What is an Aqueous All-organic Redox Flow Battery?

There is a US patent here

In Germany they are building a much larger scale storage though with slightly different technology. There seems to be quite a wide range of flow battery products emerging for grid storage solutions.


This technology is applicable for large-scale energy storage such as load-balancing the electrical grid and storing energy from intermittent renewable sources.

Problem Addressed

Flow batteries are currently limited by low energy density, low efficiency, and high costs.  This technology develops a lower cost, higher energy capacity flow battery suitable for large-scale applications.


A major cost associated with flow batteries is the chemical cost of the electrolyte.  Using water, which is much cheaper than other solvents, would be a cost-effective approach.  However, current aqueous redox chemistries employ transition metal salts that have low solubility in water, limiting the capacity of the flow battery, and are often expensive.  Together, this combination increases the overall cost of the battery system.  This technology uses quinoxaline-based organic molecules instead of transition metals as the redox chemistry.  These organic molecules are much more soluble in water, which allows for more concentrated electrolyte and increased battery capacity.  The organic molecules can also store two electrons per molecule, further increasing capacity.  Additionally, unlike the metal-based chemistries, the quinoxaline-based chemistries do not require strongly acidic or alkaline conditions so the battery can be constructed out of plastic instead of more expensive corrosion-resistant materials.


  • High energy storage capacity
  • Lower cost than metal-based flow batteries
  • Improved safety characteristics

The German project is still ongoing: German redox flow battery – a game changer for energy storage?

The utility claims that its storage system project, brine-for-power (b4p), could be the world’s biggest ‘battery’ to date.

EWE GASSPEICHER, a subsidiary of utility EWE based in Oldenburg, northern Germany, said that it wants to build the German redox flow batteries inside underground salt caverns that are normally used for storing natural gas.

EWE will collaborate with Friedrich Schiller University in Jena, about 500km from Oldenburg on b4p. The university developed the components to use in the battery, including recyclable polymers for plastic parts.    

German redox flow battery could change storage market

EWE has not revealed the exact size of the system in terms of capacity or power output but EWE GASSPEICHER Managing Director Peter Schmidt said the storage system could be large enough to “supply a major city such as Berlin with electricity for an hour”.

“If everything works, this may fundamentally change the storage market, i.e. the market for control energy,” Schmidt added.

“In contrast to other energy storage facilities that convert the electrical current into other energy carriers – for example into compressed air – we are storing the electricity directly with brine4power.”

The tech behind flow batteries

Redox flow batteries store energy in liquid electrolyte, the amount of which can be increased to satisfy capacity demands. While bulkier than lithium-ion battery systems, redox flow systems do not degrade through heavy charge and discharge cycles. This means that the systems are expected to last many years longer in the field.

EWE claims that the materials including recyclable polymers dissolved in saltwater are less polluting than the vanadium used in conventional redox flow batteries.

Until recently, American company Aquion Energy was marketing long duration batteries using saltwater electrolytes. The company has since gone bankrupt.

The university team came up with the idea of using the underground salt caverns as containers for the electrolyte. The underground caverns are often vast, providing the potential for storing large quantities of energy.

Initially, the project’s battery will be built and contained in plastic containers at another site before being transferred into the caverns.

“We need to carry out some more tests and clarify several issues before we can use the storage principle indicated by the University of Jena in underground caverns. However, I expect that we will have an operating cavern battery by about the end of 2023,” Brine4power Project Manager Ralf Riekenberg said.

Flow battery market gaining momentum

Companies such as redT, VIZn and Primus Power have already taken flow batteries to market but the largest flow battery to date is a 15MW/60MWh project in Japan by Sumitomo Electric Industries. However UniEnergy Technologies and Rongke Power are building up to 10 systems, each of 20MW/80MWh in China.

The US has unveiled the largest flow battery system to date which involved UniEnergy Technologies and is a mere 2MW/8MWh, the same size and capacity as another US system in California.     

EWE’s storage project almost mirrors a similar one in Northern Rhine-Westphalia where a retired coal mine will be converted into a pumped hydro plant.