Although lithium batteries are now the mainstream energy storage technology, the molecular and atomic science behind their charging and discharging remains a mystery.
According to a study published in *Nature Catalysis* by Argonne National Laboratory of the U.S. Department of Energy, the research team has made a breakthrough in determining the chemical composition of the solid-electrolyte interphase (SEI) between the electrode and the liquid electrolyte. Dusan Srmcnik, a chemical engineer in the Materials Science Division (MSD) at Argonne National Laboratory, stated that this will help improve the team's ability to predict battery life, which is crucial for electric vehicle manufacturers.
Scientists have long been dedicated to deciphering the SEI (Sediment Injection) in lithium-ion batteries, but they only understand that the SEI forms during battery charging, appearing as a thin film a fraction of a millimeter thick on the graphite electrode. This film protects the interface from harmful reactions while allowing lithium ions to shuttle between the electrode and the electrolyte. Therefore, a high-performance SEI is essential for lithium-ion batteries. Strmcnik points out that battery efficiency and lifespan depend on the quality of the SEI. If scientists can uncover its chemical properties and independent compositional rules, they can improve battery efficiency through the SEI.
Therefore, an international research team composed of Argonne National Laboratory, the University of Copenhagen in Denmark, the Technical University of Munich in Germany, and the BMW Group successfully deciphered lithium fluoride, a common chemical substance in the SEI of lithium batteries.
Experimental and computational results indicate that an electrochemical reaction of hydrogen fluoride occurs during battery charging, transforming the electrolyte into solid lithium fluoride and generating hydrogen gas. This type of reaction is highly dependent on electrode materials such as graphite, graphene, and metals, demonstrating the importance of battery catalysts.
The team is also developing a new method for detecting hydrogen fluoride concentration. Since hydrogen fluoride is a harmful substance formed from moisture and lithium salt (LiPF6), this detection method is crucial for future scientific research at SEI. Researcher Nenad Markovic stated that this research will be tested at the BMW Battery Research Center, and the next step is to design entirely new lithium-ion battery technology, paving another path for today's lithium-ion batteries.
