Correlation of Local Conductivity to Microstructure for Li-Ion Battery Electrodes By Use of a Contact Probe and SEM/FIB

Abstract

Electron transport in lithium-ion battery structures is a key factor in overall battery performance, but the cause of localized high and low electron transport values, or conductivity, has not been well-studied or understood. Factors that may affect such heterogeneity include high-level variables such as film composition and porosity, as well as manufacturing steps such as film drying and calendering [2]. Here we report on our efforts to correlate battery film structure to measured conductivity values, to better understand the causes of observed film heterogeneity. A modified micro 4-line probe [1] was installed in a high resolution stage with a microscope attached for localization on a µm scale. Using the associated theory, electrical conductivity of commercially manufactured battery films was mapped. Subsequently, particularly “hot” or “cold” conductivity locations were additionally investigated by scanning electron microscope (SEM) combined with focused ion beam (FIB) milling to produce planar cross sections.SEM/FIB images are segmented into 3 domains: carbon, active material, and pores. Each image is characterized using key metrics. These key metrics are then compared to mapped conductivity values in order to determine possible causes of high and low conductivity. This contributes to the goal of this work, namely to increase the uniformity of electrodes by improved control of the manufacturing process. Figure 1: Measured electrical resistivity of commercial anode (top) with SEM/FIB cross section of region with high conductivity (bottom).