 A great good morning from Stanford. My name is Will Chu. I'm the faculty co-director of the Storage X Initiative and a faculty in the Material Science Engineering Department. It is my great pleasure to host the Storage X seminar with my colleague, Itsoi the director of the Precourt Institute for Energy. So the topic today is solid state batteries and the mechanical properties of solid state electrolytes. Many of you have participated in number of our sessions on the topic. We have featured academic experts and also industry experts on the topic. I think we have maybe more than eight speakers on solid state batteries ranging from oxides electrolytes to sulfides to polymers. And today we're going to continue to expand the type of materials and architecture for solid state batteries and then also investigate some of the fundamental science that governs and limits solid state batteries. And to do that, I'm really delighted to have two wonderful speakers joining us today. Both veterans, Steve Fisco, who is the founder of PolyPlus Battery Company, one of the most seasoned battery companies in the United States. And then also I'm glad to have Eric Herbert, a faculty in Michigan Tech and an expert in mechanics and has applied it recently to solid state batteries. So let me first ask E to come to the stage and introduce Steve and we can get started. Oh, thank you, Will. Good morning, everybody. I'd like to welcome you back to StorageX symposium again and also I'd like to welcome Steve and Eric as well. Let me introduce Steve. Steve Fisco is a great friend for many years now. He is the CEO, CTO and founder of PolyPlus. Steve, you did so much. PolyPlus has been certainly a well-known battery company over I think perhaps about a couple of decades now. Yeah, well, Steve, I think started as a scientist in Lawrence Berkeley National Lab, having his amazing invention and then spun out of PolyPlus. And he has been leading that. Steve is known as a electrochemistry battery expert. He has so many awards. Let me just mention a few for today's purpose. So he's a fellow of electrochemical society. He was named by the CTO Berkeley as a visionary award for his work in the next generation of batteries. He also won the IBA award for outstanding contribution to the development of lithium air, lithium water batteries. With that introduction, Steve, I'd like to welcome you to the stage. Thanks, C, thanks very much. So should I jump? Yeah, I will share my screen now and we'll jump in. Okay, all right, so let's get started. I'm gonna walk you through, not only what's happening at PolyPlus Battery Company, but provide a bit of an overview of some of the choices that any of us working in next-gen technology have to make as we decide which solid electrolytes, which types of materials we want to introduce into next-gen batteries and what are the trade-offs and some of the decision points that are pretty critical here. So anybody who's following the news on electric vehicles has seen some type of a curve like this over the years, which is adoption of electric car technology as a function of different, well, looking across various countries. And so adoption, of course, is happening rapidly in the US and Europe. China is a big player. As we all know, the lithium ion batteries that power these EVs came out of Japan and Korea and China and now we're looking to start manufacturing those batteries that has started in the US and Europe. So there are big things at play here, but as has always been the case in the battery field, people want lighter, smaller batteries and cheaper batteries with better performances. So that's a tall order. And it's not like there haven't been hiccups. Here you see a Chevy Bolt. There was a recall recently for the Bolt. And all through San Francisco, we see these types of signs where you're prohibited from parking that car and parking garages because there's concern about fires. And of course, EV fires are not easy to put out because the battery has both the reductant and the oxidant present. And just a month ago, there was a large hurricane that hit the East Coast, actually hit Florida, the West Coast of Florida and buried or flooded a number of EVs, including a number of Teslas. And the headline said that, they were exploding all over Florida. So safety, of course, is critical in this domain, but we want to push forward. So how do we do that? How do we develop the next generation of batteries pushing energy density without compromising safety? And actually, if the batteries go into an electric vehicle, you actually can increase cost either. So that's a very tall order. So how do we do these types of things? The response to that question has been solid state and a number of, of course, are working in this domain. And there's got to various versions of what we call solid states. Let me solid state hybrid and then fully solid state. And he can go through that a bit as well. But the push to solid state in most cases, not all, but in many cases involves a transition from carbon to silicon and then ultimately to lithium metal. And here's just a comparison of the gravimetric and volumetric capacity density of lithiated electrodes moving from carbon to silicon to lithium. And the black boxes at the bottom right, you can see that lithium is more than four times better volumetrically than carbon and more than 10 times on a weight basis. So there's, and everybody knows it, that there's an incentive, right? To move in this direction, you're gonna have lighter, hopefully lighter and safer or as safe batteries. So let's, let's look at that. So PolyPlus, I'm gonna walk you through how this happened. PolyPlus has two technologies that we're developing. One is actually going commercial right now based on polycrystalline solid electrolytes, but the, and that is a single-use battery, but it does some of this, the walkthrough of this technology will show you that by moving to solid electrolytes from liquid to solid electrolytes, we can do things that have never been done in the battery space before. So those are real numbers you see at the top, middle 1900 watt-hours per liter and 2000 watt-hours per kilogram. So, we can get actually into this domain, which is typically the domain of hydrocarbon fuels, right? Energy entities that look more like gasoline than batteries, but that's a primary. And as you move to the right, you can see that we're actually developing a different technology there for a number of reasons that we'll walk through, but that also will give us a large improvement because again, we're moving to lithium metal, both these are lithium metal technologies. All right, so if we're gonna move from liquid electrolytes to solid electrolytes, we have some choices. And in fact, we kind of had, can write down a tick box of what are the requirements here if we're gonna make this transition. So I mean, clearly we need high lithium ion conductivity, hopefully at room temperature, not all these solid electrolytes conduct at room temperature, but hopefully at room temperature and below. If you're gonna work with lithium, you need to block lithium dendrites. And actually Eric will talk a little bit about the mechanical properties necessary to do that. And that means you either need thermodynamic or kinetic stability to lithium as well at the interface. You would prefer low density for your materials, why? Because the liquid electrolyte doesn't contribute energy to the cell, right? It's a passive component. So you don't want it to be heavy because that's gonna add weight to the cell. So the lower the density of the electrolyte, the better off you are. And you need a roadmap to going thin because if you look at modern lithium ion cells, those membranes that separate positive and negative electrodes are pretty damn thin. And there's certainly less than 20. In many cases, there are less than 10 microns. So you cannot be putting a thick membrane in here and hope to achieve record breaking energy densities. And then lastly, but not leastly, if these technologies are gonna end up in electric vehicles, there has to be at least a path to get to parity with lithium ion. So how do we do that? All right, so the world of solid electrolytes looks something like this. Your choices are polymers. There are solid polymer batteries, lithium metal solid polymer batteries in operation in electric vehicles in France. Bolray has done that. The other choice for solid electrolyte, of course, is polycrystalline ceramics. And in fact, this is the basis of our lithium seawater technology. And then glasses, which is a, in a sense, a newer class of materials. Conductive sulfides have been known for a while, but actually continuous sheet sulfides, that is new. And so if you look at these three possible choices for polymer, excuse me, for solid electrolytes, what are the upsides and downsides? Well, polymers typically are limited to warm temperatures. There are some polymer electrolytes that have limited conductivity at room temperature, but typically the way you see that done is the addition of liquid to the polymer, in which case it is an outside state. And you start to bring in the same old problems that lithium metal batteries in the early days of pride of lithium ion were exhibiting, which is safety problems. Polycrystalline ceramics certainly can block dendrites. They're mechanically tough. They are not easy to scale. We'll walk through that a bit for reasons that aren't immediately obvious, but in fact are well known to the ceramics industry. And then glasses, well, everybody probably, in the audience here is walking around with a smartphone that has a thin glass display. So what you see in the right there is a technician holding, that is probably 50 microns of oxide glass. You couldn't quite do that with sulfides because they need to be protected from the atmosphere. But once you get below about 100 microns, glasses can be processed in a roll-troll fashion. So they are scalable and they have been scaled, right? There's an entire industry globally to do this. So they have that advantage. Let's focus on polycrystalline ceramics for a second. Why? Because well, they're certainly interesting and there's a large world of conductive ceramic materials available to us with good lithium ion conductivity and sodium ion conductivity in some cases. But they also have this particular ceramic, lithium aluminum titanium phosphate known as LATP. There's not only highly conductive at room temperature, but it has the unusual property. And this is the only material we found that has this property of being exceptionally stable to aqueous environments for a material with such a high lithium ion conductivity and a large population of lithium ions. It's an unexpected property and it allowed polyplus to develop this very unusual water stable lithium ion electrode. You see that on the right. And these are really water stable. We can put that electrode which is sitting at the lithium potential in water for, you know, certainly in excess of a year we've done these kind of tests with a self-discharge rate of zero. Here you see a 10 amp hour. So these are very energy dense electrodes, 10 amp hour electrode. But behind that ceramic membrane is almost three millimeters of lithium. So in other words, it's very thick, very high capacity. And that distinguishes this approach from rechargeables in terms of the cost or the amount of solid electrolyte you need. So in this application where we're using these types of ceramics to build very unique high energy density batteries, we don't need much of the electrolyte, solid electrolyte because the capacity density is so high. And that makes a big difference in terms of downstream cost. So this is an affordable approach for a primary body that has, you know, very high capacity. It's going to be different when we start looking at rechargeable batteries. Quite different. And it's just a simple mathematical calculation to see the kind of trouble you get in. So let's look though for a second at this technology. So what you see here, these are actually electrodes we're making now on a line that actually a manufacturing line that is installed in Berkeley which will eventually be moved out of state as we start to actually scale this technology. That's a 27 amp hour protected lithium electrode. So it's a lithium electrode stable to water, stable to a variety of chemical environments. And on the left, you can see a stack of lithium ion cells, five amp hours. You can just get a sense of scale here in terms of the extremely high capacity density, energy density that's available in these types of electrodes. And we can compare it to, and I'll show you our numbers, the highest energy density battery to date, right? Which is thynyl chloride. This is a pretty nasty technology. It is toxic, it is explosive, and it's used throughout the ocean. So that's a pretty sensitive environment in which you're putting these toxic systems. And the reason