Lithium-ion-mediated covalent-ionic protein hydrogel electrolyte enabling adaptive flexible supercapacitors

The rapid development of human-interactive wearable devices has created urgent demands for energy storage materials that simultaneously achieve reliable electrochemical performance, skin conformability, and operational safety. However, conventional hydrogel electrolytes face persistent challenges in balancing mechanical robustness with ionic transport efficiency. In this study, a covalent-ionic hybrid protein network electrolyte was developed by exploiting the covalent cross-linking provided by the thiol-ene click reaction, and lithium-ion (Li⁺) -mediated ionic coordination. The synergistic covalent crosslinking and dynamic ionic interactions simultaneously enhance mechanical stability and ion-transport capability, thereby establishing continuous ion-migration pathways throughout the three-dimensional network. The Li⁺-protein based electrolyte (1.5 M Li⁺) delivers a specific capacitance of ∼194 mF/cm², substantially higher than that of the Li⁺-free counterpart (∼115 mF cm^-2), demonstrating the critical role of Li⁺ regulation in enhancing electrochemical performance. The assembled flexible supercapacitor exhibits excellent electrochemical reversibility, maintaining nearly unchanged cyclic voltammetry (CV) profiles and galvanostatic charge discharge (GCD) curves during continuous operation. Moreover, the device preserves stable electrochemical characteristics under bending deformations of 45° and 90°, achieving a specific capacitance of ∼265 mF cm^-2 even under 90° bending. The favorable biosafety and skin-compatible characteristics of the protein-based electrolyte further highlight its potential for wearable and human-interactive energy storage systems.