As part of their research into next-generation battery technology, scientists at the University of California, San Diego, are exploring designs that can operate in extreme temperatures, and they have already begun to make some significant progress. In their latest research, the team demonstrated a lithium battery that can not only operate in frigid and hot temperatures but can store twice the energy of current devices while being more friendly to the environment.
Last year, the same group of researchers announced an interesting breakthrough that stems from the ability to manipulate the movement of ions in lithium batteries. This was made possible by a reinvented electrolyte solution that transports lithium ions between the two electrodes of the battery, the cathode and the anode.
The team found success with an electrolyte that forms a weaker bond with lithium ions, which allows for a more uniform distribution of lithium ions during charging. This weakly bound electrolyte was incorporated into an experimental lithium battery with a high-density metal anode and a sulfur-based cathode capable of operating at sub-zero temperatures while maintaining most of its capacity.
By continuing to experiment with its electrolyte formulation, scientists have now developed a version that can also operate at the other end of the spectrum. The new electrolyte features lithium salts and dibutyl ether, a compound with a boiling point of 141°C that allows the electrolyte to remain liquid at high temperatures.
In proof-of-concept experiments with this electrolyte, these cells were able to maintain 87.5% capacity at -40°C and 115.9% capacity at 50°C. They also exhibited a high coulombic efficiency of over 98% at these temperatures, which is related to their ability to handle more charge cycles before the end of their life.
A battery that has the ability to operate at lower temperatures can give electric vehicles greater range in colder climates. Conversely, a battery capable of operating safely at higher temperatures can, among other benefits, eliminate the need for cooling systems to prevent overheating.
“You need to operate at high temperatures in areas where the ambient temperature can reach triple digits (Fahrenheit) and the roads can get even hotter,” explained study author Cheng Chen (phonetic). “In electric vehicles, the battery pack is usually under the floor, near these hot roads. In addition, the battery gets hot during operation simply because there is current passing through it. If the batteries cannot tolerate this heating at high temperatures, their performance will rapidly degrade.”
Once again, the team’s electrolyte is compatible with high-density lithium metal anodes and cathodes made from sulfur. This type of lithium-sulfur battery is expected to store as much as twice the energy of today’s lithium batteries, which could mean double the range of electric vehicles. In addition, sulfur is a more abundant source and less problematic than the relatively rare and expensive metal cobalt used in today’s lithium battery cathodes, thus reducing the pressure on the environment.
The team also says their design offers a longer cycle life than current lithium-sulfur batteries. It is now shifting its focus to further extending that cycle life, enabling the batteries to operate at higher temperatures, and then scaling up the technology.
The study will be published this week in the Proceedings of the National Academy of Sciences.