they're being used is they're high energy density and to do long duration missions, oceanographers, people doing sensing in the ocean and robotics deep ocean, haven't had many choices. I mean, this is where they go. So you'd like to get away from that. So let's compare that at 1,100 wattage per liter to one of these stacks. So this is an actual battery stack. There are three negatives there and four cathodes stacked together. So that's 81 amp hours of capacity at two volts. It's 160 watt hours. That total stack weighs 80 grams. And you can do the math, it's 0.08 kilograms. So the thing that is also interesting here, self-discharge rate, we can't measure it. We've done tests discharging these batteries for close to 15 months and you get full capacity in all cases. So there's no self-discharge because of the solid electrolyte. So that means that a 2.7 inch stack is a kilowatt hour. Exceptionally safe. Why is it so safe? Because it's not a battery actually until it's immersed in water. So the thing's being moved around. It's exceptionally safe. And here are the metrics of 2000 watt hours per kilogram in 1900 watt hours per liter. I think this record will probably stand for the next century. It's hard to imagine getting beyond these kind of numbers. And so we've done testing, of course, on this third-party testing going on now. We did some tests off the coast of Key West in the Sargasso Sea couple of miles below the surface of the ocean. So this deep ocean testing, we actually, the battery itself outperformed our internal tests of polyfluous. You can see there, there's a float which is tethered to the battery with the data and GPS link to a satellite so we could get that information back. So these batteries are performing exceptionally well. And because of that, we are actually getting ready to start selling the product. So we have a pilot manufacturing line in Berkeley to do this. And we have about four megawatt hours of capacity but we'll be outstripped at very quickly. So that's that technology and let's move on to rechargeables. So again, going back to a second for these choices. So obviously we have a lot of experience with polycrystalline ceramics. We have a product based on ceramic membranes. But if you go from single use to rechargeables, there's a rather dramatic shift in the amount of capacity per unit area. What does that mean? Means that the rechargeable battery is gonna require two orders of magnitude, more surface area for the solid electrolyte. So that solid electrolyte had better be pretty inexpensive. And you can simply compare the price per square meter to what you pay for plastics to go into lithium-ion which is dollars per square meter. And so here, if we were to use this ceramic and rechargeable, we'd be looking at 100 times the amount of material, the surface area for the solid electrolyte which is not an inconsequential issue, right? So if we look at how you make ceramic membranes typically, and this is pretty much the way it's done around the world, you start with the ceramic powder, make an aqueous suspension, you tape cast to get a thin tape and then you've got a green tape. This part of the fabrication of the ceramic component, that's pretty inexpensive, right? And that's how you make a lithium-ion cathode or ANO too. So this part's trivial. The next part is not. Now you have to remove that binder. All of the organics have to be removed. That's typically down at three to 400 C. And then you have to densify this material to something that has no pinholes and is hopefully 20 microns or thinner. That is not trivial. And quite often when you try to densify ceramics, they open up pinholes. So if you're making a porous material, okay, that's easy. If you're trying to make the thin, flat, dense, pinhole-free ceramic membrane, that's not trivial. That's quite difficult. And anybody who's done this kind of processing knows that quite often you get things that look like potato chips because you get differential densification when you're centering because those powders are not monosized. And so, and you may have variations in furnace temperature, which will also give rise to warpage and deformation. So to get a thin, flat membrane is non-trivial and typically quite expensive. We can look at that and you can just Google this. Not the bottom number, but the top number, just from CorsTech. So what does it cost to get a 200 micron, flat, pinhole-free piece of alumina? About $1,000 a meter squared. And you want to be at a dollar. So that's actually three orders of magnitude too expensive. And on the bottom, that's a material that was originally targeted for fuel cells. So it's zirconia, if you stabilize zirconia. And this company makes 40 micron membranes. I think they're a business now, but at the time they were producing this material, we reached out just to get a sense of scaling their material. We asked them if they went to EV type scaling, where could they get with the price for this material? And they gave us a price of $5,000 per meter squared. So that's clearly not in the domain of where you could have a solid electrolyte transition to say EV applications, even consumer electronics. And on the right, this is the membrane we use at smaller scale, 20 microns for the membrane that is stable to water. And at 20 microns, that's a very expensive membrane. We don't need to use 20 microns to the primary, we're 10 times that thick. So this is a problem. And then if we go back and look at the world of crystalline and non-crystalline materials for batteries, oxide, sulfides, polymers, you have to again look at density, and then it actually cost of scaling. So here are three interesting materials, LATP, garnet, LLZO, which is quite dense, and glasses, which are actually closer to the density of polymers, and that's a plus. So this is what we're doing at Polyplus for the rechargeable technology. We call them glass protected lithium metal batteries. Obviously we file a lot of patents around this. So let's look at sulfides because that's the basis of what we're doing. Now here is actually what you see there in the video is not a sulfide, that again is an oxide glass, but it just gives you a sense of how flexible glasses are when you get down to these dimensions of less than 100 micron thickness. They become, these are roll-to-roll processes, which is what we're doing as well. So the idea then is, well, the manufacturing process looks quite different. So let's compare and contrast that to what we do for polycrystalline ceramics. Here we take the raw materials, sulfide powders, and in a single step, by heating that up above the melting temperature, we produce a fully dense rod. So you get to a fully dense rod, hopefully with no bubbles or inclusions and that's where we are. And then you start processing that rod. So the next step would be making a preform if you're gonna draw thin glass. And then that preform has to go into some type of a draw tower. That's actually the tower operational in Berkeley. And then from the draw tower, you produce this continuous ribbon of thin glass sheet, which is the basis for building the rechargeable lithium metal battery. So if we look at just, again, this is like a Google search, let's look at the pricing of thin glass. So Gorilla Glass, which is in your iPhone, just a retail order of 100 pieces. You already have 40 a meter squared. Willow Glass, which is thinner, is roughly $8 a meter squared. And if you look at Chinese suppliers, you can get down to a dollar a meter squared. So this is certainly the domain you wanna be if you're competing with lithium-ion and need a path to get to parity. So the actual fabrication then occurs something like this. So what you see on the left, that's a 50 gram ingot of high conductivity sulfide glass. We have another company that's producing that for us. So they ship material to us on a monthly basis. And that can be cut. Here you can see, we can cut that into discs that are pressed into disc for electrochemical testing, or we can actually convert this to a preform. And you'll see that as well. So here you see, we're using a wire saw to cut out a disc, that's a rough cut disc. And then we can actually warm that above the glass transition temperature and just press it simply into a solid electrolyte. Again, pinhole free, fully dense, and then build cells with that. You can also see just the formability of these sulfide glasses in this picture, this photograph, where we actually put a disc of glass between two vitreous carbon plates, softened it, and just drew it up into effectively a kind of a tube there. But you obviously cannot do this type of thing with a ceramic material. I mean, you're not gonna, the melt temperatures would be outrageously high in any case, and they certainly wouldn't draw like this. So this is a unique attribute of these sulfide glasses that we can basically process them almost as if they were polymers. And Eric will go into this in more detail, but just a very quick comparison of the elastic modulus of the glass that we're working with in red, say versus a polymer electrolyte, you can see, I mean, of course they're very soft materials and lithium dendrites, as we know, penetrate polymers quite easily, particularly at room temperature. But yes, you go through these glass modulus, so you can see that we're pretty close to the strength of an oxide glass. So these are relatively strong materials, certainly strong enough to repel dendrites. Okay. So with regards just to simple testing in cells, we take these glass discs, we bond lithium metal to the glass disc, and then we can put it into a test cell, cycle it against a lithium counter or NMC cathodes. And you can see here that they cycle quite, we don't see any evidence of dendritic shorting, they cycle quite well. That's 400 microns, 200 microns glass, and we can also of course test at warmer temperatures, that's room temperature here, we're at 45C and we get about 2000 cycles as we cycle these materials. And we can also of course, we build full cells, you can see here we're cycling against NMC 622, we see good capacity retention, cycling at roughly C rate, commercial capacity. So these are behaving well. And then if we get back to just the overall flow of how we go from ingot to thin glass, it looks something like this, we start with a bar of glass, that is then taken into a precision molding press, which molds the glass into a preform, the preform is then transferred to a draw tower, again, that's all happening in our lab in Berkeley, and the draw tower can draw thin glass, we put a moisture barrier on the glass, that then is coated with lithium, and then we build cells and pouch cells from those components. And so just to show you what that tower is doing, on the left, you can see an actual preform, right? So that is a sulfide glass bar, basically about a millimeter and a half thick, that is then transferred into the draw tower, and that draw tower does the following. Inside the tower, we have a set of rollers. So the preform then is descended into a preheater from a furnace, then it descends to the rollers, then start to roll it thinner, and beneath that process, we have a linear actuator, which then pulls, it's basically a gripper that pulls the glass even thinner. So as long as we control the rate at which we're pulling and the rate of the rollers, we can actually control the thickness of the glass. So again, something that's kind of unique, and this is not unusual for processing thin glass for say displays and things like that. So we're adopting those types of processes, but unique to sulfides, as you can see, our draw tower is encased in a glove box, right? So as we're processing the glass, we have to keep it away from atmosphere. So that's an argon glove box vertical tower. And when we pull the glass, of course, this is quite thin. So we image it with a confocal microscope, this is a laser microscope, and you can see here that we can pull glass down as thin as 15 microns. So we're getting down to the dimensions that we need to get into very high energy density cells. Now for the time being, we are mechanically cutting the glass, so it's a bit of a rough edge. We are about to transition to laser cutting of these glasses. We can bond that with a six by six centimeter lithium electrode, it's about a hundred milliamp hour cell. We're building pouch cells, and we're just starting to cycle those pouch cells now and build full cells. These are lithium lithium cells, but we're building full cells now. So we're well on the path to getting to, I would say, more commercial type prototypes. And if we just calculate, and this is a projection, of where we can take the technology as we move from graphite or carbon electrodes to lithium metal electrodes, that's basically the yellow gap you see there. That's the jump in energy density in that transition. And it's plotted as a function of your choice of cathode. The lithium glass doesn't really care what your