Game-changing storage

Robert Armstrong: From MIT, this is the Energy Initiative. I’m Robert Armstrong, director of the Energy Initiative. Welcome to today’s podcast, one of a series we’re carrying out on game-changing energy technologies. We’re talking with colleagues from across MIT and beyond about the work they’re doing in defining the future of energy. Today, we’re joined by Will Chueh and Yet-Ming Chiang. Will is an assistant professor in the Department of Materials Science and Engineering at Stanford University. Yet-Ming Chiang is a professor in the Department of Materials Science and Engineering at MIT. Will and Yet-Ming, thank you for being here. Let me start with how you got to know each other. Can you tell me a little bit about that?

Yet-Ming Chiang: Sure, let me start. This is Yet-Ming Chiang. I met Will a few years ago in the context of professional meetings and realized, here was a kindred spirit. We both had a deep interest in battery technology. We were both funded for at least part of our research by the U.S. Department of Energy. We got to talking batteries. We’re both battery geeks. What turns us on is thinking about batteries, how to make them better, and what would be a better battery.

Will Chueh: That sounds about right. [Both laugh]

RA: OK, we’ll accept that. Let’s rewind a little bit from battery science and technology to materials science. You’re both material scientists. Talk to us a little bit about what is material science? What has it got to do with energy? How are you applying your material science to energy systems?

YC: Great. That’s a great question. I think we should let Will start off there.

WC: Sure. I think if we look at all types of energy transformation pathways, they inevitably involve materials, whether it’s the catalyst of battery or transmission of energy. I think being able to manipulate materials, whether it’s in a solid or other form, is absolutely crucial. I think material science is defined broadly as being able to determine what the materials ought to be to achieve the functionality to process and manufacture them at scale. Also, to know how they fail. I think this is the quintessential nature of material science. It’s really the boundary of physics, chemistry, engineering… did I miss anything?

YC: Yeah, and manufacturing. To give us a specific example, a lot of people know what a lithium ion battery is today. Everybody uses one. Everybody carries one in their pocket. It’s well-known that lithium ion batteries power today’s electric vehicles. But when you tear apart your lithium ion battery, what you find are a set of materials that are especially engineered for that purpose. If you unwind your lithium ion battery—and in fact, you do unwind it, because it’s wound as a roll, like a roll of paper towels. When you unwind it, what you find are these two electrodes. They look just like black powder. It’s black powder on the positive electrode, it’s black powder on the negative electrode. But one of them is graphite—not so different from pencil lead, just a very specific grade of graphite that’s used in the battery—and then the other is a lithium-containing metal oxide. We would call that a ceramic material. Ceramics, everybody knows what a ceramic is in the household, but these are classic materials that are inorganic compounds. We refer to them as ceramic materials. These two electrodes, that’s where all of the energy gets stored. Without those materials, energy doesn’t get stored in your lithium ion battery. They’re essential to the function of this lithium ion battery. Both Will and I have focused much of our research on how do you make those materials—this black powder, these particles—store ever more electrical energy. Power the next generation of devices, the next generation of vehicles. That’s one of the areas in which we’ve had a lot in common in terms of our technical interest.

WC: I think also materials goes beyond just energy. I think it’s worthwhile noting that. Every major breakthrough in our history has something to do with materials. Bronze, steal, information technology in terms of silicon, and then arguably, the material challenge I would define today would be something involving energy. I think this is absolutely a very good area to be working in right now and to think about how to make the materials better , for many of the things that Yet just described. For example, energy. I also want to add a little bit of other motivation as well. Why is energy transformation so important? It is intimately connected to decarbonization. We see now electricity becoming ever increasingly inexpensive, but yet it is intermittent. This is the challenge of variable generated electricity through solar and wind. You have the advent of very inexpensive wind and, increasingly so, inexpensive solar, but the wind doesn’t blow all the time, and the sun doesn’t shine all the time. Energy storage technology, like batteries, is one of the crucial technologies that are missing. It’s far too expensive today to replace conventional source of continuous electricity, for example, on natural gas turbines. We’re not able to compete purely on cost with these technologies. Although they’re very different, there is no storage there and the carbon footprint is much larger. But yet they are the preferred choice because the cost is very attractive. I think one of the goals moving forward is to not only make a better battery for the battery’s sake, but a better battery, or energy storage technology, that could enable and accelerate decarbonization, especially by making wind and solar even more attractive than they are today. I think that’s one of the big motivations on a societal level. That really motivates me and Yet.

