The Future of Safety Science: Lithium-Ion Batteries from a Global Perspective
- Hello and welcome to the Future of Safety Science, the webinar series that connects leaders in safety research and standards to the next generation of problem solvers. I'm Dr. Kelly Keenan with UL Research Institutes and I'm grateful to be your host for this series where we investigate the big questions beginning with, How is the world engineered to keep us safe? Each episode extends our work to you through dynamic conversations that describe our view of safety and sustainability, drill down into specific inquiries and research and describe the process and impacts of global standards. Today's episode will help us understand the science, global impact and safety of something that's in everyone's home. It's likely that you have five or more of these around you right now, and it is certain that the way you are reviewing this episode is on a device powered by the very thing that today's guest studies, lithium ion batteries.
As part of UL Research Institute's Electrochemical Safety Research Institute led by Dr. Judy Jeevarajan, our guest today investigates the safety and performance limits of energy technologies. (upbeat music) So let's get started. I'm pleased to introduce my colleague for this conversation. Dr. Vallabha Rikka is a lithium ion battery scientist
with nine years of experience in the development and testing of batteries for electric vehicles and stationary applications. He developed a method for rapid and effective formation of solid electrolyte interface, which you're about to hear a lot about. This is called the SEI layer on the anode surface in lithium ion batteries. Dr. Rikka is also skilled at insitu exsitu operando
characterization of electrode and electrolyte interfaces and identifying failure analysis of lithium ion batteries. He is currently a postdoctoral researcher at UL Research Institutes and our guest on the future of safety science today. Dr. Rikka, welcome. - Thank you Dr. Kelly for your kind introduction. Good morning all and welcome to my today webinar presentation.
I would like to thank our vice president, Dr. Judy Jeevarajan for giving me this wonderful opportunity to talk about lithium battery technology from Global Prospect View. Well today, 12 main technologies I just showed in schematic view from mobile internet cloud technologies Advance robotics, even automobile industries too, renewable energies, 3D printing and energy storage systems are influencing our world fleet. Among all renewable energies and energy storage technologies are at forefront and playing a significant role in changing the world into a greener place. On the other hand, the automobile industries are consuming fossil fuels around 60% of fossil fuels and releases greenhouse gas emissions causing global warming today. So it is important to note that if we can adopt and integrate the renewable energy sources and energy storage technology to the automobile industries, then it will be an ultimate and alternative solution for the global warming.
As a result, we can see the reduction in positive fuel economy and improves the ecological and the today modern societal life. So these batteries are basically in two types, primary batteries, which is also denoted as dry cells. And these are one time usable due to the main components of this primary batteries such as the cathode, anode and electrolytes are electrochemically irreversible. Whereas the secondary batteries also denoted as rechargeable batteries. These batteries are reusable due to their active components such as cathode and anode electrolytes are electrochemically reversible.
So these devices are, we are seeing in our daily uses in our portable electronics devices and it is also deploying into heavy duty industries today. So there are many different energies storage technologies are available among them batteries and fuel cells are having high energy density, whereas the capacitors and the super capacitors are high power densities. The high energy density, these, devices we can be used for store the renewable energy and we can use it as a renewable energy storage grids. And then super caps and capacitors can be useful for satellites and even sports cars, high power applications. Whereas today the batteries are developing for high energy applications as well as high power applications. If you can look at into the market, there are different types of rechargeable batteries are available, which are denoted as LED acid batteries, metal nickel metal highlight batteries and lith batteries.
Among them lithium batteries are adding high energy densities as well as high power densities. So why these lithium batteries are superior than other batteries, if you can consider. If you can look it into the lithium metal properties, the lithium is a lightest metal and it is comes under the alkaline metal groups. So if you can look at the electronic structure configuration, it has one single valency electron, hence fourth, the, it has highly reactive and it has highest reduction, negative reduction potential with compared with the hydrogen reference electrode.
And also it has highest specific capacity. So these properties made superior to this lithium battery technology. And today the lithium battery technologies are denoting with their cathode chemistries.