cathode is, so as cathodes improve, you'll see the same kind of improvement with regards to going from graphite to carbon. So you can see a pretty substantial jump. And then in cross section, this artist diagram of the cell looks something like this. You can see, again, we start with a porous metal oxide, cathode, thin glass separator, and just a bit of lithium, that's a seed layer for electro deposition on the first charge and then we leave some of that lithium as we cycle. And so that should take us for, say, relative to a conventional lithium ion from 700 watt-hours per liter to 1200 and on specific energy from roughly 260 to 400. This is still a hybrid cell. In other words, that cathode still has liquid in it. So it's kind of two-thirds solid state. We also have another approach, which is happening now within polyplus, which is a fully solid state, zero liquid cell, which requires then a solid state cathode. So of course the glass is solid state, lithium in itself is solid state, but that means transitioning to a completely solid cathode. So that work is happening now. We are building basically a three-dimensional cathode, which will have sulfide, solid electrolyte interspersed within that structure. This is, again, we don't expect to need any pressure to hold this together. This is all bonded. And because we're bonding glass to a rigid composite cathode, we should be able to go even thinner. So we think we can probably move to two to five microns of glass. That'll take us of course to higher energy density. The same type of approach has been done in solid oxide fuel cells where you use nickel YSC composites and then lay down YSC on top. And we in the past have done two microns of pinhole-free material. So it's only doable. And that approach looks something like this. Here on the left, yeah, that's a conventional lithium-ion cathode. And on the right, this is what we're doing. So that confocal microscope image is, that's actually LCO, so that there's no carbon, no binder. So there's a three-dimensional structure with porosity. And the first test we do on the cathodes are actually with liquid. And you can see that we get very good cycling. So we're moving about five milliamp hours per square. So again, it reasonable rates. So when we go fully solid state with thinner glass, that should take us into this domain, right? Where you're looking at even greater energy densities. And we expect this to be, of course, the safest of the various iterations of this technology. Just to wrap up then, that cell then is again, not gonna have any liquids of any kind. And in this case, because we have a supported glass membrane, we can take these up to dimensions where we can hit almost a factor of two on energy density. So that's the technology. We're introducing both these technologies into a variety of applications. So the lithium-C water battery course is done. That's going into commercial production now. The glass technology is still in development, but we expect to introduce it into kind of consumer electronic drone applications because they're premium markets. And then, excuse me, as we scale the technology, of course we'll take it into larger and larger applications. And I think that's it for me. That ends up my talk. Well, Steve, thank you so much. Very exciting overall development. The polycrystalline and also now glass ceramics electrolyte. Let me ask you a first question. And the solid state batteries with lithium, we always discuss quite a lot about the interface. Yes, yes. So no matter what's the ceramics or polymer, the electrolyte ceramics polymer now, or also the glass, that interface always so important. It is. Yeah, I guess for your primary cell, because it's not rechargeable. So to consume lithium, that's different from rechargeable one. But even for primary, do you see this concern of the interface because of the... Yeah, it's been rolling. It's been moving down, yeah. No, absolutely. And so on, yeah, can you make some... Yeah, so the interesting thing about the... In the case of the seaward, I'll walk through both. The seawarder technology or the lithium water technology, we do have an... So LATP is not stable to lithium at all. It's reduced at two volts. So LATP and lithium cannot be in direct contact. So we have an interlayer between those two. So that interface is controlling, it is critical. Now, in that particular technology, there's some basically vacuum pressure on that pack, right? So that keeps everything in intimate contact as that electrode discharges. And in that particular case, we virtually always get 100% of the lithium that's built into that electrode. When you transition to the glass, yeah, that's a different technology. It's a different interface. So one thing I didn't talk about, because it's still fairly proprietary is we do have an engineered interface. So we do engineer that interface because it is critical. As anybody who's worked with sulfides knows that they're not thermodynamically stable to either lithium or the cathode, which means that you do need some interfacial tailoring of basically that connection between the negative and positive electrodes to the glass. So that is something that's done post draw tower, right? So we do lay down this moisture barrier, which is also transparent to lithium and stable to lithium metal. So yeah, there are the parts to that, but you're absolutely right. Those are critical interfaces with regards to cycling and ensuring that you don't degrade the solid electrolyte itself. Yeah, similarly on the cathode side, this is the question from the audience. So the cathode active materials and the sulfide, right? So that's the ability. Yeah, it's the same. No, it's absolutely the same. So there is a coating on that cathode to protect the sulfide in that sense, not so different than what Toyota is doing. So Toyota, if you look at the Toyota approach, they also use sulfides and they use high voltage cathodes as well. They have a coating on their cathode material to protect the sulfide and we do the same. But in their case, they're actually just pushing powders together. So since you're pushing powders together, you really can't use lithium metal because powders have voids and lithium metal will find those voids very quickly. So that's a lithium ion approach, right? The Toyota approach is lithium ion with sulfides. And on the, again, on the negative side, you're actually okay in that case because the particular sulfide they use on the cathode side, they do have to protect against oxidation of the sulfides. And you do that with a coating. Yeah, yeah, makes sense. Steve also, for the all solid state, right? It's not that hybrid. I mean- That's right. Solid state. So for the cathode, you also need to add in this ceramic ion conducting path. That would, you know, what's the experience like? How much would you need to add in order to establish enough path Yeah, so, you know, I can tell you, no, it's a great, we actually, when we first started, we were not, we didn't think in fact that removing, so there's no carbon here at all, right? No binder, no conductive carbon at all. So we were concerned that trying to get this three dimensional cathode to function would be a problem, right? That you're not gonna have enough sufficient electronic conductivity through that structure. But in fact, from the get go, from the first cathodes we made, we saw that in fact that's, it's not a problem at all, right? But these are fused connections. So we're not, we don't have discrete powders that are being pushed together. This is literally a three dimensional interconnected structure. So there are no gaps. It's very different than a powder compact, right? Where you're trying to make contact between either the carbon particles and the cathode particles or the cathode and the cathode. That's a very difficult thing to do and typically takes really high compressive force. So we did not go down this path. So these cathodes are just freestanding interconnected cathodes, right? So there's maybe 20 to 25 to 30% porosity there for the solid electrolyte. But in fact, the cathode itself is, functional by itself without carbon, without binder. And interesting. So in terms of processing, is it you mix a cathode together with the ceramic particle together or is it you form a cathode for you infiltrate it? Yeah, the second approach, the second approach. Yeah, that makes sense now. Yeah, if you do the second approach. Yeah, because your cathode- It'd be difficult to do. Yeah, it'd be very difficult. So there are some people who've talked about infiltrating say liquid sulfides into such a structure. That's not how we do it. That would be difficult to do because once you soften these glasses, right? You go above the melting point, the viscosity of the glasses is pretty high. It's not like octane or water or things like that who have very low viscosity material. So we use a different approach. So even though we can soften glass and we can move the glass, you're not gonna be able to get it into the fine pore structure that way. So we have a slightly different approach. But nevertheless, it is effectively what you said. We make a discrete, porous three-dimensional cathode and then we bring the solid electrolyte into that pore structure. Yeah, yeah, yeah, okay, it makes sense. Steve, there's also overall question about the power density. Let's use the current density, you know, to do for discussion, right? Yeah, yeah. Our primary cell and also for the rechargeable, whether it's hybrid or also a state cell, could you discuss a little bit about the current density? Yeah, sure, so if we start first with the polycrystalline approach, right? Which is the water-stable electrode, we've discharged those structures as high as four milliamps per centimeter squared. And you can get virtually full capacity. So when you do that, you know, I would say we probably get 96% of the lithium capacity in that structure out. You know, if you go at lower current densities, obviously you get close to 100. So not much of a problem beyond four milliamps per centimeter squared. The problem you're gonna have is the current, if you look at the current lines, the current distribution starts to get increasingly non-uniform. So you'll start to subtract the lithium in an kind of an uneven way from the electrode. So I think above four million, it's not that we can't do it, but I would say that's probably not the domain you wanna work in with the rechargeable system with glass. So I would say we've run, we certainly run at C-rate, right? Where you're discharging three, three to four milliamp hours per square across, which means you're running at, you know, three to four milliamps per square. We have not gone much higher than that. And on charge, you know, so this is a whole question of quick charge. I would say that's still an open question. There's, you know, if fundamentally there's no reason you can't do it, but practically, and I think Eric will probably touch on this as well, the possibility of breaking the glass, right? Is gonna increase as a function of surface defects, right? So we don't want any kind of sharp kind of defects on the surface where, you know, lithium extrusion could open up a crack. And so, and I think as we continue to optimize the glass processing, we should, that'll allow us to go to higher current density. And if you look at a product like willow glass, right? Which Corning makes. So that's a very optimized process for making thin glass. If you look at the surface roughness specification on that particular glass, it's, I think the RA values are something like 0.05 nanometers. So you can get to extremely smooth surfaces with these types of glass process, but we're not there yet. So we're still optimizing. Yeah. Yeah, that's good Steve. Maybe I ask one last question for the time consideration. For the polycrystalline, you show 10 to minus three cement per centimeter only conductivity. Yes. And how high is the sulfide glass one? And also over one to see your thought about is a 10 to minus three sufficient life? Well, I think most of the applications is it absolutely important to go higher or 10 to minus three is sufficient? Yeah. But as a separator, it's certainly high enough, right? Cause if you look at the ASR value at 15 microns, I think it's like two ohms centimeter squared. So that's gonna be a trivial loss, right? Across that membrane in the composite cathode. Yeah. So it'd be nice to be even higher than 10 to minus three. I mean, obviously sulfides have achieved higher conductivity, right? There are sulfides that are as high as 10 to the minus two, but those are not glasses. Those are actually crystalline materials themselves. So there's probably still room for improvement within the sulfides in terms of the on a connectivity itself. But 10 to minus three, I'd say that's kind of a, that's certainly good enough, but I think there's room for improvement. Yeah. That's great Steve. Let