Recent developments in flexible electronics have heightened the need for electrolytes with high safety, ionic conductivity, and electrochemical stability. However, neither conventional organic electrolytes nor aqueous electrolytes can meet the above requirements simultaneously. Herein, a novel "water-in-deep eutectic solvent" gel (WIDG) electrolyte synergistically controlled by the solvation regulation and gelation strategies is reported. The water molecules introduced into deep eutectic solvent (DES) participate in the solvation structure regulation of Li+, thus endowing the WIDG electrolyte with high safety, thermal stability, and outstanding electrochemical performance, including high ionic conductivity (∼1.23 mS cm-1) and a wide electrochemical window (∼5.4 V). Besides, the polymer in the gel interacts with DES and H2O, further optimizing the electrolyte with excellent mechanical strength and higher operating voltage. Benefiting from these advantages, the lithium-ion capacitor constructed by WIDG electrolyte presents a high areal capacitance of 246 mF cm-2 with an energy density of 87.3 μWh cm-2. The use of the gel enhances the electrode structure stability, resulting in desirable cycling stability (>90% capacity retention after 1400 cycles). Moreover, the WIDG-assembled sensor exhibits high sensitivity and rapid real-time detection of motion. This work will provide guidelines for designing high-safety and high-operating-voltage electrolytes for flexible electronics.
Keywords: deep eutectic solvent; gel electrolyte; lithium-ion capacitor; solvation regulation; strain sensor.