We can call it as an NMC, LFP or NCA in the markets. So basically these cathode materials are made of a lithium with different transition metal oxides, whereas the annual materials are mostly used in commercial cells, either carbon-based materials such as graphite, carbon nanotubes, and the silicone and the germanium are either, it is a composite of all three metals. Whereas the electrolyte is made off of lithium salt and this lithium salt is dissolved in organic solvents.
These all are, these organic solvents are highly flammable. That's why the the Lithium battery technology needs the safety precautions. So if you can look at the working principle of this lithium battery, this lithium battery consists mainly three main components as we discussed in earlier. The cathode consists of lithium ion source, whereas the anode acts as a lithium host and the applied acts as a medium for lithium transportation during the charging and de-charging. For example, when you are charging the mobile during that process, the lithium ions moves from the cathode to anode and the voltage slowly it increases.
And during the usage of our mobile, the Lithium ions moves from anode two cathode and then the voltage slowly it is reduces. So the use time of our mobile for example, it depends on the properties of both cathode and anode materials. Well the lithium battery consists many lithium ion cells and which are connected in series and parallel configuration.
When we are talking about series the lithium cells, polarities means the lithium cells are connected in opposite polarity and which is meant for increases the voltages. Whereas in parallel connection, all cells are connected in a similar pol... And all the same polarities are connected in the same direction.
So these are meant for high current applications. So when you are connecting the cells in series, the voltage will increases, whereas in parallel connection the voltage remains the same. So when you look at into the, if you look at into the large scale battery systems, these battery systems are connected with modules. These modules are connected either in series are parallel connections. Each parallel connection, each module again connected with the protection electron protection circuit, which controls the abnormal operating conditions of the lithium cells. As we discussed earlier, the lithium batteries technology needs highly safe operating conditions.
So these production circuits will prevents from the overcharge over the charge even for over heating of the self heating of the cells during the usage and the charging process. If you can look at in the market the lithium cells are available with the different sizes and the different geometry at a different ratings. So these all cells are denoted with numbers. The serial numbers, for example, if you can see, the 2032 coin cell, which indicates it has 20 mm dia and 3.2 mm height. Similar way if you can consider the cylindrical cells 26, six, five, zero means it has a 26 mm diameter and 65.0 mm height. So that it represents.
Similarly, the prismatic and pouch cells are denoted with the ratings, AMP ratings, five amp hour, 20 amp hour like that. And these all lithium cells are fabricated using different components and the different fabrication processes. So those details we will discuss in the coming slides. And based on the cell geometry as well as cell rating, the overall battery pack size defines and the complexity will be increases as you decrease the cell geometry or cell rating, the complexity of the battery model is going to be increases.
And in order to prevent the abnormal operating conditions, all batteries consists the battery management systems as well as to maintain the temperature within it, the cooling systems will be provided. So this is how the battery modules our battery system looks. So these battery are connected with the several cells and each cell fabrication process is robust.
So if you can look at, it has several processing before delivering the lithium cell into the market. So each process optimization involves different engineering as well as scientific understanding. And before deliver our, before dispatch the cells from the manufacturing plant, all lithium in cells are undergoes to the formation process. And this formation process not only takes the time, it is cost effective. So how we can reduce the formation time and how it influences the overall cost of the cell. We can discuss in the further slide.
And this process is called formation. The formation is nothing bad. When you fill the electrolyte.
Once we fill the electrolyte, the active components of the lithium cells has to be activate. This activation takes place within a few initial charge discharge cycles. For example, when we are charging the cell as we discussed it earlier, all lithium most to the anode side. And during the anode side we can see the anode is going to be the anode particles or electrodes are going to be expanse. Different materials, different anode materials have its own intrinsic properties.
Some of the anode materials, the volume expand since during the lithiation and during the delithiations, the volume changes will be deferred. Some materials, for example graphite the volume changes are limited to 20% whereas the silicone are SN, Tin related anode materials. The volume expansions exhibits more than 300%. So as we are seeing during initial lithium ion cells, we can see one, one layer is forming on the surface of the anode.
This is during the electrochemical processing and this layer forms due to the decomposition of the species, the decomposition of the electrolyte at an interface of the anode. So this interface layer also denoted as a SEI layer or Solid Electrolyte Interface Layer. And this interface layer actually plays a dual role. One is it consumes the active lithium from the electrolyte and it prevents the further decomposition of the electrolyte at an interface of the anode and the electrolyte.
