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Lee, Hyun-Wook
Energy Storage and Electron Microscopy Laboratory
Research Interests
  • Energy storage, secondary batteries, transmission electron microscopy, real time analysis

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Understanding the conversion mechanism and performance of monodisperse FeF2 nanocrystal cathodes

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Title
Understanding the conversion mechanism and performance of monodisperse FeF2 nanocrystal cathodes
Author
Xiao, Albert W.Lee, Hyeon JeongCapone, IsaacRobertson, AlexWi, Tae-UngFawdon, JackWheeler, SamuelLee, Hyun-WookGrobert, NicolePasta, Mauro
Issue Date
2020-06
Publisher
Nature Publishing Group
Citation
NATURE MATERIALS, v.19, no.6, pp.644 - 654
Abstract
The application of metal fluorides as cathodes for lithium ion batteries has been hindered by inadequate understanding of their electrochemical capabilities. Reversible conversion reaction in iron fluoride nanocrystals is shown to be due to topotactic cation diffusion and nucleation of metallic particles. The application of transition metal fluorides as energy-dense cathode materials for lithium ion batteries has been hindered by inadequate understanding of their electrochemical capabilities and limitations. Here, we present an ideal system for mechanistic study through the colloidal synthesis of single-crystalline, monodisperse iron(ii) fluoride nanorods. Near theoretical capacity (570 mA h g(-1)) and extraordinary cycling stability (>90% capacity retention after 50 cycles at C/20) is achieved solely through the use of an ionic liquid electrolyte (1 m LiFSI/Pyr(1,3)FSI), which forms a stable solid electrolyte interphase and prevents the fusing of particles. This stability extends over 200 cycles at much higher rates (C/2) and temperatures (50 degrees C). High-resolution analytical transmission electron microscopy reveals intricate morphological features, lattice orientation relationships and oxidation state changes that comprehensively describe the conversion mechanism. Phase evolution, diffusion kinetics and cell failure are critically influenced by surface-specific reactions. The reversibility of the conversion reaction is governed by topotactic cation diffusion through an invariant lattice of fluoride anions and the nucleation of metallic particles on semicoherent interfaces. This new understanding is used to showcase the inherently high discharge rate capability of FeF2.
URI
https://scholarworks.unist.ac.kr/handle/201301/48696
URL
https://www.nature.com/articles/s41563-020-0621-z
DOI
10.1038/s41563-020-0621-z
ISSN
1476-1122
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