New chemistry developed by a UCL-led team could increase the energy capacity of aqueous (water-based) batteries – a step forward for a safer, more sustainable alternative to lithium-ion batteries.
Large-scale energy storage, or battery farms, are needed in the transition to net zero, to store excess energy from renewables that can be released when the sun isn’t shining and the wind isn’t blowing.
Currently, these facilities use lithium-ion batteries – the same rechargeable batteries that power laptops, e-bikes and electric cars – which can carry a fire risk, as well as requiring the mining of scarce resources such as cobalt, incurring an environmental cost.
Aqueous batteries are a potential alternative but, while safer and more sustainable, they have a relatively low energy density, limiting their practical use.
The new study, published in Nature, addressed that limitation, increasing the energy storing capacity of the main energy-storing material, iodine.
The researchers did this by enabling iodine to transfer four, rather than two, electrons during charging and discharging, effectively increasing the energy that could be stored.
One form the iodine takes, hypervalent iodine cations (I+), is highly reactive in water and previous experimental efforts had prevented unwanted chemical reactions by using highly concentrated halogen-containing electrolytes (the liquid in which the electrochemical reactions occur). However, these electrolytes are corrosive, costly, and unlikely to be manufactured easily.
The UCL-led team designed an entirely new electrolyte chemistry to prevent these unwanted reactions without requiring corrosive material. They did this through a molecular-level design of the iodine’s local environment – with some molecules preventing water from reaching the iodine, and others binding to iodine’s reactive forms.
They also showed that their new battery design worked reliably in different cell configurations, including pouch cells (the types of batteries used in laptops and mobile phones) and coin cells (disc-shaped batteries used in devices with low energy demands).
They tested their design’s durability and found that, when used in zinc-iodine batteries, it retained almost all of its storage capacity even after thousands of charge-discharge cycles.
The approach, the team said, could also be adapted for aluminium-iodine batteries, suggesting it may be useful across a range of future energy-storage technologies.
Professor Guanjie He, corresponding author from UCL Chemistry, said: “I am excited that our new chemistry can help aqueous batteries move one step closer to commercialisation and wide deployment. Next steps include testing this technology at a larger scale and to improve its performance under realistic operating conditions.
“This research demonstrates how fundamental chemistry and engineering can come together to address long-standing challenges in energy storage.”
Dr Ruwei Chen, first author from UCL Chemistry, said: “Moving beyond conventional, highly concentrated electrolytes opens new possibilities for developing more practical, affordable and sustainable aqueous batteries.
“Our study shows that making iodine batteries rechargeable isn't just about keeping the key chemicals stable. We also need to understand how they interact with the water-based electrolyte and how those interactions change as the battery charges and discharges.”
The research was supported by a European Research Council (ERC) Starting Grant, underwritten by UKRI.
Journal
Nature