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 0.35M active material and found the longest capacity retention over about 60cycles at 0.15M. To our knowledge, this is the most soluble catholyte candidate with a robust radical cation.