So that's how it is playing a dual role. And this SEI layer actually dictates the performance and the safety of the lithium ion cell over the usage of the cycles. So our ultimate aim, we have to make very thin and stable SEI layer on the anode surface surface because this SEI layer consists or it consumes the active lithium ions. So this cathode material is limited lithium sources within it. If the lithium ions will be consumed during the process of this SEI formation, then the overall cell capacity is going to be reduced.
So that is one of the challenging our bottleneck for all cell manufacturers. So, and another thing is, as we have discussed when the particles are going to be volume expansions or volume changes. What happens the already initially formed SEI layer may breakdown and it is continuously consumes the electrolyte and forms continuous growth of the SEI layer.
So the more amount of active lithium losses will be occurs during this process. That's why it is very important to control the formation of this SEI layer and we have to make it more stable SEI layer at the initial formation cycles itself. Hence fourth it will be improves the chemical stability as well as electrochemical stability and the mechanical stability of the interfaces. And then it prevents and it improves the safety of the lithium ion cells. So as we discussed before, connecting the cells into the module, or before dispatching the cells, we are processing the SEI formation method.
So this takes several hours as we've seen for one cycle it will take almost 40 hours. And this type of cycles we have to repeatedly, we have to perform at initial cycles, at beginning itself. So it will take minimum 42 some several days.
So which will actually reduce the production rate of the lithium ion cells in the manufacturer line. Also, it requests more number of channels. Each cell needs one power outlet to do the initial cycles.
For example, if you are going to fabricate a giga, if you're doing production giga level, giga numbers, mega plant levels, then what happens is thousands of cells you'll fabricate and all cells has to connect to the testing channels. So you may need thousand channels, so that will be cost effective and as well as it will lock away more space. So if you can consider the overall cost effective of this process, it will take 40 percentage of manufacturing cost And also what happens in order to reduce the capital cost of the manufacturing.
Now the researchers are doing operating these cells at a different current rates, charging current rates. If you increase the charging rate, what happens is the time duration for the formation is going to be reduced. So when you are doing, when you are increasing the charging rate, what is happening is either the cells going to be bulge or the localized resistance increases due to that. At an higher current rate, the cells if it's in the cell, the heat generation is going to be higher.
So due to this heat generation, what happens is the electrolyte starts to evaporate and it can peel off the electromaterials from the current collectors. So these side effects actually, may trigger so during the formation are later on uses of the battery. So that's why we are trying to optimize these formation test conditions without showing these effects.
Like we have to mitigate the bulging effect as well as we want to activate the entire electrodes within the lithium ion cell. For that we have carried out our research in our lab. Initially we have designed the insitu coin cell We carried these the research activities in a smaller scale to understand and to detect the characteristics of the SEI layer on this surface of the ionic materials for which we have made, we have fabricated the state of the, lithium ion cell as I showed here. The cell fabrication process is shown in schematic diagram.
It consists of a lithium metal as a reference, so as a lithium source and we have drop casted the active materials on the copper mesh. So this mesh can allow us to look at the interface of the SEI layer around the surface. And these all components we assembled as a commercial, how the commercial lithium ion cell looks as I showed here and it has a window.
From this window we can able to detect the, able to see the, growth mechanism as well as we can study its ultra chemical characteristics. And as I said, these lithium ion cells are highly, these lithium ion cell components are highly mucher sensitive and it will react with the environment. So we need to carry out these experiments using insitu setups. And it's requires many characterization procedures like for example some of the characterizations are meant for a particular applications, but when we want to strategy structural characterization or chemical characterizations, these all successful characterization tools are required for this kind of analysis. And to understand and to study these SEI layer characteristics, we have used the commercial electrolyte components and these components consist of like we can name it as electrolyte salt and the solvents and then also additives.
So these additives are working as it will improve the operating voltage window as well as it can improve the thermal stability of the electrolyte component. And with this one we have initially optimized the work means electrochemical test conditions. And then we can see here this is one electrochemical study, which is also denoted as cyclic voltametric analysis. And by using this study we can understand the, the overall operating voltages window of these all components.
