Cure Kinetics and Interfacial Effects in <scp>PEGDA</scp> ‐Based Solid Composite Electrolytes

ABSTRACT Solid composite electrolytes (SCEs) are key enablers of multifunctional structural batteries, where mechanical load‐bearing and electrochemical transport must be optimized simultaneously. In this work, poly(ethylene glycol) diacrylate (PEGDA) is combined with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and silica nanoparticles (SiNPs) to probe how salt content and interfacial area influence network formation and ionomechanical properties. Isothermal differential scanning calorimetry (DSC) reveals that interfacial effects dominate cure kinetics in salt‐free systems, act additively with ionic coordination at moderate salt content, and become masked in high‐salt regimes until excessive filler reduces the effective conducting and load‐bearing polymer volume. Rheology shows that silica delays gelation and reduces plateau modulus when combined with LiTFSI, while electrochemical impedance spectroscopy (EIS) demonstrates that ionic conductivity is robust to moderate silica addition but collapses when both salt and filler are high. Together, these results establish composition‐dependent domains in which systems are interface‐ (no salt), additive‐ (moderate salt concentration), or vitrification‐driven (high salt concentration) with an interfacial threshold, providing a mechanistic framework for linking formulation, curing behavior, and multifunctional performance in PEGDA‐based composite electrolytes.