A structural supercapacitor (SSC) is a composite material that bears mechanical loads and stores energy, and its encapsulation method of the device is vital for scale-up. Here we present an SSC with an encapsulation interface consisting of spread-tow fabric electrodes and glass fabric encapsulators infused with epoxy resin. Through surface functionalisation of fibres, a high surface area electrode of 231.43 𝑚2/𝑔 was separated by a gel polymer electrolyte (GPE) separator and encapsulated in an epoxy polymer. To study the SSC’s performance, different GPEs are produced by adding lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). The LiTFSI concentration is varied from 0% to 100% based on the weight of PVDF-HFP. The highest energy storage performance occurred at LiTFSI 60 wt% in the PVDF-HFP, with a cell-specific capacitance of 25.72 mF/g, cell-specific energy of 2.08 mWh/kg and cell-specific power of 25.04 mW/kg. With a flexural modulus of 3.39 GPa and a flexural strength of 52.07 MPa, this further develops high-performance SSCs in the future.