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

Abstract 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 LiNi_0.83Mn_0.06Co_0.11O₂ (NMC‐83) cathode delivers a high energy density of 437 Wh kg_{anode+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.