Investigation of charge carrier dynamics in positive lithium-ion battery electrodes via optical in situ observation

We present optical in situ investigations of lithium-ion dynamics in lithium iron phosphate based positive electrodes. The change in reflectivity of these cathodes during charge and discharge is used to estimate apparent diffusion coefficients for the lithiation and delithiation process of the entire electrode. Thereby, a scaling analysis of the transport process is applied, which clearly reveals its diffusive character. Results are shown for cathodes, in which the common additive carbon as well as the conductive and electrochromic marker additives (indium tin oxide and antimony tin oxide) are used. The latter leads to a substantial increase of visibility of the optical effect in the cathodes while electric properties remain qualitatively unchanged. The procedure extends common characterization techniques of positive electrode materials via a novel and integral combination of electrical and optical measurements.