A New Method for Evaluating Li-Ion Battery Anode Materials Based on Surface Compositional and Structural Characterization

Abstract

There is a global effort to develop safer lithium-ion batteries (LIB) with a high energy density and long lifetime. Material properties, their mutual interactions, and active interfaces are key factors in battery performance. Popular methods involve the mixing of different ingredients and development of a suitable fabrication process. Significant effort has been spent to understand the reaction mechanism of battery materials, but this is very challenging due to high system complexity. Different techniques have been developed to follow these reactions, and most significantly, the reactions between Li and electrode materials. Our team has developed a new method to characterize Li thermal diffusion and structural interaction on the surfaces of potential anode and cathode materials. This method is based on surface crystallographic and compositional characterization of deposited ultra-thin film of Li on potential single crystal or polycrystalline anode material. Surface crystallography characterization is done with w Low Energy Electron Diffraction (LEED) and surface composition with Auger Electron Spectroscopy (AES). This characterization monitors Li thermal diffusion into the electrode surface at room temperature and changes in surface crystalline structure and composition. The data provides a strong link between Lithium thermal diffusion and lithiation processes in LIB. The dynamic interaction of Li is monitored at the nanoscale level and gives the direct response how Li atoms interact with the substrate. The diffusion of evaporated Li on single crystals of HOPG, Si(111)-(211)-(100), SiC-6H, CVD-Diamond and LiNbO3 have been performed. The results shows that HOPG is the excellent reference substrate for this method as Li diffuses at room temperature and surface crystallography of HOPG remains unchanged. The structural reaction of Li with Si is very strong causing LEED pattern to disappear and there is no Li diffusion at room temperature as indicated from AES data. The data for SiC-6H and LiNbO3 shows better Li diffusional behavior than on Si but not as good as on HOPG. This method of using a single crystal substrate and basic surface characterization techniques is providing simple nanoscale access into the chemical reactions between Li and the substrate material that will result in better understanding of Lithium diffusion in the fabricated battery electrodes. The initial material classification for “native” Lithium thermal diffusion properties is proposed.