A team of researchers in South Korea has discovered a hidden reason why lithium-ion batteries wear out over time—and their findings could lead to longer-lasting batteries for electric vehicles and other devices.
The study, led by Professor Jihyun Hong from the Department of Battery Engineering at POSTECH and published in Advanced Energy Materials, sheds new light on how battery degradation happens, even when everything seems to be working normally.
Most electric vehicle batteries use a material called nickel-manganese-cobalt (NMC) as the cathode, which is the part of the battery that helps store and release energy.
To make batteries cheaper, manufacturers have started using more nickel and less cobalt. While this helps reduce costs, it also tends to shorten battery life.
Until now, researchers believed that overcharging was the main reason these batteries degraded. But this didn’t fully explain why some batteries still wore out during normal use.
To get to the bottom of the mystery, the research team studied what happens inside the battery during discharge—the time when the battery is being used to power a device or vehicle.
They discovered a process called the quasi-conversion reaction, which happens on the surface of the cathode when the battery is used for a long time without being recharged.
During this reaction, oxygen escapes from the cathode surface and combines with lithium to form lithium oxide (Li₂O). This happens especially when the battery is discharged down to around 3.0 volts. The lithium oxide then reacts with the battery’s liquid electrolyte, creating gas and causing the battery to swell and degrade faster.
This effect was much worse in batteries with high nickel content. When these batteries were used until almost all their power was drained, the damage was severe.
In tests, some batteries lost nearly all their capacity—keeping only 3.8% of their charge after 250 cycles. But when researchers avoided letting the battery discharge too deeply, the results were much better. Those batteries kept 73.4% of their original charge even after 300 cycles.
Professor Hong emphasized that this overlooked part of battery use—discharge—plays a much bigger role in battery health than previously thought.
The discovery not only explains a major cause of battery wear but also offers a simple fix: don’t run your batteries completely empty. This insight could lead to better battery designs and smarter ways to use them, helping extend the life of batteries in electric vehicles and more.
