Additive-free poly(vinyl alcohol)-lignin electrolyte with a highly polarizable elastomeric matrix mimics...

The performance of solid polymer electrolytes mainly depends on the nature and characteristics of the host polymer matrix. This study establishes poly(vinyl alcohol)-alkali lignin (PVA-lignin) as an environmentally conscious high-performance matrix for solid polymer electrolytes through the systematic integration of 5-45wt% lithium perchlorate (LiClO₄). In contrast to the widely used additive-based designs, we present a matrix-first, bio-based, and additive-free design to achieve liquid-like ionic conductivity (1.699 × 10^-3 S/cm) exclusively through rational host optimization, without the need for plasticizers, fillers, or multi-component systems. Progressive salt uptake drives the transition from conventional "salt-in-polymer" behaviour to a "polymer-in-salt-like" architecture. The membrane containing 45wt%LiClO₄ exhibits a room-temperature ionic conductivity of 1.699×10^-3S/cm, which is superior to the reported values for plasticizer- and filler-free PVA-based electrolytes. FTIR deconvolution demonstrated a free-ion fraction of 77.82%, while dielectric and electric-modulus analyses established complete separation (decoupling) of Li⁺ transport from the polymer segmental movements. X-ray diffraction deconvolution analysis showed that salt complexation reduced the crystallinity from 15.85% to 2.07%, which was enabled by the aromatic moieties of lignin and its hetero-functional groups. FESEM analysis shows how the surface transforms from porosity at zero salt weight to a smooth film at 45% salt content, and EDX mapping proves that the chlorine (Cl) distribution remains even throughout with uninterrupted ion pathways. The mechanical testing results showed that Li⁺ coordination functions as dynamic cross-links that transform the rigid host structure into an ionic elastomer with a Young's modulus of 2.02±0.14MPa and elongation-at-break of 181±10.8% while ensuring peelability and dimensional stability. This electrolyte demonstrated a transference number of almost one (0.998) while maintaining a 3.22V electrochemical stability window and achieved a capacitance of 74.9F/g at 0.5A/g in symmetric EDLCs with ∼80% retention after 1700 cycles. This study proves that PVA-lignin serves as an optimal green platform for future solid-state energy storage systems by achieving liquid-like conductivity, durable elasticity, and consistent electrochemical performance using only a bio-derived polymer matrix and salt.