In the first part of this series of articles, an overview of the flow batteries characteristics has been provided, extrapolated from IDTechEx’s recent report “Redox Flow Battery 2020-2030: Forecast, Challenges, Opportunities”. In this second article, a more detailed analysis about the different chemistries will show the main RFB technologies currently available or under development, beginning with the most adopted and investigated Redox Flow Batteries (RFB), the Vanadium Redox Flow Batteries (VRFB).
Initially studied by NASA, and further developed in 1980’s by the research group led by Maria Skyllas-Kazacos at New South Wales in Australia, the Vanadium redox flow battery (VRFB) are today the most studied and manufactured technology within the redox flow battery technology. Besides different type of RFBs, the vanadium technology (and similarly the All-Iron RFB) employs the same electroactive species (vanadium) in both electrolytes, with different oxidation states. The following reactions take place during charge and discharge of VRFBs:
The low round-trip efficiency and the high cost of vanadium (directly affecting the cost of electrolyte) are two of the main VRFBs’ drawbacks. The electrolyte alone accounts for 30% to 40% of the overall technology cost. To reduce the effect of vanadium cost on the overall system, an increasing number of companies started collaborations with vanadium mining companies. The aim of the collaborations is to improve the vanadium electrolyte performances by increasing the vanadium concentration (moles of Vanadium per litre of electrolyte). This would allow reaching the higher energy density of the battery, and the reducing of the cost.
According to the investigation conducted by IDTechEx, it was clear that some mining companies themself are interested in the VRFB technology. This is the case for the South African mining company Bushveld Minerals. Bushveld Minerals is in fact actively promoting the adoption of vanadium flow battery all over Africa. Outside of the African countries, Bushveld backed the merge between two VRFBs manufacturers (the English redT and the American Avalon Battery), and in 2019 announced to acquired a consistent share of Enerox-CellCube, previously known as Gildemeister AG.
Although the Vanadium technology dominated the flow battery scenario, over the last years a growing number of other redox flow batteries are populating the market.