A Highly Soluble Organic Catholyte for Non‐Aqueous Redox Flow Batteries

A phenothiazine derivative with high solubility in carbonate solvents containing lithium salts showed extensive overcharge protection and, as a result, has been evaluated as a catholyte for non‐aqueous redox flow batteries. We report the testing of 3,7‐bis(trifluoromethyl)‐ N ‐ethylphenothiazine as a catholyte and 2,3,6‐trimethylquinoxaline as the anolyte in redox flow batteries containing 0.05, 0.15, and 0.35 M active material and found the longest capacity retention over about 60 cycles at 0.15 M . To our knowledge, this is the most soluble catholyte candidate with a robust radical cation.