Ionically Tunable Gel Electrolytes Based on Gelatin-Alginate Biopolymers for High-Performance Supercapacitors.

The development of sustainable, high-performance gel polymer electrolytes (GPEs) is crucial for next-generation energy storage; however, existing materials often exhibit limited mechanical stability, suboptimal ionic transport, or environmental drawbacks. Here, for the first time gelatin-alginate organohydrogels  crosslinked with Cu(2+) and Mn(2+) are used as GPEs for supercapacitors, in combination with Li(+) incorporation to enhance ionic conductivity and transport. Small-Angle X-ray Scattering (SAXS) reveals that the choice of the crosslinking cation governs the nanoscale organization of the polymer network-reflected in distinct correlation lengths-which in turn critically influences ionic transport, mechanical stability, and electrochemical performance. Cu(2+)-crosslinked gels achieve the highest areal capacitance (591.8 mF cm(-2)), energy density (82.2 µWh cm(-2)), and power density (1957.8 µW cm(-2)), whereas Mn(2+)-crosslinked gels exhibit superior cycling stability (88.3% retention over 5000 cycles). Li(+) incorporation increases the mechanical flexibility of Mn-based gels-reducing the compressive modulus by over 60%-enhancing ion mobility and charge storage. Conversely, Cu-based gels maintain structural integrity while exhibiting improved conductivity. These findings demonstrate how biopolymer-based GPEs, designed through nanoscale engineering and ion doping, achieve an optimal balance of mechanical robustness and electrochemical performance. By combining scalability and exceptional energy storage capabilities, these materials establish a new paradigm for flexible supercapacitors and sustainable energy technologies.