Redox flow battery. Image by Colintheone, CC-BY-SA 4.0.

George Harvey

Transitioning to renewable energy and eliminating the use of fossil fuels will be far easier if we have really good battery technology. The technology we have today is vastly superior to what there was around fifty years ago, but it will almost certainly get better. A large number of people are doing the work to find better solutions.

As things stand now, there are more kinds of batteries out there than most people might imagine. One kind that is particularly promising is redox flow batteries. These are too bulky to be used in a cell phone or a car, but they can really shine for applications involving a lot of energy. For utility-scale energy storage, flow batteries have some great advantages.

According to an article that appeared at CleanTechnica, Agora Energy Technologies (AET), which is based in Vancouver, British Columbia, has come up with an ingenious design for a redox flow battery that goes beyond just storing electricity. The chemical reactions in the battery use carbon dioxide (CO₂) and can sequester it in any of a number of useful and valuable chemicals (www.bit.ly/co2-flow-battery).

Manufacture of some of these chemicals has historically been based on processes that emit abundant amounts of CO₂. Now, they can be by-products of AET’s battery storage technology, delivered in a highly pure form. That fact is one of the reasons that the design has already won a number of awards.

Redox flow batteries are very different from the batteries in cell phones, flashlights, or cars, and they look very different. The operation of most such flow batteries depends on ions flowing through a membrane that separates two liquids.

At the core of most flow batteries is a membrane stack, where electrons move between liquids by passing through the membrane. The liquids flow past each other in the stack and are otherwise held in tanks. With a given chemistry, the working surface area of the membrane stack determines the power in the battery, which could be measured in kilowatts (how many toasters you can run). The amount of energy stored, however, depends on the volume of the tanks, and this could be measured in kilowatt-hours (the energy to run all those toasters for some amount of time).

So, if you need more power, you use a bigger membrane stack. But if you need more energy, you use bigger tanks. One way or another, the system is normally closed, and the chemicals are used over and over again. It is not unusual for a flow battery to be expected to go through 10,000 charging cycles without much change in performance.

The thing that makes the AET design different from other flow batteries is the fact that its design uses CO₂ as a chemical in its reactions. When the battery is charged, the CO₂ is stored in solution, and when the battery is providing energy by being discharged, the CO₂ is released.

Vanadium redox flow battery with a capacity of 1-MW, 4-MWh. UniEnergy Technologies , CC-BY-SA 4.0 (www.bit.ly/38OKcvg)

The AET design goes further than that, however, because the system does not have to be closed, with the same chemicals reused constantly. It can be used in an open configuration, drawing CO₂ from an external source, and releasing it externally.

While this might not sound like an advantage offhand, the implications are huge. The CO₂ can be drawn down, possibly from products of combustion, instead of being released into the atmosphere, where we don’t want it. It can then be used in the battery and released in a different form, as part of a different chemical that we can use. There are many chemicals made from CO₂. Bicarbonate of soda is just one small example.

Another advantage of the AET battery is that it is inexpensive. The components of the battery are safe, inexpensive, and abundant, though some of the specifics are proprietary, so far. Cost analysis puts the AET battery as storing electricity at a price that is well below that of other batteries.

So, what we may have, if AET can commercialize the design successfully, is a way to store energy from renewable sources that draws down CO₂ as it does so.

Agora Energy Technology’s website is agoraenergy.ca.