Constructing supercapacitors with biopolymer bearing zwitterion as hydrogel electrolyte and binder for superior performance at −40 °C

This study demonstrates how to construct supercapacitors with biopolymer bearing zwitterion as hydrogel electrolyte and binder for superior performance at the temperature of −40 °C. Carboxylated chitosan (CCS) and carboxymethyl cellulose (CMC) are used as hydrogel electrolyte and binder respectively, as well as, subject to oxa-Mickael addition with sulfobetaine methacrylate (SBMA) to obtain CCS-SBMA and CMC-SBMA. For electrolytes, CCS and CCS-SBMA hydrogel electrolytes are prepared by different concentrations of NaClO4 intake at swelling ratio of 8.5. Among all electrolytes, there exist the highest ionic conductivities 9 mS cm−1 and 25 mS cm−1 in CCS and CCS-SBMA with 10 m and 12 m NaClO4 respectively. Accordingly, CCS-10 and CCS-SBMA-12 are used for Arrhenius plot from 25 °C to −40 °C. Surprisingly, the ionic conductivity in CCS-SBMA-12 at −40 °C (9.48 mS cm−1) is still higher than one in CCS-10 at 25 °C (8.23 mS cm−1). CCS-SBMA-12 is used for supercapacitors with CMC and CMC-SBMA as binders, respectively as SCs-CMC and SCs-CMC-SBMA. SCs-CMC shows poor performance below −0 °C due to the crystallization of CMC, corroborated by Differential scanning calorimetry. In contrast, SCs-CMC-SBMA still possesses 33 F∙g−1 at −40 °C. This study gives some light on the superior performance of supercapacitor with hydrogel electrolyte at −40 °C.