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Energetics of Lithium Insertion into Magnetite, Defective Magnetite, and Maghemite Christianna N. Lininger, Christina A Cama, Kenneth J. Takeuchi, Amy C. Marschilok, Esther S. Takeuchi, Alan C. West, and Mark S. Hybertsen Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b03544 • Publication Date (Web): 09 Oct 2018 Downloaded from http://pubs.acs.org on October 14, 2018
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Chemistry of Materials
Energetics of Lithium Insertion into Magnetite, Defective Magnetite, and Maghemite Christianna N. Liningera, Christina A. Camab,#, Kenneth J. Takeuchib,c, Amy C. Marschilokb,c,d, Esther S. Takeuchib,c,d, Alan C. Westa,e, Mark S. Hybertsenf,* aDepartment
of Chemical Engineering, Columbia University, New York, NY, 10027, United States
bDepartment
of Chemistry, Stony Brook University, Stony Brook, NY, 11794, United States
cDepartment of Materials Science and
Chemical Engineering, Stony Brook University, Stony Brook,
NY, 11794, United States dEnergy
and Photon Sciences Directorate, Brookhaven National Laboratory, Upton, NY, 11973,
United States eDepartment
of Earth and Environmental Engineering, Columbia University, New York, NY, 10027,
United States fCenter
for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, United
States # Current address: Department
of Chemistry, St. Cloud State University, St. Cloud, MN 56301-4498
ABSTRACT At low concentrations of lithium insertion into inverse spinel magnetite Fe3O4, a phase change to rocksalt-like LixFe3O4 has been observed. We used density functional theory based (DFT) calculations to study the structural origins of this phase change, the concentration at which it occurs, the role of iron vacancies, and the stability of the various motifs that form during the electrochemical reduction process in the Li-Fe-O ternary space up to x=1.33. We compared our results to new experimental measurements of the open circuit voltage for 8-9 nm magnetite 1
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particles over a comparable range of lithium insertion. Of the vacant sites in magnetite (16c, 8b, and 48f) lithium insertion was found to be most stable on 16c. Coulomb interactions between the added lithium and iron at the 8a site in magnetite led to substantial displacement of the iron. As further lithium was added, the most energetically favored motif involved lithium clustering in 16c sites around the shifted 8a iron up to a total of three lithiums. In competition with the lithium clustering motif, lithium insertion could be accompanied by the full displacement of all 8a iron to 16c sites, to form the rocksalt-like LixFe3O4, saturating at x=1. The defective rock-salt structure was found to be more stable than the lithium clustering motif for x≥0.5. The rocksalt-like LiFe3O4 was found to be stable in the Li-Fe-O ternary space for a continuous range of Li-Fe organization on the 16c sites, stabilized by Coulomb interactions. For x
