Reactivity of lithium toward nonaqueous solvents of relevance to energy storage applications as studied by surface analytical techniques

Wang, K.; Chottiner, Gary S.; Scherson, Daniel Alberto

doi:10.1021/j100144a029

Cited by 17 publications

(16 citation statements)

References 2 publications

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“…To avoid possible decomposition of the solvent molecules en route to the Li surface, all filaments were turned off during gas dosings. 6 All spectral data are given in terms of…”

Section: Methodsmentioning

confidence: 99%

Effects of Surface Impurities on the Reactivity of Metallic Lithium toward Propylene Carbonate

Rendek¹,

Chottiner

Scherson³

2002

Electrochem. Solid-State Lett.

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Changes in the reactivity of Li toward gas-phase propylene carbonate ͑PC͒ induced by the presence of a small amount of Li oxide or Li carbonate as a Li surface impurity have been examined in ultrahigh vacuum by infrared ͑IR͒ reflection absorption spectroscopy. Whereas the presence of Li 2 O simply attenuates the intensity of IR features characteristic of the corresponding alkoxide found upon exposure of clean Li to PC, small quantities of Li 2 CO 3 on Li led to the formation of detectable amounts of the Li alkyl carbonate derivative. Implications of these results to the interpretation of data obtained in situ for Li electrodes in electrochemical environments are discussed.The operation of Li electrodes in energy storage devices relies on the presence of a passive film on the surface, which protects the metal beneath from further reaction with the electrolyte solution while providing, at the same time, a medium for the facile transport of Li ϩ . Considerable efforts have been made toward elucidating the composition and physicochemical properties of these passive films using both in situ and ex situ techniques. 1 Attention in our laboratory has been focused more recently on the use of infrared reflection absorption spectroscopy ͑IRAS͒ to identify the nature of the products generated upon exposure of clean Li surfaces to solvents of relevance to lithium battery technology. 2 Preparation and spectroscopic characterization of Li films before and after exposure to solvent vapors are performed in an ultrahigh vacuum ͑UHV͒ to avoid problems associated with adventitious impurities. Preliminary studies employing this approach indicated that the IRAS spectrum of thin Li films vapor deposited on a clean Ni͑poly͒ foil exposed to propylene carbonate ͑PC͒ vapors in UHV is virtually identical to that obtained by dosing the same type of Li films to 1,2-propanediol ͑PD͒ vapors under otherwise identical conditions. 2 This provides conclusive evidence that one of the reaction products formed is the corresponding alkoxide derivative.This paper examines the effect of two common Li surface impurities, namely, Li oxide and Li carbonate, on the reaction pathways of PC on Li. For these experiments, metallic Li surfaces were exposed in sequence to either gas phase O 2 or CO 2 to form, respectively, Li oxide and Li carbonate, and then to vapor phase PC at room temperature, after which their spectral characteristics were examined with IRAS. As is shown, the presence of Li oxide on the surface simply reduces the reactivity of clean Li toward PC to yield attenuated IRAS spectral features ascribed to a Li alkoxide derivative. In contrast, the presence of surface Li carbonate promotes the formation of significant amounts of the corresponding alkyl carbonate in agreement with the results observed by Aurbach et al. under in situ conditions. 3,4 This provides the first illustration of the role that impurities may play in changing the nature of reaction products of solvents of relevance to Li battery technology. ExperimentalUHV-IRAS measurements we...

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“…To avoid possible decomposition of the solvent molecules en route to the Li surface, all filaments were turned off during gas dosings. 6 All spectral data are given in terms of…”

Section: Methodsmentioning

confidence: 99%

Effects of Surface Impurities on the Reactivity of Metallic Lithium toward Propylene Carbonate

Rendek¹,

Chottiner

Scherson³

2002

Electrochem. Solid-State Lett.

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“…These films are formed spontaneously by thermodynamically favorable reactions between this active metal and solution (solvent, salt anion) or atmospheric (O 2 , N 2 , CO 2 , H 2 O) compounds whenever fresh Li is exposed to the solution or to an atmosphere containing the above gases (even in trace amount at a ppm level) . Many research groups throughout the world have been studying the various surface reactions of lithium with commonly used solvents, salts, and atmospheric components using a variety of techniques including XPS, , AES, , Raman, in situ XRD, temperature-programmed desorption (TPD) in ultrahigh vacuum, and surface sensitive FTIR. − Scheme provides a comprehensive summary of the surface chemistry of Li in several important electrolyte systems based on the above work. − It is clear from this scheme that all the surface solid compounds that precipitate and form surface films are organic or inorganic Li salts. When reaching a certain thickness, these films block the active metal surface from further reactions with solution or atmospheric components and thereby passivate it.…”

