Principal and Structure
Structure of Redox Flow Battery
Power part(cells) and Capacity part(tanks) are separated in this structure. Electrolytes in the tanks are circulated by pumps.
Principle of Charge/Discharge
Charge and Discharge occurs by oxidation and reduction(Redox) reactions of the electrolytes which contain the active vanadium.
Now, almost All-Vanadium Redox Flow Batteries are using Vanadium ion as active materials for positive side and negative side. During charging, the V3+ is reduced to V2+ at negative side whereas oxidation of V4+ to V5+ occurs at the positive side. Standard electromotive force is 1.26V.
Structure of Cells
The basic VRFB cell is constructed from two half-cells, each containing a carbon felt as electrode. Redox reaction occures in active materials of ecelctrolyte impregnated in the felt.
Multiple cells are connected electrically in series as a cell stack to produce bigger electromotive force.