Interpenetrating Interface Engineering via Competitive Coordination in Ultrathin Asymmetric Solid-State Electrolytes for High-Energy Lithium Metal Batteries

Asymmetric solid-state electrolytes (ASEs) have been proven to achieve simultaneous compatibility with high-voltage cathodes and lithium metal anodes, making them attractive for high-energy-density solid-state lithium metal batteries (SSLMBs). However, conventional ASE configuration typically introduces an additional electrolyte/electrolyte interface, which results in high Li-ion (Li⁺) migration resistance and compromised electrochemical performance. Herein, we propose an interpenetrating interface engineering strategy to construct a seamless and integrated ASE. The unique interface layer is formed by a reduction-resistant poly(1,3-dioxolane) (PDOL) penetrating into an oxidation-tolerant poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer layer. In addition to achieving synchronized interfacial stability at both the cathode and the anode, the competitive coordination of PDOL with Li⁺ in the interpenetrating interface layer promotes efficient Li⁺ transport along PDOL chains, effectively reducing the Li⁺ cross-interface transport energy barrier and lowering the total interfacial resistance. The resulting ASE, with an ultra-thin thickness of 10 µm, enables a pouch cell incorporating an ultrathin Li metal anode and high-loading Li-rich Mn-based oxide cathode (7 mAh cm⁻²) to achieve a high energy density of 521.6 Wh kg⁻¹ and 1161.4 Wh L⁻¹. This interpenetrating interface design strategy provides a new pathway for developing next-generation SSLMBs with high energy density.