Zwitterion-dissociated polyoxometalate electrolytes for solid-state supercapacitors

Releasing cations from highly negatively charged polyoxometalates (POMs) is never an easy task. Herein, by using a zwitterion (1-sulfopropyl-3-methylimidazolium salt, MIMPS) to dissociate POMs, the proton conductivity of POM electrolytes was enhanced and the capacitive performance of solid-state supercapacitors (SCs) based on polyaniline was further improved. MIMPS can promote the dissolution and dissociation of POMs in polymer solutions, releasing more mobile protons, which is conducive to rapid proton transport. The MIMPS-modified SCs have higher capacitive performance, with an areal capacitance of 13 F·cm−2 at a current density of 0.5 mA·cm−2, compared to SCs without MIMPS (6.4 F·cm−2). In addition, the MIMPS-modified SCs have lower interfacial impedance, indicating that MIMPS can improve the proton conductivity and interfacial conduction. This work provides a new strategy for improving the overall performance of SCs by optimizing POM-based electrolytes with a zwitterion.