Surface Electrolyte Interphase Control on Magnetite, Fe 3 O 4 , Electrodes: Impact on Electrochemistry
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.294
Surface Electrolyte Interphase Control on Magnetite, Fe3O4, Electrodes: Impact on Electrochemistry Lisa M. Housel1,ŧ, Alyson Abraham1,ŧ, Genesis D. Renderos1,ŧ, Kenneth J. Takeuchi1,2, Esther S. Takeuchi1,2,3, Amy C. Marschilok1,2,3,* 1
Department of Chemistry, Stony Brook University, Stony Brook, NY 11794
2
Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, NY 11794 3
Energy Sciences Directorate, Brookhaven National Laboratory, Upton NY 11973
ŧ Equivalent contributions. * corresponding author: [email protected].
ABSTRACT
In battery systems, a solid electrolyte interphase (SEI) is formed through electrolyte reaction on an electrode surface. The formation of SEI can have both positive and negative effects on electrochemistry. The initial formation of the layer protects the electrode from further reactivity, which can improve both shelf and cycle life. However, if the layer continues to form, it can impede charge transfer, which increases cell resistance and limits cycle life. The role of SEI is particularly important when studying conversion electrodes, since phase transformations which unveil new electroactive surfaces during reduction/oxidation can facilitate electrolyte decomposition. This manuscript highlights recent developments in the understanding and control of SEI formation for magnetite (Fe3O4) conversion electrodes through electrolyte and electrode modification.
INTRODUCTION: Lithium ion batteries (LIB) play a critical role in technology implementation of consumer products, electric vehicles, and the electrical grid, which depend on energy sources with high utilizable capacities and long cycle life. High capacity conversion electrodes, such as magnetite (Fe3O4), are desirable as they undergo multiple electron transfer, have high theoretical capacity (924 mAh/g), are environmentally benign and naturally abundant.1 Fe3O4 has an inverse spinel structure, where the oxygen anion framework forms a cubic closed packed arrangement, Fe3+ ions are distributed among both octahedral and tetrahedral sites, and Fe2+ ions are located solely in octahedral sites (Fig. 1).2 Upon lithiation, Fe3O4
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undergoes multiple phase transformations. Li+ ions are initially inserted into octahedral sites of the spinel structure with reduction of Fe3+ to Fe2+. Upon further lithiation, a rock salt type phase, FeO like, forms along with Li2O. Full lithiation reduces the Fe sites to Fe metal.3
Figure 1: Fe3O4 crystallographic structure.
A major challenge with conversion electrodes is the ability to control the solid electrolyte interphase (SEI) layer that forms when electrolyte reacts at the surface of the electrode (Fig. 2).4,5 Since conversion electrodes under
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