RA: You both talked about materials science in broad scale and the different aspects of materials science. You’ve talked a little bit about storage, each of you. Can you tell me a little bit more about what it was that sparked your interest in storage in particular, in this broad field of materials sciences? Was it the challenge of how do we integrate intermittent renewables onto the system? Or did you come to storage from other ways? There are, for example, big storage issues with personal appliances, cell phones, for example, laptops. There’s storage involved in transportation today. What was it that was the signature calling for you in working in the storage area? Or were there many of them?

YC: For me, personally, I started working on batteries in the mid-1990s. A long time ago. The reason I became interested was because I realized that these active materials, the materials that store the energy in batteries, are ceramic materials related to other materials, other ceramics I’d studied for a long time prior to that. That’s what sucked me into this area. It really is a field that pulls people in. You look at a battery and you say, what a simple device. How hard could it be to make it better? How come these scientists and engineers can’t make it better? And you say, I bet I could make it better. And that’s how you get sucked in. But what happened after that was that about 10 years later, the mid-2000s, as we all know, all of a sudden, the recognition of climate change and its impact became widespread. That really propelled the development of the electric vehicle industry. At the same time, the cost of solar and wind was dropping, and renewable electricity became much more widely used. From that point to present, there’s been this great acceleration of interest in batteries, in storage. I would not have expected that the interest would persist in this way and continue to become important. Honestly, to someone who is a scientist and engineer, it’s kind of a gift when the area you’re naturally interested in becomes more important than you thought it might be. That’s one of the things that’s kept me working on storage for all these years.

RA: Will?

WC: To add on that, I think it is incredible to witness the development in the past few years. Ten years ago, we have the Toyota Prius, hybrid electric vehicles, and now we have a range of fully battery-powered electric vehicles that can drive 300 miles per charge. To think that all this was enabled by this one single technology, and increasingly inexpensive lithium ion battery technology, is absolutely shocking to me. I’m still shocked that we have this because in front of our eyes this happened in a one-decade timeframe. If you look earlier, back as well, if you look at consumer electronics in the 90s when I was growing up, phones are pretty big. The reason they shrink was short microelectronics are getting smaller, more dense. But the battery was always a big component of consumer electronics. Same thing for laptops as well. All these are transforming right in front of our eyes. As Yet said, it’s very hard to step away from this because it’s a massive industry. If I have the numbers right, it’s approaching I think $40 billion in the lithium ion battery space alone. It’s a huge market. That is just a sign of how much impact this is having. For my students and postdocs who are working in this field, they can see impact coming in front of their eyes as they’re working on it. I think in this sense, the reward, it’s almost instant. Especially as you now have companies commercializing this technology interested in the scientific discoveries we’re making. Then, Bob, to come back to your earlier question, why am I interested in this to begin with. I think climate and decarbonization is one of the key factors. But beyond that, I think it’s just scientifically very interesting. Because you have now the set of materials which can basically take up a massive number of something that’s not there to begin with and give it up. You do it many thousands of times over and over again. Moving electrons is pretty easy because they have almost no mass. But removing, for example, lithium ion, this is becoming heavier, or heavier atoms. From a materials science perspective, to have a material transform reversibly that many times and being able to work very well and store a large amount of energy, I think it’s a materials miracle in itself, and the fact that you can scale it up to make at the megaton level. That’s what batteries are being made of today. This is all a materials science dream come true. I wasn’t there for the steel revolution but I’m glad that I’m here for the energy storage, energy material revolution. We see this happening right in front of eyes.

RA: Let me go back to a theme you both mentioned, which is the decarbonization of our energy system or our economic system, the total economy broadly. Clearly, one of the pathways that’s been pursued is decarbonizing the power sector first because we have large central sources of carbon emissions. Then moving from a decarbonized power system to using electrification of other segments of the economy as a way to propagate that decarbonization. Storage, you both mentioned, plays a number of roles. Batteries for vehicles, batteries for storage in the power sector. I’d like to dive a little bit deeper in the power sector and talk about the many ways storage could be used in the power sector. There are a lot of different timescales that storage could act on, whether it’s very short time scales for voltage frequency control and regulation, or very long-time storage. I’d be very curious about your sense of where the biggest opportunities or biggest impacts could be in storage, as related to the power sector right now, and where you’re focusing your efforts there. Will, I’ll start with you.

