PNNL

Abstract

Grid-scale energy storage is essential for reliable electricity transmission and renewable energy integration. Redox flow batteries (RFB) provide affordable and scalable strategies for stationary energy storage. But most of the current RFB chemistries are based on expensive transition metal ions or synthetic organics. Here, we report a reversible Cl2/Cl- redox flow battery through electrolysis of aqueous NaCl electrolyte, the as-produced Cl2 is stored and extracted from carbon tetrachloride (CCl4) or mineral spirit flow. The immiscibility between the CCl4 from NaCl electrolyte enables a membrane-free design with energy efficiency of >90.6% and energy density of 171 Wh/L, which are the highest among all flow battery systems reported. With the inherently low cost of active materials (~5 $/kWh) and highly reversible redox reaction of Cl2/Cl-, the chlorine flow battery can meet the stringent price and reliability target for stationary energy storage.