The pressure of aging on lithium-ion batteries
At UL, a first-stage research study was developed to understand the potential role aging played in lithium-ion battery field failures. The research identified two critical safety concerns: the polarization effect on aged batteries (which can have a significant effect on battery efficiency and safety due to increased heating and the accelerated aging process), and the lower thermal stability of active materials in aged batteries.
Thermal stability is the stability of the cell at higher temperatures. A “hot box” test on aged and fresh samples demonstrates the effect of lower thermal stability of active materials in aged batteries. Research identified this as a critical safety concern, with data from a differential scanning calorimeter suggesting that heat-generating reactions within the cells occur earlier for an aged cell.
New risks, new science
Research is still in the early stages for assessing the effects of aging on lithium-ion batteries, and it will need to go beyond the single chemistry studied thus far, moving into other common cell chemistries. Additionally, research will be extended over more cycles and conducted on large-format lithium-ion batteries such as those in stationary energy storage applications. Discovering the full impact of aging on lithium-ion battery safety will allow independent standards organizations to update standards and help to ensure the safe use of lithium-ion batteries over time.
Innovation allows greater efficiency and productivity, but along with innovation comes risk. With the continuing development and proliferation of lithium-ion batteries, there is a need for research that informs rigorous safety standards. Devices powered by lithium-ion batteries offer tremendous opportunities, and as manufacturers respond with new technologies, there is a need to put safeguards in place that help to ensure the safety of lithium-ion batteries, affirming smooth adoption by transportation, energy, healthcare and other industries.
Laurie Florence is the principal engineer at UL for batteries, among other areas. With more than 20 years of experience in testing and certification, she has responsibility for technical competency criteria for UL staff and supports UL certification programs. Alvin Wu is research engineer, corporate research at UL, focusing on battery technology in industrial settings, including advancing battery safety research and updating battery safety. For more information on UL research, visit UL.com/newscience.
Photo by Brookhaven National Laboratory.