So in this study, initially what happens, we will do the discharge. So what happens, the lithium ions will leaves from the lithium metal and it will be intercalated into the graphite materials. So that is a first step. So that process we can see here like from one point, like for example two voltage to zero voltage. So that is called cell discharging process.
Once it reaches the zero voltage, again, we will charge the cell up to the initial potential. So during this process we have identified different current peaks. Some of the current peaks are quite reversible and some of the current peaks are irreversible. So the reversible peaks, current peaks are indicate the lithium intercalation and deintercalation of the graphite and or material, whereas the irreversible current peaks are indicates the SEI formation on the surface of the graphite. So from this analysis we have clearly identified that when we are discharging the cell below one voltage, the particular anode, the graphite anode with respect to the lithium metal around one voltage to 0.5 voltage, we can see the SEI formation is initiated over the lithiation and delithiation process, the SEI growth will be increases, it will increases and once it forms uniform, it covers the entire surface uniformly.
Then what happens is the further decomposition of the electrolyte or the SEI group mechanism is going to be stop. So that's what we can see. When during the charging the cell, we didn't identify it this irreversible peak, which means that during the first initial cycle itself, the SEI formation was completed. And to understand how this SEI growth mechanism is taking place on the surface, we have carried out some TM microscopy analysis.
We can see here in the figure here and B, it is at an initial lithiation before lithiation process of the anode material. And at initial state we didn't find any growth on the surface of the anode graphite. Whereas when it reaches the around 1.8 old days,
we can see some kind of nucleus on the surface. And this nucleation is increases over the, when we are over the discharging of the cell and the nucleation will join together and it will form such aglomeration. And then these aglomeration we can see even more densify when we are reducing even further voltage. When we are reducing further voltage we can see the more nucleus on the surface of the graphite. And when it is completed, the discharge process when we reach the point means the set discharge voltage, we can see the nucleation become looks like a complete layer and it is covered the entire surface of the graphite. So this clearly indicates that in a first electrochemical cycles, first discharge cycles itself, the SEI forms on the surface of the graphite.
And the thickness of this SEI layer is around hundred to one 150 nanometers. So it is very less thickness. So this we cannot able to see in with our naked eyes. So then based on these investigations we have derived the growth nucleation and the growth mechanisms of this SEI layer at a different voltages as I showed in the schematic diagram.
So if we can represent these two, if you can compare these two images, if you can see at an initial up to 1.8 voltage like before lithiation process, there are SEI nuclei and which are existed in the electrolyte medium itself. It is not at all deposited on the surface. When we have reduced the cell voltage, the nucleation is slowly, it is depositing on the surface of the graphite electrode. And but our aim is to reduce this formation time when we are operating this cell at an lower charging rate.
It takes minimum 40 hours to complete this process, but it will, this time can consume, actually increases the capital cost of the cell manufacturing, right? So what we did is we have increased the current rates for charging and discharging to identify the characteristics of the SEI layer and how it influences on the performance of the cell. If you can look at it here, when we are charging at low C rate, it has higher capacity and it took very long time. When we have increased the charge rate, charging current rate and the decharging current rate, the capacity slowly it is declined. It is reducing. And then the irreversible capacities are losses are very high, it is not completely recovered from the graphite anode. And then we have identified the structure, how it looks on the surface of the graphite.
If you can see at lower standard, the thickness of the SEI layer is very less as you are increasing the current rate. The thickness of the SEI layer as well as the morphology of the SEI layer is quite changing. It is changing with respect to the current traits, right? So, and when the thickness is increases, obviously it will consumes more activity. So which is not good for self performances.
So based on these investigations, we have carried out our experiments into three steps. We want, we optimize the test conditions for first initially nucleation process. Once the nucleus will be uniform, all electrolyte components will be decomposes uniformly. Then what happens is all nucleus, the nucleation process on the surface of the anode will be uniform and it will be very small size. And what happens is during the next discharge process, the nucleation allows to grow uniformly and it it covers the entire of the surface of the anode surface.
