Spatial Dynamics of Lithiation and Lithium Plating During High-Rate Operation of Graphite Electrodes

Donal Finegan, Alexander Quinn, David Wragg, Andrew Colclasure, Xuekun Lu, Chun Tan, Thomas Heenan, Rhodri Jervis, Dan Brett, Supratim Das, Tao Gao, Daniel Cogswell, Martin Bazant, Marco Michiel, Stefano Checcia, Paul Shearing, Kandler Smith

Research output: Contribution to journalArticlepeer-review

116 Scopus Citations

Abstract

The principal inhibitor of fast charging lithium ion cells is the graphite negative electrode, where favorable conditions for lithium plating occur at high charge rates, causing accelerated degradation and safety concerns. The local response of graphite, both at the electrode and particle level, when exposed to fast charging conditions of around 6C is not well understood. Consequently, the conditions that lead to the onset of lithium plating, as well as the local dynamics of lithium plating and stripping, have also remained elusive. Here, we use high-speed (100 Hz) pencil-beam X-ray diffraction to repeatedly raster along the depth of a 101 µm thick graphite electrode in 3 µm steps during fast (up to 6C) charge and discharge conditions. Consecutive depth profiles from separator to current collector were each captured in 0.5 seconds, giving an unprecedented spatial and temporal description of the state of the electrode and graphite's staging dynamics during high rate conditions. The electrode is preferentially activated near the separator, and the non-uniformity increases with rate and is influenced by free-energy barriers between graphite's lithiation stages. The onset of lithium plating and stripping was quantified, occurring only within the first 15 µm from the separator. The presence of lithium plating changed the behavior of the underlying graphite, such as causing co-existence of LiC6 and graphite in the fully discharged state. Finally, the staging behavior of graphite at different rates was quantified, revealing a high dependency on rate and drastic hysteresis between lithiation and delithiation.

Original languageAmerican English
Pages (from-to)2570-2584
Number of pages15
JournalEnergy and Environmental Science
Volume13
Issue number8
DOIs
StatePublished - 2020

Bibliographical note

Publisher Copyright:
© 2020 The Royal Society of Chemistry.

NREL Publication Number

  • NREL/JA-5400-77537

Keywords

  • fast charging
  • graphite electrodes
  • lithium ion cells
  • X-ray diffraction

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