Various aspects of the reactivity of lithium toward propylene carbonate (PC) and poly(ethylene oxide) (PEO) have been examined using ex situ and in situ spectroscopic techniques, respectively. Temperature programmed desorption of perdeuterated PC (d6-PC) layers condensed at about 150 K on a clean Li film supported on an Au foil yielded a broad m/e peak, at temperatures in the range from 220 to 520 K (and thus much lower than that found for LieCOj), which was tentatively ascribed to the thermal decomposition of a lithium alkyl carbonate. A spectroelectrochemical cell/environment controlled chamber has been designed and constructed to examine Li/PEO(LiCIO4) electrolyte interfaces formed by Li electrodeposition on to a thin Au layer sputtered on the surface of a Ge internal reflection element in situ using attenuated total reflection Fourier-transform infrared (ATR/FT-IR) spectroscopy. This assembly enables variable temperature measurements to be performed under conditions of utmost cleanliness. Preliminary results have indicated that in the case of PEO/LiCIO4 this ATR/FT-IR technique has sufficient sensitivity to observe changes in the composition of the surface and near surface region, including reaction products and perchlorate anions, which contribute to the transport of charge in the electrolyte phase.