me just make last comment and then inviting Will and Eric to the stage. Well, Steve, I have been very impressed over the years by you, by Paulie, plus we have been the person very honest to bear with the status of the art, right? So we know, sorry, electrolyte is not easy, but you have been the person I really look up to. You know, you tell me the state of life information and very honest information. Thank you so much. Yeah, you're welcome. Yeah. It's a pleasure to be here. Okay, Will, pass to you. Thank you, E and Steve. Let me add my thanks as well. It's always great to see data in presentations, especially from industry. We really appreciate it. Yeah, you bet. All right. Well, now to compliment Steve's talk on applications and manufacturing of solid state electrolyte and solid state batteries. I'm really delighted to welcome Eric Herbert from Michigan Tech to join us. And let me briefly introduce Eric. Like Steve, it also had a very extensive career spanning industry, national lab and academia. And I think you will soon also tell us back to the national lab as well. So prior to joining Michigan Tech, Eric spent a number of years in industry developing metrology and mechanical testing with a focus on mechanical testing in extreme and operating environments, especially for non-ambient mechanical property characterization. And at Michigan Tech, he has been investigating fundamental mechanical properties and mechanics and then recently extending that to explain behaviors in battery and energy storage applications. So I'm really delighted to welcome Eric and for him to give us a bit more fundamental insights to the mechanical phenomena that governs the lithium metal solid electrolyte interface that Steve just spoke about. Eric, we're delighted to have you. All right. Thank you very much for the introduction and the invitation to be here today. It is definitely an honor. They're well just to be here to do the presentation for you guys and Steve. So thank you. Right. So as you said, I'm going to talk about the critical role of mechanics and specifically I'm going to focus on the mechanical instabilities that develop at this critical interface between the lithium electrode and our solid state electrolyte. So first thing I want to do is just thank all of my collaborators because without all of their hard work I certainly wouldn't be here today participating in a seminar. So to all of them, I would like to give a hand to them. Thank you. Right. So as I'm sure many of you are all aware research in the field of solid state batteries has really begun to step out of this traditional electric chemistry box, I'll call it. And really started to try to think about how these non-uniform lithium ion transfer kinetics are driving these mechanical instabilities that form at the interface between the lithium anode here and our solid electrolyte separator. So this schematic in the center of the slide I think does a pretty good job of just trying to graphically communicate the basic problem for us. And so the idea is that these three shapes physically represent some type of morphological defect in the surface of our separator. And so those defects are going to be any sort of deviation from a plane or interface. Packs, cores, frame-bound reviews, surface roughness, there's lots of possibilities there. And so these defects are presumably going to be filled with lithium. That's going to come from previous plating and stripping or from an external required stack pressure or some combination of all those things, right? And so the upshot for us here is that these lithium-filled interface defects are what happens is, is they create a local gradient in the chemical potential and that gradient forces the incoming lithium ions to be charging the preferentially played out into these defects, right? And so as that happens, the pressure in these defects basically just climbs, right? And so it creates this mechanical instability that is thought to be the precursor to the formation and growth of the lithium-bendrites or filaments that are originating at this interface and then working their way through the separator and the cousin where they solve the short circuit, right? So ideally what we're after, what we'd like to have is just a planar plating and stripping reports of the anode, right? But we could just plate one atomic layer at a time then we'd have no gradient in the lattice parameter here and we'd just have a nominally stress-free interface, right? No instabilities. So that's what we'd like to have. The problem we have to deal with though is that these lithium-filled interface defects, right? That's gonna create this non-uniform plating and that's gonna give us this gradient in the lattice parameter here, that gradient in the lattice parameter creates a local gradient in the pressure, right? And the magnitude of that pressure is gonna depend on the elastic modulus of the lithium within this localized volume of material. It's also gonna depend on the stress-reversed and mechanisms that are available to operate not only within the lithium, but of course through here on the other side if you wanna face some separators, yeah, right? So in broad brush strokes, that's sort of what the basic problem is for us and we have to think about trying to solve that, right? So this is one of Jeff Sakamoto's micrographs. I'm sure many of you have seen this numerous occasions. So what I think is particularly fascinating about that we're not just this image, but just the deformation mechanism, the failure mechanism here is that even when we go to a single crystal version of LLZO that doesn't just solve the problem, right? The lithium just finds another defector exploit and finds another way to penetrate this ceramic separator and cause the cell to short circuit and fail. So sort of the million dollar question here from the mechanic standpoint is how involved is lithium units, right? How can it possibly support the pressures that are required to penetrate? In this case, they're coming through the rain boundaries, but a single crystal version and it's just going right through the separator, right? So how does it support the pressures that are required? Yeah, so that micrograph just illustrates perfectly the problem that we're trying to solve, right? And in order to do that, we've got to figure out how to engineer materials and design cells that can obviously prevent the formation and growth of these lithium forms, right? So to that end, as I said, the ideal goal here is to try to get this stress-free plating and stripping of the anode, but when we can achieve that, then we're going to have to rely on materials that can intentionally be engineered to alleviate this localized pressure at the interface, right? And in order to do that, we're going to have to know something about the active stress relief mechanisms that are operating in these materials and we're going to have to know how those mechanisms change in going from one anode material to the next, right? And then of course, there's the separator side of the puzzle, right? That's obviously going to play a major role in stress relief as well. And there's a bit of a kind of a whopper of a challenge in there because the stress relief mechanisms in the separators are obviously going to be really different as we go from ceramic to glasses to polymers and deposit materials, right? So there's a lot of moving parts in there, right? And if that wasn't complicated enough, then we also need to know how the efficiency of those stress relief mechanisms is going to change with operating conditions like temperature, current density, and cycling of the anode, right? So bottom line is we've learned a whole lot about that, I'd say in the past two to five years, but there's still a lot of knowledge gaps to try to fill in here, all right? So I think one of the most important things I want to try to get across and bring to your attention is the idea of relevant length scales, right? And so clearly the mechanical properties of bulk lithium metal are really important to us, right? But the mechanism of action that limits the pressure in this case to one megapascal, right? That mechanism may be completely inoperable at the length scales of these local inhomogeneities, right? These stress concentrations that are forming at this critical interface. And without those mechanisms, right? It's not clear what happened, or it'll be more clear after this presentation what happens then that mechanism is not available to keep the pressure at or below this one megapascal threshold, right? So that's really the, I think one of the fundamental messages here is that it's not just about the bulk properties of lithium, it's about what's happening at these small length scales relevant to the defects that are at the interface there between the separator and the lithium element, right? Okay. I think just to try to drive home that basic concept and give you a feel for what some of these mechanisms are and how we expect them to be operating. I just wanna walk you through this sort of simple graphical description of this whole idea of this length scale effect, right? And so we're gonna do that and try to do that in the context of these mechanisms that are controlling the pressure within these lithium-fuel interface defects, right? So this schematic over here on the left is basically just trying to communicate to us what's happening with the pressure, how much pressure can be sustained within these defects but as a function of length scale, right? And so this yellowish box down here in the corner physically that's just a length scale limit that once we get above that point self-limiting the whole lithium is capped by its flow stress, right? So in that box it's all about bigger length scales it's all about the bulk properties of lithium, okay? So now if we go to smaller length scales then the pressure initially is gonna climb, right? It's gonna move up in this direction as we go to smaller length scales. And that's happening just because it's smaller length scales it becomes statistically harder to find the mobile dislocations, the active dislocation multiplication sources or the grain boundaries or the defects that we nominally need in order to have any sort of form of efficient stress relief in our plastic definition, right? And so keep in mind for lithium even just at room temperature it's continuously annealing, right? This location density is always decreasing with time. So you're gonna room temperature, right? It's just constantly in this mode of recovery. So at some point here where it is continue to go down in length scale the idea is that there's gonna be this reversal that takes place in the pressure, right? And this reversal happens because the dominant mechanism of action that is controlling the stress relief or the pressure within that defect where it's taken to be involving diffusion, right? And so that mechanism becomes more and more efficient as the diffusion length gets shorter and shorter, right? So the net effect is that there's sort of this critical defect dimension that is just right for maximizing a stress concentration making that stress as big as possible. And that's the stresses or those are the stresses that are the most likely to cause the electrolyte to fail by the lecture. And so we refer to this critical length scale here as just the defect danger zone, all right? So the bottom line is larger defects like this one they're gonna pose less of a threat because there's volumes big enough that there's a high probability of finding the dislocations that are required to enable this stress relief by plastic flow, right? They're gonna keep the pressure a megapascal or less roughly, right? And then these smaller defects they're not gonna cause too many problems either because the stress directed diffusion is gonna be an efficient stress relief mechanism, right? But then it's the defect volumes that are in between these two, right? These are the defect volumes that are potentially gonna cause a problem. They're too big for diffusion to be an efficient stress relief mechanism but they're too large to have a high probability of finding the defects that you need to enable plastic flow keep the pressure below a megapascal, all right? So in very broad brush strokes that's the basic concept of this length scale dependent strength and then how that length scale dependence relates to the development of stress intensification at this varied interface here between a lithium anode and a solid electrolyte separator, all right? And I think just for the interest of time we're gonna skip over those two particular issues, but yeah. So this next slide, not gonna go into any of the details here but basically it's just explaining that this concept of smaller and stronger is not a new phenomenon, right? It's actually been around for a really long time. This was some work that was done by Feltland and Gebrenner in 1956 and it's just