WC: I will leave Yet to talk about the economics part of it. Let me talk about the use cases. The use cases are very different. If you talk about the electrical grid versus something like transportation, let me just give you a sense. For example, how long should a battery last? A lot of people say, the battery has got to last a long time in terms of charging it and using it in an electric vehicle. This is actually not true. If you look at an electric vehicle, say the warranty is 400,000 miles as mandated. You can drive it 300 miles per recharge, then you pretty much only have to charge it within the warranty period about 400 times. That is significantly less than what you charge your laptop or phones. The phones we charge almost daily for at least two to three years, and the batteries will last. Automatically, you can get a sense that use case is very specific. Now you go to the electrical grid. If you’re talking about balancing the diurnal cycle of solar, that means you have to recharge daily. All the sudden, if you recharge daily, if it only lasts 400 times, the battery system will only last one year. If you consider the capital investment needed to swap out the battery, the capital investment needed to create the factory to make the battery, this quickly becomes not economical. But the use case is very interesting. Another aspect is also the rate in which you use the battery. An electric vehicle is perhaps charged very quickly. Maybe you can charge it overnight. Or if you do a fast charging, maybe in two hours. But using the battery, you don’t typically, unless you’re a taxi driver, drive 300 miles a day. You drive maybe 50 miles a day. You will discharge the battery over a week period of time. But then for the electrical grid, you have to be discharging daily as well. Now you’re asking the battery to deliver a lot of power to last a significantly longer number of cycles, compared to something like transportation or consumer electronics. The use case could not be more different. In that sense, a different material set would be needed to address this challenge. This is not even mentioning the cost constraint of how many times you have to operate the system to make it economically viable. I think in that sense, there is this notion that we can simply take what we have for transportation, which is a renaissance in itself, and then translate that over to electrical grid. This is not true. You can transfer in very specific use cases, perhaps, and people are doing this now with lithium ion battery. But to really make use of it in a meaningful manner, a new set of chemistry would be needed that delivers longer life cycle, higher power outputs, a lower cost. Perhaps Yet can speak to the economical aspect as well.

YC: What Will pointed out is that the way in which you would use a battery for vehicles is actually fairly simplistic compared to the spectrum of ways in which you might use it for supporting the electric grid. The way that these technical specifications get tied into the economics is something like this. Let me a zoom out a little bit. Earlier we talked about the cost of renewable electricity getting cheap. Many people don’t fully realize that in many parts of the world, and certainly in North America, renewable electricity is today the lowest cost electricity, in terms of cents per kilowatt hour. But the issue is that you can always have it when you want it. If you add storage to it, storage is always a cost adder. It’s never free, and it doesn’t have a negative cost, so it’s a cost adder. The arithmetic problem is to take the cost of generating that electricity, let’s say from solar or wind. Now add to it the cost of storing that electricity and delivering it when you want it and have the net cost of that electricity be competitive with… well, what is our competition today? It’s really natural gas. Can renewable electricity plus storage add up to a cost of delivered electricity lower cost than the cost of natural gas? If so, we can decarbonize the electricity system very deeply. The way to think about the battery cost is therefore, how much do you pay in terms of cents per kilowatt hour for the electricity that gets delivered from that battery over its lifetime. Like a lot of assets that you might purchase—your car, for example—you have the initial cost, call that the capital cost of the asset, and then, in the case of a car, how much you pay for a mile driven. It depends on how often you use it. If you use it every day, the cost per mile driven over the lifetime of that car is relatively low. If you only use it on weekends, it costs you a lot more per mile driven. Batteries work the same way. If you have a battery that is supporting renewable electricity, and it’s in a function where you charge and discharge it all the time, then the cost of that delivery of electricity is relatively low. The units we use in this field are dollars, so a cost per unit of electrical energy stored. Dollars per kilowatt hour. Let me give you a nice round number to think about. A hundred dollars per kilowatt hour is what many would project lithium ion will eventually cost us for grid storage. Let’s say you pay $100 per kilowatt hour and you get to use that battery 10,000 times over its lifetime. That translates to a penny a kilowatt hour for the delivered electricity. We would all agree that’s pretty good. We only have to add a penny a kilowatt hour to the cost of generating that electricity. We can we can do a lot with that. But, unfortunately, lithium ion batteries today won’t last 10,000 cycles and they don’t cost $100 a kilowatt hour. You can see how we still have a need to continue driving down the cost, driving up the life of a lithium ion battery, in order to provide that low-cost delivery of electricity. That’s for a case where you’re using the asset relatively frequently. If we now think in the long term where we have renewable electricity everywhere. Deep decarbonization through the use of renewable energy, then we are going to need to store that electricity over longer durations than just, for instance, the diurnal cycles. Sun comes up, sun goes down every day. The one very simple way to look at that is to look at the seasonal variation in solar energy. We’re sitting here in Boston. At our latitude, the amount of solar energy we can collect in the summertime is roughly five times what we can collect in the winter. There you see a need for something that eventually would need to bridge the seasons. There’s some complementarity with the seasonal variation of when, but not enough. If we look forward to a world in which we have, let’s say, greater than 50%, greater than 80%, renewable electricity, we’re going to start to need to store electricity over longer durations. What that means is that we will use that asset less over its lifetime. We’re going to charge and discharge that battery fewer times over its lifetime. If the cost of the battery stays the same, the cost of the delivered electricity is going to go up a great deal. That’s what motivates us to continue to look for lower and lower cost batteries.

