This article critically evaluates the characteristics of a new in situ spectroelectrochemical cell with an optimized path of the IR beam, designed in our laboratory for study of the solid electrolyte interphase (SEI) layer formed between a porous graphite anode and alkyl carbonate solution for lithium-ion batteries. The cell was designed in view of the optical principles underlying the way the in situ cell works, to give depth of penetration of the evanescent IR beam through the attenuated total internal reflectance crystal into the electrolyte at such a small value, ranging from 0.277 to 2.77 mum, that it was possible to minimize the "masking effect" of the ethylene carbonate/diethyl carbonate solvent. Moreover, the "local compositional change" which may arise significantly from the "thin layer electrolyte configuration" cell also could be fairly avoided, since only the electrolyte in the vicinity of the electrode composed of graphite particles is reduced to form the SEI layer to a thickness of at most 0.1 mum during the application of potentials. Thus, it was possible to measure the in situ FT-IR spectra in the cell, which represents the real chemical composition and structure of the SEI layer. Taking the application of the designed in situ cell as an example, this article reports the effect of salt type and electrolyte temperature on the chemical composition and structure of the SEI layer between graphite particles and alkyl carbonate solution with the help of various measured in situ FT-IR spectra.