Single-Crystal Based Diagnostics for Li-Ion Battery Cathode Development
Authors: Chen Guoying , Kuppan Saravanan , Shukla Alpesh Khushalchand 
Published: February 2020

Lithium transition-metal oxides (Li-TM oxides) are presently the most promising high energy density cathode materials for rechargeable lithium batteries. When operated at high voltages (>4.3 V), however, these oxides suffer from structural instability, extensive side reactions with the electrolyte, poor cyclability and severe thermal runaway reactions. [1, 2] In order to develop successful strategies addressing these issues, there is a clear need in fundamental knowledge of the relationships between the material’s specific physical properties/reaction mechanisms and its reactivity. This is difficult to obtain on conventional aggregated secondary particles because isolating specific physical properties of interest from less controlled ones, such as particle porosity, grain boundaries, primary particle size and size distribution, is often challenging if not impossible. To this end, we developed a unique diagnostic approach combining carefully prepared cathode model samples and the start-of-the-art analysis techniques with high spatial resolution and chemical specificity. In this presentation, we will discuss the synthesis of high-voltage Ni/Mn spinel (LMNO) and high-capacity Li-and Mn-rich layered oxide (LMR-NMC) crystals with various physical characteristics. [3] We demonstrate the effective use of complementary microscopy and spectroscopy techniques at multi-length scale, such as aberration corrected (scanning) transmission electron microscopy, electron energy loss spectroscopy, X-ray energy dispersive spectroscopy, surface sensitive soft X-ray absorption spectroscopy and X-ray photoelectron spectroscopy, full-field transmission X-ray microscopy and X-ray absorption near edge structure imaging, to determine elemental, chemical and atomic-level structural make-up of the entire bulk as well as the surface properties of the crystals. [4, 5] Combined with electrochemical analysis, insights on the phase transformation mechanism during Li extraction/reinsertion and the key factors influencing the reactions occurring at the cathode/electrolyte interface were obtained. [6] Future directions and research in addressing some of the pressing challenges facing Li-TM oxide cathode development will also be discussed.

References:

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5. P. Yan, J. Zheng, J. Zheng, Z. Wang, G. Teng, S. Kuppan, J. Xiao, G. Chen, F. Pan, J.-G. Zhang, and C.-M. Wang, “Ni and Co Segregations on Selective Surface Facets and Their Composition Dependence in Layered Lithium Transition-Metal Oxide Cathodes,” Advanced Energy Materials, 6, 1502455 (2016).
6. S. Kuppan, H. Duncan, and G. Chen, Controlling Side Reactions and Self-Discharge in High-Voltage Spinel Cathodes: The Critical Role of Surface Crystallographic Facets, Phys. Chem. Chem. Phys., 17, 26471 (2015).

Acknowledgment

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.