Publications by authors named "Benjamin Streipert"

7 Publications

  • Page 1 of 1

Conventional Electrolyte and Inactive Electrode Materials in Lithium-Ion Batteries: Determining Cumulative Impact of Oxidative Decomposition at High Voltage.

ChemSusChem 2020 Oct 17;13(19):5301-5307. Epub 2020 Aug 17.

Helmholtz-Institute Münster (HI MS) IEK-12, Forschungszentrum Jülich GmbH, Corrensstrasse 46, 48149, Münster, Germany.

High-voltage electrodes based on, for example, LiNi Mn 0 (LNMO) active material require oxidative stability of inactive materials up to 4.95 V vs. Li|Li . Referring to literature, they are frequently supposed to be unstable, though conclusions are still controversial and clearly depend on the used investigation method. For example, the galvanostatic method, as a common method in battery research, points to the opposite, thus to a stability of the inactive materials, which can be derived from, for example, the high decomposition plateau at 5.56 V vs. Li|Li and stable performance of the LNMO charge/discharge cycling. This work aims to unravel this apparent contradiction of the galvanostatic method with the literature by a thorough investigation of possible trace oxidation reactions in cumulative manner, that is, over many charge/discharge cycles. Indeed, the cumulated irreversible specific capacity amounts to ≈10 mAh g during the initial 50 charge/discharge cycles, which is determined by imitating extreme LNMO high-voltage conditions using electrodes solely consisting of inactive materials. This can explain the ambiguities in stability interpretations of the galvanostatic method and the literature, as the respective irreversible specific capacity is obviously too low for distinct detection in conventional galvanostatic approaches and can be only detected at extreme high-voltage conditions. In this regard, the technique of chronoamperometry is shown to be an effective and proper complementary tool for electrochemical stability research in a qualitative and quantitative manner.
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http://dx.doi.org/10.1002/cssc.202001530DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7589409PMC
October 2020

Anodic Behavior of the Aluminum Current Collector in Imide-Based Electrolytes: Influence of Solvent, Operating Temperature, and Native Oxide-Layer Thickness.

ChemSusChem 2017 02 27;10(4):804-814. Epub 2017 Jan 27.

University of Münster, MEET Battery Research Center, Institute of Physical Chemistry, Corrensstraße 46, 48149, Münster, Germany.

The inability of imide salts to form a sufficiently effective passivation layer on aluminum current collectors is one of the main obstacles that limit their broad application in electrochemical energy-storage systems. However, under certain circumstances, the use of electrolytes with imide electrolyte salts in combination with the aluminum current collector is possible. In this contribution, the stability of the aluminum current collector in electrolytes containing either lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) or lithium fluorosulfonyl-(trifluoromethanesulfonyl) imide (LiFTFSI) as conductive salt was investigated by electrochemical techniques, that is, cyclic voltammetry (CV) and chronocoulometry (CC) in either room-temperature ionic liquids or in ethyl methyl sulfone. In particular, the influence of the solvent, operating temperature, and thickness of the native oxide layer of aluminum on the pit formation at the aluminum current collector surface was studied by means of scanning electron microscopy. In general, a more pronounced aluminum dissolution and pit formation was found at elevated temperatures as well as in solvents with a high dielectric constant. An enhanced thickness of the native aluminum oxide layer increases the oxidative stability versus dissolution. Furthermore, we found a different reaction rate depending on dwell time at the upper cut-off potential for aluminum dissolution in TFSI- and FTFSI-based electrolytes during the CC measurements; the use of LiFTFSI facilitated the dissolution of aluminum compared to LiTFSI. Overall, the mechanism of anodic aluminum dissolution is based on: i) the attack of the Al O surface by acidic species and ii) the dissolution of bare aluminum into the electrolyte, which, in turn, is influenced by the electrolyte's dielectric constant.
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http://dx.doi.org/10.1002/cssc.201601636DOI Listing
February 2017

Suppression of Aluminum Current Collector Dissolution by Protective Ceramic Coatings for Better High-Voltage Battery Performance.

