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 ℃.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(CF_(3)SO_(3))_(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^(-2)0 ℃,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 NaV3O8·1.5H_(2)O(NVO)cathode and hydrogel electrolyte possesses a high capacity retention ratio of 77%after 10,000 cycles at^(-2)0 ℃.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^(-2)0 ℃.