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

Abstract

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 Al2O3 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)/LiTFSI0.32/(Al2O3)(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 x 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 approximate to 240 cycles, maintaining a high Coulombic efficiency of around 95% throughout cycling.