Researchers at the Department of Energy's Pacific Northwest National Laboratory (Richland, Wash.) have developed a "hybrid" anode made of graphite and lithium that could quadruple the lifespan of lithium-sulfur batteries from 100 to 400 cycle charging rates.
Today's electric vehicles are commonly powered by rechargeable lithium-ion batteries, which are also being used to store renewable energy. But the chemistry of lithium-ion batteries limits how much energy they can store. One promising solution is the lithium-sulfur battery, which can hold as much as four times more energy per mass than lithium-ion batteries. Lithium-sulfur batteries, however, can't be charged as many times as lithium-ion batteries.
"Lithium-sulfur batteries could one day help us take electric cars on longer drives and store renewable wind energy more cheaply, but some technical challenges have to be overcome first," said PNNL Laboratory Fellow Jun Liu. "PNNL's new anode design is helping bringing us closer to that day."
The downside of using the lithium-sulfur battery is dealing with unwanted side reactions that cut the battery's life short. The battery's sulfur-containing cathode slowly disintegrates and forms polysulfide molecules that dissolve into the battery's electrolyte liquid. The dissolved sulfur eventually develops into a thin solid-state electrolyte interface film layer. The film forms on the surface of the lithium-containing anode and grows until the battery is inoperable.
Instead of stopping sulfur leakage from the cathode as is commonly attempted, PNNL researchers added a protective graphite shield to the anode. The shield moves the sulfur side reactions away from the anode's lithium surface, preventing it from growing the debilitating interference layer.
"Sulfur is still dissolved in a lithium-sulfur battery that uses our hybrid anode, but that doesn't really matter," said Liu. "Tests showed a battery with a hybrid anode can successfully be charged repeatedly at a high rate for more 400 cycles, and with just an 11 percent decrease in the battery's energy storage capacity."
The research is conducted with small, thin-film versions of the battery. Larger, thicker batteries would be needed to test to power electric cars and store renewable energy for real-world applications, said Liu.
The test results are available in Nature Communications.
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