Dual-ion electrochromic battery with long lifetime based on dimethyl sulfoxide (DMSO)-nanocluster modified hydrogel electrolytes

For application in flexible, electrochromic batteries, transparent, highly conductive and long lifetime electrolytes are necessary to achieve fast coloration and a maximum contrast. Based on a dimethyl-sulfoxide (DMSO) modified polyacrylamide (PAM) hydrogel, we developed a dual-ion Zn2+/Al3+ electrochromic battery consisting of a Zn anode and WO3 cathode. To overcome shortcomings of conventional hydrogel electrolytes, which experience low solvent retention, we introduce a DMSO:H2O mixed solvent polymerization process, which significantly increases the electrolyte retention of the hydrogel and therefore its lifetime for ionic conduction. The DMSO-modified electrolyte exhibits ionic conductivities up to 27 mS/cm at room temperature, while the formation of DMSO:H2O nanoclusters enables ionic conduction even at temperatures as low as -15°C and retention of ionic conduction over more than 28 days. The electrochromic battery based on the modified hydrogel exhibits a specific charge capacity of 16.9 μAh/cm2 at current densities of 200 μA/cm2 with 100% coulombic efficiency retention over 200 charge-discharge cycles. Based on a double layer architecture, the flexible battery shows a contrast of over 80% trough electrochromic coloration.