RA: Thanks very much. Let me shift. Will, you recently gave a talk at MIT discussing defective materials and how they’re so important to addressing renewable energy in the energy sector. Can you tell us what defective materials are, and how they relate to renewable energy?

WC: Absolutely. If we think about what a material ought to be, I think that the everyday person would say, it would be good to have a perfect material, which is the opposite of a defective material. One example of a perfect material or near-perfect material would be something like a silicon solar cell. We processed silicon to reduce the number of defects in the material as much as possible, in order to give the highest performance for the solar cell. You would think this would translate universally to all material, but this turns out not to be the case. At Stanford, I teach a class on defects in materials. The world as we know it would not be able to run without defective materials. Batteries is actually one of them. Batteries work, lithium ion batteries work, because there are defects in materials. Catalysts work because there are defects as well. To boil it down, this is something very simple, in the perfect material, the atoms are all bonded very happily. But it is not in the state in which they are the most reasonably reactive. Because in order to do things like storing energy or to catalyze chemical reactions, you want the atoms to be a little bit unhappy. One way to do this is to deviate the material from perfection. For example, you have a missing atom here, you have an extra atom here. So on and so forth. This creates an unfavorable energy landscape upon which the system wants to move in either direction. It is this very notion of defects that actually enables batteries to work. It enables battery to work better and last longer. Catalysts is exactly the same thing. If you have a perfect material without any defects, every atom is where they’re supposed to be. This is most likely the most inert material you can find. Material sciences, this is one specific discipline, looking at how to introduce defects in material intentionally. This could be done through synthesis, how you manufacture the materials. This is one thing we know how to do really, really well. But what is still escaping us is we don’t know exactly how these defects change with time. You use a battery for 10 plus years. A defect that you’ve introduced during manufacturing, does it stay as a good defect or does it become a bad effect? This dynamical nature of the material is something we care a great deal about as we approach the science of degradation. Because we want the battery, as Yet mentioned, to last for a long time in order to get the most out of the buck in terms of the levelized cost of the electricity that is stored. In the same notion, if the material loses the favorable defect, it might become less reactive, then they will not do the thing you wanted to do. One example I want to talk about is your catalytic converter. A catalytic converter in your car, which removes all the harmful gases coming out at the pipe, is full of defects. In fact, that’s how they work. If you make it defect-free, it won’t work at all in the system. That’s just an example that perhaps the audience might be familiar with that can really be used for emission control. That’s all catalyzed by defects in this case. I was actually inspired to study defects by Yet’s book. He has a book on everything about defects in ceramics material. I use it in my lecture. I think a lot of students studying materials science think that defects is a very classical topic. It’s as far from classical in the sense that every technology we have really depends on properly controlling the defects, putting them where they need to be, doing the job they are supposed to do, not one too many. If you have too many defects, this is a problem, you have too few, it’s a problem. There’s really a fine balance what they have to be. I think this is one of the next opportunities for engineering material. It’s not just about choosing what atoms go in the material. It’s also choosing what defects go into the material. Then you can engineer the properties of the material really well.

