Altering the Zn2+ Migration Mechanism Enables the Composite Hydrogel Electrolytes with High Zn2+ Conduction and Superior Anti-Dehydration

Abstract

Hydrogel electrolytes are favored for flexible zinc-ion batteries (FZIBs) due to their biocompatibility. Their application progress, however, is severely restricted by the poor water retention and low Zn2+ transference number (tZn2+). Herein, one composite polymer electrolyte (CPE) is prepared by introducing Prussian blues (PBs) as multifunctional fillers in polyvinyl alcohol (PVA) matrix to enhance tZn2+. Experimental and theoretical characterizations confirm that the PB filler can alter the Zn2+ migration mechanism and trap water of CPE. PBs as active fillers can provide extra zinc ions and unique 3D ion diffusion channels. Moreover, the metal centers in PB framework that function as the Lewis acid sites have good affinity with anions in Zn salt, facilitating the dissociation of Zn salt. Additionally, the PB framework can absorb coordination water, enhancing the anti-dehydration capability and the ionic conductivity of the hydrogel electrolytes. Consequently, P-15/Zn-15 hydrogel electrolyte shows high ionic conductivity of 16.3 mS cm⁻1 and tZn2+ of 0.63. The Zn||Zn symmetric cells with P-15/Zn-15 hydrogel electrolyte can stably operate for 1 600 h at 50 °C. The Zn||P-15/Zn-15|| NaV3O8·1.5H2O full cell exhibits excellent cycling performance of 1 600 cycles.