This video animation describes a system setup used to measure the thickness of thin conductive films such as electric vehicle (EV) battery electrodes. Typically, the EV battery electrode materials are a Lithium graphite compound deposited on either a copper or aluminum substrate. These electrodes are then wound together in combination with an electrolyte separator for insertion into a battery enclosure. It is important to monitor the electrode film thickness to ensure the final product is of the correct thickness or it will not fit into the battery enclosure.
Since the electrode film is only about 100 microns (.004” ) thick it is quite flexible and is susceptible to vibration, twisting and flapping as its being processed. Using two differential capacitance probes on either side of the film to measure the thickness can be challenging due to the electrode vibration as it adds tangential (slant) errors to the measurements.
Suggested Solution to Measuring Step Height Thickness of Film
Depicted here is a suggested solution. As the electrode films run across a roller, and kept taut, we can measure the step height of the film relative to the roller. Multiple probes (3) are used to measure not only the film step height but also the roller runout. Subtracting the roller gap from the film gap produces the film thickness relative to the roller. Adding an additional probe at the other end of the roller allows us to also compensate for other roller eccentricities such as roller tilt and surface undulations. We suggest that you would subtract the average roller surface from the electrode gap to further improve accuracy. Adding a rotary encoder to the roller could provide even more roller compensation through roller runout correction. In this case you would measure the roller gap without any electrode present, store the gap vs angular position and then subtract the stored runout from the electrode gap vs encoder position. Done properly 1um ( 0.000040”) accuracy should be achievable.
MTI’s Digital Accumeasure System can handle up to four capacitance probes and two encoder inputs. The Digital Accumeasure samples the encoder data and synchronizes the gap data with the encoder position thus eliminating the need for a separate data acquisition system. A step height measurement function is also built into the Digital Accumeasure further reducing the data acquisition burden. A simple PC is all that is required to display the conductive film thickness. Roller runout correction would require a user to make a small program to accomplish this task, but no additional data acquisition hardware would be necessary.
Typical use cases for the Accumeasure product line includes measurement of:
- EV battery plate thickness
- Non-woven conductive material thickness
- Conductive film thickness
- Roll to roll conductive material thickness
- Conductive flexible web thickness
- Continuous sheet conductive material thickness
- Step height film thickness
- Step height conductive film thickness
- EV anode plate thickness
- EV cathode plate thickness
This video animation demonstrates the setup required to measure step height thickness of non-woven conductive films on a roller at multiple points leveraging MTI’s Accumeasure product line. Done properly, micrometer level accuracy should be achievable.
Learn more about MTI Instruments Accumeasure Series of products.
Documentation and Downloads for Capacitance Sensor Measurements and our Accumeasure products.