Extending Operation Temperature of Hydrogel for Zn Ion Batteries

Aqueous zinc ion batteries (ZIBs) provide one of the most promising technologies for large-scale electrochemical energy storage because they are environmentally friendly, safe, and have a low-cost. However, there are still some major challenges for the commercialization for ZIBs, such as Zn dendrite on Zn anode surface and poor low-temperature operation. The major problem related to the operation at low temperatures is that the water freezes below 0 C as a result of the bonding between the water molecules, especially the H-bond in the aqueous electrolyte. Modifying the solvation structure by using additives and concentrated electrolytes is among the most efficient ways to widen the operation temperature range of the aqueous electrolyte. In this presentation, we developed a hydrogel made from a commercial material, para-aramid fiber, combined with polyvinyl alcohol showing excellent anti-freezing performance even at -40 C. Due to the abundant and uniformly distributed hydrophilic oxhydryl on the polymer chain, the hydrogel is able to facilitate ion absorption and dissociation to promote the ion transport. The competition between water molecules and hydrophilic oxhydryl can improve the anti-freezing performance of the hydrogel. Our hydrogel demonstrates superior mechanical properties and high ionic conductivity down to -40 C, which opens the horizons for operating these batteries in large-scale energy storage at high latitudes. In addition, the developed hydrogel shows good protection to the Zn anode by preventing Zn dendrite growth and prolonged the lifetime of the Zn symmetric cell at both room and below-room temperatures.