Journal article

Publication year: 2021

Pages: 1335-1345

Journal: ACS Applied Energy Materials

Volume number: 4

Issue number: 2

ISSN: 2574-0962

DOI Link: https://doi.org/10.1021/acsaem.0c02606

Publisher: American Chemical Society

Abstract: 
The quantitative influence of microstructure, porosity, surface area, and changes in the crystal lattice on the electric conduction mechanisms in cathode-active materials for lithium ion batteries and therefore on the performance of a battery cell is largely unknown. To correlate the transport properties of LiNi1/3Co1/3Mn1/3O2 (NCM-111) as model type layered cathode material with its structural properties, a systematic study of the temperature dependence of the impedance of the material was performed on a set of sintered NCM-111 pellets. By variation of the sintering temperature from 850 to 1000 degrees C, the porosity of the material was tuned between 2 and 45%, while the grain size of the primary particles in the pellets varied between 50 nm and 1.5 mu m. A careful analysis of the impedance spectra using selectively blocking electrodes allowed for the separation of the electronic and ionic partial conductivities of NCM-111. Depending on porosity and grain size, strong variations of the electronic partial conductivity were found ranging from 1.4 x 10(-6) to 6.8 x 10(-9) S cm(-1) accompanied by an increase in the activation energy from 0.37 to 0.61 eV. The ionic transport properties exhibit similar behavior. Rietveld refinement of the X-ray diffraction (XRD) patterns of the pellets reveals that the increase in activation energies correlates with the volume of the unit cell. A Meyer-Neldel behavior is observed for both the ionic and the electronic partial conductivities, allowing for the evaluation of the defect formation enthalpies for lithium vacancies (1.74 +/- 0.56 eV) and electron holes (1.36 +/- 0.59 eV). These findings illustrate the complex relationships among microstructure, morphology, and transport characteristics, highlighting the need for careful design of active materials.

Harvard Citation style: Zahnow, J., Bernges, T., Wagner, A., Bohn, N., Binder, J., Zeier, W., et al. (2021) Impedance Analysis of NCM Cathode Materials: Electronic and Ionic Partial Conductivities and the Influence of Microstructure, ACS Applied Energy Materials, 4(2), pp. 1335-1345. https://doi.org/10.1021/acsaem.0c02606

APA Citation style: Zahnow, J., Bernges, T., Wagner, A., Bohn, N., Binder, J., Zeier, W., Elm, M., & Janek, J. (2021). Impedance Analysis of NCM Cathode Materials: Electronic and Ionic Partial Conductivities and the Influence of Microstructure. ACS Applied Energy Materials. 4(2), 1335-1345. https://doi.org/10.1021/acsaem.0c02606