Characterization of SEI Layers on LiMn[sub 2]O[sub 4] Cathodes with In Situ Spectroscopic Ellipsometry

Lei, Jinglei; Li, Lingjie; Kostecki, Robert; Müller, Rolf; McLarnon, Frank

doi:10.1149/1.1867652

Cited by 87 publications

(75 citation statements)

References 24 publications

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“…6), suggesting gradual SEI growth during cycling. The SEI thickness obtained in this study by indentation was thicker than the reported values measured by other techniques, such as ellipsometry and TEM, 9,11,22 which reported that the SEI thickness was in the range of 2-5 nm, much smaller than the result in this study. The relatively thin SEI from TEM measurements probably appears because of SEI decomposition by the focused electron beam under high vacuum condition, 10 while the ellipsometry technique seems to underestimate the thickness due to an assumption of an optically homogeneous and isotropic SEI.…”

contrasting

confidence: 83%

Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn₂O₄

Hwang

Jang

2014

J. Electrochem. Soc.

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Thickness variation of the solid electrolyte interphase (SEI) produced during charge-discharge cycling is investigated to analyze the effect of SEI on the electrochemical properties of LiMn 2 O 4 . Atomic force microscopy (AFM) is used to measure the SEI thickness and elastic modulus on the LiMn 2 O 4 surface. The SEI shows a broad thickness distribution due to the random nature of the LiMn 2 O 4 electrode surfaces, while the average SEI thickness increases with cycling and stabilizes after the 20 th cycle. Formation of a relatively thin SEI on the LiMn 2 O 4 surface accompanies low Coulombic efficiency at early cycling stages. The SEI produced in the early stages of cycling is vulnerable to capacity fading due to inefficient surface protection against possible side reactions. A fully-grown stable SEI after 20 cycles shields the cathode surface from the electrolyte, minimizing capacity fading. © The Author Solid electrolyte interphase (SEI) is the layer produced on the surface of active materials during charge-discharge cycling of a battery. SEI affects electrochemical properties of active materials, such as capacity retention and rate performance, and a stable SEI is known to protect the active materials from electrolyte side reactions. A wellknown example is the excellent cycling performance of graphite due to the thin SEI produced on the surface. SEI control for cathode materials is, therefore, important to improve the electrochemical performance of Li-secondary batteries. In particular, much interest has been given to the study of SEI formation on LiMn 2 O 4 particles, as its SEI is relatively unstable and ineffective in protecting the electrode surface from side reactions with a protic electrolyte, causing capacity fading due to Mn 2+ ion dissolution. 3-5Although LiMn 2 O 4 has been considered as a promising cathode material for lithium ion secondary batteries due to its stability and high discharge voltage, as well as its non-toxicity and low cost, its capacity fading is known to be a part of the reason for its limited commercial application. Many researchers have studied the effect of SEI on electrochemical properties; however, the transient nature of SEI formed during cycling, and their nanoscale dimension made detailed analyses difficult. 6,7 Transmission electron microscopy (TEM) has been used for the observation of SEI,8,9 however, this has inherent shortcomings since SEI, which is composed of organic and inorganic materials (LiF, Li 2 CO 3 , R-CO 3 Li), can be decomposed at ultra-high vacuum conditions and by the high energy focused electron beam. 10 Other techniques, such as spectroscopic ellipsometry 11 and X-ray reflectivity analysis, 12 were also used to analyze SEI. They found that the thickness of the SEI layer was less than 5 nm in the early stages of cycling.10-12 Atomic force microscopy (AFM) has been used to examine electrode surfaces, while most AFM research has been focused on the change in topography, particle morphology, and electrical conductivity of the electrode surface.13-15 Recentl...

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confidence: 83%

Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn₂O₄

Hwang

Jang

2014

J. Electrochem. Soc.

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“…The samples were taken out of electrolyte, cleaned thoroughly with IPA, deionized water using ultrasonic procedures and investigated using a Spectroscopic ellipsometry setup described elsewhere. [19] Each data point in Figure 2 corresponds to an independent single sample/cell that has been in contact with electrolyte. Ellipsometry measurements were implemented at least twice on each sample on a different surface area on both sides.…”

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confidence: 99%

The mechanism of HF formation in LiPF6 based organic carbonate electrolytes

Lux

Lucas

Elam

et al. 2012

Electrochemistry Communications

414

333

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Spectroscopic ellipsometry was used to study the time-dependent formation of HF upon the thermal degradation of LiPF 6 at 50°C in a lithium ion battery electrolyte containing ethylene carbonate and diethyl carbonate. The generated HF was monitored by following the etching rate of a 300 nm thick SiO 2 layer, grown on both sides of a silicon wafer substrate, as a function of the immersion time in the electrolyte at 50°C. It was found that the formation of HF starts after 70 hours of exposure time and occurs following several different phases. The amount of generated HF was calculated using an empirical formula correlating the etching rate to the temperature. Combining the results of the HF formation with literature data, a simplified mechanism for the formation of the HF involving LiPF 6 degradation, and a simplified catalytical reaction pathway of the formed HF and silicon dioxide is proposed to describe the kinetics of HF formation.

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“…[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 .…”

mentioning

confidence: 99%

“…[3][4][5][6][7][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 .…”

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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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Characterization of SEI Layers on LiMn[sub 2]O[sub 4] Cathodes with In Situ Spectroscopic Ellipsometry

Cited by 87 publications

References 24 publications

Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn₂O₄

Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn₂O₄

The mechanism of HF formation in LiPF6 based organic carbonate electrolytes

Evaluation of the SEI Using a Multilayer Spectroscopic Ellipsometry Model

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Characterization of SEI Layers on LiMn[sub 2]O[sub 4] Cathodes with In Situ Spectroscopic Ellipsometry

Cited by 87 publications

References 24 publications

Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn2O4

Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn2O4

The mechanism of HF formation in LiPF6 based organic carbonate electrolytes

Evaluation of the SEI Using a Multilayer Spectroscopic Ellipsometry Model

Contact Info

Product

Resources

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Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn₂O₄

Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn₂O₄