Chemphyschem 2017 Jan 29;18(1):156-163. Epub 2016 Nov 29.

University of Münster, MEET Battery Research Center, Institute of Physical Chemistry, Corrensstrasse 46, 48149, Münster, Germany.

Batteries based on cathode materials that operate at high cathode potentials, such as LiNi Mn O (LNMO), in lithium-ion batteries or graphitic carbons in dual-ion batteries suffer from anodic dissolution of the aluminum (Al) current collector in organic solvent-based electrolytes based on imide salts, such as lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). In this work, we developed a protective surface modification for the Al current collector by applying ceramic coatings of chromium nitride (Cr N) and studied the anodic Al dissolution behavior. By magnetron sputter deposition, two different coating types, which differ in their composition according to the CrN and Cr N phases, were prepared and characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and their electronic conductivity. Furthermore, the anodic dissolution behavior was studied by cyclic voltammetry and chronocoulometry measurements in two different electrolyte mixtures, that is, LiTFSI in ethyl methyl sulfone and LiTFSI in ethylene carbonate/dimethyl carbonate 1:1 (by weight). These measurements showed a remarkably reduced current density or cumulative charge during the charge process, indicating an improved anodic stability of the protected Al current collector. The coating surfaces after electrochemical treatment were characterized by means of SEM and XPS, and the presence or lack of pit formation, as well as electrolyte degradation products could be well correlated to the electrochemical results.
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http://dx.doi.org/10.1002/cphc.201601095DOI Listing
January 2017

Impact of Selected LiPF Hydrolysis Products on the High Voltage Stability of Lithium-Ion Battery Cells.

ACS Appl Mater Interfaces 2016 Nov 4;8(45):30871-30878. Epub 2016 Nov 4.

MEET Battery Research Center/Institute of Physical Chemistry, University of Münster , Corrensstrasse 46, 48149 Münster, Germany.

Diverse LiPF hydrolysis products evolve during lithium-ion battery cell operation at elevated operation temperatures and high operation voltages. However, their impact on the formation and stability of the electrode/electrolyte interfaces is not yet investigated and understood. In this work, literature-known hydrolysis products of LiPF dimethyl fluorophosphate (DMFP) and diethyl fluorophosphate (DEFP) were synthesized and characterized. The use of DMFP and DEFP as electrolyte additive in 1 M LiPF in EC:EMC (1:1, by wt) was investigated in LiNiMnCoO/Li half cells. When charged to a cutoff potential of 4.6 V vs Li/Li, the additive containing cells showed improved cycling stability, increased Coulombic efficiencies, and prolonged shelf life. Furthermore, low amounts (1 wt % in this study) of the aforementioned additives did not show any negative effect on the cycling stability of graphite/Li half cells. DMFP and DEFP are susceptible to oxidation and contribute to the formation of an effective cathode/electrolyte interphase as confirmed by means of electrochemical stability window determination, and X-ray photoelectron spectroscopy characterization of pristine and cycled electrodes, and they are supported by computational calculations.
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http://dx.doi.org/10.1021/acsami.6b09164DOI Listing
November 2016

High Voltage LiNiMnO/LiTiO Lithium Ion Cells at Elevated Temperatures: Carbonate- versus Ionic Liquid-Based Electrolytes.

ACS Appl Mater Interfaces 2016 Oct 23;8(39):25971-25978. Epub 2016 Sep 23.

MEET Battery Research Center, Institute for Physical Chemistry, University of Münster , Corrensstraße 46, 48149 Münster, Germany.

