Superelastic hydrogel electrolyte incorporating helical protein molecules as zinc ion transport pathways to enhance the cycling stability of zinc metal batteries

Flexible zinc metal batteries are one of the most promising candidates for future energy storage devices, however, their performance is hampered by current hydrogel electrolytes with low ionic conductivity and low mechanical strength. Herein, a superelastic hydrogel electrolyte (alpha-HP/PVA) is developed by incorporating alpha-helical protein (alpha-HP, extracted from wool) molecules in poly(vinyl alcohol) networks. Because of the unique alpha-helical structure and abundant functional groups, the obtained superelastic hydrogel electrolyte exhibits high fracture strength (4.97 MPa) and a high elongation rate (similar to 600%). In alpha-HP/PVA, it is demonstrated that Zn2+ competitively coordinates with the N and O in the alpha-helical protein, which affords a low transport energy barrier and a short transport distance, achieving an ultra-high ionic conductivity of 93.8 mS cm-1. Moreover, alpha-HP/PVA could avoid anodic passivation and corrosion to maintain the anode activity and guide the dendrite-free deposition. Consequently, the Zn|alpha-HP/PVA|Zn symmetric cell achieves a long cycle life of over 5300 h, and the full cell with the alpha-HP/PVA electrolyte and the NaV3O8-1.5H2O cathode exhibits a high-capacity retention of similar to 96% after 800 cycles at 1 A g-1. This study of advancing ion transport with a unique helical structure provides a new way to promote the application of zinc metal batteries. A superelastic, high ionic conductivity and environment-friendly hydrogel electrolyte is developed based on the unique advantages of alpha-helical proteins.