On the Ageing of High Energy Lithium-Ion Batteries—Comprehensive Electrochemical Diffusivity Studies of Harvested Nickel Manganese Cobalt Electrodes

Abstract

This paper examines the impact of the characterisation technique considered for the determination of the Li+ solid state diffusion coefficient in uncycled as in cycled Nickel Manganese Cobalt oxide (NMC) electrodes. As major characterisation techniques, Cyclic Voltammetry (CV), Galvanostatic Intermittent Titration Technique (GITT) and Electrochemical Impedance Spectroscopy (EIS) were systematically investigated. Li+ diffusion coefficients during the lithiation process of the uncycled and cycled electrodes determined by CV at 3.71 V are shown to be equal to 3.48×10−10 cm2·s−1 and 1.56×10−10 cm2·s−1 , respectively. The dependency of the Li+ diffusion with the lithium content in the electrodes is further studied in this paper with GITT and EIS. Diffusion coefficients calculated by GITT and EIS characterisations are shown to be in the range between 1.76×10−15 cm2·s−1 and 4.06×10−12 cm2·s−1, while demonstrating the same decreasing trend with the lithiation process of the electrodes. For both electrode types, diffusion coefficients calculated by CV show greater values compared to those determined by GITT and EIS. With ageing, CV and EIS techniques lead to diffusion coefficients in the electrodes at 3.71 V that are decreasing, in contrast to GITT for which results indicate increasing diffusion coefficient. After long-term cycling, ratios of the diffusion coefficients determined by GITT compared to CV become more significant with an increase about 1 order of magnitude, while no significant variation is seen between the diffusion coefficients calculated from EIS in comparison to CV.

Impact of the Temperature in the Evaluation of Battery Performances During Long-Term Cycling—Characterisation and Modelling

“…In Tables A1 and A2, for the experimental determination of the parameters associated to the superscript (a), both NMC and Graphite electrodes sheets were recovered from the uncycled and cycled battery cells according to the procedure detailed in [47].…”

“…Solid phase electrode potential of both Graphite and NMC electrodes were measured by charging first 18 mm diameter electrodes punches (in EL cells containers (Hamburg, Germany)) to their upper cut-off potential using a CC-CV method (C/30-0.5 C) (as referred in [47]) and discharging them subsequently to their lower cut-off voltage with C/30 (ca. 250 µA).…”

“…Maximum lithium ions concentration in both electrodes were determined from XRD (X-ray Diffraction) experiments as referred by the procedure in [47].…”

“…Radius of active material (AM) particles in both electrodes were determined from the analysis of SEM (Scanning Electron Microscopy) micrographs as referred in [47].…”

“…Li + diffusion coefficient in the solid phase in both electrodes were determined from GITT (Galvanostatic Intermittent Titration Technique) according to the procedure detailed in [47].…”