Dry-processing of ceramic-infilled composite electrolyte membrane for solid-state lithium metal batteries

Abstract

This study introduces a high-performance ceramic-infill membrane (CIM) solid electrolyte to overcome the challenges of open-air, dry-processing fabrication of thin garnet-based electrolytes and to reduce the interfacial resistance of garnet-based solid-state electrolytes for Li metal batteries. An ultra-thin ceramic composite membrane (< 20 µm) is embedded in a solid polymer network interlayer prepared by a solvent-free method. Surface engineering via sonication-assisted treatment converts the surface of resistive lithium carbonate (LC) into a stable, ionically conductive amorphous layer of lithium phosphate (LPO). This process yields a bimodal particle-size distribution in LLZAO, thereby improving the density of the composite film. The dry process for 97.5% garnet-based composite membrane fabrication involves a two-step fibrillation of the 2.5% PTFE binder, coupled with cold isostatic pressing (CIP), yielding a densified framework with lower porosity and improved LLZAO interparticle contact, as reflected in the electrochemical performance. A cross-linked glyme-based ion-conductive polymer interlayer is applied to the membrane surface to bridge the electrode-electrolyte interface and grain particles, thereby forming the ceramic-infill architecture of a quasi-solid electrolyte. The resulting dual-framework architecture and surface passivation exhibit a high lithium-ion transference number of 0.75, a wide electrochemical stability window of 5.3 V, and an ionic conductivity of 1.7 × 10^–4 S cm^–1 at room temperature. The full-cell battery with LFP cathode demonstrates high stability, maintaining >71% of its capacity after 300 cycles at 0.5C. This is achieved utilizing a ∼ 17 µm ceramic composite within a CIM membrane with an overall thickness of 30 µm.