Fabrication of VB₂/Air Cells for Electrochemical Testing

The overall goal of the following experiment is to reproducibly, demonstrate a high capacity metal air battery using vanadium diboride as an anode material. This is achieved by synthesizing nano vanadium diboride, which can release up to 11 electrons per molecule to replace the low capacity zinc metal in a conventional zinc air cell, which can release only two electrons per molecule. As a second step, a conventional zinc air cell is disassembled to allow for removal of the anode material.

Next, the cell is reassembled with vanadium diboride and its discharge characteristics are measured. Results are obtained for the performance and efficiency of the vanadium diboride air battery. In comparison with a theoretical maximum, a uniform test bed reproducibly shows a high energy density for vanadium diboride air battery anode materials.

The main advantage of this technique over existing methods such as three electrode optometry, is that you, it allows you to directly be able to probe the anode material and study its characteristics. This method helps answer key questions in the multi electron storage field by providing a straightforward route to test and study new materials. Generally, individuals new to this technique will struggle with the disassembly of the commercial zinc air cell, which is quite intricate.

This process must be done quite delicately. Nanoscopic Vanadium IDE is synthesized via ball milling. To begin clean, a 50 milliliter tungsten carbide milling jar and 10 10 millimeter tungsten carbide balls dry them under air in a 100 degree Celsius oven for an hour.

When cool, wipe clean the inside of the milling jar to ensure no residue remains. Next, purge the anti chamber of a glove box with Argonne three times for 10 minutes each. Then transfer the milling jar balls and a clean spatula into the argon filled glove box.

Weigh out vanadium and boron powders in a one to two molar ratio into the milling jar. Add the balls to the milling jar and seal it. Remove the milling jar from the glove box and place it into a planetary ball mill.

Set the mill to 600 RPM and mill for four hours. Allow the milling jar to cool to room temperature before removing it from the ball mill. Once again, purge the anti chamber of a glove box with Argonne three times for 10 minutes each time, transfer the milling jar a round bottom flask, paraffin, film spatula, and a magnetic stir bar into the glove box.

To apply the zirconia oxide coating to the vanadium diboride. First, use a spatula to scrape the walls of the milling jar until the bulk of the starting mass has been recovered into a whey boat. Weigh the collected nano vanadium diboride and transfer it to a round bottom flask.

Weigh 3.5%by weight of zirconium chloride compared to the collected vanadium diboride, and add the powder to the flask. Place a magnetic stir bar in the flask and seal the flask. Using paraffin film.

Remove the flask from the glove box. Use a 10 milliliter syringe to transfer 10 milliliters of dathyl ether into the flask. Quickly cover the whole created by the syringe with an additional piece of film.

Place the flask on a stir plate and mix for one hour on a medium setting. After one hour, use a rotary evaporator to evaporate the remaining dathyl ether off of the nano vanadium diboride until it appears dry. Once it is completely dry, collected for use.

At this point, obtain freshly prepared eight molar potassium hydroxide, sodium hydroxide electrolyte composed of four molar potassium hydroxide and four molar sodium hydroxide. Open a zinc air cell by using diagonal cutting pliers to create a cut in the lip of the coin cell casing. Then crimp the outside edges of the lip outward.

Go completely around the cell twice, at which point it should be easy to open. Use a razor blade to slowly push up on the edges of the cap and gently force open the cell. Be patient and careful not to damage or crack any part during the step.

Once the cell is separated into two pieces, the bottom, which contains a separator and the cap, use a razor blade to gently remove as much of the zinc anode material from both parts. Do not scrape the bottom. It is important not to damage any parts.

Use a cotton swab to carefully wipe the remaining zinc and residue from the cap bottom and separator. Clean off the cap and outside of the cell with isopropyl alcohol. Start the fabrication of electrodes by weighing out 1.2 milligrams of zirconium coated vanadium diboride per electrode.

Transfer this into a mortar and pestle. Add a mass of IC carbon black equal to 30%of the total anodic material to the mortar and pestle and grind for 30 minutes. When the grinding is done, ensure there are no large visible clusters of material before collecting the powder.

Transfer approximately 1.7 milligrams of the 70 30 powder mixture per clean electrode cap to the cap. With a spatula. Add a single drop of isopropyl alcohol to each cap and swirl the powder with a small pointed tip until there are no clumps, and the suspension is evenly distributed across the top of the cap.

Allow the electrodes to dry for 30 minutes. Then place each cell with its upside down cap next to its corresponding bottom. Inspect each cap to ensure the anode material is evenly spread and not cracked.

Add 27 microliters of the electrolyte mixture to each bottom. Use a cotton swab and dab once in the bottoms to gently remove excess electrolyte. Carefully take each bottom, turn over and place them on top of the cap so that the anodic material is in contact with the electrolyte.

Apply pressure and seal using a fast drying epoxy. Once the fabrication process is completed, place the cells on a discharge rack and allow them to rest for 10 minutes to ensure equilibration prior to discharging. Next, take a measurement of the open circuit potential.

Then measure the discharge of a cell at a constant load of 3000 ohms using a battery tester. Plotted here, the results for several cells during a discharge under a load of 3000 ohms. The vertical axis shows the voltage.

The horizontal axis shows the discharge efficiency, which is a percentage of the maximum theoretical capacity of 4, 060 ampu hour kilogram to the minus one. The upper curves correspond to cells with nanoscopic vanadium diboride. These show higher discharge voltages and higher intrinsic capacity when compared to the lower curves, which correspond to cells with macroscopic vanadium diboride.

A similar plot is shown here for a 1000 ohm load. Again, the cells with the nanoscopic material exhibit better performance. Both figures provide evidence for the reproducibility of the results.

This plot shows the voltage is a function of time for a cell with macro vanadium diorite in blue compared with the empty cell performance in red. This data shows the discharge of a cell containing 20 milliamp hours of zinc anode material. To perform this measurement.

A zinc battery cell was first emptied and then the zinc was reintroduced. This demonstrates the suitability of the cleaned battery as a test bed for the vanadium diorite anode. Here the macro vanadium diorite cell curve in green is compared to a cell with an anode containing only packed carbon.

This final image shows the performance of a vanadium diorite cell with intentional zinc impurities. In the node note, the discharge plateaus. The lack of these plateaus in the cells produced with the protocol is evidence that they do not contain significant zinc contamination.

By following this procedure, other methods like electrical impedance spectroscopy can be performed in order to answer additional questions like internal resistance in the electrolyte and antic material.