An Adhesive Adaptation Layer Mitigates the Interfacial Instabilities of Rigid Polymer Electrolyte

Solid polymer electrolytes (SPEs) are widely recognized as promising candidates for enabling solid-state lithium metal batteries (SSLMBs) with improved safety, high energy density, and extended cycling life. The traditional perspective posits that increasing the mechanical modulus of SPEs enhances their capacity to regulate Li⁰ deposition and suppress dendrite penetration. However, this study reveals a distinct failure mechanism: a rigid SPE with a high storage modulus suffers from delamination-induced cell failure due to its inability to accommodate the volumetric changes of the Li⁰ anode. To address these limitations, we developed a hierarchical SPE incorporating an adhesive adaptation layer (AAL) positioned between the Li⁰ anode and the rigid SPE. The AAL combines strong adhesive strength, effectively mitigating delamination, with flowability, allowing it to eliminate interfacial voids and defects. Structural characterization via Cryo-TEM and SEM demonstrates that this hierarchical design facilitates uniform, dense, and whisker-free Li⁰ deposition, in sharp contrast to the uneven and porous morphology observed with the rigid SPE alone. Furthermore, the enhanced interfacial stability promotes the formation of an inorganic-enriched SEI layer, contributing to long-term cycling stability. As a result, the H-SPE exhibits superior electrochemical performance, achieving 87 % capacity over 960 cycles when paired with high-loading (1.6 mAh/cm²) NMC622 cathode.