Optimized ion-conductive pathway in UV-cured solid polymer electrolytes for all-solid lithium/sodium ion batteries

Solid electrolyte-based lithium-ion batteries (LIBs) have enormous potential to replace conventional LIBs with flammable liquid electrolytes. However, most solid electrolytes show low ionic conductivity and poor interfacial properties with electrodes, preventing them from reaching the level of conventional liquid electrolyte systems with separators. Herein, we optimized the formation of an ion-conductive pathway in a UV-cured solid polymer electrolyte (USPE) via a semi-interpenetrating polymer network with a minimal liquid content. The USPE consists of a UV-curable hard matrix (trimethylolpropane ethoxylate triacrylate, ETPTA) as a backbone film with negligible ionic conductivity and an optimized ionic channel with an ion-solvated gel polymer (Li⁺/PVdF-HFP) with a minimal liquid content for boosting the Li⁺ conduction. The hybrid solid-state film provides high ionic conductivity (up to 85%) relative to commercial liquid electrolyte systems and a stable electrochemical window. We also applied the same USPE with Na⁺ for solid electrolyte-based sodium ion batteries, and similar positive effects were also observed. Going another step forward, both the PVdF-HFP/ETPTA ratio and the HFP content in the PVdF-HFP are critical gel polymer additives for generating reinforced Li⁺ ion pathways in USPE.