Non-destructive evaluation of slot-die-coated lithium secondary battery electrodes by in-line laser caliper and IR thermography methods

Non-destructive, in-line quality control methods were adopted for evaluating the thickness and homogeneity of wet and dry lithium secondary battery electrodes. Laser caliper and infrared ( IR) thermography methods were implemented in a systematic fashion for the first time to evaluate the quality of electrodes during the coating process on a slot-die coater. Laser caliper sensors were mounted, aligned, and subsequently calibrated at the oven inlet of the coating line in order to examine the thicknesses of different cathodes and anodes. The effect of various factors such as substrate vibration, temperature, surface reflectivity and laser positions on the thickness measurement during slot-die coating were evaluated. The setup was used to monitor the wet thickness of the cathode and anode, and the precision of the in-line laser thickness measurement was determined to be less than +/- 2%. Thickness deviation for cathodes was typically +/- 2.0-2.3%, and for anodes it was typically +/- 2.2-2.6%, which confirms excellent precision of the measurement. The homogeneity of the dried electrodes was also evaluated by IR thermography at the oven outlet of the coating line. Temperature profiles from thermography images of dry electrodes were carefully examined to detect any flaws and inhomogeneity present in the electrodes. An increase or decrease in the temperature profiles indicated defects/flaws in the electrodes that could not be observed in optical images. The techniques applied in this work will be helpful for detection of electrode flaws and contamination during large-scale manufacturing and to identify flawed product prior to lithium-ion cell assembly.