3D lithium distribution in Li-ion batteries revealed in situ by neutron scattering

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1 3D lithium distribution in Li-ion batteries revealed in situ by neutron scattering Anatoliy Senyshyn 1 1 Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Garching, Germany Anatoliy.Senyshyn@frm2.tum.de Keywords: neutron, Li-ion battery, structure, homogeneity Energy storage media based on different technologies have gained in importance for a wide field of applications ranging from supplying portable devices to large electric vehicles. In recent decades the energy storage technology based on lithium ions is dominating at the marked due to its high energy and power densities (both gravimetric and volumetric), low self-discharge when not in use, tiny memory effect etc. Despite the overall success of Li-ion technology further progress permanently demands for lower-cost, longer-life, higher energy/power density batteries resulting in active development and research in this field. Nowadays modern Li-ion batteries are sophisticated electrochemical devices, possessing numerous degrees of freedom along with complicated geometries of the electrode integration. This along with the need to minimize the risks for possible materials oxidation, electrolyte evaporation, cell charge changes etc. calls for new dedicated experimental techniques capable to reveal live information about processes occurring inside the cell. In such instance neutron scattering is already a well-established experimental technique for the characterization of Li-ion batteries 1. Neutron scattering methods when combined with electrochemical characterization undergo an increasing relevance for studies of lithium-ion based electrochemical energy storage systems on different length scales, e.g. neutron imaging, reflectometry, small-angle neutron scattering, quasielastic neutron scattering and powder diffraction. In-situ experiments with neutrons are performed on self-developed/special test cells and commercial Li-ion cells of different designs depending on the research needs. Simple in principle but complicated in practice designs of modern Li-ion batteries may result in spatial inhomogeneity of current, lithium or electrolyte distribution, which are often difficult to quantify, but it will surely affect performance, cycling stability and safety. Despite the increasing popularity of neutron scattering studies of batteries at their operating conditions the problem of cell homogeneity (indirectly pointed by electrochemical measurements) and its effect on the data is often not properly accounted in literature. Here a combination of three neutron-based experimental techniques, namely computed neutron tomography, high-resolution neutron powder diffraction and spatially-resolved neutron powder diffraction, applied in situ for studies on commercial Li-ion cells of the type will be presented along with results of electrochemical studies. The details of the cell organization on different length scales and its evolution on various factors like state of charge, temperature and fatigue will be discussed in light of 3D lithium distribution in cylinder-type Li-ion batteries 2. [1] H. Ehrenberg, A. Senyshyn, M. Hinterstein, H. Fuess (2012). In Situ Diffraction Measurements: Challenges, Instrumentation, and Examples. In E.J. Mittermeijer & U. Welzel (Eds.), Modern Diffraction Methods (528). Weinheim: Wiley-VCH. [2] A. Senyshyn, M. J. Mühlbauer, O. Dolotko, M. Hofmann & H. Ehrenberg, Homogeneity of lithium distribution in cylinder-type Li-ion batteries, Scientific Reports 5 (2015) 18380

2 Neutrons Scattering in Continuous Magnetic Fields up 26 T Oleksandr Prokhnenko 1, Peter Smeibidl 1, Maciej Bartkowiak 1, Wolf-Dieter Stein 1, Norbert Stüßer 1, Hans- Jürgen Bleif 1, Sebastian Gerischer 1, Robert Wahle 1, Stephan Kempfer 1, Jochen Heinrich 1, Matthias Hoffmann 1, Hartmut Ehmler 1, Mark Bird 2, Karel Prokes 1, and Bella Lake 1 1 Helmholtz-Zentrum Berlin (HZB), Hahn-Meitner-Platz 1, Berlin, Germany 2 National High Magnetic Field Laboratory, Tallahassee, USA prokhnenko@helmholtz-berlin.de Keywords: neutron instrumentation, extreme sample environment, magnetic field Recently, the Helmholtz-Zentrum Berlin (HZB) launched a unique high magnetic field facility for neutron scattering - HFM/EXED. It enables elastic neutron scattering experiments in continuous magnetic fields up to 26 T combined with temperatures down to 0.6 K 1-2. The name HFM/EXED is derived from the acronym for two main components, the High Field Magnet and the Extreme Environment Diffractometer. The HFM is a horizontal-field hybrid magnet, designed and constructed in collaboration with the National High Magnetic Field Laboratory (Tallahassee, USA). It opens not only the new opportunities for research in high fields but is itself at the forefront of development in magnet technology. Using a set of cable-in-conduit superconducting and resistive coils, a maximum field of 26.2 T can be reached for cooling power of 4 MW for the resistive part. The inner resistive coil has a 50 mm diameter room temperature bore with conical ends to allow neutron-scattering to detectors up to 15 off the beam axis. Furthermore the magnet can be rotated by an additional 15 to access a larger reciprocal space region. The user samples can be cooled down to 0.6 K using a dedicated 3 He-cryostat developed at the HZB. The magnet is permanently installed on the EXED instrument. EXED is a multi-purpose time-of-flight (TOF) diffractometer optimized for operation with angular limitations imposed by the HFM. Due to the variable time resolution (from a few s up to the ms-range) and the width of wavelength band ( Å), the primary instrument is very flexible and adjustable to a particular problem. TOF technique combined with 15 magnet rotation provides a gapless coverage of Q-range from 0.1 up to 12 Å -1 for diffraction experiments. The low-q range can be extended beyond 10-2 Å -1 using a pin-hole TOF Small Angle Scattering mode implemented on the instrument. This year, in addition to the existing elastic capabilities, the instrument will be complimented by a direct TOF spectrometer mode. The latter will enable inelastic neutron scattering experiments over a limited Q-range < 1.8 Å -1 with an energy resolution of a few percent and E i < 25 mev. In this talk the overview and capabilities of the HFM-EXED facility will be presented together with the first experimental results. Procedures for planning experiments and applying for the beamtime will be discussed. [1] Peter Smeibidl, Mark Bird, Hartmut Ehmler, Iain Dixon, Jochen Heinrich, Matthias Hoffmann, Stephan Kempfer, Scott Bole, Jack Toth, Oleksandr Prokhnenko, and Bella Lake, IEEE Trans. Appl. Supercond, 26 (4) (2016) [2] O. Prokhnenko W.-D. Stein, H.-J. Bleif, M. Fromme, M. Bartkowiak, T. Wilpert, Rev. Sci. Instr. 86 (3) (2015) [3] M. Bartkowiak, N. Stüßer, O. Prokhnenko, Nucl. Instr. Meth. A 797 (2015)

