Electrochemistry in Ultrahigh Vacuum: Intercalation of Lithium into the Basal Plane of Highly Oriented Pyrolytic Graphite from a Poly(ethylene oxide)/LiClO4 Solid Polymer Electrolyte

Abstract

The electrochemical insertion of lithium into the basal plane of highly ordered pyrolytic graphite (HOPG-(bp)) from a LiClOdPEO solid polymer electrolyte has been examined in ultrahigh vacuum (UHV) using a carefully designed electrochemical cell. On the basis of a comparison of the data obtained with those recorded for the same interfacial system in an inert gas at atmospheric pressure, it has been concluded that the electrochemical behavior observed in UHV is indeed characteristic of the Li/L,iClO4(PEO)/HOPG(bp) system and therefore not affected in any discernible way by the ultralow pressures. Coulometric analysis of cyclic voltammetry experiments showed that the charge associated with lithium intercalation is larger than that observed during subsequent deintercalation, particularly during the first few intercalation-deintercalation cycles. However, the total amount of impurities observed in Auger electron spectra of emersed HOPG(bp) surfaces following lithium intercalation was very low. This last finding is inconsistent with the presence of a film of any significant thickness on the surface, suggesting that the charge imbalance for this interface is due to kinetic hindrances during lithium deintercalation. IntroductionThe advent of solid polymeric materials displaying high ionic mobilities at relatively low temperatures has opened new prospects for improved electrical energy-storage and energygeneration devices.' Battery technology has been focused on solid organic polymers capable of transporting lithium ions but impervious to attack by metallic lithium.* Highly promising is poly(ethy1ene oxide) (PEO),3 a material that shows moderate Li+-ion conductivities at temperatures as low as 55 "C even in the absence of cosolvents or other additives.During in situ characterization of the short-term stability of ultrapurified PEO-based electrolytes toward metallic Li using

Lithium Deposition on Polycrystalline Silver: A Comparison Between Electrochemical and Gas‐Phase Environments

“…Instrumentation.-Electrochemical measurements were conducted in a UHV chamber equipped with a Varian single-pass cylindrical mirror analyzer for Auger electron spectroscopy (AES) described in detail in Ref. 5, and also in a separate UHV chamber fitted with a Vacuum Science Workshop (VSW) hemispherical energy analyzer. 7 Nonelectrochemical Li vapor deposition experiments were performed exclusively in this latter system.…”

“…Electrochemical experiments.-The procedures employed for the purification of polyethylene oxide (PEO), which involve long-term dialysis, and the casting of LiClO 4 (PEO) films, have been described elsewhere. 5,10 These films were pre-electrolyzed in situ, 6 i.e., in the same chamber where the electrochemical measurements were performed under UHV, by pressing the Li/LiClO 4 (PEO) counter reference electrode assembly against a Ni foil attached to the other sample stage. After raising the temperature to ca.…”

“…Cyclic voltammetric data for experiments involving Ag electrodes were collected at a scan rate ϭ 5 mV/s using a Pine potentiostat at temperatures (T) in the range 323-333 K. Other details regarding these measurements are reported in earlier publications. 5,6,11…”

“…Some success toward eliminating impurity effects has been achieved in this laboratory by using ultrapure polyethylene oxide (PEO) as a solvent. 5,6 This material exhibits remarkably low vapor pressure, enabling conventional electrochemical experiments to be performed in ultrahigh vacuum (UHV) using electrode materials prepared and characterized by surface analytical techniques under conditions of utmost cleanliness. Our recent interests have focused on the study of Li underpotential deposition (UPD) on a variety of bare metal surfaces, including polycrystalline Au, Al, and Ni, and, on the way in which adsorbates, such CO and S, modify the voltammetric characteristics of Li-UPD on metal single crystals, e.g., Ni(111) and Ni(110).…”

Underpotential Deposition of Lithium on Aluminum in Ultrahigh-Vacuum Environments

“…Recent experiments performed in our laboratories have shown that a variety of poly(ethylene oxide) (PEO) electrolyte salt solutions display remarkably low vapor pressure, even in ultrahigh vacuum (UHV), 3 opening new prospects for investigating various aspects of UPD of highly reactive metals, such as lithium and sodium, under conditions which virtually eliminate problems associated with impurities both on the electrode surface and in the solution. Implementation of this novel strategy has already yielded interesting information regarding the UPD of Li on Au 4 and Ni 5 and the mechanism of Li nucleation on foreign substrates, 3,5 allowing in some cases comparisons to be made with the behavior of Li adsorbed by vapor deposition techniques on the same metal surfaces in UHV. 6 This paper examines the UPD of lithium on Al foil and on Al thin films vapor deposited on electronically conductive boron-doped diamond (BDD) substrates.…”