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 using carbon tetrachloride (CCl₄) or mineral spirit flow. The immiscibility between the CCl₄ and NaCl electrolyte enables a membrane-free design with energy efficiency of >91 % and energy density of 125.7 Wh/L. With the inherently low cost of active materials (~5 $/kWh) and highly reversible redox reaction of Cl₂/Cl^-, the chlorine flow battery leaves significant space to meet the stringent price and reliability target for stationary energy storage.