Weeks 8-9!

I have been focusing on purifying the model compound using recrystallization, which is more meticulous and involves more trial and error than I had initially expected. I am suddenly reminded of a general chemistry that I have learned but could better understand. I have been exposed to two types of recrystallization: single solvent recrystallization and multi-solvent recrystallization. Multi-component recrystallization is used when a single solvent is inadequate. Single solvent recrystallization involves dissolving both the desired compound and the impurities into the smallest volume of hot solvent necessary to make a saturated solution. The solution is then allowed to cool, and as the solution cools, the solubility of the compound drops, thus the desired compound recrystallizes. The slower the rate of cooling, the bigger the formed crystals. Multi-solvent recrystallization involved dissolving both the desired compound and the impurity in the first solvent. One can tell when solids have dissolved when the liquid is clear. Then, a second solvent is slowly added until something precipitates. The cloudiness signifies that the solution is saturated with the solute. Either the desired compound or the impurity will be insoluble in the solvent, while the desired compound or the impurity will be in solution. Then, the solution is cooled. The first picture depicts a substance which is almost fully recrystallized.

The trickiness involved in recrystallization comes from the fact that these are more applicable for solid state compounds. One of my products ended up as a viscous liquid.

Additionally, instead of the impurity dissolving and remaining dissolved after cooling in the solution, the impurity may not dissolve in the hot solution and could be removed by filtration before cooling. One must also pay close to attention to whether additional solid is dissolving as solvent is added.

My coworker has taught me multiple things. I have learned about areal capacity which has the units of mAh/cm^2. It is a normalized way of describing the capacity of a battery. The area is related to the cathode as that is the source of charge carriers. I have also learned about the components of a battery and how to assemble them. Components include a cap, spacers, spring, plastic, electrodes, and separator. Spacers are used in lithium metal batteries to distribute pressure.

During my free time when I am waiting for recrystallization to happen, I read journals, preferably on the couch facing the glorious bay. For example, I read about anionic receptors, lithium anode pretreatment, and the solid electrolyte interface (SEI). In particular, I have learned that this interface between lithium metal and liquid electrolytes plays an important role in the feasibility of a lithium metal battery, as it influences the development of the parasitic reactions between lithium metal and liquid electrolytes, dendritic electrodeposition during charge, and reaction of dissolved, cathode products with the lithium anode.

Sometimes I would also go online to define terms I read from papers. For example, battery efficiency is characterized by two efficiencies: Coulombic efficiency and voltage efficiency. Coulombic efficiency is “the ratio of the number of charges that enter the battery during charging compared to the number that can be extracted from the battery during discharging”. The number of charges that can be extracted during discharging decreases due to secondary reactions such as water electrolysis or other redox reactions.

Last week, my supervisor has given the green light on going surfing for my going away party! Do you know how excited AND SCARED I am? It’s okay. Breathe, I can float.

Today, on 7/31/17, I return to investigating the NMR of my product which is shown in the picture of the peach-colored, apple-shaped solid, reading a paper, and tackling my poster for the Molecular Foundry User Meeting. I will have to perform a one minute presentation in front of judges. I was initially going to opt out of it, but my supervisor knew this would be a learning opportunity so he signed up for it. Thank you, Dr. Frischmann!

References

  1. http://www.pvcdrom.pveducation.org/BATTERY/effic.htm