Concentrated Chlorine-Based Electrolyte Enabling Reversible Cl3–/Cl– Redox for Energy-Dense and Durable Aqueous Batteries

Redox of chlorine with high potential and specific capacity has attracted wide attention for energy storage applications, while it suffers from an undesired disproportionation reaction in aqueous electrolytes which hinders its development. Herein we propose a strategy via a unique solubilization effect of metal-halide complex ions to construct a high concentration of chloride (over 30 m) electrolyte with low cost to stabilize the oxidation products and suppress the side reactions, thus representing a high reversibility of the Cl3–/Cl– redox couple up to 96.0% with 1.0 V vs SCE. The as-fabricated Zn–Cl3– full cell based on the highly concentrated electrolyte exhibits an ultrahigh operating voltage of 2.02 V at 1.0 mA cm–2 in the nearly neutral system. In particular, an enhanced conversion efficiency at room temperature with durable cycling stability of 4000 cycles is demonstrated. These results open a new way for the development and application of aqueous chlorine-ion batteries.