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Thermally induced structural reordering in Li- and Mn-rich layered oxide Li ion cathode materials

DOI: 10.1021/acs.chemmater.9b04355 DOI Help

Authors: Florian Sigel (Karlsruhe Institute of Technology (KIT); Technische Universität Darmstadt) , Björn Schwarz (Karlsruhe Institute of Technology (KIT)) , Karin Kleiner (Diamond Light Source) , Christoph Dräger (Karlsruhe Institute of Technology (KIT)) , Lars Esmezjan (Karlsruhe Institute of Technology (KIT)) , Murat Yavuz (Karlsruhe Institute of Technology (KIT)) , Sylvio Indris (Karlsruhe Institute of Technology (KIT)) , Helmut Ehrenberg (Karlsruhe Institute of Technology (KIT); Technische Universität Darmstadt)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry Of Materials

State: Published (Approved)
Published: January 2020

Abstract: In recent years a considerable amount of effort has been put into a better understanding of the correlation of structure and electrochemical properties in Li- and Mn-rich NCM layered oxide Li ion battery cathode materials, such as the intensely investigated Li1.2Ni0.15Co0.1Mn0.55O2 composition. A gradual transformation from a trigonal R-3m layered structure towards a cubic Fd-3m spinel structure during electrochemical cycling results in an unwanted decay of the mean charge and discharge voltages, called ‘voltage fade’. This transformation proceeds via an interim phase, which is characterized by the local de-ordering of cations and the introduction of various lattice defects after the formation of the initially well-ordered material. In this study, these structural changes are studied in detail on a long-range atomic scale by synchrotron radiation powder diffraction as well as on a very-local atomic scale by 7Li nuclear magnetic resonance and X-ray absorption spectroscopy. A structural reordering was induced by a mild thermal treatment (150 °C – 300 °C) in lithiated (discharged to 2.0 V) as well as in delithiated (charged to 4.7 V) electrodes, which results either in a partial recovery of the initial well-ordered state or in an intensification of the structural degradation towards a spinel-type cation ordering, respectively. The structural reordering thus obtained was again studied on a long-range and local atomic scale and correlated with the electrochemical properties. In order to complement the experiment an electrochemically highly fatigued electrode (300 cycles, discharged to 2.0 V) showing a pronounced voltage fade was thermally treated, which resulted again in a partial recovery of the initial well-ordered structure and its accompanying electrochemical properties. Finally, the results are summarized in a model explaining the influence of the local cation ordering, lattice defects and the oxygen sublattice on the electrochemical properties, such as the oxygen redox activity and the voltage fade.

Journal Keywords: Redox reactions; Spinel; Electrodes; Transition metals; Materials

Diamond Keywords: Batteries; Lithium-ion

Subject Areas: Materials, Chemistry, Energy

Facility: PETRA III at DESY

Added On: 13/01/2020 10:34

Discipline Tags:

Physical Chemistry Energy Energy Storage Materials Science Energy Materials Chemistry

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