Excellent film-forming, ion-conductive, zwitterionic graft copolymer electrolytes for solid-state supercapacitors

Polymer electrolytes with robust mechanical properties and high ionic conductivity are highly desirable for solidstate energy storage devices. Therefore, in this study, a polymer electrolyte based on a zwitterionic graft copolymer, poly(vinyl alcohol)-graft-poly(sulfobetaine methacrylate) (PVA-g-PSBMA), is developed. Herein, we designed a graft copolymer that utilizes the excellent film-forming nature of PVA main chains and ion-conductive properties of polyzwitterionic PSBMA side chains. The PVA-g-PSBMA electrolytes exhibited microphase separated structures, wherein H3PO4 interacted more strongly with the PSBMA domains. Therefore, the transport of proton ions was facilitated through the well-defined PSBMA-based ion channels, leading to a significant increase in the ionic conductivity. The polymer electrolyte was applied to the electric double-layer capacitor (EDLC) with activated carbonbased electrode. In comparison with the neat conventional PVA-based cell, the solid EDLC with PVA-g-PSBMA zwitterionic graft copolymer electrolytes showed improved specific capacitance (46.6 F g-1), energy density (3.67 Wh kg- 1), and power density (186 W kg-1). The improved performance can be attributed to the higher ionic conductivity and better interfacial compatibility of electrode/electrolyte for the PVA-g-PSBMA electrolytes.

Automated summary

A polymer electrolyte based on a zwitterionic graft copolymer was developed in this study, utilizing the excellent properties of PVA main chains and PSBMA side chains to improve ion conductivity. When applied to EDLC, the new electrolyte showed significantly improved performance, attributed to higher ion conductivity and better electrode/electrolyte interface compatibility.