Rechargeable Zn^2+/Al³⁺ dual-ion electrochromic device with long life time utilizing dimethyl sulfoxide...

Despite recent advances in hydrogel electrolytes for flexible electrochemical energy storage, ion conductors still exhibit some major shortcomings including low ionic conductivity and short lifetimes. As such, for applications in electrochromic batteries, a transparent, highly conductive electrolyte based on a dimethyl-sulfoxide (DMSO) modified polyacrylamide (PAM) hydrogel is being developed and implemented in a dual-ion Zn²⁺/Al³⁺ electrochromic device consisting of a Zn anode and WO₃ cathode. Gelation in a DMSO : H₂O mixed solvent leads to highly increased electrolyte retention in the hydrogel and prolonged life time for ionic conduction. The hydrogel-based electrochromic device offers a specific charge capacity of 16.9 μAh cm^-2 at a high current density of 200 μA cm^-2 while retaining 100% coulombic efficiency over 200 charge-discharge cycles. While the DMSO-modified electrolyte shows ionic conductivities up to 27 mS cm^-1 at room temperature, 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 4 weeks. Furthermore, the electrochromic WO₃ cathode gives the device a controllable absorption with up to 80% change in transparency. Based on low-cost, earth abundant materials like W (tungsten), Zn (zinc) and Al (aluminum) and a scalable fabrication process, the introduced hydrogel-based electrochromic device shows great potential for next-generation flexible and wearable energy storage systems.