For decades, engineers theorized about what went on inside the cylinder of an internal combustion engine. Many of us grew up with clear plastic models showing pistons going up and down, gears whirring, and a tiny light bulb that went on at the top of the compression stroke to simulate what a spark plug does. But until recently, it was impossible to actually see inside an engine while it was running. The same problem affects those who are developing lithium-ion batteries.
We know that a lithium-ion cell can overheat while charging. When it does, lithium dendrites can pierce the outer battery shell, leading to the release of toxic gases and increasing the risk of fire or explosion. To keep that from happening, battery manufacturers and electric car companies limit how fast their batteries can be recharged, but those limits are based on theoretical calculations and may or may not correlate to the charging speed a call can safely tolerate.
Researchers at the University of Warwick in the UK say they have developed a device that can be inserted directly into a lithium-ion cell that will give instantaneous information about internal temperatures. “This could bring huge benefits to areas such as motor racing which would gain obvious benefits from being able to push the performance limits, but it also creates massive opportunities for consumers and energy storage providers,” says lead researcher Dr. Tazdin Amietszajew.
“Faster charging as always comes at the expense of overall battery life but many consumers would welcome the ability to charge a vehicle battery quickly when short journey times are required and then to switch to standard charge periods at other times. Having that flexibility in charging strategies might…help consumers benefit from financial incentives from power companies seeking to balance grid supplies using vehicles connected to the grid.
“This technology is ready to apply now to commercial batteries but we would need to ensure that battery management systems on vehicles, and that the infrastructure being put in for electric vehicles, are able to accommodate variable charging rates that would include these new more precisely tuned profiles/limits.”
According to a report in Science Daily,
“The technology the researchers have developed for this new, direct in-situ battery sensing employs miniature reference electrodes and Fiber Bragg Gratings (FBG) threaded through a bespoke strain protection layer. An outer skin of fluorinated ethylene propylene (FEP) was applied over the fiber, adding chemical protection from the corrosive electrolyte. The result is a device that can have direct contact with all the key parts of the battery and withstand electrical, chemical and mechanical stress inflicted during the batteries operation while still enabling precise temperature and potential readings.”
During testing on commercially available 18650 lithium-ion cells, the researchers determined that those cells could be safely charged up to five times faster than previously thought possible without damage. The technology can be used during normal battery operation without impeding a cell’s performance.
Associate Professor Dr. Rohit Bhagat says,
“This method gave us a novel instrumentation design for use on commercial 18650 cells that minimizes the adverse and previously unavoidable alterations to the cell geometry. The device included an in-situ reference electrode coupled with an optical fiber temperature sensor. We are confident that similar techniques can also be developed for use in pouch cells. Our research group…has been working on a number of technological solutions to this problem and this is just the first that we have brought to publication. We hope to publish our work on other innovative approaches to this challenge within the next year.”
The research was carried out as part of AMPLIFII, a collaborative research project supported by Innovate UK and the UK Government Office for Low Emission Vehicles. The full report is available online and is not hidden behind a paywall for the engineers among us who may wish to delve into the research more deeply. It is interesting to note that Jaguar is one of the sponsors of the research. Jaguar is committed to Formula E racing, so the findings from this research may directly impact its racing program in the future.