Recent Advances in Hydrogel Electrolytes for Flexible Zinc Ion Batteries and Capacitors

Rechargeable zinc ion batteries and capacitors with hydrogel electrolytes as the core component have received widespread recognition, benefiting from their prominent safety, low manufacturing cost, abundant raw material stockpiles, and excellent environmental compatibility. However, during the charge and discharge cycle of the zinc anode of this type of device, which is prone to side reactions of zinc dendrites, corrosion, and hydrogen evolution, and the coupling between the three is intensified, seriously restricting the cyclic stability and charge-discharge efficiency of the device. This paper systematically summarizes the classifications, key properties, and recent advances of representative hydrogel electrolytes, including dynamically tunable self-healing hydrogels, extreme-environment-tolerant hydrogels, and multidimensional conductive network hydrogels. The mechanism of action (zinc deposition regulation, interface kinetic optimization, and water molecule activity inhibition) is then focused on improving the inherent defects of the zinc anode. At the same time, the major breakthroughs in zinc ion energy storage devices in the field of structural engineering in recent years have been sorted out, providing new ideas for promoting the development of flexible energy storage devices based on hydrogel electrolytes.