Currently, lithium-ion batteries are the gold standard for energy storage in our electronics and electric cars, but for a long time researchers have believed that lithium-sulfur batteries would become an even better choice because of their high energy density compared to their weight and now with a new breakthrough in the technology, it appears they were right. Researchers at Oak Ridge National Laboratory in Tennessee have developed a lithium-sulfur battery that stores four times as much energy as a lithium-ion battery and is also cheaper to make and safer.
As researchers have been working on lithium-sulfur batteries, the one major problem they faced was with the liquid electrolyte being used. The liquid electrolyte was highly conductive, but the downside was that it also caused the battery to break down prematurely, which has kept the technology from moving forward. The Oak Ridge team were able to overcome the problem by using a solid electrolyte instead.
"This game-changing shift from liquid to solid electrolytes eliminates the problem of sulfur dissolution and enables us to deliver on the promise of lithium-sulfur batteries," said Chengdu Liang, the lead author of the study. "Our battery design has real potential to reduce cost, increase energy density and improve safety compared with existing lithium-ion technologies."
The researchers used a new class of sulfur-rich materials to create the solid electrolyte and the cathode for the battery. The elemental sulfur they used is an industrial byproduct of petroleum processing, which keeps costs low and also opens up a way to use a waste stream for something beneficial.
"Sulfur is practically free," Liang said. "Not only does sulfur store much more energy than the transition metal compounds used in lithium-ion battery cathodes, but a lithium-sulfur device could help recycle a waste product into a useful technology."
The real proof is in the performance though. The lithium-sulfur battery was able to maintain a capacity of 1200 milliamp-hours (mAh) per gram after 300 charge-discharge cycles. A traditional lithium-ion battery cathode has an average capacity between 140-170 mAh/g, but because the voltage of the lithium-sulfur battery is half that of the lithium-ion battery, the eight-fold increase in capacity translates into a four-fold increase in density.
The other benefit is less flammability with a solid electrolyte, which makes the battery safer.
The researchers have more work to do though. They plan on increasing the conductivity of the solid electrolyte and finding a replacement for the ceramic structure which is very brittle.