Estimation of apparent diffusion coefficients in positive lithium-ion battery electrodes by optical in situ observation


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Lithium-ion batteries face increasing demands from different applications. Therefore, further improvement of current lithium-ion battery technology is still desirable. Immediate metrological methods that work in a complementary way to previous methods are advantageous for the research and development process.

Within this context, we present facile and quick optical in-situ video microscopy investigations of lithium iron phosphate based positive electrodes. This novel approach allows for an impressive visualization of the ion dynamics during charging and discharging. In addition, this optical observation method is used for quantitative material characterization. Hence, we present experimental as well as theoretical results.
To enable much easier optical observation, electrodes were produced with marker additives indium and antimony tin oxide, which have conductive and electrochromic behavior. A comparison with a common positive electrode using carbon additive will be shown.
The correlation between the electrical charge, i.e. lithiation of the cathode, and the measured reflectivity of the positive electrode is used to estimate an apparent diffusion coefficient. Here, a scaling analysis of the ionic transport process is applied, which clearly reveals the diffusive character of the process. This type of analysis is applied for the first time within the field of battery research. The as-obtained diffusion coefficient has to be understood as characterization parameter of the entire electrode including its specific properties like tortuosity or porosity. This characterization is important for analyzing the overall electrical behavior of the battery electrode and is especially required for the simulation of battery cells as well as to design future lithium-ion- batteries. Here, the method as well as results are presented.

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