August 19, 2013
Jae working with the SEM (Scanning Electron Microscope).
My last day in Singapore was on August 2nd. The last week at work was perhaps the most difficult week that I had during the internship, both in work and emotionally. As stated in the last blog post, we wanted to vary composition of active material and other variations to achieve the optimal conditions as well as to find out why the battery hasn’t been performing as well as before. Despite many efforts, however, we could not achieve the capacity that we were hoping for. If we had more time, maybe we could have found out the cause of the problem but for the time being, it remains unknown. It would have been great if we increased the capacity up to or even beyond the goal that we set up but I will take it as part of research experience where what you think should work is not working. I believe I will remember this experience if I am in graduate school and conducting research.
Jae with his supervisor, Dr. Satya Gajjela.
Although I have been in Singapore for only 10 weeks, it was very difficult to leave on the last day. During the short time, it became my home and the lab has been the place where I spent most of my time. I couldn’t believe that I would not be seeing the people whom I was meeting and talking to everyday. It felt surreal that I may not be seeing them ever again. Though it may be difficult to meet the members of the lab again, I am grateful for the time that I had and will definitely be looking forward to the time I can visit Singapore again. It has been one of the most memorable summers of my life and this will conclude my blog post about my experience in Singapore!
July 29, 2013
Jae in the lab working under a fume hood.
There have been some problems going on in our experiments. We recently found out that the copper foils that we’ve been using vary in weight from the average value we’ve been using so far. It means that the amount of TiO2 that was thought to be in the batteries was wrong, resulting in different battery capacity. In our case, the correct copper foil weighs less than the average value, so we’ve been giving batteries less current that they are capable, which led to higher numbers than it actually is. It also explains why some batteries performed over the theoretical limit and results varied significantly. At this point, we’re trying to figure out what went wrong, as we’re making batteries with different techniques. The results are not promising, as they are averaging 50% capacity, as opposed to our goal of 70-80% capacity.
There is a couple of good things that came out of this, however. One is that the results have been more consistent than before we discovered the problem with weight of the copper foil. The results are more reliable, even though the capacity is not as high as we would like. Second is that we noticed that batteries are performing just as well when there is higher amount of current being applied. This is surprising, given that when there is more current applied, the performance is supposed to decrease but most maintained the performance and some even doing better. We are trying to test more samples to see whether this result can be reproduced, and not just one time fluke. Isolating what works and what doesn’t seems to be one of the most difficult parts of battery research. Constructing one battery takes two to three days and testing can take anywhere from a day to a week, depending on how many cycles you are running. It takes long time to verify whether the modification that you made actually works and there’s limited number of batteries we can test at a time. To verify the observations, we plan on making more high loading.
July 11, 2013
Jae out to dinner with his colleagues.
Since the last blog post, there have been developments in terms of the progress of the project. We almost achieved the goal of getting surface area of TiO2 to 135m2/g, which was reported in the paper that Professor Balaya co-authored. The improvement in surface area seems to be attributed to the changes made in the filtering stage of synthesis of TiO2 powder. However, because it was just one sample, we are trying to reproduce the data.
Last week, along with other members of the lab, I learned how to operate FESEM (Field Emission Scanning Electron Microscope). It is used to look at how materials are formed and it can be magnified up to 1nm. FESEM can be used in this project to see whether TiO2 has aggregates formed, which reduces its surface area. Not only can I closely look at the finished product, but I can also see how TiO2 particles form before and during filtering processes. I’m also hoping to operate the BET machine.
For the remaining weeks, we will see whether different heat ramping will change the morphology of TiO2, leading to increase in performance of battery. Also, we will test batteries in different charge/discharge rates to see where TiO2 can be applied. So far, we’ve been testing the batteries at the rate of C/5, meaning charging and discharging the whole battery in five hours and three hours for C/3 and so on. This rate would be ideal for devices such as laptop and cellphone batteries. As you increase the rate of C, the performance of the battery decreases dramatically. That means, even though a material performs well at a low C rate, it might not be as promising at higher C rates. We will be testing at higher C rates as well as lower C rates.
During my time in NUS, not only did I learn about batteries and material science concepts but also what it’s like to be a graduate student and a researcher. Everyday, I get to see how they work, and what they go through on a day to day basis. I feel fortunate that I get first-hand experience working in a lab before applying for graduate school. Now I know more in detail what challenges lie ahead for researchers and graduate students.
