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Batteries 2018, 4(3), 43; https://doi.org/10.3390/batteries4030043

Impedance Characterization of an LCO-NMC/Graphite Cell: Ohmic Conduction, SEI Transport and Charge-Transfer Phenomenon

Departament d’Enginyeria Electrònica, Grup de Processat d’Energia i Circuits Integrats (EPIC), Escola d’Enginyeria de Barcelona Est (EEBE), Universitat Politècnica de Catalunya-BarcelonaTech, 08019 Barcelona, Spain
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Received: 13 July 2018 / Revised: 10 August 2018 / Accepted: 21 August 2018 / Published: 10 September 2018
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Abstract

Currently, Li-ion cells are the preferred candidates as energy sources for existing portable applications and for those being developed. Thus, a proper characterization of Li-ion cells is required to optimize their use and their manufacturing process. In this study, the transport phenomena and electrochemical processes taking place in LiCoO2-Li(NiMnCo)O2/graphite (LCO-NMC/graphite) cells are identified from half-cell measurements by means of impedance spectroscopy. The results are calculated from current densities, instead of absolute values, for the future comparison of this data with other cells. In particular, impedance spectra are fitted to simple electrical models composed of an inductive part, serial resistance, and various RQ networks—the parallel combination of a resistor and a constant phase element—depending on the cell. Thus, the evolution of resistances, capacitances, and the characteristic frequencies of the various effects are tracked with the state-of-charge (SoC) at two aging levels. Concretely, two effects are identified at the impedance spectrum; one is clearly caused by the charge transfer at the positive electrode, whereas the other one is presumably caused by the transport of lithium ions across the solid electrolyte interphase (SEI) layer. Moreover, as the cells age, the characteristic frequency of the charge transfer is drastically reduced by a factor of around 70%. View Full-Text
Keywords: impedance; Electrochemical impedance spectroscopy (EIS); aging; half-cells; equivalent circuit; lithium ion; NMC; solid electrolyte interphase (SEI); charge transfer impedance; Electrochemical impedance spectroscopy (EIS); aging; half-cells; equivalent circuit; lithium ion; NMC; solid electrolyte interphase (SEI); charge transfer
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Ovejas, V.J.; Cuadras, A. Impedance Characterization of an LCO-NMC/Graphite Cell: Ohmic Conduction, SEI Transport and Charge-Transfer Phenomenon. Batteries 2018, 4, 43.

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