Cleaner, Greener Batteries – Pushing the Boundaries of Energy Storage

Society needs more and better batteries to power electric car fleets.

Thanks to the rise of renewable energies, today the limiting factor of the energy revolution is not so much the power supply as the energy storage. Cleaner and greener batteries are needed to charge our cars, e-bikes and appliances for longer.

It’s a situation we’ve all been in. You are busy with a task and the rectangular icon in the upper right corner of the screen turns red and flashes to indicate that you are almost out of battery. However, battery problems go far beyond these kinds of minor annoyances. Batteries are an essential part of our green energy future, even if it is imperfect.

In the future, a large part of our energy should come from renewable sources such as solar and wind energy. Yet we all know that there are times when the wind doesn’t blow and the sun doesn’t shine. To balance supply, we need to store excess electricity produced by renewables, until we are ready to consume it. Better batteries are an important way to achieve this. If we are to power the envisioned fleets of electric cars and mobility devices, we will need a large number of batteries.

A big, persistent problem is that even the best batteries have problems. For example, a big problem with lithium-ion cells is that they use lithium as a key component. This is mined as salt. Since Europe does not currently have large reserves, it only depends on imports from a few places, such as Australia and Chile. Other issues with lithium batteries are that they are expensive, have limited storage capacity, and lose performance after repeated charging.

If we want to improve them, we must first understand how they work. Traditional lithium-ion batteries have three key components. There are two solid components called electrodes – the anode and the cathode – and a liquid called the electrolyte. When the battery discharges, electrons flow from the anode to the cathode to power the device to which it is connected. The positive lithium ions diffuse through the electrolyte, attracted by the negative charge of the cathode. When the battery is charging, it goes in the opposite direction.

Energy density

The whole process is a reversible electrochemical reaction. There are many variations of this basic process with different types of chemicals and ions involved. A particular option explored by the ASTRABAT project is to remove the liquid electrolyte and make it a solid or gel instead. In theory, these solid-state batteries have a higher energy density, which means they can power devices for longer. They should also be safer and faster to manufacture because, unlike conventional lithium-ion batteries, they do not use a flammable liquid electrolyte.

“We must continue to invest in research to validate the next generation of batteries.”

Dr Sophie Mailley, ASTRABAT

Electrochemist Dr. Sophie Mailley of the Commissariat for Atomic Energy and Alternative Energies (CEA) in Grenoble, France, is the coordinator of the ASTRABAT project. She explains that lithium-based solid-state batteries already exist. But these batteries use gel as the electrolyte and only work well at temperatures around 60°C, which means they are not suitable for many applications. “It is clear that we need to innovate in this area to be able to deal with the problems of climate change,” said Dr Mailley.

She and her team of partners worked on developing a recipe for a better solid-state lithium battery. The job is to look at all sorts of candidate components for the battery and figure out which ones work best together. Dr Mailley says they have now identified suitable components and are working on ways to increase battery manufacturing.

One question she and her team plan to investigate next is whether it will be easier to recycle lithium and other elements from solid-state batteries compared to typical lithium-ion batteries. If so, it could increase lithium recycling and reduce reliance on imports.

Dr. Mailley believes that if the research goes well, solid-state lithium batteries like the one ASTRABAT is working on could be commercially available in electric cars by around 2030. “I don’t know if it’s these solid-state batteries that will be the next big battery innovation,” Dr. Mailley said. “There are many other possible solutions, such as using manganese or sodium (instead of lithium). These might work. But we must continue to invest in research to validate the next generation of batteries,” she said.

positively charged

When it comes to storing energy for the purpose of smoothing the supply of electrical networks, batteries must be reliable and of high capacity, i.e. expensive. Rare lithium is not the best choice. Instead, the HIGREEW Project is investigating another type of battery, known as a redox flow cell.

The main components of redox flow batteries are two liquids, one positively charged and the other negatively charged. When the battery is used, these are pumped into a chamber called a cell stack, where they are separated by a permeable membrane and exchange electrons, creating a current.

The project coordinator is chemist Dr Eduardo Sanchez from CIC energiGUNE, a research center near Bilbao in Spain. He explains that many large-scale redox flow batteries are already in use around the world and that they are designed to be stable and last around 20 years. But these existing batteries use vanadium dissolved in sulfuric acid acid, which is a toxic and corrosive process. Safety requirements mean that these batteries must be manufactured at great expense.

“I would say we have a bloom here in Europe, with many companies working on flow batteries.”

Dr. Eduardo Sanchez, HIGREEW

“Vanadium has many strengths – it’s cheap and stable,” Dr. Sanchez said. “But if you have a leak from one of these batteries, it’s not nice. You have to design the tanks to be extremely durable.

Less toxic

The HIGREEW project plans to create a redox flow battery that uses far less toxic materials such as salt solutions in water that store carbon-based ions. Sanchez and his team of colleagues worked on developing the best recipe for this battery, looking at many different combinations of salts and chemical solutions. They have now put together a shortlist of a few prototypes that work well and are working on scaling them up.

Work on a huge battery prototype is underway at the CIC energiGUNE center. “We need to make sure they maintain their good performance at scale,” Dr. Sanchez said.

His team also investigated a method of soaking commercially available battery membrane materials to chemically modify them, making them last longer.

Dr. Sanchez sees a bright future for redox flow batteries. “I would say we have a bloom here in Europe, with a lot of companies working on flow batteries.” He predicts that the manufacture of redox flow batteries could create many job opportunities in Europe in the years to come.

The research in this article was funded by the EU.

This article originally appeared in Horizon, the European research and innovation magazine.