Interpretation and Modelling of the Electrochemical Impedance of LiFePO4/Li4Ti5O12Batteries

Elahe Moazzen*, Roberto Scipioni, Miaomiao Ma, Scott Barnett

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

In this work, a comprehensive equivalent circuit model (ECM) was developed for the a commercial 26650 LiFePO4/Li4Ti5O12 cell in which the main processes at the anode and cathode electrodes and their contributions to the full-cell impedance were investigated and quantified separately. To unambiguously separate the anode and cathode processes, EIS spectra from Li4Ti5O12/Li and LiFePO4/Li half cells were modeled at different state of charge (SOCs) and SOC history and the fit results were used to develop the full-cell ECM. The distribution of relaxation times (DRT) analysis was used in all cases to better resolve the frequencies of the processes, and thereby help their accurate identification. The LiFePO4/Li4Ti5O12-cell impedance was found to be significantly dependant on the SOC history, i.e. it changes slightly only at low SOCs during charge, whereas, it changes significantly during discharge. The SOC-dependence of the full-cell impedance was found to be mainly due to the decrease of the LiFePO4 electrode's charge transfer resistance with SOC increase. While Li4Ti5O12 electrode processes did not show a significant change with SOC history, it was revealed that the SOC-histoty dependence of the LiFePO4/Li4Ti5O12 full cell was also mainly due to the variation of charge transfer frequency and resistance of LiFePO4 electrode.

Original languageEnglish (US)
Article number050519
JournalJournal of the Electrochemical Society
Volume168
Issue number5
DOIs
StatePublished - May 2021

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Materials Chemistry
  • Surfaces, Coatings and Films
  • Electrochemistry
  • Renewable Energy, Sustainability and the Environment

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