Ultrasonic Methods for Characterizing Layered Electrodes of Lithium-Ion Batteries

Abstract

Lithium-ion battery electrodes have a multilayered structure consisting of active porous electrode materials coated on one or both sides of a thin metal current collector. The porosity and tortuosity of the active materials play a vital role in determining the battery's performance metrics, such as energy density and power density. However, existing methods for quantifying these parameters are often limited and cannot be easily applied in a production environment. In this work, we propose two ultrasonic methods based on a newly developed stiffness matrix theory [1] to achieve in-production quantification. The first method establishes a quantitative relationship to link angled ultrasound transmission to the porous parameters of electrodes. This relationship is then used to inversely determine porosity and tortuosity from ultrasonic transmission measurements using a non-contact, air-coupled setup. From the first method, we observe that ultrasound is highly transmissible as guided wave modes are excited in electrodes. Based on this phenomenon, our second method directly excites guided waves in the layers using electromagnetic acoustic transducers (EMATs), enabling us to obtain more accurate measurements with a better signal-to-noise ratio. Both methods have demonstrated good sensitivity to porosity and tortuosity, thus providing accurate quantification using ultrasonic transmission and guided wave results. We anticipate that our methods have the potential to provide real-time online characterization of electrodes during production, which would enable closed-loop control of the manufacturing processes and thus dramatically reduce wastage and improve product quality. Reference [1] M. Huang, F. Cegla, and B. Lan, Stiffness matrix method for modelling wave propagation in arbitrary multilayers, http://arxiv.org/abs/2302.12868.