And then after nucleation process, we have studied carefully about the structure and its chemical composition, how the arrangements of this nucleation and the growth of the SEI layer on the surface that we have studied separately. And then in the third step we have studied the stability of the initial formation of this SEI layer at different charge current traits, whether those at these charge current traits, whether this SEI layer initial formed SEI layer whether it is stable or not. So all these three investigations actually allows us to define the optimum and the effective test method and which allows the SEI growth mechanisms uniformly.
And the systematically we can see in first up to few interval of the time scan, the SEI layer nucleation can occur. After that it will covers the surface of the anode surface uniformly. And within the same protocol we have included the stabilization process also. So these stabilization processes are involved at an higher current rates. So these all three processes are completed within the six hours. Whereas in the conventional process, the one cycle, one charge cycles are one discharge cycles, it will take 21 hours and it it has to repeat several times.
So it may take several days to months to complete this entire process. Whereas with our optimized retest method, the entire process has completed within the six hours. And these investigations we have filed recently as an Indian patent. And this method actually allows the cells for full charge and full discharge applications.
What is happening in commercial cells, the novel commercial cells, due to this SEI layer breakdown due to this SEI layer characteristics, we are not operating the cell full window, full operating window. We are limiting the operating voltage window in order to improve the safety aspects and in order to prevent the SEI layer growth mechanisms. Whereas with our test method, with our defined test method, these all cells can be extended to the, its end operating voltage limits. So when we are increasing or expanding the operating voltage window what happens is you can increase the utilization and density of the cell. So which can improve the range agility as well as it can extend the cycle for lithium ion cell. So we have, I can, I would like to show you how we have fabricated the lithium ion cell in a large scale and how we have implemented these lithium ion formation method into the large scale that I'm going to show you now.
So the lithium ion cells are like we are already said, the lithium ion cell components are highly moisture sensitive so these cells we are to fabricated in the, within the dehumidified rooms and the electrodes here we can see the electrodes are, we are making like a one batch around 30 centimeters width and 300 meters. Once the electrode fabrication is completed, then we will go for drying and slicing the electrodes according to the required dimensions of the cells. And then we will wind the all electrodes together and making as a stack.
This stack contains the both cathode anode and separators together and that separator can wipe the SAR circuit between the cathode and anode. And once we made the stack, and then we will give the tap connection. And this tap connections are, sources for the current carrying and current feeding. And once the stack is fabricated and we can put it in the case and then we will go for the laser welding and once the laser welding is over, then we will go for once laser welding is over, then we will go for the electrolyte filling with the successive cycles vacuum applying and then we can fill the electrolyte and then once electrolyte filling is over, then we will go further cell formation.
So we can see here there are many number of channels are connected and then it's like almost, the space is almost equivalent to the cell manufacturing plant place. So you can imagine it will take use amount of space and the capital cost will be used. And before dispatching the cells, we used to do the safety building conditions, one using accelerated rate colorometry.
Once the safety conditions are made, then we will integrate the battery to the vehicles and then we can, and then we have demonstrated our technology with our formation, optimized formation method. And in order I would like to tell you we have, with this optimized formation method, we have reduced the number of channels. And in one batch for example, if we make 400 lithium ion cells, these lithium ion cells in the conventional method it takes 400, it needs 400 channels and it may needs more than a week time, right? But whereas here with our test method, it is limited to only six hours formation. So there's all 400 cells, we have completed the formation within a day. And these formatted cells, we are validated with different applications like using bicycle. And then we have demonstrated with the e-scooters and then we have connected to the solar lamps.
So these all applications, our test methods, these all applications are given indication that our test methods are well optimized and it is well economical also. So thank you very much. This is what I would like to share my experience with you all. - Well, Dr. Rikka thank you so much for your presentation.
It was very informative and it was wonderful how you walked us through sort of, you know, the, need for the research that you do and then the importance of the research that you're doing. A few questions. One is thinking about the, application of this research and this reduced charging time that you're finding. Can you talk a little bit about, you know, for somebody who's looking at purchasing an electronic, you know, an e-car or e-scooter, what is the implication of your work for the consumer who is looking at buying a product like that with such a high energy demand and also one that needs a lot of time to recharge? - Yes.
