A new class of iron-based catalysts could bring scientists a step closer to developing cheaper and more sustainable rechargeable batteries that use carbon dioxide (CO₂), according to research from the University of Surrey.
Lithium-CO₂ batteries are being explored as a promising alternative to today's lithium-ion batteries because, in theory, they could store substantially more energy for the same weight. However, the technology is still in the early stages of development, with commercial lithium-ion batteries currently outperforming them in areas such as reliability and lifespan.
One of the biggest challenges with lithium-CO₂ batteries is finding catalysts – materials that speed up chemical reactions – that can help them charge and discharge efficiently. Many of the most effective catalysts rely on expensive and scarce precious metals such as platinum, ruthenium and iridium, raising concerns about their cost and suitability for large-scale production.
In a study published in the Journal of Power Sources, Surrey researchers have shown that catalysts made using more widely available metals, including iron and molybdenum, can perform in a way that is comparable to, and in some measures better than, previously reported catalysts containing expensive precious metals.
In tests, the team's best-performing catalyst delivered nearly four times the discharge capacity of an unmodified reference material, meaning it could release substantially more electrical charge. It also recovered 93 per cent of the electrical charge during recharging and completed 92 charge-discharge cycles in the laboratory, where the amount of charge released during each cycle was deliberately limited.
Dr Siddharth Gadkari, Senior Lecturer in Chemical Engineering at the University of Surrey, and corresponding author of the study, said:
“Lithium-CO₂ batteries have the potential to store substantially more energy than today's lithium-ion batteries, which could eventually mean longer-lasting electronic devices and electric vehicles that travel further without increasing battery weight.
“Our research tackles one of the key barriers preventing these batteries from reaching that potential. We've shown that strong battery performance is possible without relying on expensive precious metals, opening up a promising route towards a new generation of more affordable and sustainable batteries.”
To develop the catalysts, the Surrey team introduced iron into a molybdenum-based compound before heating it to different temperatures to see how changes in its structure affected battery performance.
They found that heating the material to 500°C produced the best results, creating a combination of molybdenum oxide and iron phosphate that helped the chemical reactions involved in charging and discharging take place more efficiently.
Dr Mahsa Masoudi, Research Fellow at the University of Surrey's School of Engineering, and lead author of the study, said:
“We found that even relatively simple changes to how these materials are prepared can make a big difference to how well they perform. The temperature we used changed the structure of the catalyst, and that had a significant impact on how efficiently the battery could charge and discharge. Understanding why those changes matter gives us a valuable starting point for improving these batteries further.”
Dr Daniel Commanduer, a Lecturer at the University of Surrey and corresponding author of the study, said:
“There's still a long way to go before we see lithium-CO₂ batteries in everyday devices, but these results are an encouraging step forward. We've shown what these materials can achieve in the lab, and the next challenge is making sure they can deliver that performance consistently over much longer periods.”
The team now hopes to build on the findings by improving the performance and durability of the catalysts, while also exploring whether they could be used in other technologies that convert carbon dioxide.
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