YC: What Will is saying is that materials are like people. It’s the defects that make them interesting. Nobody wants perfection.

RA: It’s a good thing. Let me ask you, Yet, how your work relates to Will’s. Your book obviously has had an influence on Will and his teaching. I’d also like to go to materials that maybe don’t have defects, like liquids. Is there a role for liquids in storage areas? This is something you’ve thought deeply about I know.

YC: Yes. I would say that first, Will and I have a common interest in many of these topics. And the solids. We’ve been primarily talking about solids. Solids, we think of them as many of them are crystals. Naturally, we think of crystals as something relatively perfect. But even in those crystals, it’s those defects that make them interesting and give them the functions that we want. In energy storage, the materials that store energy can be crystals. They can also be liquids. When they are liquids, you get some additional degrees of freedom in changing composition, changing formulations, changing their energy storage potential. There is a type of battery that is called the flow battery. What it uses is liquids that flow through the battery. You have to try to picture this. You have two tanks. One holds a positive electrode, the other holds a negative electrode, and both are liquids. Then there is a generator. Think of it as the motor that’s being powered by these chemicals. This power generator is an electro-chemical stack. We refer to it as a stack. What happens is that these two liquids flow through it. Then there is a chemical reaction that results in the production of electricity.

RA: Let me just ask, what size are we talking here? Is this big or is it small?

YC: I can tell you that when we do it in the lab, it’s pretty small. But when you look out in the field at the largest flow battery that’s ever been produced in the world, it’s the size of an aircraft hanger. The reason this is significant is that if we’re going to really attack the renewable electricity issue of storage, we’re going to need batteries that aren’t like this battery pack in your car, much less your cell phone or laptop battery. We’re going to be something the size of a chemical plant. When you use electros, energy storing materials that are fluids, there is this an additional ability to really scale it up to huge amounts of stored energy. Your car is kilowatt hours. Let’s think in terms of megawatt hours and even gigawatt hours. To reach that kind of scale, which is where you need to be for deep decarbonization of the electricity system, you do need technologies that can scale like that. That’s one of the reasons for this interest in liquid base batteries.

RA: To help listeners out, compare flow batteries with pumped hydro. Hydro power is a nice way to store energy by using the potential energy of water that’s been pumped uphill. In flow batteries, what’s the relative energy density of what you can store in a unit of volume of flow battery versus pumped hydro?

YC: There’s a reason we use electro chemistry. That’s because it stores so much more energy per volume, per space, or per mass, then mechanical energy. Pumped hydroelectric storage is where you pump water up into a lake, and let that water run through a hydroelectric dam to generate electricity. It is literally carrying water uphill. You carry water uphill; you pour it back down through your damn. The amount of energy that you can store per unit space or footprint compared to a flow battery, the flow battery has 500 to 1000 times more energy in the same space or footprint. That’s what we’re talking about.

RA: So there’s a materials challenge in developing the materials that have higher energy density.

YC: That’s right. The higher the energy density, the lower the cost we can drive down these flow batteries. Because the less you end up paying for the tanks that store them, the pumps, all the hardware that moves the liquid around, and even the size of this power generating stack that I referred to.

WC: Maybe one example I can highlight as to the difficulty of this. We talked about comparing that to pumped hydro, which is storing in terms of the difference in the height of the water being pumped uphill and then flown downhill. If you imagine the energy contained in burning hydrogen to make water, a lithium ion battery can deliver four times that energy. Imagine that in your pocket. Now you have to do the same with the liquid. This is really dealing with a very intense amount of energy and pumped hydro is nowhere close to that. That’s why the height difference had to be large and the volume have to be large as well. As Yet mentioned, the energy density stored in these chemical bonds, whether it’s a liquid or solid, is really what makes an electric chemical solution, I think, a preferred solution, especially when you need to densely store. This is one of the reasons why octane, our gasoline, is so popular. It is a really good way of storing energy. It just we can’t make it in a renewable matter right now. We’re getting there but we can’t quite do it. But a battery, you can think of this is as just another kind of replacement of it, then as a way to store electricity that can then run the motor rather than burning the gasoline directly. Think four times that of hydrogen burning into water. That’s what we’re dealing with.

