Redox Flow Battery

A redox flow battery is a rechargeable battery in which the chemical energy is held in two liquid electrolytes, pumped from separate storage tanks through a cell stack and kept apart by a membrane, so that unlike a conventional battery the energy is stored outside the cell in the liquid itself rather than in the solid electrode material. John Doyle patented the earliest version, a zinc bromine flow battery, in 1879, and Estonian chemist Walther Kangro first demonstrated flow batteries using dissolved transition metal ions in the 1950s, but the chemistry that became commercially viable, the vanadium redox flow battery, was developed at the University of New South Wales in the late 1980s. Vanadium remains the dominant commercial chemistry because its own ions on both sides of the membrane avoid cross contamination problems and support 15,000 to 20,000 charge cycles. In 2022 China commissioned a 400 megawatt hour vanadium flow battery, at the time the largest of its kind, reflecting the technology growing role in long duration grid storage.