Identification of Surface Films Formed on Lithium in Dimethoxyethane and Tetrahydrofuran Solutions

Abstract

Surface films formed on lithium metal in dimethoxyethane (DME) and tetrahydrofuran (THF) solutions of LiClO4 , LiAsF6 , and LiSO3CF3 were analyzed using FTIR, SIMS, and XPS spectroscopies. The films formed in both solvents were found to contain lithium alkoxides. The main reaction products detected with FTIR were LiOCH3 in DME, and normalLiOfalse(CH2)3CH3 in THF. SIMS measurements are consistent with this finding. Reaction mechanisms are discussed. When the water concentration in these systems is 0.01M or greater, normalLiOH is formed on the lithium surface and appears to be a major component in the surface films. XPS measurements gave evidence for simultaneous salt reduction on the lithium surface in addition to the solvent reactions.

Electrocatalytic Activity Studies of Select Metal Surfaces and Implications in Li-Air Batteries

“…•− in dimethylformamide ͑DMF͒ containing TBAP from cyclic voltammetry and electron spin resonance data. Similarly, Aurbach and co-workers 26 suggested the formation and oxidation ͑reversibly͒ of superoxide ion in O 2 -saturated DME with TBAP on Au and Ag. More recently, Laoire et al 30 reported high reversibility for the ORR/OER on GC in acetonitrile ͑MeCN͒ with TBAP salt, with a reversible redox potential of ϷϪ0.83 V vs Ag/AgCl ͑Ϸ2.10 V Li ͒ for Reaction 6; the large diffusion-limited currents in their RDE measurements support the facile dissolution of the reduction prod-uct͑s͒ in the electrolyte and also confirm a one-electron reduction of oxygen, perfectly consistent with Reaction 6.…”

“…In addition, the extremely low solubility of lithium ͑per͒oxides and other metal ͑per͒oxides in aprotic solvents leads to the formation of surface films that can poison the electrode in subsequent cycles ͑ORR currents can only be observed in the first voltammetric scan if these surface films are not removed on the oxidation sweep at voltages no greater than 3 V Li ͒. 26,27 Proposed ORR mechanisms in Li ϩ -containing aprotic solvents.-We propose here the ORR mechanism in Li + -containing aprotic solvents. The first step in the ORR in Li + -containing aprotic solvents may proceed according to The sum of Reaction 7a and 7c corresponds to the first reduction step proposed in a recent DFT study on the ORR in Li-air batteries.…”

“…10, with the first step being the initial one-electron reduction of oxygen to a weakly adsorbed superoxide radical, as was proposed in previous studies. 38,51,52 This is followed either by the dissolution of the superoxide radical solvated by large cations, 27 PC, 26 or lithium ions 30 or by the formation of surface adsorbed LiO 2 ͑for very low ratios of electrolyte volume to electrode surface area, as in a Li-air cell, solvated superoxide radicals likely readsorb and react͒. On catalysts with relatively strong oxygen adsorption strength ͑e.g., Pt͒, adsorbed LiO 2 is likely to get reduced all the way to Li 2 O ͑solid arrows in Fig.…”

Fluorinated End‐Groups in Electrolytes Induce Ordered Electrolyte/Anode Interface Even at Open‐Circuit Potential as Revealed by Sum Frequency Generation Vibrational Spectroscopy

“…The second potential range, between 0.9 and 0.005 V, presents us with a two‐step silicon lithiation (alloying with Li) process that has two peaks at 0.3 V (≈28 µA) and 0.1 V (≈80 µA). Below applied potentials of 0.5 V reduction pathways of linear ethers (e.g., dimethoxyethane) are possible and lithium alkoxides (e.g., LiOCH 2 CH 3 ) are the dominant SEI product …”

Solid Electrolyte Interphase Evolution on Lithium Metal in Contact with Glyme‐Based Electrolytes

“…[ 11–19 ] Aurbach was the first to investigate the composition and morphology of various SEIs formed on lithium metal in contact with various liquid electrolytes. [ 20–23 ] Recently, significant efforts have been made in the direction of in situ observation of the initial SEI formation on metallic lithium by electron microscopy, [ 24–27 ] as well as of the SEI growth in contact with solid lithium electrolyte. [ 28 ] However, the evolution of composition, morphology, and thus evolution of ionic and electronic conductivity of the SEI phases under current or voltage (conditions similar to the battery operation) remains to be better understood.…”