June 6, 2013
Sulfur-Based Battery Has Four Times The Energy Of Lithium-Ion
Brett Smith for redOrbit.com - Your Universe Online
Engineers from Oak Ridge National Laboratory (ORNL) have announced the successful testing of an all-solid lithium-sulfur battery with about four times the energy density of today´s lithium-ion batteries.Energy density is defined as the amount of energy stored in a system per unit of volume.
"Our approach is a complete change from the current battery concept of two electrodes joined by a liquid electrolyte, which has been used over the last 150 to 200 years," said ORNL scientist Chengdu Liang, lead author of a report on the battery tests published this week in the journal Angewandte Chemie International Edition.
The development of a long-lasting, commercially usable lithium-sulfur battery has eluded scientists for decades. The use of liquid electrolytes has proven to be a massive hurdle in the way of pursuing these super batteries. A liquid electrolyte helps to conduct ions through the battery by allowing lithium compounds to dissolve. However, the same dissolution process causes the battery to readily break down.
Instead of pursuing the liquid electrolyte route, the team decided to engineer groundbreaking sulfur-rich materials that conduct ions as well as those used in a conventional battery's cathode. The ORNL team then combined the new cathode and a lithium anode with an ORNL-developed solid electrolyte material.
"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," Liang said. "Our battery design has real potential to reduce cost, increase energy density and improve safety compared with existing lithium-ion technologies."
The new cathode allowed the battery to maintain a capacity of 1200 milliamp-hours (mAh) per gram after 300 charge and discharge cycles at 140 degrees Fahrenheit. By comparison, a conventional lithium-ion battery cathode has an average capacity between 140-170 mAh/g under the same conditions. However, lithium-sulfur batteries deliver about half the voltage, translating into four times the energy density of lithium-ion technologies, according to Liang.
One of the added benefits of the team's solid battery is that it increases safety by removing flammable liquid electrolytes that can react with lithium. The battery also uses elemental sulfur, an abundant industrial derivative of petroleum processing.
"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 team said they hope to see their work move quickly from the laboratory into commercial applications, despite the battery still being in the testing stages. A patent on the team's battery is currently pending.
"This project represents a synergy between basic science and applied research," Liang said. "We used fundamental research to understand a scientific phenomenon, identified the problem and then created the right material to solve that problem, which led to the success of a device with real-world applications."
The Oak Ridge National Laboratory is funded and operated by the US Department of Energy. The facility was toured earlier this week by incoming Energy Secretary Ernest Moniz, who was sworn in on May 21.