“Gel-in-Resin” Multifunctional Electrolytes for Enhanced Electrochemical and Mechanical Performance in Lithium-Ion Structural Battery Composites

Structural battery composites (SBCs) integrate mechanical load-bearing capability with energy storage functions, offering potential for significant weight reduction. However, the commercial application of SBCs remains hindered by the trade-off between electrochemical performance and mechanical properties. This study presents a novel dual-phase Gel-in-Resin (GIR) electrolyte, comprising a PVDF-HFP-based gel embedded within a porous epoxy resin framework. The epoxy skeleton effectively bonds carbon and glass fabrics while providing adequate space for the gel electrolyte. Electrostatic interactions between succinonitrile groups and Li⁺ ions stabilize the electrochemical window (5.21 V) and enhance the Li-ion transference number (t_Li⁺ = 0.59), promoting the formation of a robust LiF/Li₃N hybrid solid electrolyte interphase. The coupling of the epoxy resin and gel electrolyte improves mechanical properties, increasing the tensile modulus by 22%. Finite element modeling reveals that structural barriers and ion pathways within the epoxy framework restrict Li⁺ transverse migration and inhibit dendrite formation. As a result, lithium iron phosphate (LFP) || graphite SBCs with GIR electrolyte exhibit excellent electrochemical performance (120.43 mAh g⁻¹ at 0.2 C) and exceptional cycling stability (81.44% retention after 180 cycles). This work provides a promising pathway for the development of high-performance SBCs for practical applications.