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Title: Revisiting Conversion Reaction Mechanisms in Lithium Batteries: Lithiation-Driven Topotactic Transformation in FeF 2

Abstract

Intercalation-type electrodes have now been commonly employed in today’s batteries as such materials are capable of storing and releasing lithium reversibly via topotactic transformation, conducive to small structural change, but they have limited interstitial sites to hold Li. In contrast, conversion electrodes feature high Li-storage capacity, but often undergo large structural change during (de)lithiation, resulting in cycling instability. One exception is iron fluoride (FeF 2), a conversion-type cathode that exhibits both high capacity and high cycling stability. Herein, we report a lithiation-driven topotactic transformation in a single crystal of FeF2, unveiled by in situ visualization of the spatial and crystallographic correlation between the parent and converted phases. Specifically, conversion in FeF 2 resembles the intercalation process but involves transport of both Li + and Fe 2+ ions within the F-anion array, leading to formation of Fe preferentially along specific crystallographic orientations of FeF 2. Throughout the process, the F-anion framework is retained, creating a checkerboard-like structure, within which the volume change is largely compensated, thereby enabling the high cyclability in FeF 2. Lastly, findings from this study, with unique insights into conversion reaction mechanisms, may help to pave the way for designing conversion-type electrodes for the next-generation high energy lithiummore » batteries.« less

Authors:
 [1];  [2];  [3];  [4]; ORCiD logo [4];  [5]; ORCiD logo [2]; ORCiD logo [6]; ORCiD logo [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States). Sustainable Energy Technologies Dept.
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Dept. of Condensed Matter Physics and Materials Science
  3. Univ. of Wisconsin, Eau Claire, WI (United States). Materials Science & Engineering
  4. Univ. College Cork, Cork (Ireland). School of Chemistry and the Tyndall National Inst.; Trinity College Dublin, Dublin (Ireland)
  5. Rutgers Univ., Piscataway, NJ (United States). Dept. of Materials Science and Engineering
  6. Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN); Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science and Engineering
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1492791
Report Number(s):
BNL-210929-2019-JAAM
Journal ID: ISSN 0002-7863
Grant/Contract Number:  
SC0012704
Resource Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 140; Journal Issue: 51; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE

Citation Formats

Karki, Khim, Wu, Lijun, Ma, Ying, Armstrong, Mark J., Holmes, Justin D., Garofalini, Stephen H., Zhu, Yimei, Stach, Eric A., and Wang, Feng. Revisiting Conversion Reaction Mechanisms in Lithium Batteries: Lithiation-Driven Topotactic Transformation in FeF2. United States: N. p., 2018. Web. doi:10.1021/jacs.8b07740.
Karki, Khim, Wu, Lijun, Ma, Ying, Armstrong, Mark J., Holmes, Justin D., Garofalini, Stephen H., Zhu, Yimei, Stach, Eric A., & Wang, Feng. Revisiting Conversion Reaction Mechanisms in Lithium Batteries: Lithiation-Driven Topotactic Transformation in FeF2. United States. doi:10.1021/jacs.8b07740.
Karki, Khim, Wu, Lijun, Ma, Ying, Armstrong, Mark J., Holmes, Justin D., Garofalini, Stephen H., Zhu, Yimei, Stach, Eric A., and Wang, Feng. Tue . "Revisiting Conversion Reaction Mechanisms in Lithium Batteries: Lithiation-Driven Topotactic Transformation in FeF2". United States. doi:10.1021/jacs.8b07740. https://www.osti.gov/servlets/purl/1492791.
@article{osti_1492791,
title = {Revisiting Conversion Reaction Mechanisms in Lithium Batteries: Lithiation-Driven Topotactic Transformation in FeF2},
author = {Karki, Khim and Wu, Lijun and Ma, Ying and Armstrong, Mark J. and Holmes, Justin D. and Garofalini, Stephen H. and Zhu, Yimei and Stach, Eric A. and Wang, Feng},
abstractNote = {Intercalation-type electrodes have now been commonly employed in today’s batteries as such materials are capable of storing and releasing lithium reversibly via topotactic transformation, conducive to small structural change, but they have limited interstitial sites to hold Li. In contrast, conversion electrodes feature high Li-storage capacity, but often undergo large structural change during (de)lithiation, resulting in cycling instability. One exception is iron fluoride (FeF2), a conversion-type cathode that exhibits both high capacity and high cycling stability. Herein, we report a lithiation-driven topotactic transformation in a single crystal of FeF2, unveiled by in situ visualization of the spatial and crystallographic correlation between the parent and converted phases. Specifically, conversion in FeF2 resembles the intercalation process but involves transport of both Li+ and Fe2+ ions within the F-anion array, leading to formation of Fe preferentially along specific crystallographic orientations of FeF2. Throughout the process, the F-anion framework is retained, creating a checkerboard-like structure, within which the volume change is largely compensated, thereby enabling the high cyclability in FeF2. Lastly, findings from this study, with unique insights into conversion reaction mechanisms, may help to pave the way for designing conversion-type electrodes for the next-generation high energy lithium batteries.},
doi = {10.1021/jacs.8b07740},
journal = {Journal of the American Chemical Society},
number = 51,
volume = 140,
place = {United States},
year = {2018},
month = {11}
}

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Figures / Tables:

Figure 1 Figure 1: Lithium conversion and phase propagation within a single crystal of FeF2. (a, b) Brightfield TEM image of a typical single-crystalline FeF2 particle and the corresponding electron diffraction pattern taken from a local region (as labeled by a circle in (a)). Scale bar: 100 nm. (c) Time-lapse TEM imagesmore » from a local area (as labeled in a) during lithiation (See Supporting Movie M1). Scale bar: 5 nm. (d, e) HRTEM images of pristine FeF2 (t = 0 s) from the blue framed region in (a), and an inverse FFT image from the selected white framed area. Scale bar: 2 nm. (f) HRTEM image of lithiated FeF2 (at t = 30 s), from the same blue framed area in (a). Scale bar: 2 nm. (g) Inverse FFT image from the selected white framed area showing dislocations (denoted as “T”).« less

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