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

Abstract

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 Cu2+ and Mn2+ 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. Cu2+-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 Mn2+-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.