Ultrasonic spectroscopic measurements for the testing of filling and wetting processes

Ultrasonic methods can be used to monitor the filling and wetting process during cell production. These methods allow manufacturing defects or insufficient wetting of the cell with the electrolyte to be detected early on in the value chain.

The evaluation of such signals requires the use of very short and therefore very broadband pulses, which are transmitted through the lithium-ion batteries via the transmission arrangement of the sensors. The time signal of the incoming ultrasonic waves measured at the receiver transducer makes it possible to draw conclusions about the filling and wetting status. The evaluation of the sound velocity and attenuation thus provides even more accurate information about the state of the electrolyte being scanned, as these offer significantly more accurate values with regard to the scattering and absorption of the ultrasonic waves than the pure evaluation of the temporal amplitude maxima. Such ultrasonic spectroscopic methods are being developed at Fraunhofer ZESS and are already being used in a wide variety of applications.

In almost all chemical substances, aging causes a change in density and thus also in the sound velocity or attenuation of ultrasonic waves as they penetrate the substance. This means that ultrasonic-based measurements can also be used later on to make statements about the state of charge and degradation of the battery cell.