First we have to look at the cell properties that we have to initially investigate with the initial cycles. Whether the cells or the battery as processed develop formation cycles are not. If the cells are well formatted at initial cycles, then it can allows us to even rapid charging also. - Hmm, right. - So that is one important and this can be detected based on different approaches.
Several approaches are there. One, we can see the identifying the cell internal resistance or we can identify the initial charge, the charge capacity loss. At the beginning itself if the in beginning initial cycle section, if there is no capacity loss in the charging and discharging, which indicates that the SEI formation was good. That confidence will allow us to define the fast charging test methods, rapid charging test methods. - Excellent.
And then the safety of that obviously increases? - Yes. - [Kelly] That develops. - Yes, once the SEI formation forms, as I said earlier during the, my presentation, this SEI layer primarily dictates the self performance as well as the safety of the lithium ion cells, individual lithium ion cells. - I think this is really wonderful because we do hear, you know, we see in the media, we hear in stories that there are issues with the, you know, with charging electronic vehicles or electronic scooters.
And I just want to reiterate that the safety of that is something that is being developed and looked at from many perspectives and this being one very important component of that safety. - Yes. - [Kelly] That's awesome. - Yep. - And then from a manufacturing perspective, you obviously spoke to the cost involved and in the time involved in this, what is the process to go from your labs to the patent to the uptake in the manufacturing industry? - Yeah, our process actually clearly confirms that it is well optimized and the entire, like in the process itself, the SEI formation and the stabilization we have identified, it was well defined actually.
So this process method for example, when you are going for large cell production plants, it may needs use number of channels and it may need use a space also, right? So that capital investments are the capital cost can be reduces. So once the processing cost will be reduced, then what happens is the selling price is also going to be reduced. The sell cost will be reduced, right? So then it can be, it allows to like, you know, reduce the ownership cost also who are using the cells like the devices related to this battery integrated one. So the overall cost is also going to be reduced. So this method actually benefits for manufacturers site also as well as, as we are saying this protocol is improves the SEI layer characteristics.
So it dictates the safety. So what happens is for end users also this method will be benefit. - It's fantastic. I think when we speak in terms of cost savings, it helps us, you know going all the way back to the beginning of your presentation with that beautiful slide of all the applications. It really does help us think about this as part of our green energy future.
- Yes. In a really doable way from a manufacturing perspective, - Right, right, right. - I love this and I wanna thank you for informing me on what an SEI layer is because now I feel like I have a great understanding of that. Vallabha we speak to a lot of students who are very interested in being part of the green future for our planet and for our wellbeing.
And I wonder if you can just speak to what your career path has been like. How did you come into this space, into this very specific research that you do that's obviously going to have big implications for all of us? - Well it is very interesting to share about my experience always, chosen this field especially. So when I was in BTech, we are very interested in contributing our abilities into the green energy technologies.
So, and this green energy technology for example, whatever we are today, the technologies are developing in every technology. The battery is going to be one of the main component. And this battery technology actually we can say the green energy driving technology, we can say. So it is actually changing our world into the greener place. And it is also well interdisciplinary engineering technologies.
And I have a motivated, and in the early stage where how the materials can be store the energy and what is the lifetime of this materials. So these questions have actually made me passionate towards more technology side. And then as I, my passion into the green energy sector side at that time, the lithium battery technologies, like we are fortunate that the lithium battery technology is also developing. So this is one best good choice for us to contribute our means, our part into the battery technology. And then that's how we chosen this field.
And it is very encouraging to us nowadays. - It's wonderful. It's so lovely to meet people who have such passion for the work that they do. And that was very clear from your presentation. - Yeah, yeah, yeah, yeah, thank you.
- Excellent. Well I would like to thank you very much for your presentation and more so for your work and the contributions that your work is giving us for a more sustainable future. And so thanks for, thank you for everything. - Thank you very much.
Thank you very much for giving me this wonderful opportunity. - Thank you for joining us for today's episode. For more of these wonderful conversations, head over to ul.org or you can find us on our
Future of Safety Science YouTube channel. we will see you there for more ways to discover the fascinating world of safety science.
2023-02-13 21:48
