Separation of charge transfer and contact resistance in LiFePO 4-Cathodes by impedance Modeling

J. Illig, M. Ender, T. Chrobak, J. P. Schmidt, D. Klotz, E. Ivers-Tiffée

Research output: Contribution to journalArticlepeer-review

Abstract

Lithium iron phosphate is a promising candidate material for Li-Ion batteries. In this study, the rate determining processes are assessed in more detail in order to separate performance limiting factors. Electrochemical impedance spectroscopy (EIS) data of experimental LiFePO4/Lithium- cells are deconvoluted by the method of distribution of relaxation times (DRT), what necessitates a pre-processing of the capacitive branch. This results in a separation into cathode and anode polarization processes and in a proposition of a physically motivated equivalent circuit model. We identify three different polarization processes of the LiFePO4-cathode (i) solid state diffusion, (ii) charge transfer (cathode/electrolyte) and (iii) contact resistance (cathode/current collector). Our model is then applied to EIS data sets covering varied temperature (0° to 30°C) and state of charge (10% to 100%). Activation energy, polarization resistance and frequency range are determined separately for all cathode processes involved. Finally, the tape-casted LiFePO4-cathode sheet is modified in porosity, thickness and contact area between cathode/electrolyte and cathode/current collector by a calendering process. Charge transfer resistance and contact resistance respond readily in polarization and relaxation frequency.

Original languageEnglish
Pages (from-to)A952-A960
JournalJournal of the Electrochemical Society
Volume159
Issue number7
DOIs
Publication statusPublished - 2012
Externally publishedYes

All Science Journal Classification (ASJC) codes

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

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