Ultralow‐Salt‐Concentration Electrolyte for High‐Voltage Aqueous Zn Metal Batteries

Abstract Aqueous Zn metal batteries are regarded as a promising pathway for large‐scale energy storage systems due to their green, low‐cost, and intrinsically safe characteristics. However, they have long been suffered from narrow voltage windows and severe parasitic reactions (e.g., hydrogen evolution, corrosion, etc.), which hinder their further development. The above challenges are essentially related to the existence of hydrated ions (i.e., Zn(H 2 O) x 2+ and SO 4 2− ·(H 2 O) x ), which are highly reactive species. Herein, a counterintuitive ultralow‐salt‐concentration electrolyte strategy to solve the aforementioned problems by decreasing Zn salt concentration to reduce active hydrated ions is presented, so as to minimize water‐induced side reactions and thus anomalously enlarge the electrolyte splitting voltage window. Additionally, the gap between the charge and discharge medium voltages of full cells is also narrowed due to the reduced polarization in the ultralow‐salt‐concentration electrolyte. By adopting this strategy, the Zn‐Fe 4 [Fe(CN) 6 ] 3 full cell stably works at a high‐voltage of 1.40–2.30 V with a high cathode loading of ≈7 mg cm −2 and the Zn‐polyaniline full cell can stably work at 0.50–1.50 V with a high cathode loading of ≈11 mg cm −2 .