Solvent Oligomerization during SEI Formation on Model Systems for Li-Ion Battery Anodes

Tavassol, Hadi; Buthker, Joseph W.; Ferguson, G. A.; Curtiss, Larry A.; Gewirth, Andrew A.

doi:10.1149/2.067206jes

Cited by 100 publications

(165 citation statements)

References 84 publications

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“…This layer may also contain some oligomerized products from the 1 e − of EC which initiates with an electrochemically generated radical that then polymerizes with unreacted electrolyte compounds. 27,28 The second region (II) initiates at 1.2 V and is marked by the continual increase in the thickness of the inner layer. This increase can be attributed to Eqns.…”

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confidence: 99%

Evaluation of the SEI Using a Multilayer Spectroscopic Ellipsometry Model

Dufek

2014

ECS Electrochemistry Letters

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A multilayer spectroscopic ellipsometry (SE) model has been developed to characterize SEI formation. The model, which consists of two Cauchy layers, is constructed with an inner layer meant to model primarily inorganic compounds adjacent to an electrode and an outer layer which mirrors polymeric, organic constituents on the exterior of the SEI. Comparison of 1:1 EC:EMC and 1:4 EC:EMC with 1.0 M LiPF 6 shows distinct differences in the two modeled layers. The data suggest that the thickness of both layers change over a wide potential range. These changes have been linked with other reports on the growth of the SEI. In Li-ion batteries (LIBs) the electrolyte has a unique role, not only for transport of Li, but also for the formation of the solid electrolyte interphase (SEI) which provides cell stability and practical existence. 1As a film formed from electrolyte components, SEI growth is related to the reduction of electrolyte components at the anode interface. 2Generally the SEI is viewed as consisting of multiple components with a primarily inorganic inner layer (adjacent to the electrode) with a more organic outer layer (adjacent to the electrolyte).3-8 Spectroscopic ellipsometry (SE), by following changes in the polarization of light as it interacts with surface films, provides an in situ route to follow thickness changes in the SEI. [9][10][11][12][13][14] In typical experiments, the amplitude ratio ( ) and the phase difference ( ) are used to describe the orientation of the reflected light based on Fresnel amplitude reflection coefficients. As the optical properties and thicknesses of surface films change, so do and .To appropriately analyze experimental data, optical models for SE analysis are constructed. A model which uses realistic refraction index (n), extinction coefficient (k) and other measures of physicality such as the number of films present is important when interpreting SE data. When applied to monitoring SEI growth, prior SE works have largely relied on describing the SEI as a single layer. 10,12,14 This is partially due to the desire to obtain a fit with the fewest variables possible. Keeping this tenant in mind, the present work looks to build on prior studies of SEI formation using SE by looking at an optical model for SEI growth which incorporates two layers to more closely align with non-SE studies of SEI composition and growth. 3-8Experimental SE experiments used an M2000V spectroscopic ellipsometer (JA Woollam) and a custom designed cell (Figure 1) which consisted of a fused silica tube (19 mm od) with one end enclosed and the other end capped using a Swagelok vacuum fitting. 12,15 No loss or change in electrolyte appearance was observed during evaporation studies of up to two weeks indicating the cell maintained an inert atmosphere. Two Teflon blocks were used to maintain parallel electrode placement (5.5 mm spacing). This spacing allows acquisition of SE data at angles near the Brewster angle for many solid-liquid interfaces (70-75• ) while minimizing electrolyte volume (nominally 1 mL...

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confidence: 99%

Evaluation of the SEI Using a Multilayer Spectroscopic Ellipsometry Model

Dufek

2014

ECS Electrochemistry Letters

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“…This is a different characteristic to conventional liquid electrolyte cells containing Sn which exhibit a continual formation of a solid-electrolyte-interphase (SEI) layer at the interface between active material and electrolyte. 27 For ease of reference, the voltage profile has been separated into distinct regions over the course of lithiation and delithiation and outlined in Table I. These correspond to the well-defined phase transformations of the Li-Sn alloy.…”

Section: Resultsmentioning

confidence: 99%

Tin Networked Electrode Providing Enhanced Volumetric Capacity and Pressureless Operation for All-Solid-State Li-Ion Batteries

