Role of Bicontinuous Structure in Elastomeric Electrolytes for High‐Energy Solid‐State Lithium‐Metal Batteries

Solid-state lithium (Li)-metal batteries (LMBs) are garnering attention as a next-generation battery technology that can surpass conventional Li-ion batteries in terms of energy density and operational safety under the condition that the issue of uncontrolled Li dendrite is resolved. In this study, various plastic crystal-embedded elastomer electrolytes (PCEEs) are investigated with different phase-separated structures, prepared by systematically adjusting the volume ratio of the phases, to elucidate the structure-property-electrochemical performance relationship of the PCEE in the LMBs. At an optimal volume ratio of elastomer phase to plastic-crystal phase (i.e., 1:1), bicontinuous-structured PCEE, consisting of efficient ion-conducting, plastic-crystal pathways with long-range connectivity within a crosslinked elastomer matrix, exhibits exceptionally high ionic conductivity (≈10-3 S cm-1 ) at 20 °C and excellent mechanical resilience (elongation at break ≈ 300%). A full cell featuring this optimized PCEE, a 35 µm thick Li anode, and a high loading LiNi0.83 Mn0.06 Co0.11 O2 (NMC-83) cathode delivers a high energy density of 437 Wh kganode+cathode+electrolyte-1 . The established structure-property-electrochemical performance relationship of the PCEE for solid-state LMBs is expected to inform the development of the elastomeric electrolytes for various electrochemical energy systems.