Bone-Inspired Sustainable Hydrogel Electrolytes for Zn Metal Batteries

Hydrogels are promising electrolytes for use in aqueous Zn metal batteries (AZMBs). However, the problems associated with the Zn anodes cannot be eliminated using current hydrogel electrolytes, and their poor sustainability has also been neglected. We have developed a bone-inspired hydrogel electrolyte (Zn-HA-Gel) composed of Zn-doped hydroxyapatite (Zn-HA) nanofibers and a gelatin matrix derived from animal bones. The bone-like structure and strong molecular interactions in the biodegradable, recyclable, and biocompatible components endow Zn-HA-Gel with excellent sustainability, water retention, and mechanical properties, which solves the problems currently associated with Zn anodes. Moreover, the Zn-HA superionic conductor exhibits an ultrahigh intrinsic ionic conductivity and accelerated Zn2+ desolvation process. The dual-channels for Zn2+ transport in Zn-HA-Gel result in high ionic conductivity (32.5 mS cm-1) and transference number (0.80), facilitating uniform Zn plating/stripping and durable working stability. As a result, Zn-HA-Gel ensures ultra-stable cycling performance with a cumulative capacity of 5 Ah cm-2 at 5 mA cm-2/5 mAh cm-2 for Zn/Zn cells, and a superior cycling performance with a capacity retention of 82.4% after 2000 cycles for full cells, surpassing the capabilities of current hydrogel electrolytes, and has potential applications in sustainable and functional energy-storage devices.