Characterization of mechanical properties of thin-film Li-ion battery electrodes from laser excitation and measurements of zero group velocity resonances

Abstract

The mechanical properties of thin-film Li-ion battery electrodes are controlled by the microstructure of the constituent materials. In this work, a noncontact and nondestructive measurement of the mechanical properties of electrode films is performed by measurement of zero-group velocity (ZGV) resonances. Theoretical models are used to quantify the sensitivity of the ZGV resonances to changes in mechanical properties. The ZGV Lamb modes of a solid bilayer consisting of a thin metallic layer and a thin compliant coating layer are shown to be dependent on Young’s moduli, thicknesses, densities, and Poisson’s ratios of the layers. Experimental ZGV resonances are excited using a pulsed infrared laser and detected using a laser interferometer. Commercial-grade battery films with different coating materials, densities, and thicknesses are measured. Young’s moduli of the battery electrode layers are estimated using the combination of a theoretical model and experimental results. The effect of the calendering process on the battery materials is also investigated. Results suggest that Young’s modulus of the electrode coating increases drastically after the battery films are calendered. This technique can be used to quantitatively study the mechanical properties of Li-ion battery electrodes in order to improve overall battery performance.