This not only accentuates the aforementioned phenomena, but is also likely to affect the stability of the electrolyte over extended cycling. 6 An approach to increase the capacity per cycle with intercalation electrode materials consists in forcing a larger number of Li-ions to participate in the electrochemical process by cycling to a higher upper cut-off voltage, which corresponds to a greater fraction of Li removal from the transition metal oxide crystal structure at higher voltages. Furthermore, Li-ion concentration gradients within individual particles, caused by uneven active lithium loss during extended cycling can contribute to these internal stresses, which ultimately may result in particle cracking. 5 Repeated intercalation of Li-ions during electrochemical cycling can lead to internal stresses within particles of active material due to cyclical expansion and shrinking. Intercalation battery cathodes are formed by transition metal oxide solid matrices from which Li-ions travel from and intercalate into a carbonaceous anode during charging (and vice versa during discharge). 4 However, to meet the demands of modern applications, improvements are required to increase the cycle life, capacity and safety of these materials. 3 High cobalt costs and its inherent toxicity have driven the exploration of other chemistries with reduced Co content, such as lithium nickel manganese cobalt oxide (NMC), where the slightly lower capacity is compensated by excellent power and low self-heating during cycling. Since its discovery, lithium cobalt oxide (LCO) has been one of the most commonly used materials in Li-ion electrochemical storage devices and has been employed in numerous applications. 1,2 While lithium-ion (Li-ion) batteries have emerged over the last few decades as the prime choice for powering portable consumer electronics, they are also being employed for a wider range of applications due to their high energy densities and specific capacities. Introduction Environmental considerations and a further electrification of the global automotive fleet and energy grid systems are driving the need for robust electrochemical energy storage devices. Finally, the technique facilitates the detection of parts of the electrode that have inhomogeneous lattice parameters that deviate from the bulk of the sample, further highlighting the effectiveness of the technique as a diagnostic tool, bridging the gap between crystal structure and electrochemical performance. Additionally, focused ion beam-scanning electron microscope cross-sections indicate extensive particle cracking as a function of upper cut-off voltage, further confirming that severe cycling stresses exacerbate degradation. An overall decrease of 0.4% and 0.6% was observed for the unit cell volume after 100 cycles for the electrodes cycled to 4.2 and 4.7 V. The nature of the technique permits the spatial localization of the diffraction information in 3D and mapping of heterogeneities from the electrode to the particle level. This study presents the application of X-ray diffraction computed tomography for the first time to analyze the crystal dimensions of LiNi 0.33Mn 0.33Co 0.33O 2 electrodes cycled to 4.2 and 4.7 V in full cells with graphite as negative electrodes at 1 μm spatial resolution to determine the change in unit cell dimensions as a result of electrochemical cycling. E-mail: e Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK f National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, USA g Research Complex at Harwell, Harwell Science and Innovation Campus, Rutherford Appleton Laboratories, Harwell, Didcot, Oxon OX11 0FA, UK h Johnson Matthey Technology Centre, Blounts Court Road, Sonning Common, Reading RG4 9NH, UK E-mail: b The Faraday Institution, Quad One, Harwell Science and Innovation Campus, Didcot, OX11 0RA, UK c ESRF, The European Synchrotron, 71 Avenue des Martyrs, 38000 Grenoble, France d Finden Limited, Merchant House, 5 East Saint Helens Street, Abingdon, OX14 5EG, UK. * ab a Electrochemical Innovation Lab, Department of Chemical Engineering, University College London, London WC1E 7JE, UK. ![]() Phys., 2020, 22, 17814-17823 Exploring cycling induced crystallographic change in NMC with X-ray diffraction computed tomography †
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