Cation-driven hydrogen bond dynamics in energy storage hydrogel electrolytes: unraveling ion-water-carbon interactions†

Hydrogel electrolytes, recognized for their flexibility and superior ionic conductivity, present a viable substitute for liquid electrolytes in energy storage systems. Although Li⁺ and Na⁺ ions have been thoroughly investigated, the intercalation of Cs⁺ ions remains unexamined, despite the significant water solubility of cesium salts. This study designates CsBr as the most effective electrolyte additive owing to its exceptional ionic conductivity (Cs⁺ > K⁺ > Na⁺ > Li⁺ and Br⁻ > Cl⁻ > CH₃COO⁻). A novel hydrogel electrolyte, comprising CsBr, polyacrylamide (PAM), and hyaluronic acid (HA), is developed to tackle the issues of water dehydration. This electrolyte demonstrates high ionic conductivity (10⁴ mS cm⁻¹) and outstanding electrochemical performance in supercapacitors, featuring a specific capacitance of 100 F g⁻¹, approximately 100% coulombic efficiency, and stability over 10 000 cycles. DFT calculations indicate that Cs⁺ generates significant electrostatic interactions, improving charge retention and device efficacy. The results underscore the CsBr@PAM/HA hydrogel as a revolutionary electrolyte for enhanced energy storage, integrating elevated energy and power densities with superior cycling stability.