Lithium-ion batteries have already entered all aspects of people's lives. How to design safer, high-performance lithium batteries is a matter of great concern to everyone. During the charging and discharging process of a lithium ion battery, the electrode material and the electrolyte solution will react at the solid-liquid interface to form a passivation layer covering the surface of the electrode material, called solid-electrolyte interface (SEI) Floor. The researchers found that the SEI layer determines the performance of most batteries, but people's understanding of the structure and properties of the SEI layer is still very limited.
Wang Yanting, a researcher at the Institute of Theoretical Physics, Chinese Academy of Sciences, and Su Mao, a Ph.D. Physical and chemical properties were studied. Related results were published in Nature Nanotechnology magazine.
When the lithium ion battery is charged for the first time, before any phase interface chemistry occurs, due to the role of lithium ions and the surface potential of the electrode, the solvent molecules will quickly self-assemble at the electrode and electrolyte interface to form an electric double layer. The structure of this electric double layer determines the phase interface chemistry of the battery. In particular, when the electrode is negatively charged, the electric double-layer structure on the surface will evacuate anions (such as fluoride ions, etc.), thereby forming a thin, dense, inorganic SEI inner layer. The main function of this dense layer is to conduct lithium ions and insulate electrons. After the inner layer of SEI is formed, an outer layer rich in organic molecules that can penetrate into the electrolyte will be further formed. The study found that the main component of the SEI inner layer is lithium oxide, which negates the traditional view that lithium fluoride is contained on the phase interface. For some types of batteries, because fluoride ions play a very important role on the phase interface, it is necessary to introduce a solvent or additive containing fluorine.
This study solves the problem of SEI layer characteristics that have long plagued people.
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