Elucidating the sodiation mechanism in hard carbon by operando raman spectroscopy

Julia S. Weaving, Alvin Lim, Jason Millichamp, Tobias P. Neville, Daniela Ledwoch, Emma Kendrick, Paul F. McMillan, Paul R. Shearing, Christopher A. Howard*, Dan J.L. Brett

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


Operando microbeam Raman spectroscopy is used to map the changes in hard carbon during sodiation and desodiation in unprecedented detail, elucidating several important and unresolved aspects of the sodiation mechanism. On sodiation a substantial, reversible decrease in G-peak energy is observed, which corresponds directly to the sloping part of the voltage profile and we argue can only be due to steady intercalation of sodium between the turbostratic layers of the hard carbon. The corresponding reversibility of the D-peak energy change is consistent with intercalation rather than representing a permanent increase in disorder. No change in energy of the graphitic phonons occurs over the low-voltage plateau, indicating that intercalation saturates before sodium clusters form in micropores in this region. At the start of the initial sodiation there is no change in G- and D-peak energy as the solid electrolyte interphase (SEI) forms. After SEI formation, the background slope of the spectra increases irreversibly due to fluorescence. The importance of in situ/operando experiments over ex situ studies is demonstrated; washing the samples or air exposure causes the G- and D-peaks to revert back to their original states because of SEI removal and sodium deintercalation and confirms no permanent damage to the carbon structure.

Original languageEnglish
Pages (from-to)7474-7484
Number of pages11
JournalACS Applied Energy Materials
Issue number8
Publication statusPublished - 24 Aug 2020


  • Energy storage
  • Hard carbon
  • Operando Raman spectroscopy
  • Sodiation mechanism
  • Sodium-ion batteries

ASJC Scopus subject areas

  • Chemical Engineering (miscellaneous)
  • Energy Engineering and Power Technology
  • Electrochemistry
  • Materials Chemistry
  • Electrical and Electronic Engineering


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