Flow battery – what you need to know about flow batteries

Lithium-ion batteries and energy storage

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 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 battery – 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 flow battery 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.

What is redox flow battery?

Redox batteries (RFB) are one of the classes of electrochemical devices that store energy. The name redox refers to chemical reduction. RFB uses oxidation to store energy in liquid electrolyte solutions, which causes them to flow through electrical cells during discharging and charging.

The electron is released as a result of the oxidation reaction. It happens during each discharge cycle. Then the electron passes through the outer circumference and is reduced. It is worth remembering that when charging, the direction of the current is reversed.

How does flow battery technology works? What determines the electricity produced by the battery? First of all, it determines the number of atoms and active molecules. The voltage generated by the RFB battery system is specific to the chemicals involved in the reactions and the number of cells connected in series. The power delivered by the RFB is the product of the total current and the full voltage generated in the electrochemical cells. The amount of energy stored in the RFB is determined by the total amount of active chemicals available in the system’s volume of electrolyte.

What are redox flow batteries used for?

Since 2000, the number of scientific publications and commercial activities of RFB redox flow batteries has been steadily increasing. There are many possible combinations for creating new types of RFB flow batteries. By 2015, there were approximately 78 different types of RFBs flow batteries, but only a few could be used commercially.

RFB redox flow batteries are an idea that was ahead of its time. However, with the significant increase in renewable energy over the past 15 years, the need for better energy storage solutions has increased. Currently, lithium-ion batteries lead to several different problems: social (cobalt mining in Congo), hazards (fire), recycling (environmental aspects) of many hazardous substances (cobalt, nickel, organic electrolytes). This battery type do not seem to be sustainable and green technology.

The demand for stationary energy storage and electric mobility is growing every year. The great advantage of RFB flow batteries is the significant cost reduction that has taken place over the last ten years. As the number of RFBs flow batteries increases and production is optimized towards mass production, it will be possible to reduce costs even further. Thanks to this, flow batteries have a chance to become the leading technology in the storage of renewable electricity.

Are flow batteries the future of energy storage?

Will flow batteries become the leading solution for energy storage in the future? These batteries’ numerous advantages can make the flow batteries even more popular in energy management in the coming years. Essential benefits of flow batteries include:

Long service life: this is one of the most significant advantages of flow battery systems. Flow battery allow for a large number of complete cycles of both charging and discharging. Importantly, electrons do not undergo any physical changes to be freely upgraded for catalytic and electrical properties. Besides, convective cooling of the electrodes supported by the pumped electrolyte helps in managing and distributing heat.

No standby losses: flow batteries are the ideal solution for devices with long periods of disuse. The flow-through battery will not discharge because the charge-carrying electrolyte is stored in separate reservoirs.

Low maintenance costs: the flow batteries are incredibly ergonomic. One electrolyte is used for all cells, ensuring that the battery is charged uniformly.

Environmentally friendly: flow battery waste can be reused. Additionally, electrolytes are not very toxic.

Charging method: fluctuating power demand, charging, and discharging rates do not affect the operation of redox flow batteries. Therefore, flow battery systems are the right solution for complex energy management systems.