Construction of Hydrogel Electrolytes With Wide Potential Windows Based on Dimethyl Sulfone-Mediated Interface...

Water-based electrolytes with wide electrochemical stable windows (ESW) are crucial for high-energy-density supercapacitors. Herein, an interfacial engineering strategy to broaden the ESW of water-based electrolytes is proposed. It is found that although introducing dimethyl sulfone (MSM) to aqueous electrolytes reduces water activity through hydrogen bonding, at high salt concentrations, MSM enters the ionic solvation layer and weakens its hydrogen bonding, which results in an ESW approximately 0.2 V higher than at low salt concentrations. Further mechanistic studies have revealed that the barrier layer formed by the enrichment of MSM at the electrode/electrolyte interface increases the overpotential of the water splitting reaction. Simultaneously, MSM contributes significantly to the high ESW by binding to and stabilizing the active intermediates generated during the water splitting process. Subsequently, a scalable solvent exchange-ion cross-linking phase separation strategy is developed. The synergistic effects of NaClO₄, MSM, water, and the hydrogel framework enable an ESW of 5.2 V. The supercapacitor assembled with laser-induced graphene (LIG) electrodes exhibits an operating voltage up to 2.4 V, with a capacitance retention rate of 98% after 10 000 charge/discharge cycles. In addition, the device demonstrates excellent adaptability at various folding angles and across a wide temperature range of -40°C to 45°C.