Forging a stronger connection between mesoscale geometry, performance, and processing techniques can realize practical approaches for controlling battery performance using mesoscale geometry. To this end, 3D X-ray imaging, microstructural characterization, and computational modeling have been applied to analyze the intercalation behavior of Li(Ni 1/3 Mn 1/3 Co 1/3 )O 2 (NMC) cathodes. Samples extracted from pristine cathodes were imaged using X-ray nanotomography. Active material particle geometry was characterized and compared for samples from four cathodes treated with distinct preparation steps. Significant size reduction was observed in calendered and ball milled samples, and distinct differences were observed in particle morphology. Tomographic data for a representative particle was applied in a numerical transport model to assess the effect of particle geometry on intercalation. This assessment proved critical in determining an appropriate estimate of particle size for defining dimensionless parameters that permit rapid estimation of intercalation time. Defining an effective particle radius based on a sphere of equivalent surface area to volume ratio was found to provide the most accurate estimate of intercalation time. Informed by this analysis, dimensionless parameters were used to assess intercalation behavior of the cathode materials. This assessment revealed a substantial change in rate capability connected to particle size reductions achieved in calendering and ball milling.
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.
Tin intermetallic alloy anodes for Li-ion batteries present a route for incorporating the high capacity of tin while potentially mitigating the attendant volumetric expansion issues. While initial cycling performance of these alloy anodes is encouraging, significant capacity fade is observed as cycle number increases. In an effort to better understand the coupling of microstructural changes and electrochemical stimuli for intermetallic alloy anodes a combined electrochemical and 3D microstructural investigation was performed for Cu-Sn alloy anodes. The tin intermetallic alloy Cu6Sn5 was produced by pressing and sintering copper and tin powders mixed in stoichiometric proportions. The resulting pellet electrodes measured 13 mm in diameter by 1 mm thick. Using these pellets as the working electrode, half cells were assembled using Li foil as the counter electrode and LiPF6 in diethyl carbonate as the electrolyte. The half cells were tested in a galvanostatic configuration. Lithiation and cycling of the pellet electrodes were performed within two voltage windows: 0.2-1.5 V vs. Li/Li+ and 0-1.5 V vs. Li/Li+. It has been proposed that distinct reaction products are formed in these two voltage windows. In the higher voltage window a lithiated Cu-Sn phase is formed, while in the lower voltage window Sn is fully lithiated and Cu is expelled from the alloy phase. Distinct structural changes are expected to occur in these voltage windows, particularly due to the volume change that occurs on full lithiation of Sn. To test for these structural changes synchrotron-based x-ray microtomography was performed on samples extracted from the pellet electrodes. Applying microtomography at a resolution of 1.3 μm, imaging of the full sample cross-section was achieved. This permitted observation of affected and unaffected sample regions. Samples from lithiated, cycled, and pristine electrodes were imaged and compared. Significant structural changes were observed in the tested electrodes, particularly those lithiated and cycled in the window of 0-1.5 V vs. Li/Li+. In this window pulverization of the active electrode is clearly observed at the working electrode interface that was closest to counter electrode in the half cells. These observations appear to support structural evolution mechanisms proposed in the literature.
Tin (Sn) alloy electrodes show great potential for advancing battery performance due to the high capacity of tin. To realize this potential, the volumetric expansion during the lithiation process must be mitigated. One means of mitigating volumetric expansion of tin is to alloy it with copper to create Cu6Sn5. Such alloy electrodes retain some of the high capacity of tin, while attempting to accommodate volumetric changes with the addition of the malleable copper. Lithiation and delithiation tests were conducted with the Cu6Sn5 pellet electrodes to produce microstructural changes at the electrode surface. To observe and quantify these microstructural changes, x-ray microtomography was performed on electrode samples after electrochemical testing. The microtomography data was reconstructed into a 3D image, segmented, and the continuous phase size distribution (PSD) of each electrode sample was analyzed. The electrodes lithiated to 0 V vs Li/Li+ and then delithiated to 0.2 V vs. Li/Li+ showed the most substantial reduction in overall PSD compared to the other samples. This suggests that full lithiation of the Sn present in the alloy electrodes followed by partial delithiation of the Li4.4Sn to Li2CuSn can cause substantial microstructural changes related to volume expansion on lithiation and structural collapse upon delithiation. The electrodes fully lithiated to 0 V vs Li/Li+ and not delithiated show a higher overall phase size distribution, including all solid phases, than the pristine sample and the electrode samples that were partially lithiated to 0.2 V vs. Li/Li+ and delithiated to 1.5 V vs. Li/Li+. The higher overall phase size distribution that is shown by the sample that was fully lithiated and not delithiated is evidence of the significant volumetric expansion of the Cu6Sn5 compound due to lithiation. During this process of volumetric expansion, the phase size distribution of the Cu6Sn5/Sn phase is shown to decrease. When the volumetric expansion of the lithiated electrode samples and the volumetric contraction of the delithiated electrode sample are considered together, it can be inferred that the microstructural changes that are observed, such as the decrease in phase size distribution of the Cu6Sn5/Sn phase, can be attributed to the volumetric expansion and contraction of the compound during the lithiation and delithiation process.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.