A team led by University College London (UCL) has developed a new electrolyte chemistry - the liquid in which electrochemical reactions take place. This increased the energy capacity of aqueous batteries. The work was published in the journal Nature.
Aqueous batteries are seen as a promising replacement for lithium-ion ones: they are safer because they do not catch fire, and more environmentally friendly because they do not require mining scarce cobalt. But their energy density - the energy stored per unit of mass or volume - is lower, which limits applications such as large-scale storage for solar and wind power.
The key idea of the work is to make iodine, the main material for energy storage, exchange not two but four electrons during charging and discharging. This increases the amount of energy stored. The problem is that one form of iodine - hypervalent iodine cations (I+) - is very active in water and enters into unwanted reactions. Previously this was countered with concentrated electrolytes containing halogens, but they are corrosive, expensive and difficult to produce.
The authors engineered a molecular environment for iodine: some molecules keep water away, while others bind the active forms of iodine. This made it possible to do without aggressive substances.
Tests showed that the new design works in different cell formats - from pouch cells, as in laptops, to coin cells, as in watches. In zinc-iodine batteries, almost all capacity was retained after thousands of charge-discharge cycles. The scientists suggest the approach could also be adapted for aluminum-iodine batteries.
The lead researcher, Professor Guanjie He, noted that the new chemistry brings aqueous batteries closer to commercialization. The next steps are scaling up and testing in real-world conditions. First author Dr Ruwei Chen adds that moving away from concentrated electrolytes opens the way to more practical and affordable aqueous batteries.
For now this is a laboratory result, not a finished product. There is no word on timelines for market entry or cost.