Bidirectional pH Buffer Effect Facilitates High‐Reversible Aqueous Zinc Ion Batteries

Abstract Aqueous zinc ion batteries (AZIBs) stand out from the crowd of energy storage equipment for their superior energy density, enhanced safety features, and affordability. However, the notorious side reaction in the zinc anode and the dissolution of the cathode materials led to poor cycling stability has hindered their further development. Herein, ammonium salicylate (AS) is a bidirectional electrolyte additive to promote prolonged stable cycles in AZIBs. NH₄⁺ and C₆H₄OHCOO⁻ collaboratively stabilize the pH at the interface of the electrolyte/electrode and guide the homogeneous deposition of Zn²⁺ at the zinc anode. The higher adsorption energy of NH₄⁺ compared to H₂O on the Zn (002) crystal plane mitigates the side reactions on the anode surface. Moreover, NH₄⁺ is similarly adsorbed on the cathode surface, maintaining the stability of the electrode. C₆H₄OHCOO⁻ and Zn²⁺ are co‐intercalation/deintercalation during the cycling process, contributing to the higher electrochemical performance of the full cell. As a result, with the presence of AS additive, the Zn//Zn symmetric cells achieved 700 h of highly reversible cycling at 5 mA cm⁻². In addition, the assembled NH₄V₄O₁₀(NVO)//Zn coin and pouch batteries achieved higher capacity and higher cycle lifetime, demonstrating the practicality of the AS electrolyte additive.