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.