DES-Based Elastomeric Electrolytes with Bicontinuous Architecture for Durable Solid-State Lithium Metal Batteries

Solid-state lithium metal batteries (SLMBs) have garnered significant attention for their high energy density and enhanced safety. However, traditional polyether-based polymer electrolytes (e.g., PEO) suffer from low ionic conductivity and insufficient lithium-ion transference numbers. Herein, we design a series of deep eutectic solvent (DES)-based polymer elastomeric electrolytes (DES-PEEs) through the combination of a DES-based plastic crystal phase and a fluorinated polymer-based elastomer phase. Through UV-initiated free-radical polymerization, the optimized DES-PEE forms an elastic polymer network with interconnected DES-rich ion-conducting pathways, delivering a high ionic conductivity of 1.65 mS cm–1 at room temperature, a superior lithium-ion transference number of 0.75 and an electrochemical stability window extending to 4.94 V (vs Li+/Li). The symmetric Li||Li cells demonstrate exceptional interfacial stability, withstanding current densities up to 2 mA cm–2 and cycling for over 1000 h under a current density of 1 mA cm–2 with minimal voltage hysteresis (<20 mV). The assembled Li||LFP full cells exhibit a superior rate capability and maintain a high capacity retention over 80% after 200 cycles at 0.1 C, with a Coulombic efficiency >99%. This study resolves the trade-off between ionic conductivity and mechanical properties in solid-state electrolytes through a phase-separation engineering strategy, offering a new direction for the development of high-performance SLMBs.