BioSolar is developing electrode material technologies to increase the storage capacity, lower the cost and extend the life of lithium-ion batteries.
Increasing the Storage Capacity of Lithium Batteries
Dr. Sung-Jin Cho | NC A&T University
Tell us about BioSolar.
BioSolar is developing electrode material technologies to increase the storage capacity, lower the cost and extend the life of lithium-ion batteries. BioSolar initially focused its development effort on high capacity cathode materials since most of today’s Li-ion batteries are “cathode limited.” With the goal of creating the company’s next generation super battery technology, BioSolar is also investigating high energy anode materials recognizing the fact that the overall battery capacity is determined by combination of both cathode and anode.
Tell us a little bit about yourself and what brought you to this work at BioSolar.
I have been working on lithium-ion battery development since 1998 when I was a graduate student in South Korea. I remember how exciting and happy I was with certain battery materials I was able to synthesize in the lab. Prior to starting my PhD work at Marquette University, I worked for LG developing batteries. After obtaining my PhD in Electronic Material, I then joined Johnson Controls Inc., Battery Tech Center also located in Milwaukee, WI in 2008.
During six plus years’ of my engineering career at Johnson Controls, I’ve met and worked with many high profile strategic partners, suppliers, collaborators from academia, DOE national labs and others. I left Johnson Controls in Aug. 2014, and I am now an independent research leader and assistant professor at North Carolina A&T State University. As a lead investigator of a BioSolar sponsored research project at the university, I am also bringing in advanced Silicon material technology to match BioSolar’s super cathode technology.
You are an expert in lithium-ion batteries, give our readers a brief summary of lithium-ion.
Lithium-ion battery is an indispensable device that is comprised of four main components: cathode, anode, electrolyte and separator. Among commercially available battery technologies, lithium-ion battery is the highest capacity energy storage device at this point of time and for at least a decade to come. Lithium-ion batteries function as Lithium ions commute from cathode to anode (de-intercalation) for charging and from anode to cathode (intercalation) during discharge. Ideally, we would like to retain and not lose any lithium ions during and after intercalation/de-intercalation processes. That would be the perfect battery from our technical point of view.
What are the biggest technical obstacles to lithium-ion battery?
Two of the most important and challenging subjects related to lithium-ion batteries are increasing the energy density and reducing the charging time. Increased energy density corresponds to increased battery specific capacity (mAh/g), which means that the device will stay on longer before having to be recharged. Reduced charging time means that the device will be ready for use in shorter time after each discharging cycle. There are many other technical challenges associated with improving lithium-ion batteries, but these are the top priorities to address in the near future.
What things plays a crucial role to increase energy density (Wh/L or Wh/Kg)?
Research at many different levels (material, electrodes, cells, batteries, manufacturing process, etc.) needs to be conducted in search of improving the energy density. At the material level, which I am currently focusing on, high capacity cathode material along with an appropriate anode material must be chosen. The amount of active material in battery electrode slurry composition should be maximized while still meeting other requirements. At the electrode level, maximizing loading is highly critical to improve energy density.
How do we improve the battery charging speed?
Typically charging speed depends on anode material and electrode design. It has been proven that selection of high dimensional structured anode material plays an important role in determining the charging speed. At the material level, it is desirable to have more lithium ions pass through all 3 (X, Y and Z) dimensions, whereas certain anode materials that allow just 2 (X and Y) dimensions are not as desirable. Therefore, the most important first step is to choose the best anode material. After choosing the anode material, we can further improve the charging speed with a thinner electrode design that accelerate lithium ion diffusion as well as electron transfer from cathode to anode.
What technology do you believe can significantly enhance battery performances that are veiled on current lithium-ion batteries?
Most existing lithium-ion battery cathode materials have higher than 270mAh/g of theoretical capacity at 4.7-4.8V, but we haven’t been able to reach these numbers yet. In reality, we have not even tried to get there due to multitude of technical issues associated with the high operating voltage. At this point of time, we currently utilize only about 55% of existing material’s theoretical capacity. We definitely need to continue searching for new materials with higher theoretical capacity, but at the same time, we should expand our investigation on how to extract more capacity out of the existing materials. I believe it is possible for us to extract more than 60% of the theoretical capacity from the existing the material currently in use.
Any thoughts on beyond lithium-ion batteries?
There are very few potentially viable approaches that have been extensively investigated as of 2016. It seems that the only viable way to significantly increase energy density is to explore a new battery architecture that includes lithium-air battery (3800mAh/g) and lithium-sulfur battery (1675mAh/g) since a typical lithium cobalt oxide battery for all IT devices can only reach 160-170mAh/g. High energy density numbers associated with lithium-air and lithium-sulfur batteries should definitely be our goal. We definitely want to be there in the future, but it is not clear how long it will actually take before we can commercialize these technologies. It is interesting to note that there have not been any major breakthroughs with battery capacity improvement since the first battery cathode chemistry is discovered in 1979 by Dr. John Goodenough, and we are still stuck at 160-170 mAh/g with Lithium Cobalt Oxide.
Where do you see battery technology 5 years from now?
Using existing battery materials, I do not expect to see drastic increase of battery performance in commercially available forms in the next 5 years, but many different design platforms (flexible, wearables, foldable batteries, textile, etc.) will find better use of existing battery materials and technologies.
In terms of battery development cycle, 5 years is not a sufficient time to adopt any new technical breakthroughs. For an example, the automotive industry takes at least 3 years to validate any technology-based products in the engineering stage before proceeding toward preproduction planning.
It took more than 2 years to increase 100mV (or 0.1V) of upper limit voltage from current number of around 4.35V, which corresponds to less than 5-6% improvement in capacity. On the other hand, we can probably improve the overall battery capacity by a sizable 10-50% by the use of advanced anode materials such as Silicon, Tin, or Lithium metal, which will be significant enhancement on battery energy density.
About Dr. Sung-Jin Cho
Dr. Sung-Jin Cho is an Assistant Professor at the Joint School of Nanoscience and Nanoengineering at North Carolina Agricultural and Technical State University and is working as a lead researcher with BioSolar to strengthen the strategic commercialization planning and prototyping activities.
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