Whiteley

Kim

Kang

et al. 2015

J. Electrochem. Soc.

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Pure tin (Sn) metal nano-powder is investigated as a high capacity negative electrode for rechargeable all-solid-state Li-ion batteries. Sn is used to form a fully dense network intertwining with solid electrolyte negating necessary conductive additive. Galvanostatic cycling of the Sn composite electrode delivers a reversible capacity 800 mAh g −1 of Sn with a constant coulombic efficiency over 99.2%. We report on the effect of pressure and rate upon the delithiation mechanics, drawing correlations between Sn volume increase factors and stress accumulation over the course of Sn-Li phase transformations. Due to the fabricated electrode microstructure, we are able to operate the cell at ambient pressure conditions -the next step toward commercialization of the solid-state battery. We believe that this initial work provides new opportunities to study the electrochemical expansion of Sn with the inclusion of rigid electrolyte particles. In 1997, Fuji announced a tin (Sn)-based amorphous composite oxide material for commercial Li-ion batteries.1 Ensuing anode deployments include the Sony developed Sn-based compound (Sn-Co-C) in 2005.2 Although these were the first commercial deployments of Sn-based anodes, Sn has been extensively studied for decades as a candidate in rechargeable Li-ion batteries because of its substantial lithium storage capabilities and quicker charging times.3 Despite the theoretical capacity of Sn being lower than the currently spotlighted silicon (Si) anode, Sn has exceptionally appealing features: high gravimetric and volumetric capacity (959 mAh g −1 and 2,476 mAh mL −1 for 4.25 Li-ions), 4 excellent electrical conductivity (9.17 × 10 6 S m −1 ), and room temperature Li-ion diffusivity (5.9 × 10 −7 cm 2 s −1 of Li 4.4 Sn). 5 The commercialized Sn-Co-C anode by Sony provides a significant capacity advantage over the currently utilized graphite anode material (372 mAh g −1 ). However, wide use of the Sn-Co-C anode has been limited due to the high cost and environmental concerns about cobalt. Iron and nickel have been introduced as replacements for cobalt forming amorphous Sn-Fe and Sn-Ni with similar electrochemical properties to the Sn-Co alloy.6-10 Despite the low cost and high capacity of the Sn-Fe and Sn-Ni anodes, poor cycling stability and coulombic efficiency (CE) hinder their practical use in Li-ion batteries. These drawbacks mainly result from the notorious volume change of Sn (∼255% when 4.25 Li-ion inserted), 4,11 leading to a loss of electric contact, pulverization, and cracking.12 Therefore, controlling the microstructure of the expandable active material during lithiation/delithiation processes is a key point to realize a high energy-dense Li-ion battery using Sn-based anode materials.Recently, Molina Piper et al. reported the effect of compressive stress on the electrochemical performance of a Si anode in an allsolid-state Li-ion cell, which similarly suffers from pulverization due to immense volume changes.13 By applying external compressive stress to the silicon/solid-state elec...

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“…However, most commercially available sensor quartzes are coated with gold, platinum or aluminum. Therefore, many research groups study SEI formation processes and accompanied layer thickness with model systems, using gold quartz crystals as working electrodes (WE) [22,23] for instance. Copper or nickel surfaces have been made in the laboratory, for example, by electrochemical deposition or via sputtering [14,20].…”

Section: Introductionmentioning

confidence: 99%

Results from a Novel Method for Corrosion Studies of Electroplated Lithium Metal Based on Measurements with an Impedance Scanning Electrochemical Quartz Crystal Microbalance

et al. 2013

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Abstract:A new approach to study the chemical stability of electrodeposited lithium on a copper metal substrate via measurements with a fast impedance scanning electrochemical quartz crystal microbalance is presented. The corrosion of electrochemically deposited lithium was compared in two different electrolytes, based on lithium difluoro(oxalato) borate (LiDFOB) and lithium hexafluorophosphate, both salts being dissolved in solvent blends of ethylene carbonate and diethyl carbonate. For a better understanding of the corrosion mechanisms, scanning electron microscopy images of electrodeposited lithium were also consulted. The results of the EQCM experiments were supported by AC impedance measurements and clearly showed two different corrosion mechanisms caused by the different salts and the formed SEIs. The observed mass decrease of the quartz sensor of the LiDFOB-based electrolyte is not smooth, but rather composed of a series of abrupt mass fluctuations in contrast to that of the lithium hexafluorophosphate-based electrolyte. After each slow decrease of mass a rather fast increase of mass is observed several times. The slow mass decrease can be attributed to a consolidation process of the SEI or to the partial dissolution of the SEI leaving finally lithium metal unprotected so that a fast film formation sets in entailing the observed fast mass increases.

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Solvent Oligomerization during SEI Formation on Model Systems for Li-Ion Battery Anodes

Cited by 100 publications

References 84 publications

Evaluation of the SEI Using a Multilayer Spectroscopic Ellipsometry Model

Evaluation of the SEI Using a Multilayer Spectroscopic Ellipsometry Model

Tin Networked Electrode Providing Enhanced Volumetric Capacity and Pressureless Operation for All-Solid-State Li-Ion Batteries

Results from a Novel Method for Corrosion Studies of Electroplated Lithium Metal Based on Measurements with an Impedance Scanning Electrochemical Quartz Crystal Microbalance

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