Overcoming Interphasial Ion Transport Bottleneck by In Situ Hybrid Solid Electrolytes for Ambient Temperature Lithium Metal Batteries

ABSTRACT The construction of polymer/ceramic composite electrolytes has significantly enhanced ionic conductivity and alleviated electrolyte–electrode interfacial contact, representing a promising strategy for tackling the challenges of ambient‐temperature lithium‐metal‐based solid‐state batteries (SSBs). However, the critical issue of impeded ion transport at the polymer–ceramic interphase within these composites remains unresolved. Polymers provide chemical compatibility yet suffer from intrinsically low conductivity, whereas ceramics exhibit high conductivity yet suffer from interfacial reactivity. Blending the two often yields heterogeneous composites in which Li ⁺ transport is blocked at poorly connected polymer–ceramic interphases, preventing continuous ion flux and hindering room‐temperature cycling. Here, we overcome this interphasial bottleneck by chemically bonding polymers to ceramic surfaces via a surface‐initiated polymerization strategy, thereby creating a molecularly integrated hybrid electrolyte. Direct electrochemical evidence showed that chemical bonding substantially suppresses polymer–ceramic interphasial impedance and reduces electrode–electrolyte interfacial resistance. The resulting continuous Li ⁺ transport pathways yielded a conductivity of 1.1 × 10 ⁻⁴ S cm ⁻¹ at 30°C, 4 times that of mixed composites, enabling dendrite‐free Li plating for 1,200 h alongside stable ambient‐temperature SSB operation. These findings elucidate how interfacial chemistry modulates ion transport across heterogeneous solid phases, offering a basis for designing next‐generation hybrid solid electrolytes.