RA: Talk to me a little bit about obstacles to making progress in materials science today. Is it the chemical space that’s so broad to look at? Is it characterization methods, new instrumentation? What do you see as big roadblocks that you’re working to overcome so you can move this field forward even faster?

WC: One of the challenges, and it’s not specific to energy storage, is that there are dozens of criteria that you have to meet at the same time. Energy density, longevity, safety costs, so on so forth. It’s very difficult to have one material that meets all of them at the same time. It really becomes a challenge of relentless optimization to find the material that can do as much of it as well as possible. I think this is one of the crucial challenges. For every single component of the battery, they all have their weaknesses and strengths and we’re pairing them up in a way to maximize the benefit total. I think another challenge is also the scale of the problem. We’re talking about terawatt hour of storage. Yet mentioned kilowatt hour. Terawatt hour is a much larger number. We have to think about collecting enough raw materials to turn it into the process material. We have to think about manufacturing it. At some point, we have to think about recycling. Lead acid battery is what it is today because of recycling. But we currently do not have a very effective recycling program. If you look at the life cycle analysis of battery, this is really a daunting task, because you’re dealing with such a large energy scale. I would say this is probably one of the toughest challenges. To envision how the material can be extracted from the ground, made into a technology, when you’re done with it you can turn it back. This is going to be I think one of the biggest challenges. It comes with the territory of becoming a successful technology. Now you have to actually worry about how to do it from beginning to end.

RA: Yet, I know you’ve thought a lot about this issue of scale.

YC: And to build on what Will just mentioned, we have to meet all of these requirements. The menu we actually have to choose from is very limited. When you’re learning as a high school student about the periodic table, it looks like a very big space with a huge amount of complexity. Unfortunately, it’s actually a very limited palette that we get to work with. We just don’t have enough elements in a way. What I mean by that is in order to get to these terawatt hours of energy storage, what we will need to use are the elements that are present in very high crystal abundance. There just aren’t that many of them. For example, when we’ve recently looked at this problem of very low cost, large scale storage, we gravitated towards some of those elements, one of which is sulfur. Sulfur is present in very high concentrations and, importantly, it’s a byproduct, a waste product, of oil and gas refining. Every time a refinery produces, for instance, low-sulfur diesel, that sulfur went somewhere. It went in a stockpile that might be used for something else. But there’s a great deal of software available to us. So we are already trying to find in that very limited periodic table where the chemicals are, where the elements are, that will allow us to build batteries that scale to terawatt hours. That’s challenging.

RA: I’d like each of you to tell me something surprising about materials science or energy that they may not know. What would be a surprise, do you think, Will?

WC: As someone who has been doing this only for about 15 years, I’m really surprised how quickly it has developed. It really reminds me of the information technology revolution, except from a materials scientist view, it deals with a lot more materials. In information technology, we’re largely dealing with silicon. It took several decades to figure it out. But with energy storage and transformation, we’re dealing with dozens or hundreds of materials. It really surprised me that we are beginning to get it to work. It’s not done yet. The problem is far from solved. But I think being propelled with the climate issue, the need to decarbonize, I’m really surprised that the worldwide community has moved so quickly to address this challenge. The speed and the pace which this is happening is very encouraging. Because we need a solution relatively soon. In my lifetime, we’ll need the solution in place. I’m encouraged by the fact that it’s happening. I’m also happy that there’s so many scientists like Yet contributing to making this happen both academically and also industrially as well. I’m very optimistic that in the next decade or two, we’re going to see some dramatic improvements in the technology which will substantially change the way we live. Absolutely. I think this is going to be something to watch.

RA: Thank you. Yet?

