Engineering
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Preparation of Graphene Liquid Cells for the Observation of Lithium-ion Battery Material
Chapters
Summary February 5th, 2019
Here, we present a protocol for the fabrication and preparation of a graphene liquid cell for in situ transmission electron microscopy observation, along with a synthesis of electrode materials and electrochemical battery cell tests.
Transcript
This graphene liquid cell enables transmission electron microscopy for these dynamics in a liquid electrolyte. Such dynamics can provide rich information of the working mechanisms of Lithium-ion batteries and contributes to designing advanced battery devices. The advantages of graphene liquid cell is that it allows TEM imaging in liquid electrolyte providing good spatial resolution and high imaging contrast.
In addition to a superior quality of the image, it can also provide information of various morphological phase and interfacial transitions. With only a written protocol, it is difficult to follow this method because many technical steps are conducted by hand. A lot of the skills require accuracy and precision, where the use of patience is highly recommended.
Even though you follow every protocol correctly, you can still fail the experiment because handling graphene and the graphene transfer grids is difficult. To begin, prepare the electrospinning solution as described in the accompanying text protocol. Transfer it into a ten milliliter syringe and equip the syringe with a 25 gauge needle.
Then wash the target. Take a rectangular piece of flexible stainless steel and wash it with deionized water, followed by ethanol. Repeat this process two to five times.
Once clean, air dry the steel at 60 degrees Celsius for 10 minutes. Once dry, fix the flexible stainless steel onto the drummer with tape. Next, open the electrospinning controller software and enter a flow rate of 10 microliters per minute, requiring a total solution volume of five milliliters.
Fix the syringe with the 25 gauge needle into the electrospinning device and use tape to fix it in place. Now press the syringe towards the collector until the electrospinning solution flows well through the 25 gauge needle. Then connect the tip of the needle to the double-ended crocodile clips which are also connected to the collector.
Before initiating the electrospinning program, turn on the roller and spin the collector at 100 rpm. Then initiate the electrospinning program software. When the spinning begins, modulate the applied voltage to 16 kilovolts so that the Taylor cone forms.
When the electrospinning process is finished, scrap the as-spun nanofibers on the flexible stainless steel with a razor and transfer them into an alumina box. Then insert the alumina box into the box furnace and set the heat treatment conditions for the box furnace. After calcination, cool down the furnace to 50 degrees Celsius and then transfer the calcined nanotubes to a glass vial.
To begin, prepare the electrode slurry. Place it on the top side of the copper foil on the glass substrate and cast it evenly to a thickness of around 60 microns using a casting roller. Then air dry the slurry cast foil at 60 degrees Celsius for 10 minutes.
Once dry, seal it inside a plastic bag until ready for cell assembly. To begin cell assembly, heat a convection oven to 150 degrees Celsius and place the slurry cast copper foil into the oven. Pull the vacuum in the oven using a rotary pump to dry the residual solvent in the slurry while avoiding oxidation of the copper foil.
After heating the slurry cast copper foil at 150 degrees Celsius for two hours, refill the convection oven with air by closing the vacuum line and opening the vent line in the rotary pump to open the chamber. Then take the slurry cast copper foil out of the chamber and punch it with a circle puncher. Weigh the punched slurry cast copper foil.
Use half a cell for the assembly of the battery cells and place the slurry cast copper foil into the bottom of the battery cell. Then transfer the samples to the ante-chamber of the glove box. Vacuum the ante-chamber for 30 minutes and then transfer the samples to the inside glove box.
In the glove box, assemble the battery cells, starting with the bottom battery cell, then the slurry cast copper foil, the separator, the gasket, the spacer, the spring, and finally, the top battery cell. Use a compactor to compress the battery cell into a complete battery cell. Then move the battery cells into the ante-chamber of the glove box.
Once the vacuum has been released, remove the battery cells from the glove box. Age the battery at room temperature for one to two days. Then insert the cells in the battery cell tester.
Calculate the appropriate current and then apply the proper current for each battery cell using the battery cell tester program. To begin, synthesize graphene by chemical vapor deposition and use a pair of scissors to cut the copper foil with the graphene to three by three millimeter squares. Place four copper foil pieces between two glass slides and press to make them flat.
Next place fully carbon gold grids on each piece of copper foil. Drop 20 microliters of isopropyl alcohol on the gold grid copper foil combo. Then remove the alcohol and dry the sample at 50 degrees Celsius for five minutes.
Next clean a six centimeter glass Petri dish with isopropyl alcohol and deionized water to avoid contamination with silicon particles. Then add ten milliliters of 0.1 molar ammonium persulfate to the dish and etch the copper foil. Incubate the sample in the solution for six hours.
Use a platinum loop to move the gold grids to a glass Petri dish filled with deionized water and heat it to 50 degrees Celsius in order to fully remove any remaining contaminants from the etched. Then remove the grids and dry them for six hours at room temperature. Prepare the electrolyte and nanotube mixture by dispersing 0.06 grams of the nanotube powder in 10 milliliters of electrolyte, which is composed of 1.3 molar lithium hexafluorophospate and ethylene carbonate and diethylene carbonate in a three to seven volume ratio with 10 weight percent of fluoroethylene carbonate.
Then move the graphene transferred grids and the electrolyte mixture into a glove box that is filled with argon. To assemble the cell, first place one grid on the bottom. Then drop 20 microliters of the electrolyte mixture on the bottom grid.
Quickly use a pair of tweezers to place another grid on top of the bottom grid before the electrolyte dries. Dry the sample inside the glove box for 30 minutes, during which the liquid is spontaneously encapsulated between the two graphene sheets as it dries. The tin iv oxide nanotubes fabricated by electrospinning and subsequent calcination are shown here in an SEM image.
TEM shows that such porous sites are more visually clear, indicated by a number of white spots within the nanotubes. This is because the crystal structures of tin iv oxide are polycrystalline cassiterite structures. In terms of electrochemical characteristics of the tin iv oxide nanotubes, the charge and discharge profile exhibits stable voltage profiles with an initial coulombic efficiency of 67.8%The voltage plateau, which exists at 0.9 volts, can be attributed to the two phase reaction.
The tin iv oxide nanotubes exhibit stable cycling at 500 milliamps per gram with coulombic efficiencies above 98%In addition, the nanotubes retain considerable capacity, even at a high current density of 1, 000 milliamps per gram. A time series TEM video of graphene liquid cells shows at the multiple liquid pockets whose sizes range from 300-400 nanometers. Through constant electron beam irradiation, dissolved electrons and radicals trigger a secondary reaction with a salt and solvent.
Here the decomposition of electrolyte and the formation of a SEI layer were observed at the initial stage. Take extra care when handling graphene and TEM grid. If you don't handle graphene and grid properly, they can be easily damaged.
In the cell assembly, it is important to compress the cell tightly so that the electrolyte does not come out of the cells. This procedure can also be utilized in observing dynamics of sodium-ion batteries, magnesium-ion batteries, and secondary-ion batteries.
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