Overview of redox circulation battery chemistries, market gamers


Two weeks ago we investigated how redox flow batteries (RFB) stacked up to form lithium batteries. Today we dig deeper into the most important RFB technologies currently available or in development, starting with the most widely used and studied redox flow batteries (RFB), the vanadium redox flow batteries (VRFB). This analysis comes from the most recent report by IDTechEx “Redox Flow Battery 2020-2030: Forecast, Challenges, Opportunities”.

The vanadium redox flow battery (VRFB) was originally studied by NASA and further developed in the 1980s by the research group led by Maria Skyllas-Kazacos in New South Wales, Australia. It is the best researched and manufactured technology within redox flow battery technology today. In addition to different types of RFBs, the vanadium technology (and similarly the all-iron RFB) uses the same electroactive species (vanadium) with different oxidation states in both electrolytes. The following reactions take place during the loading and unloading of VRFBs:


Figure 1. Right side – chemical reaction at the interface between anode and cathode. Left side – Different colors of the vanadium electrolyte due to the different oxidation states.

The low circulation efficiency and the high vanadium cost (which directly impacts the electrolyte cost) are two of the main disadvantages of VRFBs. The electrolyte alone accounts for 30% to 40% of the total technology costs. To reduce the impact of vanadium costs on the overall system, more and more companies began working with vanadium miners. The aim of the cooperation is to improve the vanadium electrolyte performance by increasing the vanadium concentration (moles of vanadium per liter of electrolyte). This would make it possible to achieve the higher energy density of the battery and reduce costs.

According to the research conducted by IDTechEx, it was clear that some mining companies are interested in VRFB technology themselves. This is the case with the South African mining company Bushveld Minerals. Bushveld Minerals is in fact actively promoting the adoption of vanadium flow batteries across Africa. Outside the African countries, Bushveld supported the merger of two VRFB manufacturers (the English redT and the American Avalon Battery) and announced in 2019 that it would acquire a consistent stake in Enerox-CellCube, which was previously known as Gildemeister AG.

Although vanadium technology dominated the flow-through battery scenario, other redox flow-through batteries have been populating the market in recent years.

Zinc bromine redox flow batteries (ZBB): In addition to the vanadium flow batteries, the zinc-bromine technology is the second in the rank of the technologies used.

Technically different from a VRFB, the ZBB are based on a solid zinc electrode and a liquid bromine electrolyte, which gives this technology a higher energy density than VRFBs.

With the Australian Redflow and America Primus dominating the scenario, this technology is slowly (but not too slowly) gaining its share of the flow battery market.

All-Iron Redox Flow Batteries (Fe-RFB): The promising all-iron RFB was developed by the American company ESS Inc. and is characterized by the use of iron as an electroactive species in both electrolytes (catholyte and anolyte). The inexpensive iron electrolyte brings a great cost advantage; although other constraints, such as hydrogen evolution, affect these types of batteries.

Organic redox flow batteries (ORFB): Another type of flow-through battery present in the scene are the organic flow-through batteries, which are technically similar to a VRFB but use an organic electrolyte.

While the vanadium flow batteries use an inorganic electrolyte based on vanadium salts, the ORFB – or sometimes also referred to as “metal-free flow battery” – is based on organic electrolytes such as quinone, pyridine or “TEMPO” (2,2,6 , 6-tetramethyl-1-piperidinyloxy) molecules.

Although they are getting closer to the market, several companies are developing this type of flow battery, including the German Jena batteries and the French Kemiwatt.

In addition, the European HIGREEW projects for the development of the ORFB are currently underway.

Other flow battery chemistry: The hydrogen-bromine flow-through battery has been on the market for a number of years and is one of the future redox flow-through batteries that is approaching the market. Behind the development of this technology was the Dutch company Elestor, which in 2019 received an investment of several million from the Dutch conglomerate Koolen Industries in addition to EIT Innoenergy, which invested in Elestor early on. In addition, the company is involved in the European MELODY project, which relates to the development of a sustainable redox flow battery technology that can effectively reduce the cost of electricity storage to support large-scale systems.

The increasing number of redox flow battery chemistries, along with the interest in this technology, increases competition. As highlighted in the IDTechEx report, the CAGR is around 30% expected over the next 10 years, although the increasing adoption of renewable energies and environmentally friendly measures to reduce pollutants could lead to greater adoption of this technology.

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