Polyzwitterionic double-network ionogel electrolytes for supercapacitors with cryogenic-effective stability

Although hydrogel electrolytes have been widely used in the field of energy storage devices, additional conductive fillers with mismatched structural characteristics will inevitably reduce their both mechanical and electrochemical properties. How to achieve high ionic conductivity together with good mechanical strength is still a challenge. Herein, a high strength double-network polyzwitterionic electrolyte is designed by introducing water-soluble ionic liquids (EMIM-BF4) into a zwitterionic hydrogel through the superfast solvent exchange. The resulting polyzwitterionic electrolytes are superior to traditional polyzwitterionic hydrogels or polyvinyl alcohol (PVA) hydrogels with respect to their better tensile strength (1.9 MPa), higher ionic conductivity (7.24 mS/cm), and wider temperature adaptability (−60 to 50 °C). More importantly, the optimized symmetric assembled supercapacitor delivers high areal capacitance of 227.7 mF/cm2 at 0.5 mA/cm2, excellent rate capability, and high energy/power densities, greatly surpassing the performances of the system without polyzwitterions. It could be anticipated that the performance of this novel polyzwitterionic electrolyte-based supercapacitors will be further greatly improved with better structural electrodes. Moreover, we also implanted designed energy-storage systems to the subcutaneous tissue of the experimental rats and exhibited potential “on–off” variation of fault indicator LED. This work provides an effective method for the development of robust supercapacitors suitable for harsh environments, showing a great potential for real wearable and implanted applications in some extreme circumstances.