Lithium-ion batteries certainly have made life easier for anyone who uses a cell phone, e-reader or laptop. Compared to the classic lead acid battery, lithium-ion cells are little powerhouses that can store the same amount of energy in a fraction of the size and weight. All that portability comes with a price, though.
In a few very scary cases, the batteries have failed, releasing all that stored energy in a rush and causing a fire or explosion. Was it the age of the battery? Did extreme heat cause the problem? Could puncturing the battery cause an explosion?
UL is working to find out more about why those batteries failed and to apply these findings to safety standards in a world that’s clamoring for lighter batteries with longer lives. In recent studies, researchers took a commonly used lithium-ion cell type—the 18650-type lithium-ion battery with a lithium cobalt oxide (LiCoOx) chemistry—and studied how the battery responded to recharging and abuse at difference temperatures.
Our engineers tested the batteries at 25°C and 45°C, putting the 2,800-milliamp-hour battery through its paces. The tests covered 50, 100, 200, 300, 350 and 400 charging cycles while researchers tracked what happened to the battery as it aged and how well it could tolerate abuse. As the battery got older, we watched how it responded to overcharging, heat extremes and induced internal short circuits. In general, we found two safety concerns: Batteries became more likely to fail as they got older and their charging efficiency declined, and when they were exposed to more than 60°C.
It’s only the first step in our research to track how aging and the rigors of use affect lithium-ion batteries. Next, researchers will study lithium-ion batteries with different chemistries, such as NMC (lithium nickel manganese cobalt oxide) and LFP (lithium iron phosphate).
Lithium-ion batteries already are in 95 percent of the world’s cell phones, but the market is expected to double by 2016. And as interest in electric vehicles grows, that type of use for lithium-ion cells will jump by 10 times. Our research will help update the safety standards to reflect the findings and to help drive the safe use of lithium-ion batteries over time and in different products.