High-energy and low-cost membrane-free chlorine flow battery

Grid-scale energy storage is essential for reliable electricity transmission and renewable energy integration. Redox flow batteries (RFB) provide affordable and scalable solutions for stationary energy storage. However, most of the current RFB chemistries are based on expensive transition metal ions or synthetic organics. Here, we report a reversible chlorine redox flow battery starting from the electrolysis of aqueous NaCl electrolyte and the as-produced Cl₂ is extracted and stored in the carbon tetrachloride (CCl₄) or mineral spirit flow. The immiscibility between the CCl₄ or mineral spirit and NaCl electrolyte enables a membrane-free design with an energy efficiency of >91% at 10 mA/cm² and an energy density of 125.7 Wh/L. The chlorine flow battery can meet the stringent price and reliability target for stationary energy storage with the inherently low-cost active materials (∼$5/kWh) and the highly reversible Cl₂/Cl⁻ redox reaction.

Singyuk Hou, Long Chen, Xiulin Fan, Xiaotong Fan, Xiao Ji, Boyu Wang, Chunyu Cui, Ji Chen, Chongyin Yang, Wei Wang, Chunzhong Li, Chunsheng Wang