Meaning
Measurement of the energy loss of ultrasonic waves as they propagate through a medium provides a non-destructive method to evaluate the internal physical structure of battery cells. This process, known as acoustic attenuation, registers the decay in wave amplitude caused by scattering and absorption within the active layers. Low attenuation typically indicates a uniform solid structure and thorough electrolyte wetting, while high attenuation highlights voids or gas pockets.
Testing Method
Transducers placed on opposite sides of a cell send longitudinal waves through the casing and the internal stack to measure the amplitude of the transmitted energy. Any gas pocket, dry spot, or gap between the electrode and the separator blocks the sound path and creates a drop in the received signal strength. This method maps the entire surface of the cell to produce a detailed two-dimensional image of the electrolyte distribution.
Manufacturers use these scans to adjust the pressure applied during the filling stage.
Sourcing Selection
Sourcing specifications for pouch and prismatic cells use specific decibel loss limits to define acceptable wetting quality. A high rate of wetting accelerates line throughput, making the acoustic attenuation of incoming batches a metric for electrolyte wetting speed. Cells exceeding the maximum attenuation threshold are rejected before the pack assembly stage to avoid premature capacity fade.
Operating Boundary
The sensitivity of the test decreases at high wave frequencies because of the natural absorption limits of polymer separators and current collectors. Cell thickness also affects the measurement, restricting the application of the test to cells below fifty millimetres in depth. Beyond this thickness, the signal-to-noise ratio drops too low to resolve internal defects.
