Researchers say they've developed a new material as an electrolyte for lithium batteries that will make them both more powerful and more efficient.
The electrolyte will reduce the formation of dendrites, microscopic needle-shaped fibers that can cause an internal short circuit in a battery, creating a fire hazard and reducing its ability to store energy over a long period of time, they say.
"Our new electrolyte helps lithium batteries be more than 99 percent efficient and enables them to carry more than ten times more electric current per area than previous technologies," says Ji-Guang Zhang, a physicist with the Pacific Northwest National Laboratory of the U.S. Department of Energy.
"This new discovery could kick-start the development of powerful and practical next-generation rechargeable batteries such as lithium-sulfur, lithium-air and lithium-metal batteries," he says.
Most rechargeable batteries in use today are the lithium-ion type, with one electrode containing lithium and the other usually composed of graphite.
Electrical power is created by electrons moving along a wire connecting the positive and negative electrodes, controlled by positively charged lithium atoms returning along a different path, through an electrolyte solution surrounding the electrodes.
In the 1970s when rechargeable batteries first came on the scene, lithium was chosen for a negative electrode, also known as the anode, because it displayed a storage capacity for energy ten times that of graphite, but a problem arose when the lithium-transporting electrolyte reacted with the lithium electrode, resulting in the growth of dendrites and early battery failure.
There have been many attempts to solve the problem of dendrites, including using different materials for the electrodes or coating a lithium electrode with some protective layer, but the result was often batteries with reduced power.
That led Zhang and his colleagues to look for an electrolyte formula that could function well inside batteries equipped with high-capacity lithium negative electrodes.
They developed an electrolyte with a high concentration of a compound known as lithium bis(fluorosulfonyl)imide salt, combining it with dimethoxyethane, a solvent.
A test battery, about the size of a quarter, was created using their electrolyte with a lithium anode, and researchers found that instead of dendrites, the anode grew a thin, mostly smooth film of lithium nodules that would not short-circuit their battery.
After a thousand cycles of charging and discharging, the circular test battery held around 99 percent of its starting energy while developing a healthy 4 milliAmps of electrical current per square centimeter of area, the research team reported in the journal Nature Communications.
The electrolyte will need some refining before it's ready for mainstream use, they note, and an evaluation of various additives is underway that hopefully will bring the efficiency to 99.9 percent, a level desirable for commercial adoption.
