Construction of Protective Films on Zn Metal Anodes Natural Protein Additives Enabling High-Performance Zinc Ion Batteries.

The strong activity of water molecules causes a series of parasitic side reactions on Zn anodes in the aqueous electrolytes. Herein, we introduce silk fibroin (SF) as a multifunctional electrolyte additive for aqueous zinc-ion (Zn-ion) batteries. The secondary structure transformation of SF molecules from α-helices to random coils in the aqueous electrolytes allows them to break the hydrogen bond network among free water molecules and participate in Zn ion solvation structure. The SF molecules released from the [Zn(HO)(SF)] solvation sheath appear to be gradually adsorbed on the surface of Zn anodes and form a hydrostable and self-healable protective film. This SF-based protective film not only shows strong Zn ion affinity to promote homogeneous Zn deposition but also has good insulating behavior to suppress parasitic reactions. Benefiting from these multifunctional advantages, the cycle life of the Zn||Zn symmetric cells reaches over 1600 h in SF-containing ZnSO electrolytes. In addition, by adopting a potassium vanadate cathode, the full cell shows excellent cycling stability for 1000 cycles at 3 A g. The construction of a protective film on the Zn anode from natural protein molecules provides an effective strategy to achieve high-performance Zn metal anodes for Zn-ion batteries.