte (SSE) and electrodes. Herein, a phase‐changeable interlayer is developed to construct the self‐adhesive and dynamic conformal electrode/SSE contact in Li‐SSBs. The strong adhesive and cohesive strengths of the phase‐changeable interlayer enable Li‐SSBs to resist up to 250 N pulling force (=1.9 MPa), affording Li‐SSBs ideal interfacial integrality even without extra stack pressure. Remarkably, this interlayer exhibits a high ionic conductivity of 1.3 × 10⁻³ S cm⁻¹, attributed to the shortened steric solvation hindrance and optimized Li⁺ coordination structure. Furthermore, the changeable phase property of the interlayer endows Li‐SSBs with a healable Li/SSE interface, accommodating the stress–strain evolution of the lithium metal and constructing the dynamic conformal interface. Consequently, the contact impedance of the modified solid symmetric cell exhibits a pressure‐independent manner and does not increase over 700 h (0.2 MPa). The LiFePO₄ pouch cell with the phase‐changeable interlayer shows 85% capacity retention after 400 cycles at a low pressure of 0.1 MPa.