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Letter 4
Structural Transformation of LiFePO During Ultrafast Delithiation Christian Kuss, Ngoc Duc Trinh, Stefan Andjelic, Mathieu Saulnier, Eric M. Dufresne, Guoxian Liang, and Steen B. Schougaard J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.7b02569 • Publication Date (Web): 05 Dec 2017 Downloaded from http://pubs.acs.org on December 8, 2017
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The Journal of Physical Chemistry Letters
Structural Transformation of LiFePO4 During Ultrafast Delithiation Christian Kuss,a† Ngoc Duc Trinh,a Stefan Andjelic,a Mathieu Saulnier,a Eric M. Dufresne,b Guoxian Liangc and Steen B. Schougaarda*. AUTHOR ADDRESS a
Université du Québec à Montréal, Département de chimie, C.P. 8888, Succ. Centre-ville, Montreal (QC), Canada H3C 3P8. b
Argonne National Laboratory, Advanced Photon Source, 9700 South Cass Ave, Argonne IL 60439, USA. c
Johnson Matthey Battery Materials Ltd, 280 ave Liberté, Candiac (QC), Canada J5R 6X1.
AUTHOR INFORMATION † Present Affiliation: University of Oxford, Department of Materials, Parks Road, Oxford, UK OX1 3PH. Corresponding Author *
[email protected].
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ABSTRACT
The prolific lithium battery electrode material lithium iron phosphate (LiFePO4) stores and releases lithium ions by undergoing a crystallographic phase change. Nevertheless, it performs unexpectedly well at high rate and exhibits good cycling stability. We investigate here the ultrafast charging reaction to resolve the underlying mechanism, while avoiding the limitations of prevailing electrochemical methods by using a gaseous oxidant to deintercalate lithium from the LiFePO4 structure. Oxidizing LiFePO4 with nitrogen dioxide gas reveals structural changes through in situ synchrotron X-ray diffraction and electronic changes through in situ UV/Vis reflectance spectroscopy. This study clearly shows that ultra-high rates reaching 100% state of charge in 10s, does not lead to a particle-wide union of the olivine and heterosite structures. An extensive solid solution phase is therefore not a prerequisite for ultra-fast charge/discharge.
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KEYWORDS In-Situ, structural analysis, electronic structure, biphasic, XRD, Uv-vis, reaction mechanism, lithium-ion.
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The Journal of Physical Chemistry Letters
Improving charging rates is a major challenge in renewable electrical energy storage. E.g. consumers would be more accepting of a 200 km electric car driving range, if recharging required only minutes rather than hours. Focusing on the lithium-ion technology due to its high energy density, the charging rate is ultimately determined by the constituent materials. Among these, lithium iron phosphate LiFePO4 is a safe, environmentally benign, economical and competitively performing positive electrode material.1 During charging and discharging, intermediate compositions LixFePO4 (1
