researchers at university college london (ucl) have developed a novel technique for observing the behavior of lithium-ion batteries during short-circuit conditions to help improve the safety and reliability of high-density batteries, according to a report on the university website.
thermal image showing thermal runaway of an 18650 cell with an implanted internal short
circuiting device. (donal finegan/ucl, nasa and nrel)
previous efforts at monitoring a battery’s response to thermal runaway have included 3-d and real-time but the ucl team was able to track the temperature and the structure of the cells as the battery is short-circuited through high-speed x-ray imaging.
the research was performed in partnership with nasa’s johnson space center, the u.s. department of energy’s national renewable energy laboratory, wmg at the university of warwick (u.k.), diamond light source, the european synchrotron, and the national physical laboratory.
a temperature-activated internal short circuit device was created in 2015 and was used in this research to start a chain of events leading to short-circuit. using x-ray imaging, scientists could monitor the cells during the moments leading up to and during catastrophic failure.
the article explained, “individual cells, as well as small cell modules, were tested under conditions that represented a worst-case battery failure scenario. short circuits were initiated inside the batteries at ~60°c. during the failure process, cell temperatures reached in excess of 1,085°c.”
it added, “from analysing the high-speed imaging frame by frame, the team looked at the effects of gas pockets forming, venting and increasing temperatures on the layers inside two distinct commercial li-ion batteries and identified consistent failure mechanisms.”
researchers expressed surprise at the susceptibility of neighboring cells to spreading thermal runaway and it indicated a need for isolating cells in future battery designs.
the research was recently published in energy and environmental science. the abstract stated:
“lithium-ion batteries are being used in increasingly demanding applications where safety and reliability are of utmost importance. thermal runaway presents the greatest safety hazard, and needs to be fully understood in order to progress towards safer cell and battery designs.
“here, we demonstrate the application of an internal short circuiting device for controlled, on-demand, initiation of thermal runaway. through its use, the location and timing of thermal runaway initiation is pre-determined, allowing analysis of the nucleation and propagation of failure within 18650 cells through the use of high-speed x-ray imaging at 2000 frames per second.
“the cause of unfavourable occurrences such as sidewall rupture, cell bursting, and cell-to-cell propagation within modules is elucidated, and steps towards improved safety of 18650 cells and batteries are discussed.”