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Structure of SEI film of lithium battery

by:dcfpower     2021-03-21

Predecessors have conducted extensive research on the structure and composition of the SEI film of lithium batteries. Now the generally accepted model of the passivation film on the surface of the lithium electrode is:

( 1) The inner dense part is composed of inorganic salt with low oxidation state;

(2) The outer part is porous part composed of organic layer. The depth analysis of the SEI film formed by the lithium electrode in the alkyl carbonate-based electrolyte by X-ray photoelectron spectroscopy (XPS) shows that the SEI film is a mosaic-like multilayer structure, and the closer to the passivation layer on the lithium surface, The lower the oxidation state of the SEI film components. Analysis of the surface of freshly prepared lithium electrodes in electrolytes such as LiAsF6-based dimethyl carbonate (DMC), dry hexenyl carbonate-diene carbonate (EC-DEC) and wet C-DEC showed that the more Close to the Li surface, the SEI film contains more low-oxidation inorganic components. The SEI film near the surface of the lithium electrode is mainly composed of some low oxidation state inorganic salts such as Li20, Li3N, Lix (representing F, C1, etc.), and the outside of the SEI film is mainly composed of some high oxidation state components such as ROLi, ROCO2Li, LiH, LixIMFz, etc. [11]. Atomic Force Microscopy (AFM) research results show that the nanostructure on the surface of lithium is composed of grain boundaries, ridges and flat areas. The grain boundaries are mainly composed of Li2C03, Li20, and electrolyte reduction products such as LiC1. Its structure There are many dislocations and defects. The change of morphology during lithium deposition is mainly caused by the diffusion of lithium ions through grain boundaries and ridges. Therefore, the grain boundaries and ridges play an important role in controlling the lithium deposition morphology, such as the formation of dendrites. The results of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) showed that the electrodeposition of lithium in almost all non-aqueous carbonate electrolytes is dendritic, and S is formed on the lithium dendrites. The outer layer of the sub-I film is mainly composed of Li0C02R, Li2C03, LioH and the inner layer Li20. When the electrolyte contains a small amount of field, the electrodeposition on the hemispherical lithium is very smooth. These smooth lithium surfaces are covered by a very thin (2~5rm) u200bu200bsurface film composed of LiF/Li20 layer, and the composition of the surface film has nothing to do with the type of carbonate solvent containing HF. The composition of the SEI film on the lithium surface It is very sensitive to the presence of a small amount of F, which may be because LiF is a very stable product in the electrolyte.

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