Scientists have devised a solution for lithium batteries overheating and possibly catching fire.
While lithium-ion batteries are seen as one of the most effective and environmentally-sound battery technologies, these contain carbonated organic solvents, highly flammable substances that could burst into flame within a narrow temperature range. This prompted researchers at the University of California – San Diego (UCSD) to consider possible solutions to prevent lithium-ion batteries from catching fire when used at extreme temperatures.
As a result, Professor Shirley Meng and her team at UCSD’s Army Research Laboratory recently developed a new set of liquefied gas electrolytes that can be used to produce lithium batteries that can be safely operated in temperatures ranging from -60 to 55ºC.
According to Yijie Yin, one of the researchers on Meng’s team, they came up with the concept for the liquefied gas electrolyte (LGE) back in 2017, presenting it in a paper published in the journal Science. Over the next five years, they came up with an electrolyte composed of several fluorocarbon gasses which, when subjected to pressure, liquefy into a chemically stable electrolyte with a low freezing point.
Yin added that the cost of producing such electrolytes is considerably minimal.
What Makes This Electrolyte Different?
The original LGE designed by the Meng team in 2017 was based on fluoromethane and difluoromethane. But while the resulting liquefied electrolyte was stable, it remained flammable under moderate operational pressure.
To overcome flammability and other safety concerns, the team sought to make the LGEs safer to use by incorporating clean fire-extinguishing components into their molecular composition – a capability specific to LGEs. The addition of fire-retardants 1,1,1,2 tetrafluoroethane (TFE) and pentafluoroethane (PFE) enabled the electrolyte to keep its low freezing point under reduced vapor pressure.
The addition of TFE and PFE thus increases the electrolyte’s safety and significantly reduces the flammability of a lithium-ion battery when used at a high temperature.
80% of the resulting LGE is now made up of these fire-extinguishing components. Yin added that the team also used dimethyl ether to dissolve salts in the compound to form an electrolyte with a highly concentrated ratio of salt to ether to give it a wider electrochemical window and greater stability.
The unique solvation structure enables the new electrolyte to maintain near-constant conductivity through a much wider range of temperatures over 130º, thus ensuring that the lithium cation serves as a dominant transport specie. In tandem, these factors will help create batteries with better performance even at lower temperatures.