The overall goal of the following experiment is to study structural changes in electrodes, undergoing cycling in batteries in real time. This is achieved by assembling test cells modified so that electrode processes can be studied in the beamline at a synchrotron radiation facility as the devices undergo charge and discharge. As a second step, data is collected on the test cells at the beamline as a function of time and working conditions.
Next, the data is processed and analyzed in order to observe the structural changes that occur as a function of state of charge. Results are obtained that provide insight into the functioning of the electrodes, including phase changes and degradation processes based on refinement of de faction data and interpretation. The main advantage of this technique over existing conventional methods like x-ray powder diffraction, is that the signal strength is much higher and the acquisition time much faster, allowing rapid acquisition of data.
This allows us to monitor devices in real time. Undergoing charge and discharge In situ methods can help answer key questions in the battery field. Battery performance, lifetime and safety all depend on maintaining the chemical and physical integrity of the battery components.
Syn turn, x-ray defraction techniques allow us to get information on structure changes, face transitions, and the formation of impurities while the batteries operating. These may have far reaching implications for a performance. I'm a beamline scientist at a syn claron facility.
I collaborate with battery scientists on designing and studying of experiments, help with collection of data, its analysis, and final interpretation of results. Visual demonstration of this method is helpful as the details of cell assembly are critical to the success of the experiment. We want to ensure that the experiment is representative of larger scale batteries operating in the real world.
Demonstrating the procedures will be doctors Ang, Hong Yi and Mona. She post doctoral associates at Lawrence Berkeley National Laboratory, Lei Chang, a graduate student, and Dr.Guang Chen, a scientist at the lab. The first step is to characterize the material of interest using x-ray powder diffraction.
Make two to three grams of a sample by grinding powder and cing it to ensure uniform particle size distribution. For this experiment. Nickel, manganese, cobalt or NMC is used for the best placement of the powder.
Remove the back plate from the sample holder of the x-ray diffract meter. Place the sample holder against a glass slide and fill the cavity with the sample powder. Reattach the back plate, flip the holder and remove the slide.
Now insert the sample holder into the defactor meter and properly align it. When this is done, close the doors of the instrument, set the appropriate parameters for refractometry and start the scan. Once data collection is complete, analyze the pattern to identify the presence of impurities and to determine if it matches that of reference materials or calculated patterns.
Once done properly, shut down the refractometer and remove the sample particle morphologies are determined. Using scanning electron microscopy or SEM. Prepare the sample for SEM by attaching carbon tape to an aluminum stub.
Then sprinkling powder onto the sticky side. Ensure the assembly is non-magnetic by holding a kitchen magnet over the sample. Next, insert the sample into the SEM chamber via the airlock and start evacuation.
Once a vacuum is established, turn on the accelerating voltage. Work in low magnification mode and use the automatic contrast in brightness button to adjust the image. Find an area of interest by manually scanning in the X and Y directions.
After finding an area, choose the SEM mode. Select the detector. Then set the necessary working distance, followed by the contrast and brightness.
Focus the image with the Z control. Align the beam and correct astigmatism and focus. Using the X and Y controls, take the desired pictures and save them.
When finished, shut down the SEM and remove the sample via the airlock fabrication Begins with creating a solution of five to six weight percent of polyvinyl iodine fluoride. Next, mixed 240 milligrams of NMC, the active material and 30 milligrams of acetylene lack a conductive additive mill. This mixture at 300 RPM for two hours.
Once the milling is completed, take 180 milligrams of the milled mixture and add 0.4 milliliters of the NMP solution. Next, prepare a doctor blade with the current collector material in this case carbon coated aluminum foil. Use the doctor blade to cast electrode slurry into the current collector.
Remove the electrodes and start the drying process. For this video. A heat lamp is used before drying.
This is how the electrodes appear. This is how they look after about 30 minutes under the heat lamp. At this point, cut or punch them to the size needed for use in a coin cell.
Weigh each of the electrodes. Transfer the electrodes to an inert atmosphere glove box with a heated vacuum anti chamber. Use the anti chamber to perform an additional 12 hour drying step to remove all residual moisture.
The electrodes are now ready for use in a coin cell. Cut the lithium foil and the microporous separator to the desired size. Gather all needed components in the inner atmosphere.
Glove box for assembly into a coin cell. Now layer the components in the cell. Put the electrode in first, followed by the separator, the electrolytic solution, and then the foil seal the cell using a coin cell press for an NC two X-ray diffraction experiment.
Attach tabs to either side of the cell. Then seal the device in a polyester pouch for this part of the experiment. Secure beam time at a synchrotron facility.
Safely transport the sample to the location and prepare for the experiment. Begin by calibrating the beam to find the right beam conditions. Then measure a reference pattern of lanthanum heide.
Return to the access point of the beam line. Continue with the NC two x-ray diffraction Experiment by inserting the pouch containing the cell into aluminum pressure plates. Ensure that the holes are properly aligned to allow the x-ray beam to transmit Attach leads from the potential stat to the device back at the controls.
Find the optimum beam and exposure time before the electrochemistry is started. Take an initial pattern and start the electrochemistry experiment. Collect data and monitor the experiment.
This in C two X-ray diffraction data was obtained from a cell that contained a lithium anode and a metal oxide cathode. The cathode belonged to a family of electrode materials known as NMCs for nickel, manganese, and cobalt. The cell underwent charge shown in the black traces and discharge shown in green after calibration and conversion of the ring pattern to line scans.
Each scan represents the state of charge of the system at a moment in time. Under constant current, the peak sparked in blue are due to the aluminum current collector. Those in red are due to the polymer pouch and separator in the beam path.
The lithium in the cell is essentially transparent to x-rays. Index reflections attributable to the active material of the cell are marked because the unit cell parameters changed as a function of lithium content. Some peaks due to this phase overlapped with those of the aluminum current collector.
In some patterns, Once mastered, an nstitute experiment can be done at the beam line in 10 to 20 hours Following this procedure. Other methods like x-ray absorption spectroscopy can be performed to answer additional questions such as how the structure of the material and the redox states of the transition metals change as a function of state of charge. After watching this video, you should have a good understanding of how to assemble a coin cell super for study in a sync tron beamline and require x-ray diffraction patterns while the cell is undergoing charge and discharge.
