Emerging Technologies · By Brian Fulcher
A wind farm can make plenty of electricity at a time when the grid has little use for it. Saving that power for later takes batteries that can handle years of charging and discharging at a cost utilities can live with. A UCL-led team has found a way to get more charge out of iodine in a water-based battery. The result is promising enough to test in bigger cells.
Prototype or demonstration. Researchers tested the chemistry in laboratory batteries, including coin and pouch cells.
Last reviewed November 14, 2026.
What changed
Chen, Dong and colleagues published their study in Nature on November 11, 2026. University College London reported the results on November 13. The team showed that iodine could repeatedly go through two charge-transfer steps in a water-based electrolyte without the highly concentrated halide salts used in earlier approaches. An electrolyte is the liquid that carries charged particles inside the cell.
How iodine stores more charge
Iodine at the positive electrode changes chemical form as the battery charges and discharges. A common reaction transfers two electrons per iodine molecule. The team made a second step reversible, bringing that total to four. That increases the charge the iodine itself can hold. The energy a whole battery delivers also depends on voltage and how much of the cell is taken up by the electrolyte, the other electrode and the packaging.
The additional step produces a reactive, positively charged form of iodine. Water can interfere with the molecules that would otherwise keep it stable. The researchers chose dissolved ions that make the area right next to the electrode less water-rich and help free up molecules that bind to the reactive iodine. With both effects working together, the cell could cycle through the extra iodine reaction.
What the lab cells showed
The paper reports that zinc–iodine cells retained 94% of their measured capacity after 2,000 cycles under one laboratory test condition. The team also tried the chemistry in pouch cells and in cells with an aluminium–zinc alloy electrode. The researchers found that some iodine became unavailable over time, with more permanent losses when they loaded more iodine into the electrode. That matters because raising the loading is one way to get more energy out of a cell of a given size.
Where it might fit
A stationary battery beside a wind or solar farm can tolerate more bulk than a battery in a car. Water-based electrolytes may also reduce one source of flammability, but pack safety still needs direct testing. The paper includes a model of possible cost savings. The public evidence describes lab work led by UCL in the UK. It gives no commercial availability, grid installation or delivered system price for this formulation.
Root Access Take
For a utility, the number to watch is usable energy from an entire system over its service life. It is worth asking how much energy comes back out after long idle periods, how much equipment the cells need around them and what happens when one cell fails. The extra iodine reaction earns its place if it helps the pack deliver more electricity over time at a competitive cost.
What to watch next
Look for larger cells tested at practical electrode loadings and over realistic charge, discharge and idle periods. Pack-level efficiency, safety tests and actual manufacturing costs would tell us more about whether this chemistry can help store power for the grid.
Primary sources
Chen, Dong and colleagues, Nature paper and supporting data, November 11, 2026.
University College London research account, November 13, 2026.
Related reading on Root Access Guy. Could sodium batteries store more energy without a built-in anode?