Quantifying Transport, Geometrical, and Morphological Parameters in Li-Ion Cathode Phases Using X-ray Microtomography

Abstract

The charge/discharge capabilities of Li-ion cathodes are influenced by the meso-scale geometry, transport properties, and morphological parameters of the constituent phases in the cathode: active material, binder, conductive additive, and pore. Electrode processing influences the structure and attendant properties of these constituents. Thus, performance of the battery can be enhanced by correlating various electrode processing techniques with the charge/discharge behavior in the lithium-ion cathodes. X-ray microtomography was used to image samples obtained from pristine Li(Ni 1/3 Mn 1/3 Co 1/3 )O 2 (NMC) cathodes subjected to distinct processing approaches. Two sample preparation approaches were applied to the samples prior to microtomography. Casting the samples in epoxy yielded only the cathode active material domain. Encapsulating the sample with Kapton tape yielded phase contrast data that permitted segmentation of the active material and combined carbon/binder and pore regions. Geometrical and morphological details of the active material and the secondary phases were characterized and compared between the varied processing approaches. Calendered and ball-milled samples exhibited distinct differences in both geometry and morphology. Drying modes demonstrated variation in the distribution of the secondary and pore phases. Applying phase contrast capabilities, the processing−morphology relationship can be better understood to enhance overall battery performance across multiple scales.

Cation reordering instead of phase transitions: Origins and implications of contrasting lithiation mechanisms in 1D ζ- and 2D α-V 2 O 5

“…Notably, the electrode specifications have been kept as similar as possible across the two polymorphs to enable comparison of the effects of crystal structure on electrochemical processes. Practical electrode architectures must further enable effective utilization of the active material through incorporation of curvature, optimization of crystallite as well as particle dimensions and morphologies, and appropriate mesoscale structuring of the electrode ( 19 , 40 ). As such, even without optimization of crystallite geometries, ζ-V 2 O 5 exhibits vastly improved cycling stability, which can be ascribed to its structure retention during Li-ion intercalation/deintercalation.…”

The Influence of Structure on the Electrochemical and Thermal Response of Li-Ion Battery Electrodes

“…However, for thin electrodes, the change in the particle size does not show a significant change in capacity. In previous work, the particle size showed more dominance of short-range phenomena over long-range phenomena in the thin electrode [20]. For the thin electrode, kinetic overpotential influences more to charge and discharge behavior over particle size [20].…”

“…In previous work, the particle size showed more dominance of short-range phenomena over long-range phenomena in the thin electrode [20]. For the thin electrode, kinetic overpotential influences more to charge and discharge behavior over particle size [20]. For the thick electrode, the change in particle size has a significant effect on capacity.…”

“…Considering this, the incoming lithium ions need to migrate longer distances to intercalate/deintercalate in the underlying regions of the electrode. The thinner electrode is therefore more dominated by kinetics and diffusion within the active material particle [20]. High charge-discharge rate shows less capacity due to the ohmic resistance as well as polarization effects, as indicated by the increased slope of the capacity curve.…”

“…This is because with the increasing particle size, the lithium-ion transport resistance increases and the full capacity of the active material particle becomes less accessible during a fixed charge or discharge time. This accessibility can be readily quantified based on a mass transfer Fourier number [20,21]. Also, the smaller particles have a more specific surface area, so the reaction rate is more rapid compared to the bigger particles.…”