Battery farms are a quiet backbone of the clean-energy shift. They soak up surplus solar and wind power and hand it back when the sky is dark and the air is still. Most of them rely on lithium-ion cells, the same family that powers laptops and e-bikes. A research team led by University College London has now reported a chemistry that could widen the options: a water-based battery whose iodine stores roughly twice as much charge as before.
The work was published in Nature and announced by UCL on 13 November 2026. It is laboratory research, not a product, but the idea behind it is a neat example of how rethinking the liquid inside a battery can matter as much as the metals around it.
Why water-based batteries are attractive
According to UCL’s announcement, today’s grid-scale storage mostly uses lithium-ion batteries, which can carry a fire risk and depend on scarce materials such as cobalt, with an environmental cost from mining. Aqueous batteries, whose electrolyte is mostly water, are a potential alternative. They are safer and more sustainable, but they have a weakness: relatively low energy density, which limits where they can be used.
That trade-off is why aqueous designs have stayed mostly in the research pipeline. If they could hold more energy in the same space, their safety and materials advantages would count for much more.
The trick: four electrons instead of two
The main energy-storing material in this design is iodine. In earlier aqueous iodine batteries, each iodine unit moved two electrons during charging and discharging. The UCL-led team got it to transfer four, which effectively raises the energy that can be stored.
The extra capacity comes from a highly reactive form of iodine, hypervalent iodine cations (I+). In water, that form tends to react in unwanted ways. Earlier efforts held those reactions back with very concentrated electrolytes containing halogens. The UCL release describes those liquids as corrosive, costly and unlikely to be manufactured easily, so they are hard to turn into a practical battery.
A new electrolyte built at the molecular level
The researchers took a different route. They designed an entirely new electrolyte chemistry that avoids the unwanted reactions without corrosive material. The approach works at the molecular level, shaping the local environment around the iodine. Some molecules keep water away from the iodine, while others bind to its reactive forms and keep them stable.
Dr Ruwei Chen, first author from UCL Chemistry, said in the release that making iodine batteries rechargeable is not only about keeping the key chemicals stable. It also requires understanding how they interact with the water-based electrolyte and how those interactions change as the battery charges and discharges.
What the team tested
The team reports that the design worked reliably in different cell configurations, including pouch cells, the format used in laptops and phones, and coin cells, the small discs found in low-power devices. In zinc-iodine batteries, the cells kept almost all of their storage capacity after thousands of charge-discharge cycles, according to UCL. The release does not give a single capacity or cycle-count figure, so the full numbers sit in the Nature paper.
The team also says the approach could be adapted for aluminium-iodine batteries, which suggests the electrolyte idea may carry over to a range of future storage technologies rather than a single cell type.
What it means
For energy planners, the headline is not a finished battery but a removed obstacle. If water-based cells can store more energy without needing corrosive, expensive electrolytes, they become a more realistic candidate for stationary storage, where weight and size matter less than safety, cost and material supply.
For researchers, the result is a reminder that the electrolyte is an active design space. Tuning how molecules surround a reactive ion, rather than simply packing in more salt, is a transferable idea.
The caveats are important. The work is at an early stage. Professor Guanjie He, the corresponding author, said the next steps include testing the technology at a larger scale and improving its performance under realistic operating conditions. Cost, manufacturing and long-term field behaviour have not yet been shown. This article reports research news and does not predict a commercial timeline.
Conclusion
UCL’s four-electron iodine chemistry is a promising step for safer, more sustainable storage. If it scales, it could give grid operators another tool for holding renewable power. For now, it is a clear lab result worth watching as the team moves from coin and pouch cells toward larger systems. The research was supported by a European Research Council Starting Grant, underwritten by UKRI.