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Flow Batteries – what you need to know about them?

In search of energy efficiency, the energy storage market has been experimenting with different technologies to deliver a perfect battery – the one that will last longer and could be used on a global scale for both individual and business purposes. Is flow battery a chance for achieving this goal?

Lithium-ion batteries

Batteries have been powering up our world for quite a while now. They’re the power source of nearly all types of electronic devices and vehicles we can think of, from toys and household equipment, through advanced tools, cars, and machines. The most common are lithium-ion batteries. We use them on a daily basis, like the ones in our smartphones. Despite how practical they may seem, this type of battery is difficult in usage on a global, business scale.

The problem is in their size and capacity. As small elements, those batteries are viable. However, if you try to use it on a grid-scale, it occurs to be quite expensive due to the cost of materials for large amounts of full-sized batteries necessary for such an undertaking. Lithium-ion batteries require rare resources for manufacturing thus they are still expensive, although mass production has changed a lot in that matter and we could observe them in use on the grid-scale. But there are other weaknesses worth mentioning, like mediocre capacity. Li-ion batteries are not the most effective source of power. As they degrade over time, their capacity decreases, which brings the necessity of replacing them. Scalability is their next blind spot and that makes the system they are part of hard to develop. Finally, they are highly flammable and easy to explode if exposed to heat, so precautions like additional preservation and backup are obligatory.

Flow batteries – reborn technology

Having in mind all the possible objections for lithium-ion batteries, the world has begun to search for alternatives. One of the results is a flow battery, nowadays also called redox vanadium flow battery, as currently, this is the most popular chemical element used in this technology.

Although the technology of flow batteries looks pretty modern, its history dates back to 1884 and La France airship, which was powered with the very first zinc-chlorine flow battery designed by Charles Renard and Arthur Constantin Krebs. The technology went practically silent for almost a century, until in 1973 NASA created the first iron-and-chromium redox flow battery for the future moon base energy storage. Eleven years later, at the University of New South Wales, Maria Skyllas-Kazacos conducted the first successful demonstration of her design, a vanadium redox flow battery, patented in 1986. Ever since we can observe how this type of battery has been evolving and maturing and flow batteries have been adopted as a viable alternative for lithium-ion technology or, at least, its supplement.

How does it work

A flow battery is an electrochemical conversion device that uses energy differences in the oxidation states of certain elements. There are three types of flow batteries: redox, hybrid, and membraneless. Let’s focus on the first one, as this battery type is the most common. Redox flow batteries use a liquid phase reduction-oxidation reaction when liquid electrolyte flows through the electrodes. The used electrolyte can be recharged by pumping it back through the electrodes to the tanks.

Is it better than a li-ion battery?

One of the biggest advantages of flow batteries is their modularity. They can be easily configured to the desired energy capacity by combining multiple electrolyte tanks or simply including bigger tanks in the storage system for increased capacity. That means they are a proper choice for the large energy storage systems with their scalability, in opposite to li-ion ones.

Flow batteries have the ability to completely discharge the system for long periods without any negative results for their capacity. Even if the electrolytes would mix accidentally, the battery suffers no permanent damage. This means almost no time-degradation and nearly unlimited longevity, as V-flows have 15,000 – 20,000 charge/discharge cycles, while the live cycle of a solid-state battery has a much smaller range, around 4,000 – 5,000 charges/discharge cycles. Flow battery will handle the storage system much longer than li-ion one, which results in bigger periods between the necessity of replacing the battery.

V-flows are also non-flammable and that makes them safer to operate, however, they have relatively high toxicity due to the oxides of vanadium. The greatest problem with flow batteries is their weight. To achieve significant capacity, the electrolyte tanks have to be large enough. Along with the aqueous electrolyte, that makest the battery very heavy and suitable only for stationary applications. And even with the large-sized batteries, the energy-to volume ratio is comparatively low.

Considering all pros and cons regarding the flow batteries in energy storage systems, V-flows seem to be a perfect match for sizable installations that should provide power for a long time. This technology has great potential and offers a lot but still needs more time to be tested in grid-scale installation. In the meanwhile, flow batteries may stand as a perfect supplement for the lithium-ion batteries, where lithium-ion could provide instant reaction and V-flows could be long-time storage. As technology will be developed, we will certainly hear a lot about flow batteries in the future.

 

Author: Mariusz Kraj, Chief Innovation Officer in Codibly

 

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