Li-Ion batteries degrade even without charging — scientists have discovered this and found a solution

Scientists from Pohang University of Science and Technology in South Korea have discovered a previously unknown The mechanism of degradation of lithium-ion batteries in the process of using them.

The research team, which included Seunggyun Jeong and Dr. Gookhyun Lim, led by Professor Jihyun Hong of POSTECH’s Battery Engineering Department, together with a group of scientists led by Professor Jongsun Kim of Sungkyunkwan University, found that lithium-ion batteries used in electric vehicles batteries, mainly have ternary nickel-manganese-cobalt cathodes with a high nickel content and a minimum content of more expensive cobalt. This reduces the cost of manufacturing these batteries, but the high nickel content reduces the overall battery life.

Decreased performance of lithium-ion batteries is traditionally associated with an excessive number of charging cycles. However, researchers have discovered a previously unknown degradation cycle that occurs even under stable voltage conditions.

The researchers found, that use of the battery without recharging for a long time provokes a quasi-conversion reaction on the cathode surface. As part of this reaction, oxygen is released from the cathode surface and reacts with lithium to form lithium oxide, especially when the low charge level is close to 3.0 V. The lithium oxide then reacts with the electrolyte, causing it to decompose and form gaseous byproducts, which contributes to the loss of energy efficiency of the battery.

At the same time, such reactions have more serious consequences in cathodes with a high nickel content. The researchers found that degradation processes, including swelling, are more pronounced in batteries that are used until they are completely discharged.

Meanwhile, the researchers offer a simple but effective solution — optimizing battery usage and preventing complete battery discharge. Experiments have shown that severely discharged batteries with a high nickel content (over 90%), which leads to the onset of the quasi-conversion reaction, retained only 3.8% of their capacity after 250 cycles. At the same time, batteries with controlled use retained 73.4% of their capacity even after 300 cycles.

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The results of the study were published in the journal Advanced Energy Materials

Source: TechXplore