Abstract
SummaryLithium‐ion battery performance is intrinsically linked to electrode microstructure. Quantitative measurement of key structural parameters of lithium‐ion battery electrode microstructures will enable optimization as well as motivate systematic numerical studies for the improvement of battery performance. With the rapid development of 3‐D imaging techniques, quantitative assessment of 3‐D microstructures from 2‐D image sections by stereological methods appears outmoded; however, in spite of the proliferation of tomographic imaging techniques, it remains significantly easier to obtain two‐dimensional (2‐D) data sets. In this study, stereological prediction and three‐dimensional (3‐D) analysis techniques for quantitative assessment of key geometric parameters for characterizing battery electrode microstructures are examined and compared. Lithium‐ion battery electrodes were imaged using synchrotron‐based X‐ray tomographic microscopy. For each electrode sample investigated, stereological analysis was performed on reconstructed 2‐D image sections generated from tomographic imaging, whereas direct 3‐D analysis was performed on reconstructed image volumes. The analysis showed that geometric parameter estimation using 2‐D image sections is bound to be associated with ambiguity and that volume‐based 3‐D characterization of nonconvex, irregular and interconnected particles can be used to more accurately quantify spatially‐dependent parameters, such as tortuosity and pore‐phase connectivity.
Highlights
Reactions that take place within lithium-ion batteries are supported by porous composite electrodes possessing complex microstructures, and as with all functional materials, there is a direct relationship between electrode microstructure and battery performance
Based on a 2 % relative error criterion, the profiles for pore volume fraction, volume-specific surface area, as well as geometric tortuosity along the x, y and z directions presented in Figures 3(D), 4(D) and 6, respectively show that the three electrode sample volumes yield parameter values that are representative of the bulk electrode volume
Quantitative analysis was carried out on image data obtained from imaging battery electrode samples using synchrotron-based X-ray tomographic microscopy
Summary
Reactions that take place within lithium-ion batteries are supported by porous composite electrodes possessing complex microstructures, and as with all functional materials, there is a direct relationship between electrode microstructure and battery performance. A quantitative understanding of microstructure and transport pathways within lithium ion battery electrodes is crucial for improving their design, manufacture, performance and durability. To this end, characterization techniques for revealing all relevant, detailed microstructural morphology and for assessing quantitative geometric parameters are essential. The second approach is by direct viewing and measurement of 3-D datasets obtained by tomographic imaging of the material of interest or serial sectioning techniques. X-ray tomography (Chen-Wiegart et al, 2012; Shearing et al, 2012; Ebner et al, 2013) and FIB-SEM tomography (Ender et al, 2011; Wilson et al, 2011; Hutzenlaub et al, 2012) are the most commonly applied imaging techniques for obtaining complete microstructural models of lithium-ion battery electrodes (Shearing et al, 2012)
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