illustrating the same concept that we're using to describe what's going on with the lithium. I'm not gonna get into the details of this. Happy to chat about it afterwards if you have any questions, but this is not an idea that we came up with on any stretch, it's been around for quite a while, all right? So in order to really try to examine these length scale dependent strength issues in lithium we turn to an experimental technique called nano-inventation, right? And so the basic idea is that we're gonna drive this probe of some known geometry into the surface of the lithium and that we're gonna simultaneously record the applied load and then this measured displacements, right? And so it's data like these that we're gonna use to extract the mechanical properties of interest and initially the properties we're after are the hardness and then the elastic modulus, right? And so over here on the left is kind of a big long, laundry list of why we've opted to go this route. I'm not gonna take the time to discuss any of those now but again, if you have any questions about that I'd be happy to explain why I think the nano-inventation is really well suited to trying to better understand this problem, right? So this is just a schematic illustration of what our electromagnetic actuator looks like and again, we really don't need to get into any of the details of that but if you're interested in learning more about that I'm happy to tell you all about it and why some of the design features for that are particularly relevant to the experiments that we're trying to do with olefin, right? So here, yeah, I'm not gonna go into these details either but I would be very remiss to not point out that these experiments are really pretty challenging. So as my old advisor used to joke around and say there'll just a lot of snakes in the wood pile here so it's really difficult to do all the hoop jumping and dotting the eyes across on the tees to make sure that you're really measuring what you think you're measuring in these experiments so a lot of things to discuss there. Right, so anyway, moving on from that this is just a picture of our nano-inventation system and it's a dedicated glove box so you can see here's the actuator here there's a test specimen and then this of course is the microscope that we use for targeting and any sort of post-test analysis of the residual hardness impressions here and so the lion's share of the work is just right there inside the glove box. Right, so I wanna get started just by taking a look at the measured elastic modulus, right? And so we're interested in the modulus that we measure in the lithium films for these three basic reasons, right? So first the magnitude plays a really key role in telling us what the pressure is gonna be within these lithium filled interface defects and the tube gives us some insight into any contaminants that are forming on the surface of our lithium and then the three it allows us to indirectly verify the area calculations that we're gonna use to determine the hardness and that's telling us what the pressure is, right? So this plot in the middle here this is showing us the average elastic modulus for five micron thick vapor-deposited lithium film on a glass substrate and so these open squares up here represent the nominally measured modulus which is strongly influenced by the glass substrate you can see and then these half filled symbols here those represent the actual modulus of the lithium film once the substrate effect has been removed using a spin film model developed by Jennifer Hay and Brian Crawford, right? And so as you can see once we get the substrate effect out and the modulus data are predominantly dependent and they're in good agreement with the literature values, right? And so this is also telling us that the film is not significant and contaminated, right? So moving on from that just a few more experiments to really take a look at the modulus and see what we can learn about the texture in the film thickness. So this plot is showing us the cumulative probability for the elastic modulus as measured from three different arrays and two different films. So one's five micron thick the other one's 19, sorry, 18 microns, right? And so the range in modulus that we see here is really consistent with the elastic or isotropy that we would expect. And the difference in the mean value is telling us that there is a slight texture effect with the film thickness there, right? So the next thing I wanna do is take a look at the hardness, right? But before we look at the hardness of the lithium I wanna give you an idea of what to nominate expect, right? So mathematically over here hardness is just the applied load normalized by this projected contact area, right? So when we define it that way hardness is just the applied, sorry, hardness is just physically it's representing the mean pressure that the surface is capable of supporting, right? And so when you think about that in the context of a bulk homogeneous crystalline metal at a low homologous temperature what we nominate expect is that plasticity is gonna be controlled by dislocation wide and that at that case the hardness that we measure out here at deep depths is not only gonna be three times the flow stress or in this case, three times the yield stress. And so for our lithium our expectation would be that out here at deep depths the hardness is gonna be somewhere in the neighborhood of about one and a half to three megapascals, right? And so as you work your way to smaller depths there's kind of an interesting thing that happens when you get to a depth of about one to three microns and below that range the hardness starts trending up and the reason for that even in a bulk homogeneous material it's something called the indentation size effect, right? And so I'm not gonna talk about that in any details but this is this red line physically represents what we would nominally expect to see for this bulk homogeneous crystalline material, right? And our expected hardness is gonna be somewhere in the neighborhood of this one to three megapascals, right? Clearly for the lithium we're not in the realm of bulk, right? Because we're looking at relatively small volumes it is certainly homogeneous, it's crystalline but we are not at a low homologous temperature either, right? And so all of that is gonna translate into giving us a very, very different data set because our hardness as a function of depth that's nothing like this red curve, all right? And so here it is. In this data set, right? We're looking at the average of 100 measurements in the hardness, right? Performed on a single lithium film. And so over here on the right we've got several representative load displacement curves and these curves help us try to rationalize and figure out what's going on over here in the hardness data, right? So the first thing I would point out is that this depth dependence in the hardness doesn't look anything like what we nominally expect, right? There's a ton of scatter in the data but the average values are remarkably repeatable. And beyond that, this pressure that we're measuring it surprisingly is climbing here, right? It's not going up, it's not constant, it's in fact, it's climbing, right? So it's climbing to this peak value of nearly 40 megapascals and that's at about 400 nanometers, right? And then after that, it abruptly falls off, you know, just headed down this cliff, basically. So when you look at what's happening over here in the load displacement curves, this peak corresponds to these strain bursts that show up over here in the load displacement data, all right? And so it's a little bit easier to see that if we take a look at these individual curves now. And so here we've got six out of the hundred curves that went into creating this set of average data here, right? And so as you can see, the average peak here corresponds to these strain bursts, right? And yeah, so that's it. So as I mentioned, the yield strength of the bulk lithium is about three, or sorry, about one MPA. So the expected value is somewhere around three and clearly we're way above that. And even if you bring in the indentation size effect, you know, to get from one to 40, we're way beyond what we would expect to see for the indentation size effect as well. What I would also point out though, is that we're not anywhere near the theoretical shear strength of lithium either. At 40 MPA, we're somewhere in the neighborhood of about 14% of that value, right? Assuming it's somewhere in the range of G over two pi to G over 30, right? So the important takeaway here, right, is that before this transition occurs, right, before you get to this peak, these pressures are climbing in a way that is pretty difficult to rationalize. And if there's dislocation motion over here, it is clearly extremely inefficient, right? And then once this avalanche event occurs, the data here are characteristic of stick slip behavior and in general are sort of consistent with what we expect out of the indentation size effect, right? So with all of that information there about what's happening experimentally, the way that we rationalize that is that prior to this peak, we think that all of this deformation here is being accommodated by stress-directed diffusion, right? And that's what gives rise to this unexpected depth dependence. So as you drive the indenter in, the diffusion length is getting longer and longer. And as a result, that mechanism becomes less and less efficient. So the pressure climbs, right? And then eventually the stressed volume is big enough so that the threshold and stress and threshold and volume, those two things are large enough, right? Clearly it's stochastic, right? It varies from one location to the next. But that volume becomes large enough to encompass either a mobile dislocation or in this case, right, with this avalanche, it's gotta be some type of dislocation, multiplication source. And that's what allows this pressure to fall off and then we get into more dislocation mediated flow, right? But that's our basic picture of what we think is happening with the lithium. And so as you go to higher strain rates, right? Basically what we see is that low strain rates, we have no difficulty here rationalizing that with this volume diffusion mechanism, that's this Nabarro herring. It doesn't work nearly as well as we go to higher strain rates but at least it has the same sort of trend. And then at the highest strain rate still, then the hardness does trend down, right? And it begins to take on the shape of that indentation size effect but it is not consistent with any of that behavior in the way that we nominally expect it. So when we look at other diffusion mechanisms we can rationalize this pretty well with something called Harper-Dorn. And this is just a non-conservative climb process. Still requires the dislocations but a very different mechanism from Nabarro herring and clearly it's just a much less efficient mechanism, right? So at any rate, this is what we see in the context of what sort of pressures can be supported by lithium at relatively small length scales. And when you look at these numbers, right? These are huge. They're orders of magnitude larger than what we would nominally expect, okay? And so that's gonna create some problems for us when we try to think about how to mitigate these stresses that are developing at this interface. When I'm looking at the clock and time is running away. So let me just skip through some of these, sorry. What I wanna really try to get to and it was just sort of at the tail end, clearly in order to alleviate that pressure, we're gonna have to figure out how to engineer some micro-scaled ductility into the lithium. There's a lot of ways to potentially do that. But we're also gonna have to figure out how to do that into the solid electrolyte separators, right? And so there's lots of ways to think about enabling some sort of micro-scaled ductility through densification and some shear flow maybe. There's lots of interesting tricks to potentially do that. And when we look at some of these stress relaxation mechanisms and materials like lipon, it's really interesting what we see and to think about how you might alter the structure property relationships and other materials to try to work towards these types of goals so that you can have stress relief from the separator. So this is the stress exponent for creep that we measure in lipon. So that's telling us something unique about the stress relaxation mechanisms in that material. And in fact, when we look at data from these cyclic experiments in lipon, again, you see this very interesting energy dissipation capability in lipon. And so the next step is to think about how we would do sort of a more targeted approach to measure the mechanical properties and subject it to the sinusoidal loading. So we can do that for a 600 second block and then look at these data in terms of