The overall goal of this procedure is to prepare and test half coin cells for laboratory research. First, prepare a working electrode, a counter electrode, and others cell components. Then meticulously assemble the coin cell in a glove box and seal by crimping.
Finally, perform electrochemical testing of the coin cell to determine its key properties like the charge and discharge capacities, rate capabilities, and other valuable coin cell information. Generally, cell construction is challenging because the performance of the cell is highly sensitive to the construction procedure. First, prepare an NMP binder mixture of approximately six 8%PVDF binder in NMP.
Next, mix the active material and see black by vortex for one minute. After adding some NMP binder mixture, transfer the ingredients to a small glass vial. Vortex the sample at maximum RPM for about 30 minutes.
If necessary, add two zirconia balls of five millimeters diameter for better mixing. Continue to add NMP as needed to obtain a slurry of required consistency. See next, spread a metal foil of the current collector onto a glass plate.
Aluminum is used as the current collector for the cathode and copper is used as the current collector for the anode. Use acetone and remove any air bubbles between the foil and the glass plate. Now, position two layers of masking tape to define the region to be coated with a stainless steel spatula.
Apply the slurry onto the metal foil. Spread the slurry uniformly onto the track using a razor blade, depending on the material and binder used. Dry the coating in air or vacuum at approximately 90 to 120 degrees Celsius for about two to eight hours.
After cutting the dried coating place the coated metal foil between two steel plates lined with two weighing papers to protect the coating. Then press under a load of approximately 3000 pounds. Now punch eight millimeter discs of the dried coated metal foil.
Next, weigh the cathodes. Wrap them and place them into the glove box. Also, punch eight millimeter discs of the uncoated metal foil of the same material, and weigh them as the electrolyte is photo sensitive.
Store it in an Nalgene bottle wrapped in aluminum foil inside an Argonne glove box. Use a nylon brush or stainless steel scalpel to clean the surface of the lithium foil until a shiny silvery surface appears. Then punch 12.7 millimeter discs of the lithium foil.
The components of the coin cell case are meticulously ordered. Prepare 19 millimeter discs of cell guard C four 80 membrane for separators. After flushing the exchanger five times with argonne, transfer the working electrode coin cell cases springs and spacers and separators onto the glove box working surface.
To start assembly, add two drops of the electrolyte onto the cell cup and position the working electrode. Next, add three drops of the electrolyte and place two separators with two drops of electrolyte between them. Proceed to add two more drops of the electrolyte and position the lithium counter electrode.
Now place the two stainless steel spacers and a spring on the lithium disc. Finally close with the cell cap and crimp the cell three to four times. Handle the finished cell with plastic tweezers to avoid shortcircuiting and wipe off the excess electrolyte as soon as it is assembled.
Connect the coin cell to the battery tester in the open circuit voltage mode for one hour. Define the voltage window for testing the cell based on the active material used in a working electrode. Now for the theoretical capacity for the cell, first, calculate the weight of the electrode material.
Then compute the weight of the active material in the electrode, and determine the theoretical capacity for the electrode disc. Now test the coin cell to charge discharge cycles at the required C rate. In the preparation of the working electrode, it is important to create a slurry of good consistency.
These results compare good and bad coatings. After drying note, a cracked coating typically results from a slurry that has excess. NMP and a porous coating typically results from a slurry that has insufficient NMP.
After the cells are assembled, they're crimped to obtain a tight seal to protect from moisture. Typically, a badly crimped coin cell splits open after a few hours in ambient temperature due to the swelling of the lithium foil after reaction with moisture. These data are representative of a coin cell constructed from a working electrode of lithium cobalt oxide and a lithium foil counter electrode.
The plot shows the first charge and first discharge curves For the coin cell. Note, the voltage window was set to be between three and 4.3 volts. The capacity was 155 milliamp hours per gram for the first charge cycle and 140 milliamp hours per gram for the first discharge cycle.
Once mastered, this technique can be used to construct and evaluate coin cells using different cathode materials While attempting to this procedure, it's important to remember to keep the work desk as dry as possible. After watching this video, you should have a good understanding of how to construct and test coin cells.
