Directionally Cast Multilevel Channels in Hydrogel Electrolyte for Low-Temperature Aqueous Zinc-Ion Batteries

Abstract

Aqueous zinc-ion batteries have attracted widespread attention due to their high safety and energy density. However, their practical application is hindered by insufficient low-temperature performance and rampant side reactions on Zn metal anode. In this work, a freeze-casting method is utilized to acquire the unidirectional and multilevel pore structure in polyvinyl alcohol (PVA)-based hydrogel. Then, strengthen the PVA chain and rearrange its hydrogen bonds via a solution substitution process. The ordered arrangement of molecular chains, formation of multilevel channels, and introduced glycerin enhance the mechanical properties, water-retention and anti-freezing capability of the hydrogel. Hence, the hydrogel electrolyte can effectively suppress side reactions at the anode interface, while enabling stable and fast Zn²⁺ ion transport. Consequently, it realizes a high average Coulombic efficiency of 99.2% of the Zn||Cu cell and a long lifespan of 1200 h of the Zn||Zn cell. When coupled with the NH₄V₄O₁₀ cathode, it delivers the faster electrochemical reactions kinetics and an excellent capacity retention rate of 87.3% after 1130 cycles. Even under an ultralow temperature of −20 °C, the designed hydrogel can still endow fast and stable Zn deposition/stripping cycles. This work provides a feasible design strategy for the development of hydrogel electrolytes for low-temperature aqueous zinc-ion batteries.