Protocol of Electrochemical Test and Characterization of Aprotic Li-O₂ Battery

The overall goal of this procedure, is to demonstrate a systematic and efficient arrangement of routine tests of an aprotic lithium-oxygen battery, including an electro-chemical test and characterization of the battery materials. This protocol involves the study of the aprotic lithium-oxygen battery mechanism, and the development of battery materials, such as active materials or electro-catalysts, cathodes, aprotic electrolytes, and anode materials. The main advantage of this protocol is that involves components that can affect electro-chemical reactions in lithium-oxygen battery, such as nitrogen, carbon dioxide, and moisture from the atmosphere.

It also reduces bi-products such as lithium hydroxide and lithium carbonate. To begin this procedure, mix previously prepared cathode material and polyvinylidene fluoride, or PVDF, in a four to one weight ratio. Add MP at about three times the weight of the mixture.

Stir the mixture to make an even-textured slurry. Coat the slurry with a thickness around 100 micrometers onto carbon paper using a doctor blade. Then, dry the laminate overnight in a vacuum oven at 100 degrees Celsius.

On the next day, punch the laminate into disks with a hole puncher and weigh them. For aprotic electrolyte preparation, dry lithium triflate overnight in a vacuum oven at 100 degrees Celsius. In an argon-filled glove box, prepare a one mole per liter solution of the dried lithium triflate in tetraethylene glycol dimethyl ether.

Stir the solution with magnetic stirring until the salt is dissolved. To prepare the anode, punch lithium chips into disks with a hole puncher. Assemble the Swagelok Cell as shown here.

Tighten the anode end and loosen the cathode end. Next, place one of the lithium disks on top of the stainless steel rod of the anode end. Place a glass fiber separator on the top of the lithium metal anode.

Add five to seven drops of electrolyte to fully wet the glass fiber separator. Then, gently press the separator to remove bubbles. Following this, place a piece of cathode on the top of of the wetted separator with the active material facing the anode.

Cover the cathode with a piece of aluminum mesh. Press the layers with the aluminum tube, and tighten the cathode end. Seal the whole Swagelok Cell in a glass chamber and fix the chamber with a clamp.

After removing the cell from the glove box, connect the glass chamber to an ultrahigh purity oxygen tank. Purge the chamber with continuous oxygen flow at one atmosphere for 30 minutes. At this point, be sure the thermostat is set to 25 degrees Celsius.

Place the cell and electrodes into the thermostat and fix them, then clip the cathode and anode on the glass chamber with the corresponding electronic clips. Next, open the operating software of the battery test system and select the Channel connected with the cable. Set the Discharge Cutoff Voltage to 2.2 volts for the discharge test.

Set the Discharge Charge Step Time to 10 hours for the capacity-controlled cycling test. Then, set the Discharge Cutoff Voltage to 2.2 volts, and the Charge Cutoff Voltage to 4.5 volts for the voltage-controlled cycling test. Following this, run the procedure by clicking the run button on the software interface.

Once the run is complete, disassemble the cell in the glove box. Place the electrodes in glass vials for further characterization. After removing the remaining cell parts from the glove box, place the Swagelok parts, stainless steel rod, aluminum tubes, and aluminum meshes, in a beaker containing deionized water.

Then, clean them with ultrasonication for 15 to 30 minutes. Finally, dry the cell parts and glass chamber in a thermostat set to 60 to 80 degrees Celsius. SCM images of the carbon powder before, and after the catalyst loading, demonstrate preservation of the porous surface structure.

TEM images show the electro-catalyst nano particles, uniformly distribute on the carbon substrate, and well crystallized nano particles are shown in the high resolution TEM image. XANES spectra show that the electro-catalyst nano particles are partly oxidized, due to the preparation of cathodes in air. Typical voltage profiles for discharge and discharge-charge cycles are shown here.

In the SCM image of the discharged cathode, the products have a toroidal shape, which is widely accepted as the primary morphology of lithium peroxide in a lithium-oxygen cell. Lithium peroxide and carbon peaks are observed in the XRD pattern of the discharged cathode, suggesting that side reactions are minimized in the cell. XPS spectra show that lithium peroxide and lithium hydroxide form on the cathode surface after discharging.

Lithium peroxide is reduced, but lithium hydroxide remains after charging. A trace amount of lithium superoxide is detected by Raman spectroscopy. The hydroxide and carbonyl vibration signals in the FTIR spectra, indicate the presence of the ether electrolyte, as well as other hydroxide, carbonate, or carbonyl species, which are formed in side reactions.

Once mastered, this type of cell can be assembled in five minutes, if it is performed appropriately. After its development, this technique paved the way for researchers in the metal-air battery field to explore battery performance in both electro-chemical testing and categorization of battery materials. While attempting this procedure, it is important to remember to operate in a glove box filled with argon to avoid side reactions and by-products.

After watching this video, you should have a good understanding of how to study lithium-oxygen batteries systematically and efficiently. Don't forget that working with alkaline metals and organic solvents can be extremely hazardous, and precautions such as wearing gloves, working in a glove box, and working in a chemical fume hood, should be taken while performing this procedure.