Reactivity of Metallic Lithium Toward γ-Butyrolactone, Propylene Carbonate, and Dioxalane

Abstract

The nature of the reaction products generated by exposure of a model cyclic ester, ␥-butyrolactone ͑␥-BL͒, two cyclic ethers, dioxalane ͑DIOX͒ and tetrahydrofuran ͑THF͒, and a cyclic alkyl carbonate, propylene carbonate ͑PC͒, toward metallic Li at room temperature was examined in ultrahigh vacuum by infrared reflection absorption, Auger electron ͑AES͒, and X-ray photoelectron ͑XPS͒ spectroscopies. The features observed in the spectra were consistent with Li butyrate and Li ␤-keto ester in the case of ␥-BL, and a dialkoxide derivative of Li with small amounts of Li oxide for experiments involving PC as the main reaction products. The behavior of both these solvents differs greatly from that found of the cyclic ethers DIOX and THF, for which the XPS spectra yielded small amounts of Li oxide and Li carbide as the only reaction products. These two species are most likely not derived from reactions involving DIOX or THF but rather from reactions between metallic Li and CO desorbed from the walls of the chamber during prolonged dosings. The extent of the reaction involving ␥-BL, as evidenced by the loss of the AES peak at 52 eV characteristic of metallic Li, far exceeded that observed with PC and the linear alkyl carbonates reported previously in this laboratory, for which the aforementioned feature could be discerned clearly even after extensive exposure. All these findings agree with those reported by Aurbach et al. 1 for experiments involving Li metal exposure to the same solvents in liquid phase, which suggests that conclusions drawn from ex situ experiments of the type originally devised by our research group may also be applicable to reactions in condensed phase, including electrochemical environments.Procedures have been developed in our research group for the identification of reaction products formed on clean Li surfaces upon exposure to solvents of relevance to lithium batteries in gas phase. These experiments are carried out in ultrahigh vacuum ͑UHV͒, using infrared reflection absorption spectroscopy ͑IRAS͒, Auger electron spectroscopy ͑AES͒ and X-ray photoelectron ͑XPS͒ spectroscopy as complementary vibrational and electronic probes. This paper extends the suite of linear and cyclic alkyl carbonates investigated in previous work, to ␥-butyrolactone ͑␥-BL͒, a model cyclic ester, as well as 1,3-dioxalane ͑DIOX͒ and tetrahydrofuran ͑THF͒, two model cyclic ethers, to compare the reactivity of these latter solvents toward metallic Li with that of linear alkyl carbonates. ExperimentalAll measurements were performed in a custom designed UHV chamber equipped with instrumentation required for the cleaning of Li specimens and their subsequent spectral characterization with AES, XPS, and IRAS. 2 As described elsewhere, p-polarized infrared ͑IR͒ light emerging from a Mattson Cygnus 25 Fourier transform IR ͑FTIR͒ spectrometer was focused at an incident angle of 69°onto the surface of a coin-shaped Li foil ͑ca. 12 mm diam, 1 mm thick͒ mounted onto the UHV sample stage ͑see below͒. As is customary, IRAS spectra are report...

Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries

“…Among the limited choices of candidates intended to replace cyclic carbonates, γ-butyrolactone (γBL) seemed to be the most promising and therefore closest to practical application. γBL has long been considered a possible component for electrolytes in lithium/lithium ion cells due to its moderately high dielectric constant, relatively low viscosity, EC-like structure, and excellent solvating ability. − Its reductive behavior has been studied on inert electrode surfaces, , lithium surfaces, , and graphite surfaces . Unfortunately, in the early era of lithium ion technology, Aurbach and co-workers had found that γBL/LiAsF 6 solution failed to perform satisfactorily in lithium ion cells based on the graphite anode unless under an atmosphere of CO 2 , thus diminishing its possible application .…”