Accelerated proton transport modulates dynamic hydrogen bonding networks in eutectic gel electrolytes for low-temperature aqueous Zn-metal batteries

Abstract

Aqueous Zn-metal batteries (AZMBs) performance is hampered by freezing water at low temperatures, which hampers their multi-scenario application. Hydrogen bonds (HBs) play a pivotal role in water freezing, and proton transport is indispensable for the establishment of HBs. Here, the accelerated proton transport modulates the dynamic hydrogen bonding network of a Zn (BF₄)₂/EMIMBF₄ impregnated polyacrylamide/poly (vinyl alcohol)/xanthan gum dual network eutectic gel electrolyte (PPX-ILZSE) for low-temperature AZMBs. The PPX-ILZSE forms more HBs, shorter HBs lifetimes, higher tetrahedral entropy, and faster desolvation processes, as demonstrated by experimental and theoretical calculations. This enhanced dynamic proton transport promotes rapid cycling of HBs formation-failure, and for polyaniline cathode (PANI) abundant redox sites of proton, confers excellent low temperature electrochemical performance to the Zn//PANI full cell. Specific capacities for 1000 and 5000 cycles at 1 and 5 A g⁻¹ were 149.8 and 128.4 mA h g⁻¹ at room temperature, respectively. Furthermore, specific capacities of 131.1 mA h g⁻¹ (92.4% capacity retention) and 0.0066% capacity decay per lap were achieved for 3000 and 3500 laps at −30 and 40 °C, respectively, at 0.5 A g⁻¹. Furthermore, in-situ protective layer of ZnOHF nano-arrays on the Zn anode surface to eliminate dendrite growth and accelerate Zn-ions adsorption and charge transfer.