Development of flexible Zn/MnO₂ secondary batteries using a fumed silica-doped hydrogel electrolyte

Hydrogel electrolytes have received tremendous research interest in designing flexible zinc-ion secondary batteries, making them highly promising for flexible energy storage and wearable electronic devices. Herein, we report a composite hydrogel electrolyte (CHE) prepared using a fumed silica-doped gelatin hydrogel. This electrolyte is specifically designed for use in rechargeable aqueous Zn/MnO₂ batteries (ReAZMBs). Experimental results showed that after fumed silica was added, the porosity and ionic conductivity of the gelatin hydrogel electrolyte increased. Meanwhile, adding fumed silica to the hydrogel electrolyte contributed to reducing self-corrosion and promoting rapid and uniform deposition of zinc ions. When the addition of fumed silica to gelatin was 10 wt%, ReAZMBs with this CHE exhibited a superior rate and cycling performance. More specifically, ReAZMBs with this CHE achieved an initial specific capacity of 150 mA h g^-1 at a current density of 1.5 A g^-1 and a capacity retention rate of 67% after 1000 cycles, which was much higher than that of the battery with the pure gelatin hydrogel electrolyte (33%). This was because of the improved interface stability between the zinc anode and electrolyte and the reduced formation of by-products (3Zn(OH)₂·ZnSO₄·3H₂O and 3Zn(OH)₂·ZnSO₄·5H₂O), according to the results of the charge-discharge test of Zn//Zn symmetric batteries and SEM and XRD characterizations of post-run zinc anodes. In addition, the ReAZMBs with the CHE demonstrated good flexibility and could supply power reliably even when bent.