3 Structural Investigation of Single and Interacting Soft Interfaces by Neutron Reflectometry Emanuel Schneck Max Planck Institute of Colloids and Interfaces, Potsdam, Germany Keywords: biological interfaces, neutron reflectometry, interfacial forces, polymer brushes Soft interfaces constituted by molecular assemblies in two dimensions play important roles in numerous technological applications and are major components of all biological matter, for example in the form of biomembranes. The understanding of important biological or technological processes involving single (isolated) or interacting soft interfaces typically relies on detailed structural insight. Neutron reflectometry (NR) is uniquely suited for the structural investigation of soft and dynamic interfaces at molecular length scales. Here, this great potential will be illustrated exemplarily for surfaces rendered with hydrated layers of linear macromolecules: (i) Surfaces functionalized with polymer brushes in order to prevent protein adsorption and (ii) the lipopolysaccharide surfaces of Gram-negative bacteria.

4 Magnetic SANS on Bulk Ferromagnets Andreas Michels Physics and Materials Science Research Unit, University of Luxembourg Keywords: small-angle neutron scattering, magnetic materials, micromagnetics, spin textures Small-angle neutron scattering (SANS) is a very powerful technique for the investigation of magnetic materials, since it provides information from within the bulk of magnetic media and on a length scale between a few nanometers and a few hundred of nanometers ( nm). In this talk, we summarize recent theoretical and experimental work in the field of magnetic SANS of bulk ferromagnets. 1 The response of the magnetization to spatially inhomogeneous magnetic anisotropy and magnetostatic stray fields is computed using micromagnetic theory, and the ensuing spin-misalignment SANS is deduced. This approach originally pioneered by Kronmüller, Seeger, and Wilkens (Ref. 2), goes beyond the traditional description of SANS in terms of particle form and structure factors. Analysis of experimental magnetic-field-dependent SANS data corroborates the usefulness of the approach, which provides important quantitative information on the magnetic-interaction parameters such as the exchange-stiffness constant, the Dzyaloshinski-Moriya interaction, the mean magnetic anisotropy field, or the mean magnetostatic field due to jumps M of the magnetization at internal interfaces. Besides the value of the applied magnetic field, it turns out to be the ratio of the magnetic anisotropy field H p to M, which determines the properties of the magnetic SANS cross section of bulk ferromagnets; specifically, the angular anisotropy on a two-dimensional detector (see figure below), the asymptotic power-law exponent, and the characteristic decay length of spin-misalignment correlations. Unpolarized and polarized neutron data on hard and soft magnetic nanocomposites will be discussed. (a)-(d) Contour plots of the normalized magnetic SANS cross section at applied magnetic fields as indicated (k 0 H 0); H 0 is horizontal in the detector plane). The change in angular anisotropy with increasing field that becomes visible in (a)- (d) reflects the competition between anisotropy-related and magnetostatic correlations. (e)-(h) Corresponding twodimensional correlation functions C(y,z) (for further details see Ref. [1]). [1] A. Michels, Journal of Physics: Condensed Matter 26, (2014); D. Honecker and A. Michels, Physical Review B 87, (2013); D. Honecker et al., Physical Review B 88, (2013); D. Mettus and A. Michels, Journal of Applied Crystallography 48, (2015). [2] H. Kronmüller, A. Seeger, and M. Wilkens, Zeitschrift für Physik 171, 291 (1963).

5 Magnetization Distribution and Shape Induced Aggregation Behavior in Magnetic Nanoparticles Sabrina Disch Department für Chemie, Universität zu Köln, Köln, Germany Keywords: magnetic nanoparticles, surface spin disorder, self-organization Magnetic nanoparticles reveal unique magnetic properties which make them relevant for data storage, electronic and mechanical engineering, and biomedical applications 1,2. With regard to these applications, the main aspects of fundamental interest include magnetic anisotropy and the related magnetization distribution in individual nanoparticles as well interparticle interactions leading to aggregation or even ordered assemblies of nanoparticles. Shape anisotropy has a substantial influence on the nanoparticle magnetization and magnetization relaxation as well as interparticle interactions. In this contribution, we will give an overview of our studies of spherical and cubic iron oxide nanoparticles aiming at both intraparticle magnetization and interparticle correlations. Particular emphasis is on the impact of particle shape and size on the spatial magnetization distribution and surface spin disorder 3,4 as well as the aggregation behavior of cubic particles in concentrated dispersion. Geometric orientation and agglomeration of the particles will be discussed as suggested by field-dependent SANS data. [1] S. D. Bader, Rev. Mod. Phys. 78, 1 (2006); DOI: /RevModPhys.78.1 [2] Q. A. Pankhurst et al., J. Phys. D: Appl. Phys. 36, R167 (2003); DOI: / /36/13/201 [3] S. Disch et al., New J. Phys. 14, (2012). DOI: / /14/1/ [4] M. Herlitschke, S. Disch et al., J. Phys.: Conf. Ser. 711, (2016); DOI: / /711/1/012002