Multifunctional Structural Electrolyte with Glass Fiber‐Reinforced Polyvinyl Alcohol/Epoxy Matrix with Optimized Lithium Salt and Nanofiller

A novel multifunctional structural electrolyte is developed using plain–weave glass fiber reinforced with a composite polymer matrix for load‐bearing energy‐storage applications such as structural batteries. The composite matrix comprises polyvinyl alcohol (PVA) blended with epoxy, LiTFSI salt, and Al 2 O 3 at optimized ratios. A set of techniques is used to evaluate and optimize the thermo‐electro‐mechanical properties of the matrix, including dynamic mechanical analysis (DMA), potentiostatic electrochemical impedance spectroscopy (PEIS), thermogravimetric analysis, differential scanning calorimetry, and X‐ray diffraction. The optimization reveals a clear trade‐off: increasing salt content enhances ionic conductivity but compromises mechanical properties, while the addition of nanofiller improves stiffness but reduces ionic conductivity. Based on multifunctionally balancing, a formulation of PVA 0.34 /epoxy 0.14 /LiTFSI 0.32 /(Al 2 O 3 ) 0.2 is obtained. The structural electrolyte, composed of glass fiber impregnated with the optimized matrix, is characterized using PEIS, DMA, tensile testing, and charge–discharge tests within lithium iron phosphate (LFP)/lithium metal and LFP/graphite cells. The electrolyte exhibits a storage modulus of 3 GPa, an ionic conductivity of 1.74 × 10 −4 S cm −1 , a bulk stiffness of 1.82 GPa, and a tensile strength of 56.9 MPa. Full‐cell testing demonstrates long cycle life and stable cyclability for ≈240 cycles, maintaining a high Coulombic efficiency of around 95% throughout cycling.