Sustainable and high-performance Zn dual-ion batteries with a hydrogel-based water-in-salt electrolyte

Pollution of the discarded batteries to the environment has become a challenge that needs to be solved urgently. The innovation of energy storage devices with degradable materials are essential to this mission. Here, an environmentally friendly PVA-gelatin hydrogel-based water-in-salt electrolytes (HiSE) was developed for the high-performance Zn dual-ion battery (ZDIB) with transient degradation advantage. Specifically, PVA and gelatin collectively constrain the water coordinated with ZnCl2 inside the polymer network, which enhances battery reaction dynamics due to the reduced radius of Zn hydrate ion. Several advantages are combined into a single platform in this battery, including not only fast degradation in water, high ionic conductivity, dendrite suppression and high operating voltage, but also easy replication and expansion. The HiSE-based ZDIB exhibits operating voltage of 2.0 V, excellent rate performance and good stability with a capacity retention of 96.2% after 8000 cycles. Our work paves a way towards sustainable and high-performance energy storage systems.