A team of scientists in South Korea has discovered a hidden problem that causes lithium-ion batteries to wear out faster—and they’ve found a simple way to stop it.
These batteries are widely used in electric vehicles and other electronics.
They usually use a special material in the cathode (the battery’s positive side) made from a mix of nickel, manganese, and cobalt, also called NMC.
To save money, battery makers have been using more nickel and less cobalt, since cobalt is expensive. But using more nickel makes the batteries wear out more quickly.
Until now, most experts believed battery damage mostly happened when the battery was overcharged.
But this didn’t explain why some batteries still lost power even when they weren’t overcharged.
So, researchers looked more closely at what happens during discharging—the time when a battery is actually being used.
Led by Professor Jihyun Hong at POSTECH (Pohang University of Science and Technology), along with Professor Jongsoon Kim’s team at Sungkyunkwan University, the researchers found something new.
They discovered that when a battery is used for a long time without being recharged—especially when the battery level drops very low—a reaction happens on the surface of the cathode. It’s called a “quasi-conversion reaction.”
Here’s what happens: oxygen escapes from the surface and reacts with lithium, forming a substance called lithium oxide (Li₂O).
This mostly happens when the battery drops to around 3.0 volts. Then, the lithium oxide reacts with the battery’s liquid (called the electrolyte), creating gas and damaging the battery even more. The battery can even swell up as a result.
This hidden problem is worse in batteries with high nickel content. The team tested batteries made with over 90% nickel.
If these batteries were used until they were almost fully drained, they only kept 3.8% of their capacity after 250 charge cycles. But if the battery was used more carefully and not fully discharged, it still held 73.4% of its capacity after 300 cycles.
This means that avoiding deep discharging can make batteries last much longer.
Professor Hong said, “People have mostly focused on charging as the cause of battery damage, but this research shows that discharging is just as important.”
The study was published in the journal Advanced Energy Materials. The findings could help electric vehicle makers and everyday users make better use of their batteries—and save money by making them last longer.
