This month, federally sponsored scientists at the Oak Ridge National Lab (ORNL) publicized their creation of an all-solid lithium-sulfur battery with about four-times the energy density of a lithium-ion battery – and this one is being prepared for commercial applications.
Stories of close-but-not-quite-ready battery chemistry promising to one day multiply electric car range and vault EVs into the mainstream have been fairly common. But while more has yet to happen with this story, and the ORNL didn’t at this early stage discuss automotive applications, researchers have applied for a patent for what they say is a solution that’s safer and cheaper than lithium-ion.
“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 Chengdu Liang, lead author on the ORNL study published this month in Angewandte Chemie International Edition.
The ORNL researchers say that their new ionically-conductive cathode enabled their Li-S battery to maintain a capacity of 1200 milliamp-hours (mAh) per gram after 300 charge-discharge cycles at 60 degrees Celsius (140 degrees Fahrenheit).
This eclipses a traditional lithium-ion battery cathode which has an average capacity between 140-170 mAh/g. Because lithium-sulfur batteries deliver about half the voltage of lithium-ion versions, Liang said this eight-fold capacity increase in the ORNL battery cathode translates to four times the gravimetric energy density of lithium-ion technologies.
Despite rhetoric from various critics to the effect that the federal government never created anything but a boondoggle, and future growth belongs to private industry, it appears at this point that taxpayer dollars may have actually struck pay dirt.
Or so would go the implications of the synthesis and characterization of the new battery that was conducted at the Center for Nanophase Materials Sciences (CNMS) at ORNL. This in turn was done under research sponsored by the U.S. Department of Energy, through the Office of Energy Efficiency and Renewable Energy’s Vehicle Technologies Office.
The discovery was described as bypassing a “catch-22” that had baffled researchers for decades. In previous attempts to develop lithium-sulfur batteries, liquid electrolyte was shown to help conduct ions through the battery by allowing lithium polysulfide compounds to dissolve. This was never commercially viable however because the same dissolution process caused the battery to prematurely break down.
“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.”
How did they get the “device with real world applications?” The ORNL researchers said they first synthesized a new class of sulfur-rich materials that conduct ions as well as the lithium metal oxides conventionally used in the battery’s cathode.
They then combined the new sulfur-rich cathode and a lithium anode with a solid electrolyte material that they also developed and created the energy-dense, all-solid battery.
“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.”
What’s more, Liang told Gizmag that the new lithium-sulfur batteries are stable.
“We did not observe self-discharge. A charged cell was put on shelf for over a week, and it still delivered the same capacity. The essence of our all-solid battery design is to eliminate the self-discharge through the all-solid configuration,” Liang said.
“This battery charges slower than Li-ion battery at the current status for a simple reason; the ionic conductivity of both the solid electrolyte and cathode are not high energy to have high current density. Much better performance at elevated temperatures such as 60 degrees C or higher,” he added.
At the same time, the ORNL researchers say they enhanced safety and cut costs because their chemistry relies on sulfur – a compound presently considered a waste byproduct of petroleum processing.
Could it be an ironic twist that a solution toward overcoming the “addiction to oil” was discovered within petroleum itself?
This does remain to be seen, but the researchers’ all-solid battery design also eliminates flammable liquid electrolytes that can react with lithium metal, thus it’s more fire resistant, and, as mentioned, it’s also low cost.
“Sulfur is practically free,” Liang said of the byproduct of petroleum processing. “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 investigation of the ionic conductivity of the new compounds was supported by the Energy Department’s Office of Science. The Center for Nanophase Materials Sciences is one of the five Energy Department Nanoscale Science Research Centers (NSRCs) supported by Energy Department’s Office of Science national user facilities for interdisciplinary research at the nanoscale.
But what does this “game-changing” technology mean for the electric car? Anything? Or does it only mean cell phones will get longer talk time, and laptops will go day and night? We are eager to find out, and have put in inquiries for further information. The following is what ORNL initially said upon publicizing the discovery:
“Although the team’s new battery is still in the demonstration stage, Liang and his colleagues hope to see their research move quickly from the laboratory into commercial applications,” the lab offered in a statement. “A patent on the team’s design is pending.”
We will let you know more when we learn more.