Borax-crosslinked hydrogel electrolyte membranes for quasi-solid state aqueous energy storage devices

Abstract

A novel borax-crosslinked hydrogel electrolyte membrane is synthesized using radical polymerization to achieve superior electrochemical performances and outstanding mechanical properties. The as-synthesized electrolyte membrane displays high ionic conductivity (1.72 × 10−2 S cm−1), wide electrochemical stable window (∼2.21 V), large fracture stress (42.17 kPa) and fracture strain (205.10%). The membrane enables highly uniform Zn plating/stripping with lower overpotential and longer lifespan from the symmetric Zn cells compared with that using the liquid electrolyte. To demonstrate the applicability of the electrolyte membrane, they are used in quasi-solid state Zn metal batteries (Zn||MnO2) and Zn-ion hybrid supercapacitors (Zn||AC), respectively. The resultant Zn||MnO2 cell delivers a high discharge specific capacity retention of 95% after 1000 cycles at 0.5 A g−1, and the Zn||AC supercapacitor exhibits satisfactory specific capacitance of 290 F g−1 at 1.0 A g−1 and good rate performance. Furthermore, the flexible Zn||MnO2 and Zn||AC devices are also assembled, which can still work even at the bent and compressed states. This work provides a promising route to design the hydrogel electrolytes for the quasi-solid state aqueous energy storage devices.