load and displacement. This is not on lipon, but this is where we're headed next. And we're looking for this energy dissipation capability so that we can figure out how to relate that back to structure property relationships and then use that to inform decisions about processing so that we can try to create interfaces that are capable of mitigating these unwanted stresses that build up, right? So I guess just in closing here, a lot of takeaways from all of this, but I think the most important message to get in relation to generating future models to try to address these issues is that you really have to think about the mechanical properties of these materials at relevant length scales. And those relevant length scales are gonna be the length scales of defects at the interface, right? The bulk properties are clearly important, but those properties alone are not gonna allow you to solve this problem, right? So we need length scale effects and we need to think about how those length scale effects are gonna be impacted by a number of operating conditions. So temperature, current density, cycling, right? And so there's a lot of ways to potentially do that by controlling these structure property processing relationships and it's on the anode side and the separator side. So there's just a lot of really interesting space to explore there to try to engineer stress relief mechanisms and create mechanically stable interfaces. So with that, I will end and I'm happy to take any questions you have. Eric, thank you so much for the presentation, really appreciate it. Let me start just with one question on interfaces. So Eric, you highlighted the importance of length scale dependence in the mechanical property of lithium metal. And your depth dependence really illustrates that as well. So I'm curious if you can comment a little bit on the interaction between the mechanical property and the chemistry. So whether it's intentional or unintentional, there's always a considerable impurity segregations at the surface of lithium metal, for example. And these can really be quite deep. Certainly tens of nanometers, some cases hundreds, depending on how the impurity was introduced, whether it was pre-existing and because the mobility of the impurities is also very high in lithium. So I'm curious if you're able to draw some connection between the mechanical property and the chemistry at the interface. So my only insight into that is by looking at lithium surfaces that have been intentionally, for lack of a better term, I'll say contaminated, right? And yes, we see a huge change in the behavior. And the problem is that at least the contamination layers that we've looked at so far, they effectively inhibit this surface diffusion capability. And so you're robbing that stress relief mechanism of the lithium. And so, yeah, the pressures that we observe at small depths get, again, really high. And even when we're at slow strain rates or low strain rates, the difference between the best lithium surfaces we can produce and look at, it's very different than when the surface is intentionally contaminated, right? And when we look at just the effect of operating conditions, well, never mind, I guess we'll leave that alone. So does that answer your question? Absolutely, Eric. So let me just make sure I understand. So your current thinking is that impurities would decrease the mechanical strength of lithium, will be detrimental to lithium metal in terms of reversible plating and stripping. So from a mechanic standpoint, and I guess I should be really careful about that, you've worded that really well. So, no, it's conceivable that adding alloying elements maybe something like aluminum, right? Obviously you're gonna pay an energy density penalty, but it could be that there are ways to alloy the lithium that promote this self-diffusion capability and make that mechanism more efficient. And therefore it becomes much more capable of creating a mechanically stable interface, right? So that possibility is definitely there. And we're actually, looking at that right now. So what I was speaking to was the existence of a contamination layer. So it's, you know, lithium that's been freshly deposited and then immediately introducing a CO2 atmosphere to the deposition chamber, the evaporation chamber, and then depositing this contamination layer on the surface, right? The other place that we see something like that is when we look at lithium from commercial suppliers, you know, the lithium has some contamination layer on the surface and that layer has a profound impact on what we see in the mechanics near the free surface. And you'd obviously expect that to be there, but the effect was really profound. So I guess the moral of the story there was, okay, we really need to try to figure out how to either clean those surfaces off or just deposit the lithium in a way that those contaminants just aren't there or they're minimized, right? Yeah, we should definitely talk about this in the panel discussion with Steve on the challenges of processing lithium and essentially choose up everything. So it's very good at scavenging everything on the surface. Maybe let me just ask one more question and then we can bring Steve into the panel discussion. Your work that you presented mostly focuses on the property of these nano-intentation in thin and thick films of lithium. Have you also explored size effects in lithium? I'm not sure how easy this is to do, but it's being increasingly recognized that after repeated stripping and plating cycle, that de-wetting of lithium from solid electrolyte can lead to smaller and smaller structures at the interface, creating porosity. And I imagine that would also have a really substantial impact on mechanical properties as well. Yeah, certainly could. And we have high hopes of being able to do that. We're trying to figure out just how to do the integration to be able to cycle the lithium in our glove box and then do experiments on the cycled surfaces. Nancy Dudney came up with a clever way to create a cell that would allow us to do that and still have an exposed lithium surface, even though it had been cycled many times. So we're trying to figure out how to do that right now. But yes, you're exactly right. And that's why we're doing it because we expect there to be a difference. And that will be a really incredibly informative experiment, especially if you start with no lithium and just the plated. It should be the purest lithium you can get. That's right. Lithium-free cell basically to begin with. Right, exactly. That would be really exciting. Wonderful, Eric. So I see Steve has already joined us. So if I can ask Justin to spotlight the three of us. Perfect. And I think he unfortunately had to attend to another matter. So let me begin just continuing along the same line of discussion. You know, when it comes to manufacturing, right? Of solid-state batteries, you know, impurities, defects are all very critical as both of you highlighted repeatedly. Yeah. Can you give us some sense the impurity and the defect requirements of solid-electro in comparison to other technical material? So Steve, you mentioned, you know, glasses are obviously scaled and manufactured very inexpensively, but I think we don't have a good idea, you know, is that good enough in terms of impurity and defects or is the requirement for solid-state battery pushing even those glasses even to a higher territory? So basically I'm trying to understand a little bit of how the requirements of a solid-state battery may impact the cost of processing moving forward and whether or not what is a good comparison is another material that sort of have similar requirements in terms of defects and impurities. Yeah, you're right. It's pretty early, you know, in that process of looking at impurities and performance and how this is gonna map out in terms of cost. I can tell you that in a very simple sense, if we're melting raw materials to form glass and then the idea is that you're gonna pull, say thin ribbons of glass from that, you can imagine that if you have 50 micron inclusions, that then becomes an impossibility. You're not gonna be able to pull 20 micron glass if there are particles embedded. And absolutely as when we started this work, that was certainly a problem, right? You know, many of these, so the sulfide glasses typically when you make them are being, they're done in quartz ampules of some type because they have to be isolated from oxygen and moisture. So that puts a certain requirement on the, actually on the quartz itself because these can be corrosive materials. So quite often then you're coating the quartz with a protective layer. And if that protective layer spalls and gets into the melt, yeah, then that is it. So all of those things are issues, you know, absolutely. I think in terms of the raw materials for glass making themselves, lithium sulfide tends to be very high purity. There are a number of producers now, in fact, Toyota's entrance into this domain, right? Working with sulfides has in some ways pushed suppliers to look at these kind of impurities and scaling a little bit more carefully. That's helped us as well. So we don't see any problem right now with, I would say at least the LI2S source that's, and it's a big part of the glass, by the way. Many of these glasses are 70 mole percent LI2S, right? So it's very much a big part of the glass melting and glass processing. And then in the other side, so that that's the network modifier, then the network formers are typically chosen from P2S5, B2S3 and SIS2, right? Those are the key constituents. And yeah, absolutely, you have to be very careful how that is kind of, you know, one, where are you getting your raw materials from? Two, how you're processing them? Absolutely, it's for sure a part of this. And I don't know if I mentioned it, but if you look at, I think E had a question about, you know, surface topography. If you look at silica glasses, that's a very mature industry, obviously, right? And you would look at something like willow glass, which is a corning product, and then look at the spec for surface roughness on that drawn glass. It's pretty remarkable. I think the RA value is spec'd at 0.05 nanometers, right? So these are 0.05 nanometers, yeah. Nanometers. Yeah, basically, atomically smooth. And actually, if you look at the bend strength of a lot of these, you know, thin glass display materials, if they're laser cut, you know, so that you have a near perfect edge, because that's typically the way these glasses break. If you have a mechanically cut edge, you're gonna have defects at the edge. They'll break because of defects at the edge of the glass, not really from the surface of the glass. But if you look at laser cut, thin glass, the bend strength approaches the bond strength of the silicon oxygen bond. So you can get really, really strong materials if you're careful about, yeah, surface defects and edge control. And, you know, this is one of the reasons, another one of the reasons we're pushing down this path, is that you can get, you can, certainly theoretically get to very, very smooth, almost defect-free surfaces, right, in the long term. We're not there yet. And in fact, if you were to look at, there are a variety of ways to make thin glass sheet. You can imagine, obviously there's a float process that's not gonna work for sulfides. Corning has something known as the fusion process where you have effectively two molten streams of glass coming over a platinum structure. And so that flowing glass, the outside edge of the glass has never touched the surface. The inside edge has touched the platinum surface, but then, you know, they basically blow the two surfaces together and fuse them. So you have a single glass sheet coming down. And in that case, neither the top or bottom surface of the glass has ever touched anything. And that's how you get to these remarkably smooth materials, right? So there are different ways to, and that may in fact work for that kind of a fusion process might work long-term, but the scale of doing fusion glasses is huge, right? So, you know, we don't have the, you know, multiple truckloads of sulfide glass right now that would be required to do that. But I think in the long-term, you should be able to get to, you know, I would say ideally defect-free glass. See, this is really exciting. So I think what you're describing here is there are materials today massively produced that has the right defect density for solid-state batteries. That's right. Right? If it's nanometer, you know, type of defect and roughness, that's, we're all set, right? Yes. So am I correct to interpret that? Then you feel manufacturing these completely defect-free glass should not be a problem. Yeah, right. I mean, well, it'll be, it'll be technically challenging like it, you know, if you go back to the early days of making thin glass display glass, right? I mean, there's, you know, there's