YC: I’m going to leave you with a couple of things that the next time you look at a battery, you ask yourself. First, I’m going to go way back to that grade school battery. You took two nails, a copper and zinc nail, and stuck them in a lemon and a potato and maybe in a cup of salt water. What I want listeners today to remember is that it’s not about the potato and it’s not about the lemon. It’s about the two nails. What you get the voltage from are the copper and the zinc nails. Now, the second thing is that when you look at your battery, your lithium ion battery for your laptop, for your cell phone. If you’re able to actually read the packaging on one, you’ll notice that it has a voltage of about three and a half to four volts. I want our listeners to think about what that means with respect to their electrolysis experiment that they did in science class at some point. If you think back to that experiment, a little over one and a quarter volts, you were able to split water into hydrogen and oxygen. Now we have a battery which has liquid in it, which is our liquid electrolyte, and this battery is at three and a half to four volts. Why isn’t it generating hydrogen and oxygen all the time? The reason for that is because in your lithium ion battery at this high voltage, that electrolyte is not water based. We call that a non-aqueous battery. It’s a non-aqueous electrolyte. Batteries are fascinating. They are chemically fascinating. Materials are fascinating. I just want to leave that. The next time you confront a battery, ask yourself a couple of questions about what’s in it and why does it operate at the voltage it does. What are the materials that are giving it the energy that it provides?

RA: The good news is it doesn’t sound like it affects what you buy at the grocery store. [Both laugh] What do the next five or 10 years look like to you in materials science and energy in particular? What do you see as the next challenge beyond your flow battery or your battery for day/night storage?

WC: I think in the near term, what we’re going to witness is a massive ramp up of production of battery technology, which is connected to electric vehicles. We’re going to see a lot of difficulties in increasing the supply of batteries. This will be connected to your availability of raw materials. I think many people have heard about issues surrounding cobalt, which is one of the key ingredients in batteries for consumer electronics and a component also in batteries for electric vehicles. I think beyond materials science these things have to be dealt with because we have to have a full supply chain of this. There will likewise be other difficulty associated with safety. As we make this en masse, I think many of you have heard about safety incidents related to consumer electronics in the past couple of years. These are issues that will haunt us for a while. I think these are all engineering challenges that have to be dealt with and we’ll learn. Failure analysis would be crucial. There will be some accidents. This is unavoidable. But we’ll learn how to make them better. But I think in terms of the near term, finding the resources, ramping up production, thinking about how to deal with safety, are going to be crucial. Ten years and beyond, what I’m personally excited about, is batteries, to some extent, are still a little mysterious. In fact, it’s quite miraculous that they work. Because we don’t understand every single aspect of batteries. If you ask an engineer about a computer or microelectronics, they know everything inside. The material properties, circuitries, every single aspect. If you ask me, if you ask Yet, there will be some parts of batteries that we don’t know how it works, but it just does. I think this points to the need for university research. We really need to understand what is making them work well and how to improve them. What are the rules for designing them? I think in addition to pushing the engineering front, to come up with better, less expensive materials for batteries, you also go back and say, can we understand the fundamentals of batteries? Next time my student asks me, how does this work in a battery? I can actually have an answer for them. Most of the time I just say, we don’t know, but it works. I would like to, on a personal level, be able to offer a better answer than that. I think in the next decade, the fundamental understanding around batteries being fueled by better tools, for characterization better theoretical tools for simulating, we’re going to learn a lot more. We’re going to see interesting intersections also with informatics and artificial intelligence as a way to recognize weak patterns in the system. All of these will come into play. I think probably in the next 10 years, we’re going to see the innovation cycle for batteries shortened dramatically. Because we can get something from a laboratory curiosity to a prototype to mass production because we have figured out how to translate each one at scale. I think that’s something that could be exciting to look forward to.

RA: Yet, what’s your take on the next five to 10 years?

YC: I think in the next 10 years, one of the things we’ll see is the rise of very low-cost renewable electricity. That’s really one of the big trends that’s happening in the world of energy today. The question to folks like us is, how can you best make use of that? The reason we talk about batteries is certainly that storing that electricity to use it at a different time is one of the ways that you can use that. I think we’ll also start to think about out how to integrate systems at a different level. Where you not only have that storage of the electrical energy that arrived at the wrong time, but maybe, at the same time, we can use it for another purpose. Conversion of something to liquid fuel for example. We can use it in in order to run an industrial process that might otherwise have taken a lot of energy. I think that batteries and electrical energy storage, we’ll have to start thinking about a larger scale system where we in net make the best use of their very low-cost renewable electricity.

