Zwitterionic polymer coupled with high concentrated electrolytes to achieve high ionic conductivity and wide electrochemical window for supreme specific energy aqueous supercapacitors

In this study, we demonstrate how to prepare the hydrogel electrolytes with high ionic conductivity and wide electrochemical window (EW) through zwitterionic polymer (ZP) with high concentrated electrolytes (ZPEs). The ZP is prepared by UV-polymerization of equimolar [2-(acryloyloxy)ethyl]trimethylammonium chloride, 2-acrylamido-2-methyl-1-propanesulfonic acid sodium with poly(ethylene glycol) diacrylate. ZPES are simply prepared by 1 m, 5 m, 10 m, 15 m, and 17 m NaClO_4(aq) intake, being denoted as ZPE-S1, ZPE-S5, ZPE-S10, ZPE-S15, and ZPE-S17, respectively. Among them, ZPE-S17 shows 1.12 times EW of 17 m NaClO_4(aq). However, the ionic conductivities of NaClO_4(aq) decrease with the increasing concentration from 5 m to 17 m. Interestingly, ionic conductivity of ZPEs gradually increase with increasing concentration until 15 m. ZPE-S17 still keep the high ionic conductivity of 106.1 mS cm⁻¹ which is about 2.73 times higher than 17 m NaClO_4(aq). Furthermore, the electrochemical performances of electrolytes are studied using carbon-based symmetric supercapacitors (CSSs) which are assembled with 1m NaClO_4(aq) (CSS-aq1), 17 m NaClO_4(aq) (CSS-aq17), ZPE-S1 (CSS-ZPE1), ZPE-S15 (CSS-ZPE15) and ZPE-S17 (CSS-ZPE17). CSS-ZPE17 exhibits the wide EW of 2.4 V and the superior electrochemical performance by delivering a supreme specific energy of 133.5 Wh kg⁻¹ at a specific power of 2313.5 W kg⁻¹, demonstrating the great potential for aqueous energy storage devices.