Monitoring of Lithium-Ion Cells with Elastic Guided Waves

Abstract

The application of lithium-ion batteries is widely spread nowadays. They can be found especially in consumer electronics such as mobile phones and notebooks, as well as in the rapidly growing field of electric cars. Highly available power and energy density of a lithium-ion battery over its lifetime are crucial for their effective operation. A replacement of the battery is recommended if the capacity is reduced by aging to below 80% of the initial capacity. For the estimation of the remaining cell-life, a precise estimation of the state of charge (SoC) and state of health (SoH) is necessary. This cannot be assured by common battery management systems, which only rely on current counting and cell voltage measurements. This work presents the potential to determine the SoC and SoH of lithium-ion cells with elastic guided waves. As the propagation of guided waves is dependent on the density and elastic modulus of a media, a correlation between the state of charge and the measured amplitude and phase of the wave can be shown, as the porosity of the anode will change during charge and discharge. Experimental studies in a pitch-catch arrangement of piezoelectric transducers were conducted on a representative pouch cell. The attached transducer network allows the examination of multiple travel paths through the battery.