Abstract
The pursuit of structural supercapacitors (SSCs) lies at the forefront of next-generation energy storage, demanding electrolytes that combine high ionic conductivity with mechanical strength. Reconciling these properties has remained a formidable challenge. This thesis advances the field by developing a single-phase Polyethylene Terephthalate (PET) and Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solid polymer electrolyte (PET/LiTFSI), fabricated through humidity-controlled injection molding and melt casting, and subsequently tuned through controlled uptake of water and organic solvents including Dimethylformamide (DMF), Acetonitrile (ACN), and Dimethyl sulfoxide (DMSO) using a custom-designed vapor-enclosure system not reported elsewhere in the literature. By suppressing hydrolysis through low-humidity processing (< 6 % RH), high salt incorporation was achieved without catastrophic loss of stiffness. The optimized 80/20 PET/LiTFSI formulation attained a flexural modulus of 3.93 – 4.0 GPa while maintaining a baseline ionic conductivity of 1.71–1.90 nS cm⁻¹ a rare convergence of structural and electrochemical performance. Post-fabrication conditioning revealed striking opportunities for performance tailoring: water uptake of only 1–3 wt. % elevated conductivity from the baseline to 9.8, 44.1, and 62.5 µS cm⁻¹, respectively, while reducing stiffness from ~2.1 to ~1.6 GPa. Organic solvent exposure within the customized enclosure enabled more nuanced modulation ACN at ~4 wt. % raised conductivity to 136.8 nS cm⁻¹, DMF at ~4 wt. % achieved 99.3 nS cm⁻¹ while retaining high stiffness (~3.3 GPa at 2 wt. % uptake), and DMSO at ~4 wt. % produced only a marginal increase (~2–3 nS cm⁻¹), underscoring the complex interplay between solvation and transport. These findings outline a framework for engineering ionic transport through solvent parameters while safeguarding structural performance. Beyond demonstrating a practical processing window for PET/LiTFSI, this work introduces a novel vapor-enclosure methodology absent from prior literature, positioning controlled solvent-mediated conditioning as a transformative pathway toward SSCs that simultaneously bear load and store energy a milestone in realizing multifunctional structural power systems.