A flexible zinc-ion battery based on the optimized concentrated hydrogel electrolyte for enhanced performance at subzero temperature

The emerging aqueous zinc-ion rechargeable batteries have attracted much attention, owing to their intrinsic safety and low cost. However, it is not practical to use zinc-ion batteries in frigid environments due to their liquid water-based electrolytes. To alleviate this issue, we have developed a flexible zinc-ion battery consisting of an optimized concentrated hydrogel electrolyte sandwiched between an ultrathin zinc anode and a NH4V3O8•1•9H2O cathode for enhanced performance at subzero temperature. The hydrogel electrolytes, synthesized by simply mixing xanthan gum and aqueous ZnCl2 solution, are examined via various characterizations, such as thermogravimetric analysis, tensile tests, adhesion tests, and impedance measurements, for understanding their fundamental properties. The contents of the xanthan gum and the zinc salt can be facilely tuned and optimized for maximized battery performance. It is found that when a concentrated hydrogel electrolyte is prepared using 1.2 g xanthan gum mixed in 4 m ZnCl2 solution, the resulted flexible battery delivers the best performance, exhibiting a very high capacity of 201 mAh g − 1 and 83 mAh g − 1 under 0.2 A g − 1 at -20 °C and -40 °C, respectively. The battery also exhibits remarkable cyclability over 1500 cycles at -20 °C. Additionally, the battery shows capacity retention of 92% capacity over 100 cycles while being bent by 90° then 180° at -20 °C. As such, this battery demonstrates excellent electrochemical performance and mechanical durability/flexibility as well as anti-freezing property, showing high potential to be used to power wearable electronics in cold environments or where safety is most crucial.