Section: Introductionmentioning

confidence: 99%

Impedance Spectroscopy of Li Electrodes. 4. A General Simple Model of the Li−Solution Interphase in Polar Aprotic Systems

1996

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In this work Li electrodes were studied in a variety of electrolye systems using impedance spectroscopy. The Li electrodes were all prepared in situ by shearing the surfaces in the same solutions in which the experiments were performed. The electrolyte systems included propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), tetrahydrofuran (THF), 2Me−THF, and 1,3-dioxolane (DN) as the solvents, LiAsF6, LiClO4, LiBF4, and LiPF6 as the salts, and trace water up to a concentration of 200 ppm. The electrochemical behavior of these systems is controlled by films formed spontaneously on the Li surfaces in solutions through which Li ions migrate under an electrical field, and therefore, Li+ migration in fact determines the interfacial resistance measured. It is assumed that these surface films have a multilayer structure to which a “Voigt” type analog of RC circuits in series can be fitted. All the spectra could be modeled by five RC circuits in series (one of which also contains a “Warburg” type element). From the R and C values, the thickness and resistivity of the various layers comprising the Li−solution interphase formed in all the above electrolyte systems could be calculated. The above model was examined using four different experimental routes: (1) studying the influence of the solution composition (solvent, salt, and the presence of H2O) and of storage time; (2) studying the effect of temperature; (3) experiments in which the solutions were changed during storage; (4) current passage. The significance of the model was explored by following the changes in parameters such as the layers' resistivity, thickness, and activation energy for Li+ migration as a function of the experimental conditions (e.g. solution composition, storage time, temperature, and current passage).

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“…Many researchers have investigated the surface film formed on lithium with many electrochemical analyses, [4][5][6][7][8][9][10][11][12][13] spectroscopic analyses, [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] and other analytical methods. [33][34][35] Some additives (CO 2 , 36-38 2-Me-furan 39 ) were suggested in order to modify the surface film on lithium, in a practical sense.…”

Section: Introductionmentioning

confidence: 99%

“…Many researchers have investigated the surface film formed on lithium with many electrochemical analyses, − spectroscopic analyses, − and other analytical methods. − Some additives (CO 2 , − 2-Me-furan 39 ) were suggested in order to modify the surface film on lithium, in a practical sense. However, the relationship between the morphology and the surface film composition is still unclear in spite of the many efforts.…”

Section: Introductionmentioning

confidence: 99%

Study of the Surface Composition of Highly Smooth Lithium Deposited in Various Carbonate Electrolytes Containing HF

1997

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We investigated the physical state of the surface film on lithium electrodeposited in various carbonate electrolytes containing HF in order to clarify the interfacial reaction and the electrodeposition process of lithium in nonaqueous electrolyte under a presence of a small amount of HF. The morphology and surface composition of lithium were analyzed with a scanning electron microscope and X-ray photoelectron spectroscopy (XPS). Propylene carbonate, ethylene carbonate, dimethyl carbonate, and diethyl carbonate were selected as solvents, and LiCF 3SO3, LiBF4, and LiClO4 were selected as electrolyte salts. A small amount of aqueous hydrogen fluoride solution was used as a source of HF. The lithium electrodeposited in all electrolytes without HF was in a dendritic shape. On the other hand, the morphology of the lithium deposited in all electrolytes containing HF was highly smooth with a hemispherical shape. The surface composition and morphology of electrodeposited-lithium were strongly affected by the presence of HF in carbonate electrolytes rather than by the solvents or salts. Various basic lithium compounds in the surface film were converted to LiF through acid-base reactions with HF. These results suggested that the surface film on lithium and morphology of lithium seemed to be more sensitive to a minor component, HF, in carbonate electrolytes. Moreover, the XPS analysis revealed that lithium electrodeposited in carbonate electrolytes containing HF was covered with a highly stable and ultrathin (20-50 Å) film consisting of a LiF/Li 2O bilayer. From these results, it can be concluded that such a stable thin surface film promotes the highly smooth deposition of lithium.

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Reactivity of lithium toward nonaqueous solvents of relevance to energy storage applications as studied by surface analytical techniques

Cited by 17 publications

References 2 publications

Effects of Surface Impurities on the Reactivity of Metallic Lithium toward Propylene Carbonate

Effects of Surface Impurities on the Reactivity of Metallic Lithium toward Propylene Carbonate

Impedance Spectroscopy of Li Electrodes. 4. A General Simple Model of the Li−Solution Interphase in Polar Aprotic Systems

Study of the Surface Composition of Highly Smooth Lithium Deposited in Various Carbonate Electrolytes Containing HF

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