This protocol overcomes the existing fixed-size supercapacitor and provides a method to produce a free-form supercapacitor through precise inkjet printing. Through this protocol, the efficiency of human and material resources can be secured. Also, providing users with software control method for inkjet printers could help manufacture more precise supercapacitors.
This technology provides a way to handle inkjet printers, therefore, this protocol can be used not only to produce supercapacitors, but also to produce other devices. Before designing the pattern of electrochemical double-layer capacitors, or EDLCs, start by running the CAD program. Go to the File button atop the program window and click on the New and Project buttons to form a new project file.
To generate the board file, click on the File, New, and Board buttons in order. At the top left of the created board file window, click on the mesh-shaped grid button to set the grid Size, Multiple, and Alt values. Change the grid Size and Alt value from millimeters to the inch so that the inkjet printer can read the PCB CAD pattern Press Finest to make fine adjustments.
Once the parameters are set, design the pattern of the current collector and EDLC line in an interdigitated form. Design the gel polymer electrolyte, or GPE, pattern and current collector pads in a rectangular form. For three types of final patterns, such as conductive line, EDLC, and GPE, set the three layers by clicking on View and Layer settings in order.
Create new layers by pressing the New layer button at the bottom left of the visible layers window. In the new window of New layer, set up the Name and Color for the new layer. For visually distinguishing the layers, set the names of the three layers to current collector, EDLC, and GPE, and change the corresponding colors by clicking on the box to the right of Color.
Press Line at the bottom left of the screen. To change the thickness of the line, input the value of width located at the top center in inch scale. Then, click on the main field and drag to draw a line.
To edit the length of a line, right click on the line and click on properties at the bottom. In the From and To fields, input the X and Y values of the starting and ending points. For the reference point of the pattern, set the upper-left corner to 0, 0.
Draw the rest of the pattern based on the information shared before. To set the drawn pattern to the desired layer, right click on the pattern and click on Properties. Then, click on Layer and choose the desired layer.
Draw rectangular patterns of the current collector pad in GPE by pressing RECT at the bottom-left of the main window. Click and drag on the screen where the previously drawn pattern exists. Next, right click on the rectangular surface and click on Properties at the bottom.
Input the upper-left and lower-right X, Y values of the rectangle in the From and To fields, respectively. Set the rectangle to the desired layer as mentioned earlier. Before converting the CAD file of the designed pattern into the Gerber file format, save the board file in brd format by clicking on the file and Save.
After saving the file, click on the File tab at the top of the window and click on CAM Processor. To create a Gerber file of the desired layer, modify the items under the Gerber tab of the output files by deleting the sub lists, such as top copper and bottom copper by pressing the minus sign. Press plus and click on New Gerber output to create Gerber output.
On the right side of the screen, set the layer name in Name and Function to Copper by pressing the gear on the right. Then, set the Layer type to Top and set Gerber layer number of the current collector, EDLC, and GPE to L1, L2, and L3 in order. In the Layers window at the bottom of the Gerber file, click on the Edit Layers at the bottom left to select each desired layer.
To set the name of the output file to be created, set the Gerber filename of Output at the bottom of the window to prefix/name.gbr. Finally, click on the Save Job at the top left of the window to save the settings. Click on the Process Job at the bottom right to create a Gerber file.
To set the inkjet printer software parameters, run the printer program, then click on the Print button, select Simple, and choose Flexible Conductive Ink. Upload the Gerber file of the designed pattern by clicking the Choose File button. Choose and open the Gerber file of the conductive line.
Click on the Next button as indicated by the yellow box. Next fix the PCB board and mount the probe. Once done, adjust the zero point of the PCB printer through the probe by clicking on the Outline button.
Move the pattern image on the screen by dragging and clicking on the Outline button. Check whether the probe moves through the desired path. Then, hit the Next tab.
Click on the probe to measure the height of the substrate to check whether the substrate is flat. When the height measurement is complete, remove the probe and insert the ink cartridge into the ink dispenser and connect the nozzle of an inner-diameter of 230 micrometers to prepare the dispenser. After mounting ink dispensers for conductive line, EDLC, and GPE, print a sample pattern by pressing the Calibrate button while adjusting the parameters of each ink.
Visually check the printing result and record the parameter values for each ink. Erase the sample printing pattern with a cleaning wipe moistened with ethanol before pressing the Start button to print the designed pattern of the conductive line. After printing, flip the board and cure the conductive line at 180 degrees Celsius for 30 minutes, followed by measuring the combined weight of the substrate and the conductive line.
On the Start screen of the printer program, select the Aligned option, load the EDLC line pattern file, and click on the Next. Ensure the position of the conductive line is detected through two alignment points to align the pattern positions of the EDLC line and the conductive line. Then, move to a random point and check whether the location is correct.
Measure the overall height of the conductive line to check the height of the dispenser nozzle above the conductive line by clicking on the Probe button. Change the software parameter values of EDLC inks. Once done, print a sample pattern to check whether the software parameter values are appropriate.
Later, erase the sample printing pattern with a cleaning wipe moistened with ethanol to print the EDLC line by pressing the Start button. Perform the electrochemical measurements for the inkjet-printed supercapacitor device. Click on Apply to Ch and run the sequence file of the cyclic voltammetry test to obtain the result.
Click on Apply to Ch and run the sequence file of the galvanostatic charge/discharge test to obtain the result. Click on Apply to Ch and run the sequence file of the electrochemical impedance spectroscopy test to get the result. The structural properties of the conductive ink and EDLC ink were analyzed with scanning electron microscopy.
The conductive ink was well centered to form continuous conducting paths. All components of the ink were well dispersed, with no visible elements that could cause clogging during printing. The rheological properties of the EDLC ink were reported, and it was observed that the viscosity of the ink increased with shear time, indicating a shear-thickening behavior without any stress-induced structural extension, stretching, or rearrangement.
In the study, a printed supercapacitor was obtained successfully. The print quality is considered good. if the printed pattern has fewer or no defects, with minimal surface roughness and uniform thickness.
The printing results with a minimum 100 millimeters per minute feed rate showed uniform lines with no visible disconnection. The overall printing time was decreased when the feed rate was maximum at 600 millimeters per minute. Compared with the results printed with a feed rate of 500 millimeters per minute, the lines formed at 600 millimeters per minute were cut off or cracked because the dispenser moved rapidly.
A feed rate of 300 milliliters per minute was optimal for a proper printing time and to prevent cracked formation. Printing results were checked for corresponding changes in the kick. All lines were disconnected when the kick was too low.
However, the high pressure at a high kick created a bottleneck, resulting in nozzle clogging. At the appropriate kick value, the line did not break and the nozzle did not clog. More precise printing is possible through software parameter control, allowing many researchers to utilize inkjet printing under optimal conditions in various fields.