June 24, 2013
Stirring stage in the making of TiO2.
Since the last blog entry, I have been making mesoporous TiO2 powder, following up from the procedures done by the postdoc, Satya, and then varying the processes a little each time, such as using 50% of the materials and stirring for less time. The reason for making 50% of the material is to test whether scalability applies to the synthesis of mesoporous TiO2. Following the standard procedure, we were able to get around 240mAhr/g of charge capacity (which is still less than the reported value) but when making the powder with half the material and less stirring time, the performance reduces even further to 180mAhr/g. The result of the battery performance can be further supported by the BET analysis of the powders. BET analysis shows the surface area and pore sizes of the substance. It can be seen that TiO2 powder made from the standard procedure has higher surface area, which allows it to carry more Li ions, resulting in higher charge capacity values.
In one of the variations, we unexpectedly got very high surface area values. There were two batches, one using 100% and the other 50% of the materials to prepare the powder, and both resulted in the highest surface area but still lower than Satya’s reported value. We believe that the high surface area value can be attributed to changes in either the filtering or stirring stage. We hope that by the end of this week, we can reproduce the value reported in the paper and identify which stage of the synthesis can be reduced and the reason for the values.
Comparison shot of a shipyard not too far from the campus during and after the haze.
On a side note, there has been a heavy haze in Singapore. Singapore usually has a clean air quality, with PSI (Pollution Standard Index) levels between 50-100, which is considered moderate. However, during this time of the year, palm oil producers in Indonesia finish harvesting and start to clear the land for the next crop cycle by burning the land. The ashes are then carried to Singapore and Malaysia, reaching as far as Brunei. PSI here in Singapore has reached an all-time high, up to 401, topping the previous record of 226 in 1997. Singapore’s National Environmental Agency (NEA) lists PSI values of 101-200 as unhealthy, 201-300 very unhealthy, and above 300 hazardous. The difference in air quality was very noticeable, both in smell and visibility. Thankfully, it has subsided back to the normal levels but it could come back if the burning in Indonesia continues.
June 10, 2013
View from the Engineering Building at NUS.
For the next couple of weeks, I will be conducting lithium-ion battery research at the National University of Singapore (NUS), under Professor Palani Balaya. To start off I have been getting acquainted with the graduate students, postdocs, and the lab that I will be working in. I have also been reading papers on lithium-ion batteries and modifications that others have experimented with. The lab members have been very kind, welcoming and patient with me adjusting to the new environment.
The biggest challenge I have encountered since arriving is adjusting to the weather and the lab. Although I have lived in sunny Southern California for more than ten years, I was not prepared for humidity in Singapore. In the first week, just walking from one engineering building to another couldn’t be done without breaking a sweat. On the day of the orientation I decided to walk around the campus to get myself familiar with the area. However, after five minutes of walking near my residence hall, I looked as if I had just ran ten miles so I came back to the residence hall and took the shuttle bus to the place where orientation was being held. It took about a week for me to get used to the weather and to not mind it as much.
The lab I am working in revolves around battery research so there are a lot of precautions one must take when dealing with chemicals. Although I have taken a couple of chemistry courses in high school and in college, it is different in that broken equipment can stop the whole lab, delaying research conducted by Ph.D. students and postdocs. Because of safety issues, I had to take online safety training courses on how to handle chemicals, deal with fires and conduct an overall risk assessment with a postdoc. NUS takes safety very seriously, which is both good and bad. It can be good in that everyone is professional and is trying their best to keep the lab accident-free. The downside is that to use some of the equipment, such as the glove-box and twin-roller, one needs a license to do so. To use this kind of equipment, I have to ask the lab technician to operate them but thankfully, he is always more than happy to do it for me.
Finally, the title of the project is “Optimization of Synthesis Conditions of Mesoporous TiO2 for High Capacity Li-ion Batteries.” In the lithium-ion battery, the anode is copper coated with mesoporous TiO2, which has pores size of 7nm. TiO2 is shown to have promising results as coating material for copper anode, having high charge capacity (which determines how long a battery will last) as well as packing density (allowing the battery to be smaller) but its properties decline when making it in larger quantities (>2g). Therefore, the goal of the project is to investigate what will be the effect when making 3-4g of TiO2 on the performance of Li-ion battery and eventually scaling up the production to 20g of TiO2, without sacrificing the battery performance.