Structural Analysis of Cathode Slurry Under Flow Using New Probe for Rheo-Impedance Measurements

Abstract

A battery slurry will experience a variety of shear stresses as it goes through the manufacturing process. The full characterization of a slurry for quality control is challenging due to the complex and changing relationship between active material particles, binder, and the carbon black conductive network as a function of these different shear environments. Rheology is a powerful tool for measuring suspension stability and the viscosity at different shear stresses. However, it cannot characterize the structure of the carbon black conductive network because the rheological properties are dominated by the larger active material particles. Poor distribution or aggregation of the carbon black additive will create an electrode with higher electrical resistance, resulting in more heat generation and a shorter cycle life. Electrochemical impedance spectroscopy is an information dense technique that probes the sample using an alternating current or potential at a range of frequencies. Amongst its many applications, EIS can discriminate between simultaneous events that take place over different time scales, such as the measurement of conductivity within a solid electrode vs the ionic conductivity of the electrolyte. Combining these techniques into a simultaneous measurement will characterize the rheological behavior and the structure of the carbon black conductive network under flow and temperature conditions that are relevant for a manufacturing environment. A novel probe for the simultaneous measurement of rheological properties and electrochemical impedance spectroscopy (Rheo-EIS) is herein presented. A structural analysis of Li-ion battery cathode slurries and carbon paste is used to demonstrate the technique.