Thanks to its high operating voltage, the LiNiMnO (LNMO) spinel represents a promising next-generation cathode material candidate for Lithium ion batteries. However, LNMO-based full-cells with organic carbonate solvent electrolytes suffer from severe capacity fading issues, associated with electrolyte decomposition and concurrent degradative reactions at the electrode/electrolyte interface, especially at elevated temperatures. As promising alternatives, two selected LiTFSI/pyrrolidinium bis(trifluoromethane-sulfonyl)imide room temperature ionic liquid (RTIL) based electrolytes with inherent thermal stability were investigated in this work. Linear sweep voltammetry (LSV) profiles of the investigated LiTFSI/RTIL electrolytes display much higher oxidative stability compared to the state-of-the-art LiPF/organic carbonate based electrolyte at elevated temperatures. Cycling performance of the LNMO/LiTiO (LTO) full-cells with LiTFSI/RTIL electrolytes reveals remarkable improvements with respect to capacity retention and Coulombic efficiency. Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns indicate maintained pristine morphology and structure of LNMO particles after 50 cycles at 0.5C. The investigated LiTFSI/RTIL based electrolytes outperform the LiPF/organic carbonate-based electrolyte in terms of cycling performance in LNMO/LTO full-cells at elevated temperatures.
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http://dx.doi.org/10.1021/acsami.6b07687DOI Listing
October 2016

Lithium-cyclo-difluoromethane-1,1-bis(sulfonyl)imide as a stabilizing electrolyte additive for improved high voltage applications in lithium-ion batteries.

Phys Chem Chem Phys 2015 Apr 11;17(14):9352-8. Epub 2015 Mar 11.

Westfälische Wilhelms-Universität Münster, Institute of Physical Chemistry, MEET Battery Research Center, Corrensstr. 46, 48149 Muenster, Germany.

Lithium-cyclo-difluoromethane-1,1-bis(sulfonyl)imide (LiDMSI) was evaluated as an electrolyte additive in lithium-ion batteries for improved high voltage applications. Cycling the cathode at high potentials leads to the electrochemical oxidation of the salt to form a cathode electrolyte interphase (CEI) layer on the cathode surface. With the addition of 2 wt% of LiDMSI to the 1 M LiPF6 in 1 : 1 (by wt) EC : DEC electrolyte, the capacity retention and the Coulombic efficiency in LiNi1/3Co1/3Mn1/3O2/Li-half-cells as well as in LiNi1/3Co1/3Mn1/3O2/graphite-full-cells were improved. The cycling results point out the less over-potential and resistance at the cathode/electrolyte interface. These improvements are studied by SEM, EIS and XPS techniques.
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http://dx.doi.org/10.1039/c5cp00483gDOI Listing
April 2015

Comparative fluorescence two-dimensional gel electrophoresis using a gel strip sandwich assembly for the simultaneous on-gel generation of a reference protein spot grid.

Electrophoresis 2012 May;33(9-10):1406-10

Integrated Functional Genomics,, Interdisciplinary Center for Clinical Research, University of Münster, Germany.

The comparison of proteins separated on 2DE is difficult due to gel-to-gel variability. Here, a method named comparative fluorescence gel electrophoresis (CoFGE) is presented, which allows the generation of an artificial protein grid in parallel to the separation of an analytical sample on the same gel. Different fluorescent stains are used to distinguish sample and marker on the gel. The technology combines elements of 1DE and 2DE. Special gel combs with V-shaped wells are placed in a stacking gel above the pI strip. Proteins separated on the pI strip are electrophoresed at the same time as marker proteins (commercially available purified protein of different molecular weight) placed in V-wells. In that way, grids providing approximately 100 nodes as landmarks for the determination of protein spot coordinates are generated. Data analysis is possible with commercial 2DE software capable of warping. The method improves comparability of 2DE protein gels, because they are generated in combination with regular in-gel anchor points formed by protein standards. This was shown here for two comparative experiments with three gels each using Escherichia coli lysate. For a set of 47 well-defined samples spots, the deviation of the coordinates was improved from 7% to less than 1% applying warping using the marker grid. Conclusively, as long as the same protein markers, the same size of pI-strips and the same technology are used, gel matching is reproducibly possible. This is an important advancement for projects involving comparison of 2DE-gels produced over several years and in different laboratories.
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http://dx.doi.org/10.1002/elps.201200039DOI Listing
May 2012
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