Although lithium-ion batteries have become the mainstream of today's energy storage, the molecular and atomic basic science of their charge and discharge is still a mystery.

According to the "NatureCatalysis" study by the U.S. Department of Energy's Argonne National Laboratory, the research team has made a breakthrough in obtaining the chemical composition of the solid-electrolyteinterphase (SEI) between the electrode and the liquid electrolyte. This will help improve the team's ability to predict battery life, which is critical for electric vehicle manufacturers, said Dusan Strmcnik, a chemical engineer in the Materials Science Division (MSD) at Argonne National Laboratory.

Scientists have been working on deciphering the SEI of lithium-ion batteries for a long time, but they only understand that SEI is formed when the battery is charged, and a thousandth of a millimeter thick film appears on the graphite electrode, which protects the interface from harmful reactions, while allowing lithium ions It shuttles between the electrode and the electrolyte, so for lithium-ion batteries, a good SEI is a necessary condition. Strmcnik pointed out that battery efficiency and lifetime depend on the quality of SEI, and if scientists can figure out its chemical properties and independent composition rules, SEI can improve battery efficiency.

Therefore, an international research team formed by Argonne National Laboratory and the University of Copenhagen in Denmark, the Technical University of Munich in Germany and the BMW Group successfully solved the common chemical substance lithium fluoride (lithium fluoride) in the SEI of lithium-ion batteries.

The experimental and computational results indicate that the electrochemical reaction of hydrogen fluoride occurs during battery charging, from electrolyte to solid lithium fluoride and generates hydrogen. This type of reaction is highly dependent on electrode materials such as graphite, graphene and metal, proving that the battery catalyst importance.

The team also developed a new method to detect the concentration of hydrogen fluoride. Since hydrogen fluoride is a harmful substance formed by moisture and lithium salt (LipF6), this detection method will play a key role in the future scientific research of SEI. Researcher Nenad Markovic said that the study will be tested at the BMW battery research and development center in the future.