WC: I’ll add one more thing as well. It’s very exciting to think beyond transportation and the grid. What other use case could inexpensive and effective energy storage bring? Could we change the way goods are moved across the Pacific, across the Atlantic? Can we think about aviation? What are the possibilities there? It doesn’t have to stop with just vehicle transportation. I think there’s a lot of excitement around what new heights in energy storage could we bring about. We can see this in the coming decades. This will be really remarkable to watch. It will unfold in front of our eyes.

YC: I totally agree with Will. Electric aviation is starting to become more and more interesting. It’s electric transportation in just another form. The way that electric aviation is being discussed today reminds me a lot of what happened in the right around the early 2000s, late 1990s, when hybrid electric vehicles were first being discussed. It was something that people had a very difficult time wrapping their heads around. How do I think about this? I see that same kind of a discussion going on with electric aviation today. We think it’s going to be pretty short range, at least initially. But how far can we go with concepts like vertical takeoff and landing; air taxis that bring commuting to a third dimension, as it were. I think that whole area is going to be a very exciting area and will propel us to develop still better batteries.

RA: Storage is also going to play a key role in developing countries. One of the big challenges we have as a society on this planet is to bring energy access to people who don’t have it today. Roughly a billion people around the planet. Doing that in Sub-Saharan Africa, for example, is will surely involve micro grids or off-grid applications where some generation source like solar plus storage provides a solution that, although possibly not perfect, is much better than no access at all. Do you have thoughts on the specific needs or unique needs for storage in the developing world as we electrify populations that don’t have access?

WC: I think one of the key advantages of variable generation plus storage, say solar plus batteries, is that it scales really well down. You just don’t need to build a 100-megawatt power plant, which is very capital intensive, a significant issue in developing countries. You can build very small. I have 20 kilowatt solar panels on my roof. One can envision a very small set of homes been connected by that. I think that’s one aspect. It can perform well in a small power and energy scale. What is also exciting to think about is imagining—and I don’t have to answer today—not only a distributed use of batteries and solar cells. Can you also think about distributed manufacturing? Say you don’t want to mass produce. You want to produce it locally. Can you take the two nails put in a lemon, something bigger than that, and reimagine what distributed manufacturing would look like manufactured locally? That can change the equation quite a bit. Maybe you don’t need the high-performance battery because you have no electricity to begin with. The bar is pretty low. Then you think about how to locally make a battery. Maybe you don’t use a new battery. Maybe you use a recycled battery. Maybe you take a battery that we don’t use the United States, and you sell it for a much-reduced price in a second life or second use situation in a developing country. I think the fact that there’s not much in terms of pre-existing infrastructure combined with the availability of capital really points at these distributed settings for the electrical with the micro grids or even smaller than that. I think there are some real opportunities and it changes the equation. I think many of our colleagues are thinking about how to tackle that challenge. It will have its unique solution that will be different than how we’re tackling the challenges we have here today.

RA: I think you meant the unavailability of capital in the developing world.

WC: Unavailability, exactly.

RA: Which is a problem and a great advantage for these distributed small-scale systems. Yet, do you have any comments on that, particularly about flow batteries? Do you see those having a role, maybe not as the first enabler, but in next generation developing countries?

YC: Yes. As Will just pointed out, low cost is essential. A path to driving down that cost is these trends that I mentioned earlier, of looking for very large-scale systems that use very low-cost materials. That pursuit will, I think, result in lower cost battery chemistries period. And Which then can be scaled back down to the level of homes or villages. The flow battery has probably a natural minimum size, which is far above a laptop. Somewhere between one to a few homes. That’s a pretty good natural size for a flow battery. I can see that happening in which we take that large-scale technology and transfer it the other way.

RA: I’d like to thank both of you, Will and Yet, for being here today. This has been a fascinating conversation. I really enjoyed your comments.

WC: Thank you, Bob.

YC: Thank you, Bob. Great to be here.

RA: Show notes and links for this episode are at energy.mit.edu/podcast. Tweet us @mitenergywith your questions, comments, and show ideas. And subscribe and review us where you get your podcasts. From the MIT Energy Initiative, I’m Robert Armstrong, thanks for listening.