A mechanical reinforced and antifreezing polyacrylate hydrogel electrolyte for high-performance zinc-ion batteries

The operation of aqueous zinc-ion batteries in flexible energy storage field is plagued by the uncontrollable growth of Zn-dendrite and inevitable freeze of water below 0 °C. Therefore, it is necessary to design a hydrogel electrolyte with good mechanical property and freezing resistance to uniform the Zn-deposition and resist flexibility loss at low temperature. We find that the mechanical property (strength and toughness) of hydrogel electrolyte has a significant impact on the suppression of dendrite growth and the uniform deposition of zinc ions. Herein, a polyacrylate hydrogel is prepared in one step by ultraviolet (UV) curing method with Zn(CF3SO3)2 salt and polyvinyl alcohol (PVA) addition to increase the antifreezing ability and mechanical properties. The adsorption of water molecules by 2-hydroxyethyl acrylate (HEA) and PVA reduces the freezing point of the hydrogel, which is beneficial for enhancing the electrochemical stability at low temperature. On this basis, the Zn-symmetrical battery with hydrogel electrolyte has a long lifespan of 4710 h at 0.5 mA·cm−2 and 0.5 mAh·cm−2 at room temperature. Furthermore, the hydrogel electrolyte exhibits an outstanding stability at low temperature of −20 °C, the lifespan of symmetrical battery reaches to 4000 h at 0.5 mA·cm−2 and 0.5 mAh·cm−2. The assembled full cell with NaV3O8·1.5H2O (NVO) cathode and hydrogel electrolyte possesses a high capacity retention ratio of 77% after 10,000 cycles at −20 °C. The flexible cell can power light-emitting diode (LED) lamp under bending, warping and cutting without liquid leakage and an electronic watch at the operating temperature of −20 °C.