Integrated Janus gel with bilayered heterostructure for high-performance supercapacitors

A persistent challenge for electrolytes is achieving simultaneous compatibility with both electrodes under high-voltage conditions, which has restricted the power output of energy storage devices. Herein, we developed an integrated Janus gel electrolyte with a bilayer heterostructure to extend the potential limits on both the cathode and anode. This electrolyte consisted of a deep eutectic solvent (DES) gel phase and an ionic liquid (IL) gel phase. The DES gel layer functioned as the anolyte, benefiting from its reduction tolerance through internal H-bond interactions, while the IL gel phase served as the catholyte, taking advantage of the high oxidation resistance of TFSI - . Moreover, the miscibility between DES and IL enabled full integration of the intermediate layer, effectively reducing interfacial transmission impedance and promoting ions migration. The fabricated Janus gel demonstrated a wide electrochemical window (4.70 V), satisfactory ionic conductivity (3.57 mS/cm), and excellent temperature tolerance. A supercapacitor incorporating this Janus gel electrolyte delivered an energy density of 89.4 Wh/kg at the power density of 646.2 W/kg under the voltage window of 3.6 V (−1.8∼1.8 V), along with robust cycling stability over 10,000 charge–discharge cycles. An energy density of 31.4 Wh/kg at a power density of 386.5 W/kg could be maintained in the voltage range of 0∼1.8 V. This research provides novel insights into the design of engineered electrolytes that are high compatible with both the cathode and anode in high-voltage applications.