Low-cost, high-voltage and durable aqueous zinc-chlorine battery enabled by condensed choline chloride electrolytes

Aqueous zinc‑chlorine batteries are emerging as promising candidates for large-scale energy storage due to their high energy density, safety, environmentally friendliness and low cost. However, one of the primary issues for zinc‑chlorine batteries is the narrow electrochemical stability window (∼1.23 V) of the aqueous electrolyte, which restricts the energy density and the operating output voltage of the batteries. Additionally, the redox reaction of chlorine ions cannot occur at high potential, which hinders the utilization of chlorine ions and affects the cycling performance of the battery. Herein, we propose a high-concentration electrolyte strategy to design a green, safe, and inexpensive 30 m choline chloride (ChCl) aqueous electrolyte for zinc battery, which exhibits an expanded electrochemical stability window of ca. 3.2 V. The zinc‑chlorine battery using zinc metal anode, carbonaceous cathode material (graphene (G), activated carbon (Ac), and nitrogen-doped activated carbon (NAc)), and 30 m ChCl electrolyte exhibits excellent electrochemical properties. Especially, nitrogen-doped activated carbon cathode delivers an average discharge voltage of ca. 2.2 V and a specific capacity of 112.8 mAh g−1 at a current density of 1.0 A g−1 and retains a stable cycling performance over 3700 cycles. In addition, the reversible chloride storage of the zinc‑chlorine battery is investigated by X-ray photoelectron spectroscopy, infrared spectroscopy, and X-ray diffraction measurements, which indicate a reversible insertion of Cl− in the NAc interlayer guarantee the impressive capacity and stable cycling life of the battery.