Redox Flow Battery Storage: How an Old Idea Is Making a Comeback Today and What NASA Has to Do With It

In fact, the idea behind this technology is by no means new. The first flow batteries were patented as early as the 19th century and since then, researchers and engineers have continued to work on their development - including in the field of space research. Today, in the age of renewable energy, this technology is experiencing a resurgence. But what exactly is a redox flow battery, and why is it being discussed so intensively right now?

In the context of current discussions about the energy transition, the question of reliable, safe and long-lasting electricity storage quickly arises. Alongside pumped-storage plants and lithium-ion batteries, a term is cropping up more and more often that evokes images of laboratories and space exploration: redox flow.

In the 1950s, experiments were conducted with metal-based electrolytes. NASA was particularly interested in this technology. The goal was to find a battery technology for the lunar landing module.

But what exactly is a redox flow battery?

Unlike a conventional battery, a redox flow battery (also known as a “flow battery”) operates on a different principle.

• Energy is stored in liquid electrolytes housed in tanks.
• Power is generated in the cell stack, where the liquids flow through and generate electricity via electrochemical reactions.

This means that increasing energy efficiency leads to larger tanks. Higher power output goes hand in hand with a larger stack. It is therefore possible to scale energy and power output relatively independently of one another. This is a significant advantage when storage for several hours is required, for example, to store solar power from midday into the night.

Early History: From Electrochemical Fundamentals to the “Flow” Concept

The idea of using chemical reactions for electricity storage is not new. Redox flow involves two liquid redox pairs that circulate separately and “work” together within a cell via a membrane or separator.

In the 1950s and 1960s, the modern form of the flow battery underwent a decisive development - in the U.S., when energy crises and grid stability suddenly became very pressing issues. Scientific reviews identify this phase as the starting point for intensive development programs.

NASA as a Driving Force: Why the Space Agency, of All Organizations, Was Researching Energy Storage

To this day, the feasibility of a lunar landing is being evaluated and active research is underway to find solutions for energy, energy storage and energy management. When considering the requirements for a battery storage system in space, it quickly becomes clear why redox flow batteries are the only viable technology.

• Maximum reliability
• Compliance with the highest safety standards; non-flammable and non-explosive
• Easy maintenance and diagnostic capabilities
• Scalability for various applications in a wide range of environments

In the 1960s and 1970s, NASA (including at the NASA Lewis Research Center, now the Glenn Research Center) expanded its research on redox flow batteries and used this work to develop a concrete development and demonstration program. This was done in part in cooperation with the U.S. Department of Energy (DOE).

What particularly concerned NASA (and what it carefully weighed)

NASA has conducted an in-depth study of the subject and carried out a thorough evaluation. The project was not viewed merely as “a battery”; instead, the technical and economic feasibility was thoroughly examined. NASA documents describe how iron-chromium redox pairs were selected and extensive work was done on the components.

During the course of the project, typical questions related to flow batteries were raised, which remain relevant to this day.

• Membrane-related issue: How can we prevent the active species from “mixing” too much (crossover), which reduces capacity?
• Materials: Which electrode materials and surfaces remain stable over many cycles?
• System engineering: Pumps, seals, corrosion. Everything that makes a chemically active, circulating system reliable in everyday operation.
• Costs and scaling: Tanks, stack, balance-of-plant. What really drives the total costs?

NASA's work from that period is so interesting because it doesn't romanticize flow batteries but instead views them as a systems engineering approach: chemistry + materials + engineering + operational concept.

Practical demonstration instead of just theory
This work is later described as the foundation for today’s “spin-off” stories. NASA emphasizes that demonstration facilities were built at that time and that today’s companies can draw on insights from this research when developing flow batteries.

The next big step: Vanadium and the breakthrough of the 1980s

The next major advancement in this field was the development of vanadium and the associated breakthrough in the 1980s. Parallel to NASA’s research on iron/chromium, another line of research was initiated that is now the most widely used: the vanadium redox flow battery (VRFB).

The underlying concept is simple: vanadium is present on both sides of the battery, but in different oxidation states. This reduces a core problem of many flow systems: the mixing of electrolytes and the potential reduction in efficiency. VRFBs offer the advantage that no foreign chemicals can be automatically released into the tanks.

Maria Skyllas-Kazacos plays a central role. She presented the first successful all-vanadium demonstration in the 1980s and filed the corresponding patents in the latter half of the 1980s. At this point, it is worth noting the connection to NASA. Retrospective accounts indicate that NASA researchers also considered VRFB approaches in the 1970s but had not yet achieved a decisive breakthrough, whereas Australian research subsequently succeeded in taking this step.

Why Flow Batteries Are Only Now Gaining Traction

If all this has been known for decades, why are flow batteries only becoming more common today?

1. In the past, the key driver - renewables - was missing
   Large-scale storage systems were discussed, but the economic incentive was often insufficient. Today, renewable energy is at the heart of energy strategy and has become indispensable. What remains is the challenge of storing energy for the long term and releasing it when needed.
   
   
2. Material and system costs were too high for a long time
   Tanks, membranes, stacks, pumps: many components first had to reach industrial maturity. Today, these components are significantly cheaper than they were in the early 2000s.
   
   
3. Lithium-ion has dominated the market for years
   Lithium-ion is the most widely used technology, particularly for short- to medium-term storage and mobile applications. It is found almost everywhere in everyday life, as lithium-ion batteries work even on a very small scale and the capital expenditure costs are relatively low.

Now the requirements are shifting: Grids with a high proportion of solar and wind power increasingly need long-term storage solutions that can withstand many cycles, are thermally stable, and where, when in doubt, it’s better to manage “one tank” than “thousands of cells.”

This is exactly where redox flow systems come into the picture - not as a “one-size-fits-all solution,” but as a very useful addition to the energy mix.

Sustainable Energy Storage

FlexBase Redox Flow Battery Storage

A cutting-edge redox flow battery storage facility is being built at the Laufenburg Technology Center, featuring sustainable, safe, and fully recyclable technology. It supports the integration of renewable energy by storing excess electricity and releasing it when needed. In this way, it stabilizes the grid, reduces the risk of outages and strengthens the security of supply in Switzerland and Europe.

Learn more

What we can still learn from NASA's perspective today

What is truly valuable about NASA's history is not so much “the perfect chemistry” as the thinking behind it:

• The system comes first: A battery is not just a chemical reaction, but an entire system involving operation, maintenance and risks.
• Safety and robustness as key criteria: It’s not just about maximum energy density.
• Honest trade-offs: Membrane crossover, efficiency, materials, costs - it all goes hand in hand.

And it is precisely this pragmatic approach that is needed again today if flow batteries are to move from pilot plants to widespread use.

Sources:
https://spinoff.nasa.gov/Spinoff2008/er_2.html
https://www.nasa.gov/directorates/stmd/tech-transfer/spinoffs/giant-batteries-deliver-renewable-energy-when-its-needed/
https://en.wikipedia.org/wiki/Vanadium_redox_battery
https://www.sciencedirect.com/science/article/abs/pii/0378775389800370