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2. Lithium Redistribution Mechanism within Silicon-Graphite Electrodes: Multi-Method Approach and Method Validation.

Author

Hogrefe, Christin, Paul, Neelima, Boveleth, Lioba, Bolsinger, Marius, Flügel, Marius, Danner, Timo, Latz, Arnulf, Gilles, Ralph, Knoblauch, Volker, Wohlfahrt-Mehrens, Margret, Hölzle, Markus, and Waldmann, Thomas

Subjects
X-ray diffraction, ELECTRODES, MICROSCOPY, ALUMINUM-lithium alloys, LITHIATION, CHARGE measurement
Abstract

Li redistribution processes within Si-graphite composite (SiG) electrodes are analyzed using in situ and operando X-ray diffraction (XRD), ex situ light microscopy (LM), in situ optical microscopy of cross-sectioned full cells (CS-IOM), and 3D microstructure-resolved simulations of full cells. First, the lithiation behavior of graphite and SiG full cells (Si content 20.8 wt.-%) is analyzed. The results are used as validation of the methods (XRD, LM, CS-IOM, simulation). Second, the Li redistribution between the graphite component and Si component within SiG electrodes is investigated: By operando XRD measurements during charging in comparison with relaxed cells, a higher lithiation degree in the graphite component is found during charging compared to the relaxed state, indicating Li redistribution from graphite to Si during relaxation. The Li redistribution is directly observed by in situ and ex situ optical microscopy, where the golden LiC6 phase disappears during a 24 h relaxation period. The results are supported by simulations showing the variation in the Li concentration, not only in graphite but also within the Si component. Furthermore, all methods find that the Li redistribution is more pronounced at a higher C-rate of 0.5 C, suggesting a preference for graphite lithiation over Si lithiation. [ABSTRACT FROM AUTHOR]

Published
2024
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4. Onset Shift of Li Plating on Si/Graphite Anodes with Increasing Si Content

Author

Flügel, Marius, Bolsinger, Marius, Marinaro, Mario, Knoblauch, Volker, Hölzle, Markus, Wohlfahrt-Mehrens, Margret, and Waldmann, Thomas

Subjects
Technology, ddc:600
Abstract

Mixing graphite with Si particles in anodes of Li-ion batteries provides increased specific energy. In addition, higher Si contents lead to thinner anode coatings at constant areal capacity. In the present study, we systematically investigated the influence of the Si content on the susceptibility of Li plating on Si/graphite anodes. Si/graphite anodes with Si contents from 0 to 20.8 wt% combined with NMC622 cathodes were manufactured on pilot-scale. After initial characterization in coin half cells and by SEM, pouch full cells with fixed N/P ratios were built. Rate capability at different temperatures, and Post-Mortem analysis were carried out. Results from voltage relaxation, Li stripping, SEM measurements, glow discharge optical emission spectroscopy (GD-OES) depth profiling, and optical microscopy were validated against each other. A decreasing susceptibility to Li plating with increasing Si content in the anodes could be clearly observed. A critical C-rate was defined, at which Li plating was detected for the first time. It was also found that at 0 °C the critical C-rate increases with increasing Si contents. At 23 °C the SOC at which Li dendrites were first observed on the anode also increased with higher Si content.

Published
2023

9. Efficient Workflows for Detecting Li Depositions in Lithium-Ion Batteries

Author

Waldmann, Thomas, Hogrefe, Christin, Flügel, Marius, Pivarníková, Ivana, Weisenberger, Christian, Delz, Estefane, Bolsinger, Marius, Boveleth, Lioba, Paul, Neelima, Kasper, Michael, Feinauer, Max, Schäfer, Robin, Bischof, Katharina, Danner, Timo, Knoblauch, Volker, Müller-Buschbaum, Peter, Gilles, Ralph, Latz, Arnulf, Hölzle, Markus, and Wohlfahrt-Mehrens, Margret

Abstract

Lithium deposition on anode surfaces can lead to fast capacity degradation and decreased safety properties of Li-ion cells. To avoid the critical aging mechanism of lithium deposition, its detection is essential. We present workflows for the efficient detection of Li deposition on electrode and cell level. The workflows are based on a variety of complementary advanced physico-chemical methods which were validated against each other for both graphite and graphite/Si electrodes: Electrochemical analysis, scanning electron microscopy, glow discharge-optical emission spectroscopy and neutron depth profiling, ex situ optical microscopy, in situ optical microscopy of cross-sectioned full cells, measurements in 3-electrode full cells, as well as 3D microstructurally resolved simulations. General considerations for workflows for analysis of battery cells and materials are discussed. The efficiency can be increased by parallel or serial execution of methods, stop criteria, and design of experiments planning. An important point in case of investigation of Li depositions are rest times during which Li can re-intercalate into the anode or react with electrolyte. Three workflows are presented to solve the questions on the occurrence of lithium deposition in an aged cell, the positions of lithium deposition in a cell, and operating conditions which avoid lithium depositions in a cell.

Published
2024
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