ADELPHI, Md. -- Army scientists and their partners at the University of Maryland and Johns Hopkins Applied Physics Laboratory have developed a high-energy aqueous lithium-ion battery that won't catch fire no matter how damaged it becomes. These new batteries continue to operate in conditions where traditional batteries fail.
Lithium-ion batteries have the potential to deliver enormous amounts of energy, but that power often comes at the cost of safety. When lithium-ion batteries get punctured or become overheated, they can cause deadly fires that even water can't extinguish.
For the Army, a battery that can power high-energy electronic devices while withstanding extreme abuse would be vital for enhancing Soldier capability and survivability in the modern battlefield.
"Our project addresses the risk by allowing high-energy or high-power batteries to be put on the soldier with no risk of the batteries catching on fire," said Dr. Arthur von Wald Cresce, a materials engineer at the U.S. Army Combat Capabilities Development Command's Army Research Laboratory. "We're hoping that by designing safety into the battery, this concern goes away and Soldiers can use their batteries as they please."
Traditional lithium-ion batteries catch fire because the electrolyte in the battery is oftentimes a flammable organic compound that is sensitive to temperature, he said. When these batteries become damaged, they can generate significant amounts of heat and ignite a fire with the electrolyte as the fuel.
Aqueous lithium-ion batteries navigate around this problem by using a nonflammable, water-based solvent as the electrolyte for the battery. In addition, this new technology uses a lithium salt that is not heat-sensitive, allowing for the battery to be stored at a much wider range of temperatures.
"If the battery's temperature in storage happens to spike to 150 degrees Fahrenheit, the battery won't cease to operate," Cresce said. "In fact, it'll probably still operate the same. Most importantly, it will not sustain a flame, so any damage to the battery will result in, at worst, a battery that doesn't deliver anymore voltage."
This research, part of the laboratory's Center for Research in Extreme Batteries, began in late 2014 with the goal to promote research collaboration the lab and partners in industry and academia.
Cresce and the team first collaborated with scientists at the University of Maryland to study the properties of a new class of aqueous electrolytes known as water-in-salt electrolytes. In November 2015, they published their findings in the journal Science.
Recently, Cresce and the team made a major breakthrough in their research when they created an aqueous lithium-ion battery prototype with a maximum potential of 4 volts, which is around the same amount of energy found in typical lithium-ion batteries.
"We had batteries that delivered high power but they were limited in potential and therefore limited in their energy," Cresce said. "The maximum potential we got from our early batteries was about 3 volts. But we didn't want to sacrifice energy, because Soldier batteries need a very large reserve of energy to operate for long times. So our most recent advance was to make full prototypes of the 4-volt high-energy aqueous lithium-ion battery."
Army scientists significantly improved the design of the battery to make it even easier to produce.
For previous versions of the battery, Cresce and the team established a protection layer composed of a lithium electrolyte dispersed in a very hydrophobic ether solvent around the graphite anode in order to shield it from the electrolyte; however, the ether solvent was so volatile that it would evaporate in just a couple of minutes, making it difficult to manufacture.
The aqueous lithium-ion battery uses a graphite anode, which reacts poorly with the water-based electrolyte.
With the latest version of the aqueous lithium-ion battery, Cresce and the team created a special polymer gel to encase the anode instead. This gel layer not only does a very good job of repelling water, but it is also much less volatile than the ether solvent, he said.
"We are now able to construct batteries without worrying if the protective layer has evaporated or not," Cresce said. "Additionally, the gel is very easy to make. We have been using short doses of ultraviolet light to cure the gels just like any plastics manufacturer or label and packaging printer."
Cresce envisions that when safe 4-volt lithium batteries are available for the Soldier, energy supplies would come equipped with less bulky, protective packaging, which would reduce the weight of the gear that Soldiers would have to carry.
"Every Soldier we talked to would like to carry less batteries and would like to be able to use their equipment without having to really think about how it's powered, and the aqueous lithium-ion batteries allow them to do these things," Cresce said. "The batteries can be packaged less heavily so they can carry more energy effectively, which means less battery changes and less batteries carried."
Not only that, aqueous lithium-ion batteries may influence the development of future electronic devices because the batteries can be made in different shapes and sizes, allowing for a more flexible and efficient design.
Cresce said the Army hopes to integrate the aqueous lithium-ion batteries into hybrid and electric military vehicles with the added possibility of expanding the technology into the commercial vehicle industry.
He largely credits the growth of the aqueous lithium-ion battery research at the laboratory to the efforts of his fellow team members and the support of Army leadership.
"With just one year accelerated funding, we were able to take our bench technology and turn it into a prototype," Cresce said. "We're going to manufacture prototypes with the hopes that we can get this into the field between 2026 and 2028 on a device that the soldier can wear and use in the field. I really hope we can stick that timeline, because it would fit in very much with the modernization of the U.S. Army as we move forward."
The CCDC Army Research Laboratory (ARL) is an element of the U.S. Army Combat Capabilities Development Command. As the Army's corporate research laboratory, ARL discovers, innovates and transitions science and technology to ensure dominant strategic land power. Through collaboration across the command's core technical competencies, CCDC leads in the discovery, development and delivery of the technology-based capabilities required to make Soldiers more lethal to win our Nation's wars and come home safely. CCDC is a major subordinate command of the U.S. Army Futures Command.