Characterization of mechanical properties of battery electrode films from acoustic resonance measurements

Abstract

and Computer Engineering, BYU Master of Science Measurements of the mechanical properties of lithium-ion battery electrode films can be used to quantify and improve manufacturing processes and to predict the mechanical and electrochemical performance of the battery. This thesis demonstrates the use of acoustic resonances to distinguish among commercial-grade battery films with different active electrode materials, thicknesses, and densities. Resonances are excited in a clamped circular area of the film using a pulsed infrared laser or speaker and responses are measured using an electret condenser microphone. A numerical model is used to quantify the sensitivity of resonances to changes in mechanical properties. When the numerical model is compared to simple analytical models for thin plates and membranes, the battery films measured here trend more similarly to the membrane m odel. Resonance measurements are also used to monitor the drying process. Results from a scanning laser Doppler vibrometer verify the modes excited in the films, and a combination of experimental and simulated results is used to estimate the Young's modulus of the battery electrode coating layer.

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

“…calculated the elasticity of a cathode coating to be about 40 GPa using the rule of mixtures. Dallon et al [10].…”

“…The current collector layer is commonly made of thin aluminum for cathode or copper for anodes. On top of the current collector is the coating layer composed of large active material particles, carbon additive for better conductivity, polymeric binder, and pores [10]. The distribution of this mixture of materials can vary significantly in structure due to manufacturing differences, thus causing the heterogeneity on the micron as well as on the millimeter-scale [9], [11].…”

“…The resonance can be excited by a pulsed laser or a wide frequency range of sound burst, and can be measured using a laser interferometer or a speaker. This method can estimate the Young's modulus and thickness [10]. But due to uneven clamping resulting in variations of the boundary conditions, the method has exhibited greater systematic variation than would be ideal for monitoring changes in battery properties [10].…”

“…These two films were cut into many pieces each approximately 8 mm×8 mm and then stacked up together as shown in The Young's modulus values of different battery films apparently have been measured from the MPa into the GPa range [10], [47], [48]. Forouzan et al [47] measured the elasticity of coating (delaminated from the current collector) to be about 11.3 MPa.…”