certainly a lot of very clever innovation down there. But that's right. There's an existence proof, right? For virtually defect-free materials. And, you know, you just, you know, it's gonna be very difficult to replicate that with any kind of a crystalline material. I mean, I don't know how you do it. But with glasses, you know, you have that, you definitely have that path, right? Where you can get to these defect-free materials. And if you look at the, for instance, a product like Willow Glass, right? Which is sold commercially, it's relatively inexpensive, right? So you're getting to these near-perfect materials. I mean, that's driven, obviously, by the large LCD flat-panel TV, you know, markets. They're very large, very profitable. But those glass sheets are produced at low cost and in high, high volume. And it certainly was one of the drivers for us to move in this direction. Well, this is very exciting. Thank you, Stephen. Eric, I was wondering if you can also comment a bit on this aspect of defect, sort of the minimum defect, or the maximum allowed defect density at the electrolyte interface that will be needed. Sure. So I think everything Steve just said is, you know, that's wonderful, right? That's what we should definitely be shooting for to the extent that we can achieve that. Definitely headed in the right direction. The only thing that is a bit of a red flag that still exists for me in that, you know, even if Elvis showed up and just made a perfectly flat interface for us, right? It's tomically flat. One of the things that Jeff Sakamoto showed is that these failure events can occur from just localized regions at the interface where there's some perturbation. And I guess it's not a battery person here. So I think it was an over-potential or the exchange current density, right? Some minor perturbation in there that creates this preferential diffusion of lithium into sort of a hotspot, right? So it's plain interface, but still that perturbation. And that scenario creates the same problem that we're trying to solve with physical defect, right? So, you know, I think in the end, I would, I'd go after it on two fronts if I could. I'd do exactly what Steve just outlined. I'd be gunning for that. And then I would also follow this path of trying to figure out how to engineer my material to alleviate stress, right? I would engineer it to have these stress relaxation mechanisms that can cope with the pressures that develop these, you know, stress concentrations, mechanical instabilities, whatever you want to call them. Wherever they show up, whether it's at a defect or a planar interface that has this, you know, variation in the electrochemical properties. So that's my immediate thought there. And then the second question, or sorry, second point I wanted to make to your question was, you know, we did exactly what you were talking about. We went back and said, okay, let's try to create a deformation mechanism map that says, here's the defect dimension. You know, what is the defect danger zone I was talking about, right? What are the physical dimensions for that? And can we have some shot of just avoiding that, right? Don't go there. And the problem with that is that that defect danger zone depends pretty heavily on a lot of operating conditions. So it's current density, it's the modulus of the lithium that's in the defect. It's the physical geometry of the defect, right? And so now that critical, you know, dimension that defect danger zone, it's very much a moving target. So it's not like you can just say, hey, here's the, you know, the dimension we need to avoid. Well, okay, it's that dimension for these conditions, but we're gonna change the conditions and now it's a different one. So that doesn't seem like a very attractive approach to take. So, you know, what Steve's talking about just, okay, let's, you know, try to make that surface as smooth as we possibly can. That's gonna be the best way to mitigate, you know, the instabilities that would form in other defects, right? That's how you solve that problem. But, so anyway, that's my two cents worth on that. Yeah, and I think, you know, the other part of it, I think it points to some of the things you've been talking about, Eric, is also uniform current density as much as that is, and that's good for all battery systems, right? You kind of prefer to have uniform plating. I mean, that'll get worse as you go to higher and higher charging rates, right? So there may be a limit, right? On how, you know, this kind of quick charge, which is obviously desirable for things like EVs, that might be pushed, you know, a goal too far, we'll have to see. But we know, you know, with virtually all the electrical systems we work with, as you push current density up, the chance to have a more non-uniform current distribution increases, right? Because everything has to be near perfect otherwise to achieve that. I mean, on the other side too, you look at, now these are not particularly high current densities, but you look at these lipon cells, which was our original inspiration. Rather remarkable that you, you know, there have been reports of 10 to 15,000, you know, cycles at 100% depth of discharge. So there is something pretty unique about these lithium glass interfaces that can allow you to do that. And, you know, it's probably a combination of these things that we're talking about, but clearly it's possible. The question is like, you know, how difficult is it to get there? And how much? And how much? Yeah, yeah, right. Steve, this is a great segue to my next question. You know, which is sort of the converse of what we've been talking about. So Steve, you and Eric have been talking about mechanical damages or mechanical indentations on solid electrolytes. But I think a converse could also be that you have global stresses being applied to the battery. So Steve, you mentioned edge effects. I can also imagine, you know, slight bending in the cell when you put it into a multi-layer stack or a battery pack. And you know, we're putting these things really close together. So pressure non-uniformity will exist, no matter what, you know, you may have even inclusions and particles that you put into between the layers and that creates local stresses as well. So it would be great if we can also talk about a little bit of the manufacturing challenges again, how sensitive everything is to pressure uniformity. Is there going to be a challenge or what is the requirement in terms of how mechanically uniform the system has to be in terms of pressure? You know, we're dealing with very, very small cells here, but when we go to the lower cells, 20-layer cells. Man, I can only imagine what the non-uniformity must be. Yeah, I don't know, do you have a view on that, Eric, or do you want me to jump in? I guess, you know, what comes to mind for me is in that context is you're right. It does get kind of crazy because just pick a simple one like stack pressure, right? Stack pressure does all sorts of things to create these interface shear stresses that are opposing the flow of lithium, right? So you get this friction hill that develops and the friction hill depends on what the friction conditions are. Nobody really knows what values to plug in for that. And you get some really complex states of stress there that complicate this whole picture. So it's not immediately clear how all that fits together, right? It's a pretty challenging problem. And one of the most challenging aspects of it is those frictional stresses that develop at the interface. They change as you cycle the cell, right? So as you get thinner and thinner anodes, right? Cycling the cell and the radial dimensions, it's nominally the same. Is that ratio changes? Then the friction hill is totally changing as well. And so it's just a whole nother dimension of what gets added to the state of stress that is difficult to see how that influences, you know, your ability to maintain mechanically stable interfaces, right? So that's what immediately pops into my head when you start talking about these macroscopic stresses. Yeah, and I would, you know, I mean, take maybe some lesson from some of the work that's been done in adding silicon, right? To lithium ion cells, which is, you know, the stress is associated with expansion of the silicon. And, you know, so you see some companies now moving from pouch cells to cylindrical cells to take care of those stresses that are being generated. So, you know, anytime we start moving in a new direction in terms of cell configuration, cell structure, there will be unexpected, I would say, challenges. So as we start building up these multi-layer cells, I'm sure we're gonna have to address some of these things as well. So it's probably a bit early for us to project what that's gonna look like, but I'm sure that, you know, I can tell you in the early days of even building out these water stable electrodes where we were cycle, we're actually making rechargeable lithium air cells at that time. And you can imagine you've got a volume change in the lithium electrode, pretty substantial. You got a volume change in the air electrode because this is a rather unique structure. And all of those things have to be an intimate electrochemical contact to survive. And we were, so we in fact were able to engineer a solution to that particular technology where we had these, I would call them kind of pseudo springs, you know, these kind of silicone type springs that would actually maintain kind of a relatively constant pressure among components. And, you know, part of that kind of engineering is gonna be necessary here too because we have a lot of volume change in the negative electrode, right? In these glass structures. So there's absolutely some engineering challenges. It's a little bit difficult to say exactly what that's gonna do. I would say, I mean, relative to cost in, so for almost any new technology in the early days of introduction, it'll be a high priced technology, right? It wouldn't matter. Lithium ion I think in the early days was $8 a watt hour or something like that, right? Now it's, you know, I've seen far, far below that. So that's gonna be almost certainly the case with any of these new chemistries is, you know, as you introduce them to the market, you're gonna introduce them in premium markets that can afford to pay a price for this, you know, boon in energy density and specific energy. And then as, you know, as that engineering and manufacturing bachelors, you know, you start to find ways to do it in a kind of a, you know, a more elegant kind of cost effective way. So there'll be a learning curve here for sure. Steve absolutely agreed. You know, maybe continuing along this theme of manufacturing, especially high volume manufacturing. So maybe I can offer maybe a provocative point. You know, in the talk today, we compared a lot to, you know, solar cells and displays and so forth. Couldn't help to recognize that, you know, current density for batteries are generally pretty low, right? You know, they're a milliamp per square centimeter. That's right, that's right. If you compare this to solar cell, it's, you know, it's quite a bit lower. If I look at my computer, you know, I probably need about 10 to 20 times the area of my display for my battery, right? So, you know, you know, my, my whatever, you know, six by six inch display. Right. I'm guessing I need 20 or 30 layers of that to make a battery to support the computer. So that means, you know, even the cost comparison may not be fully valid because you have to make a lot more or you have to make a lot faster. And I think this presents an opportunity, but also a really big challenge. And I'm trying to understand sort of, you know, you know, audiences also spans the manufacturing industry as well. And I'm sure they're thinking about, you know, how do I get there? We can't just make it like Gorilla Glass. It has to be probably 10 times the speed and, you know, whatever the 10 times less the cost. So I want to sort of explore how big that gap is going for and a higher level in the air it goes. So from your industry experience as well is, you know, how much more do we need to reach this gap, to bridge to this gap? You know, we always think as, you know, several years away, I think we've been sharing and hearing that for decades. Several years. Yeah. So sorry for the provocative question, but I wanted to just, you know, maybe focus on this comparison to solar cells and display a little bit more to sort of see what more we need to do. Yeah, well, that's a tough question, clearly. Again, I would go back and look a bit at the history of the introduction of lithium ion, right? 