A safer, lower-cost variation on the lithium ion battery has become a realistic possibility, now that scientists have found a way to add water to it. A group of researchers has found that by eliminating the oxygen in a lithium-sulfate-and-water electrolyte solution, they were able to significantly improve the batteries' capacity retention—but only for very small capacities.

Aqueous lithium ion batteries are a less-dangerous, inexpensive replacement to standard lithium ion batteries, which use electrolyte solutions that can be toxic and flammable. However, battery makers typically avoid aqueous electrolytes for one reason: they don't work well at all.

A typical aqueous lithium ion battery retains only 50 percent of its charge capacity after one hundred cycles. As any notebook computer owner can tell you, a capacity of 50 percent after a thousand cycles is hardly acceptable in a battery, and less than that is cause for loud complaint.

However, by playing around with the aqueous solution, a group of scientists found that the pH of the liquid didn't matter much to the effectiveness of the battery. They tried removing as much oxygen as possible from the battery and readjusting the pH, and found that, in combination with carbon-coated electrodes, the batteries' capacity retention improved to 90 percent after a thousand cycles.

So will notebook batteries soon last forever, impervious to trifles like charge cycles? Unlikely— the battery with the impressive retention only provided about 10 minutes of power. Another similar battery that lasted eight hours at low current output retained 85 percent capacity after only 50 cycles.

So, the aqueous lithium ion battery is still a long way from replacing its toxic brethren. Still, the authors speculate that cheaper batteries may find use in "short-distance city-buses" and as storage for energy from wind turbines and solar panels. Notebook users will continue to wait for a capacity retention hero.

Nature Chemistry, 2010. DOI: 10.1038/NCHEM.763 (About DOIs).