Research results have shown that using an electric vehicle battery until it is completely drained reduces its lifespan.
A research team led by Professor Hong Ji-hyun of the Battery Engineering Department at Pohang University of Science and Technology (POSTECH) collaborated with Professor Kim Jong-sun and his research team from Sungkyunkwan University to reveal the cause of the shortened lifespan of lithium-ion batteries when used until they are discharged, they noted on the 31st. The findings of this research were published in the international academic journal 'Advanced Energy Materials.'
Typically, lithium-ion batteries composed of nickel, manganese, and cobalt are used in electric vehicles. Recently, 'high-nickel batteries,' which increase the amount of nickel instead of cobalt, have been widely used. However, there has been a problem where the lifespan is shorter with a higher nickel content. It has been known that battery performance degradation has mainly been due to overcharging, but the reasons for lifespan reduction during normal use have not been properly identified.
The research team discovered that a phenomenon called 'quasi-conversion reaction' occurs when continuously using the battery without charging it. This reaction involves oxygen escaping from the surface of the battery's anode and combining with lithium to create lithium oxide, which reacts with internal materials to generate gas, causing the battery to swell and degrade its performance.
Especially, the higher the nickel content, the more severe the performance degradation was. Additionally, the research team confirmed that when the battery is used long enough to deplete most of its capacity, the deterioration in performance, such as swelling of the battery, accelerates.
The research team proved that the battery lifespan can be significantly extended depending on the usage rate, i.e., how much it is used and charged. When the battery was charged after being nearly depleted, only 3.8% of the capacity remained after 250 uses. However, when charged after using it only to a certain level, it maintained 73.4% of its capacity even after 300 uses.
Professor Hong Ji-hyun said, "The impact of discharging, which is the actual battery usage process, has been overlooked," and added, "This research presents an important development direction for creating batteries that can last longer."
References
Advanced Energy Materials, DOI: https://onlinelibrary.wiley.com/doi/10.1002/aenm.202404193