Redox flow – the longest-lived battery yet?

Scientist looking through a microscope

Batteries are everywhere, from the tiny, rechargeable types in our mobile phones to the many one-use versions which power our various gadgets and the industrial versions used to store energy at power plants.

Lithium ion (Li-ion) batteries in particular have made the gadget revolution possible as a relatively low-cost, adaptable way to store electricity. But they have disadvantages including problems with heat, their use of rare, toxic elements and the fact that they don’t scale up very well.

So the hunt is on for the next generation of batteries that can last longer and work more efficiently, and scale to suit whatever demands are placed on them.

Battery life

A strong contender for an alternative is the redox flow battery (RFB). There are various types in development, but all offer advantages over Li-ion and other standard batteries such as lead-acid and NAS.

They could be around ten times cheaper to produce than an equivalent Li-ion and can potentially handle up to five times more recharges too (5,000 rather than 1,000). This gives them a considerably longer lifespan (an estimated 15 years), according to Sri Narayan, professor of chemistry at California’s USC Dornsife College of Letters, Arts and Sciences.

Scalable and flexible

RFBs are also easily scalable and have great potential to harness the power of more eco-friendly power sources – anything from electric cars to large wind farms and solar power stations.

How does redox flow work?

The key difference between RFBs and standard batteries is that they separate power and energy, like a fuel cell – indeed, a similar one was created to power NASA’s Helios drones.

Rather than storing power in a solid material (such as metal or metal salts), an RFB consists of two tanks, each containing a solution of electroactive chemicals. When activated, these are pumped into a cell which is divided by a membrane. The solutions interact through the membrane, producing electricity.

Better storage facility

Another difference is that they’re more flexible in shape, and can be made small or large as demanded, because the tanks can be of any size in comparison to the cells. So the total amount of energy that can be stored depends on how large the tanks are.

Eco-friendly developments

There’s still some development work to do. Existing RFB designs often use the heavy metal vanadium, dissolved in sulphuric acid as electrolyte – a highly corrosive and expensive combination. But researchers are working on developing elements from synthetic, non-corrosive materials, while some of the more forward-thinking are experimenting with naturally occurring hydrocarbons. And the plan is to eventually get them directly from sustainable, eco-friendly carbon dioxide.

More energy, but less damage?

More efficient batteries are unlikely to encourage us to use less energy – quite the reverse – but the potential of the RFB means that batteries will be created with less harm to the environment, and that energy will be stored more efficiently.

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