Characterization of SEI Layers on LiMn[sub 2]O[sub 4] Cathodes with In Situ Spectroscopic Ellipsometry

In situ spectroscopic ellipsometry was employed to study the initial stage of solid electrolyte interphase (SEI) layer formation on thin-film electrodes. The SEI layer formed immediately upon exposure of the electrode to ethylene carbonate/dimethyl carbonate (1:1 by vol) electrolyte. The SEI layer thickness then increased in proportion to a logarithmic function of elapsed time. In comparison, the SEI layer thickness on a cycled electrode increased in proportion to a linear function of the number of cycles.