Infrared Photothermal Deflection Spectroscopy: A New Probe for the Investigation of Electrochemical Interfaces

An infrared photothermal deflection spectroscopy system has been developed using infrared tunable diode lasers in the wavelength region from 8 to 16 {micro}m. This system allows the collection of in situ optical absorption spectra of species at electrode/electrolyte interfaces in an electrochemical cell. The infrared spectra of LiOH and Li{sub 2}CO{sub 3} formed on the surface of a lithium foil were recorded. The infrared photothermal deflection spectroscopy technique has been used to monitor the lithium electrode surface in an operating cell, Li/P(EO){sub 8}-LiN(CF{sub 3}SO{sub 2}){sub 2}/Ni. The in situ spectra (in the 800--1,000 cm{sup {minus}1} region) show that the film formation at Li/polymer electrolyte interfaces is dominated by LiOH, although there also appears to be organic species in the surface film.