Structural Properties of Solid Electrolyte Interphase on Lithium Metal.

To gain an understanding of the structural properties of the solid electrolyte interphase (SEI) created on the surface of lithium during an electrochemical deposition/dissolution reaction in propylene carbonate (PC) containing different concentrations of LiClO4 (1.09, 3.27 mol kg(-1)), the surface of lithium was examined through transmission electron microscopy (TEM) after 30 cycles. The poor cyclability of the electrodes in the 1.09 mol kg(-1) solution was improved considerably when employing 3.27 mol kg(-1) solution. TEM showed that the latter solution produced a thinner SEI with smaller resistance on the electrode posited lithium than the former solution, e.g., -120 nm in 1.28 mol kg(-1) versus -34 nm in 3.27 mol kg(-1) solutions. Results of chemical treatment using chloroform to dissolve part of the components constituting the SEI suggested that the principal component of SEI in direct contact with the lithium was an inorganic material, while the component of SEI directly contacting the electrolyte was an organic material. That is, the SEI consisted of 2 layers, which were almost of equal thickness. These results partly supported the compact-stratified layer (CSL) model previously presented. In this study, a modified CSL model of the SEI structure was presented based on the results obtained through TEM analyses.