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Investigation of Conductivity and Ionic Transport of VO2(M) and VO2(R) via Electrochemical Study Lisa M. Housel, Calvin D. Quilty, Alyson Abraham, Christopher R. Tang, Alison H. McCarthy, Genesis D. Renderos, Ping Liu, Esther S. Takeuchi, Amy C. Marschilok, and Kenneth J. Takeuchi Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b02665 • Publication Date (Web): 12 Oct 2018 Downloaded from http://pubs.acs.org on October 15, 2018
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Chemistry of Materials
Investigation of Conductivity and Ionic Transport of VO2(M) and VO2(R) via Electrochemical Study Lisa M. Housela, Calvin D. Quiltya, Alyson Abrahama, Christopher R. Tangb, Alison H. McCarthyb, Genesis D. Renderosa, Ping Liuc, Esther S. Takeuchia,b,c,*, Amy C. Marschiloka,b,c*, and Kenneth J. Takeuchia,b* aDepartment of Chemistry, Stony Brook University, Stony Brook, NY 11794 bDepartment of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, NY 11794 cEnergy
and Photon Sciences Directorate, Brookhaven National Laboratory, Upton NY 11973
Supporting Information: Rietveld refinement and electrochemical impedance spectroscopy parameters ABSTRACT: Vanadium dioxides exist as a variety of polymorphs, each with differing structural and electrochemical capabilities. The monoclinic to rutile transition is an interesting system for study as the transition temperature is easily accessible at moderate temperature and corresponds to an increase in electrical conductivity by two orders of magnitude. The transition from monoclinic to rutile is characterized structurally herein using synchrotron-based x-ray diffraction and related to lithium ion electrochemistry using electrochemical impedance spectroscopy and intermittent pulsatile galvanostatic discharge tests. The experimental results indicate a decrease in ohmic resistance for lithium-based cells tested under higher temperatures. Complementary density functional theory calculations described the experimentally measured intercalation voltages and identified a possible Li-induced LixVO2(M) to LixVO2(R) phase transition during the discharging process rationalizing the favorable impact on the function of a lithium based electrochemical cell. To our knowledge, this is the first observation of the metal—insulator transition of VO2 in a full electrochemical cell.
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INTRODUCTION The transition metal vanadium has proven useful in a variety of applications due to access of multiple oxidation states and coordination geometries where the applications range from energy related to catalysis1-2 to biological applications3-7. Relevant to this manuscript are the experimental and theoretical investigations that have probed the VO2 metal to insulator transition.8-9 At 68ºC, VO2 undergoes a structural change from a monoclinic [VO2(M)] to rutile [VO2(R)] phase, which is accompanied by an electrical conductivity increase of several orders of magnitude.10-11 The changes to strain,12-13 electric field,14 and optical excitation15 resulting from this phase transition have led to interest in thermo/electrochromatics and sensing applications.16-17 Recent work attempts to control the transition temperature through controlled thin film synthesis18, doping with tungsten19-20 or titanium21, applying internal/external stress22-23, or changing microstructure and controlling crystallite size.24-25 Other studies are centered on understanding the electronic and structural aspects of the phase transition at the microscopic level 16, made possible by advanced characterizations such as ultrafast electron diffraction26 Xray absorption spectroscopy27 and nanoscale imaging28-29. Additionally, VO2 and other vanadium oxides are recognized as potential lithium ion battery electrodes due to their high theoretical energy density, which arises from the variable oxidation state of vanadium.30 Studies have used the VO2(B) polymorph as a cathode material31-34 due to its high reported specific capacity (325 mAh/g)35 relative to VO2(M) (
