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

Abstract

For lithium batteries, we present facile 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. 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 and the measured reflectivity of the positive electrode is used to estimate an apparent diffusion coefficient. a scaling analysis of the ionic transport process is applied, which reveals the diffusive character of the process. 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 especially required for the simulation of battery cells as well as to design future lithium-ion- batteries.