Credit: Michael J. Counihan et al.
Researchers at the Argonne National Laboratory have published new information describing early warning signs of battery failure. The findings provide battery researchers with valuable information to help shape the future of electric vehicle battery designs.
In the study, published in Joule, researchers focused their attention on all-solid batteries containing a lithium metal anode. These batteries are often viewed as the “holy grail” of current batteries thanks to their energy density.
During the development of a novel solid electrolyte for use in EVs, the team noticed brief voltage fluctuations in the battery. Upon further testing, the team discovered that the batteries were experiencing soft-shorts, or small temporary short circuits. Similar to a short circuit, soft-shorts are caused by the growth of lithium filaments. However, soft-shorts present a smaller amount of growth and while some electrons may stay within the battery, others may flow to the external device.
Testing revealed that batteries can continue operating with soft-shorts, however, the filaments will grow and lead to battery failure over time. “Soft-shorts are the first step off the cliff to permanent battery failure,” said Michael Counihan, Argonne postdoctoral appointee. The researchers also discovered that soft-shorts are highly dynamic, forming and disappearing within a matter of microseconds or milliseconds.
“This is an important takeaway for battery researchers,” said Counihan. “With typical battery testing in the lab, researchers may only measure voltage every minute or so. During that time, you could have missed the formation and death of thousands of soft-shorts. They’re like little ghosts that are destroying your battery without you knowing it.”
Heat was identified as the most common reason for the disappearance of soft-shorts. Heat is generated when electrons flow through the lithium filaments, this heat is sufficient to melt the filaments especially if the electrolyte is thermally insulating.
To assist future researchers, the team compiled a list of 20 detection and analysis methods for soft-shorts. “We realized that there are no papers in the literature that use more than two of these techniques,” said Counihan. “To make the list more useful for researchers, we included information on each method’s advantages and disadvantages. Since soft-shorts are so dynamic, it’s good for researchers to have many tools available to better understand the impacts of soft-shorts.”
The analysis and detection methods compiled by the researchers will aid the formation of the next generation of battery technology. Armed with information, battery researchers can formulate designs to stem the growth of lithium filaments. “When researchers understand the dynamics of the soft-shorts in their batteries, they are better equipped to refine their materials to avoid these failure pathways,” said Counihan.