1991, Sony introduces this technology to the world. And back, you know, at that time, I don't think those cells did more than a couple of hundred cycles, right? But nevertheless, you had a battery that was being charged, you know, basically close to the instability of the electrolyte, which obviously was a safety concern. And Sony had, as you probably know, but they had a bunch of electronic controls on each cell, right, to turn the cell off if you got into trouble. And all of that, I can certainly remember when it was introduced, most of the American manufacturers, I mean, battery manufacturers said, this is just, you know, nothing, right? It's not possible. You can't do that. It's not gonna be economically, it's never gonna scale. And so, yeah, obviously that mapped out quite differently, right? So these batteries were introduced in the three C's, you know, cell phones, camcorders, you know, and computers, right? Again, a pretty high price point. And then I think even at that time when American manufacturers looked at what was necessary, in terms of the tolerances of, you know, the cathode and anode coding processes and just, you know, just teetering on the edge of instability, which sound, and there were fires, as everybody knows, there were actually laptops that got in fire. There was a bunch, there were certainly a bunch of things that had to happen, you know. And in fact, there was, you know, this energy density improvement, right? The fact that these batteries were lighter and smaller, you know, that compelled, you know, the industry, right? To make rapid advances in manufacturing and chemistry. And this, you know, shortly after the introduction into the, say the three C's at presentations, largely by Japanese companies, the next, you know, one of the questions was, well, you know, are these batteries ever gonna see application in power tools? And I honestly got people laughed, right? It's just no way that's crazy. You know, you're just gonna have exploding power tools and, you know, that's irresponsible to even suggest that lithium line could end up in a power tool. And well, a couple of years later, they're in power tools. And then the next question was, you know, can they ever possibly see application in electric vehicles? And if you look at the early days when DOE was, you know, funding some of the work in the US and putting up cost targets, everybody thought that these DOE cost targets were crazy and could never be met, you know, both from a raw materials and low and behold, were there, right? And it continues to drop these costs. So, you know, the market, you know, if the market's there and it is, right? It's remarkable that will drive its own type of innovation which is a bit unpredictable, you know, as, and I can remember back when L.I.P.F.6 was a, you know, pretty expensive salt for lithium-ion that was controlled largely by Japanese manufacturers and low and behold, you know, company in China of, you know, basically engineers a solution that gets them at like half the price for L.I.P.F.6. No one saw that coming. Now they control that market. So there are gonna be parts of this process that are difficult to predict. But I think given the opportunities and the size of the market for advanced batteries, you know, I do think that that will drive innovation in ways that are a little bit difficult to predict. So, you know, and our course will be focused on certain parts of the technology that to get it into the market, but it's almost certain that there'll be other, once that's done, there'll be other players that will do rather ingenious things that are kind of difficult to predict, right? That will kind of lead the way. Now, there are, you know, clearly paths that you can't go down where you can just see that this is gonna be too expensive, right? You know, from kind of the get-go. And I mean, even when you look at things like the L.I.P. on batteries, it's not like people didn't. So that's a very interesting technology. I mean, cycles well, it's completely solid state. There were some pretty serious attempts to scale that technology, right? To actually take it into things like cell phones. And Apple was one of those contributors, right? They bought one of the like one type companies, I think it was IPS, Infinite Power Solutions, they were absorbed into the Apple sphere. And they, I think they did some, you know, of course they're quite tight-lipped about it, but they did some really innovative work there. And in fact, I was told by one of the kind of prime, one of the key scientists there that they can actually power an iPhone with this type of a battery. Which I found, you know, surprising because that requires some very innovative work on the cathode, right? To be able to have a composite cathode it, because normally those are, you know, just single material sputtered LCO type cathodes. In any case, they claim that they had it. And I asked them, well, okay, so when do we see it in an iPhone? And they said, well, there's a problem. And I said, well, you know, I can guess what their problem is, but how big? And they said, well, that's about a thousand times more expensive than a lithium-ion battery. So not everything can, you know, is going to transition that way, right? There are some approaches that I think you can say right from the get-go are going to be far too expensive downstream to ever, you know, see introduction into large commercial, you know, applications. But I think on the glass side, certainly we can look to other industries that take advantage of the way glasses manufactured, but that doesn't mean there won't be hurdles. There will be, right? We know we're certainly not there yet. I absolutely share your optimism, Steven. I think you're absolutely right that the glasses are a lot closer to others. And it's a great starting point. Absolutely. Eric, how about scientific gaps? That what we still need to cross? So from my standpoint, it's really just, you know, filling these knowledge gaps in relation to the mechanical properties as a functional length scale, right? So how do you engineer the materials to optimize their stress relaxation capabilities? So either alloying the lithium or orienting the lithium. So it has some preferential texture relative to the interface or doing some clever tricks with the electrolyte, right? That's what seems to me to be the the important element from materials engineering side, I guess, right? But I can only speak to that. I really don't even know how that stacks up in relation to the electrochemical issues that, you know, also have to be met, right? It's just one little piece of the puzzle. If I can build on that, Eric, you know, one thing I think it's really exciting. I think I alluded to this early and you emphasize this is this is the mechanical property of a highly reactive system. Actually, you know, can you maybe give us a sense of is there another reactive system in which the mechanical property is so critical? None that I'm aware of. I think this is really the frontier question that makes it so special scientifically. I mean, it's one of the most reactive metal. It is the most reactive metal. Maybe sodium is a little bit more reactive, but I think to me, scientifically, it's really rich. Oh, undoubtedly, yeah. And even, you know, take away the reactivity element of it, and it's just a matter of trying to understand the fundamentals of plasticity at small length scales in a material at a high homologous temperature, right? And we really don't do that very often either, right? I mean, all of our nuclear materials are probably the closest you come to that, but it's always about bulk properties, typically, certainly not always. And from a scientific standpoint, trying to explore those stress relaxation mechanisms in those materials is a lot harder because you got to be at temperatures that are, you know, 800 degrees C and above, right? And by the way, they are super inert, right? So, sure, right, exactly. So, we're a high homologous temperature, super reactive. So, yeah, right. That combination is unparalleled in lithium. Yeah, and to add to something, I think you said earlier, Eric, about, you know, the contamination of the surface of the lithium. Most people's experience with lithium, if you're buying it from any of these commercial suppliers is pretty, certainly the surfaces are quite dirty, right? I mean, they're actually intentionally contaminated, right? So, most producers of lithium foils will extrude and possibly calendar the lithium and then intentionally expose it to CO2 because they want to give it a surface that's reproducible, right, but it's always contaminated. And so, you know, there are quite a few, I would say, studies where people are trying to join lithium with a solid electrolyte, that's not so trivial unless you're evaporating and evaporation is kind of a clear path. But to make a connection between commercial lithium foils and solid electrolytes is pretty damn tough because of this contamination, which is either unintentional or intentional, but always there. Yeah, well, it certainly isn't a good thing for a mechanic standpoint. Right, right. Yep, yep. Yeah. So, Eric and Steve, you know, thank you so much for sharing all the deep insights. I thought I could end this session with a short question to the both of you. You know, in looking at your careers, I couldn't help to notice you're both extremely interdisciplinary. Steve, I think you mentioned you came from the solid oxide fuel cell world and there are a lot of commonalities and you know, we have a lot of students and young scientists and engineers in the audience. I was hoping that maybe you can comment on sort of your career path and how you were able to bring different fields together in a synergistic manner to solve problems, say here for energy storage and the energy transition. Yeah, I mean, certainly. So the fact, you know, my work in solid oxide fuels was kind of interesting because, and it did inform quite a bit of the work we do in solid state batteries. It was partly motivated by the fact that Polyplus is one of the first companies that was spun out of the Lawrence Berkeley National Labs. I think we were number two. We're certainly the only company that still exists from that era. At that time, it was a relatively new process for the national labs and universities, right? And there was a lot of concern regarding conflict of interest. So when we spun the company out, I retained my position at the lab. I was basically running both, which was a bit chaotic but in any case, I was told in no uncertain terms that I could no longer do battery research at the lab because it was too close to what we were doing offsite so this would be a conflict of interest. So I said, well, batteries is kind of what I know. So what do I do next? And I said, oh, fuel cells. So we actually embarked on and developed a program. And in fact, we, I think within a few years had the highest power density SOFC on the planet. And it was using kind of similar techniques to what I described today where we actually supported thin zirconium membranes on composite structures and co-fired them and densified them into pinhole-free structures. So we had, yeah, we had two micron to five micron thick zirconia and that allowed us to run. Of course, the current densities there are a lot different than battery current densities, right? They're amps per square centimeter, not milliamps. So it's a quite a different domain but in any case, it's certainly informed a lot of the work that we're doing now at Polyplus. And, you know, it's a, it's not a bad, you know all these electrical systems share some commonalities even though there may be orders of magnitude differences in terms of the current you're running and different temperature regimes but I certainly would recommend a multi-test learning approach to anybody working in this field because there's so many materials at play here and there's so many different interfaces that we have to accommodate that, you know that there's no doubt that having, I would say a kind of multi-disciplinary background is gonna help I think people be a bit more adventurous in their thinking. And I got a couple of dogs that just joined me but... And I guess you can always thank compliance requirements at National Labs as the origin of innovation. Yeah, yeah, that's right. That's absolutely right. Eric, your thoughts. So, yeah, a lot of what Steve said, I would say the same thing. I think the collaborations, right? That's really the only key piece of the puzzle. Without that, I never would have gotten anywhere in the battery materials. In fact, I still remember the very first day I ever saw any data come back from lithium and nano indentation experiment. And I just sort of looked at the computer screen and was like, yeah, how many things to do with that? That's messy and I was ready to go. And where I had come from, I was doing a lot of work with the micro electronics industry at the time and we were doing a lot of work on low-key dialectrics and they're thin films. Boy, you could do just 10 experiments and you'd have 10 load displacement curves that were right on top of one another, right? It was just remarkably reproducible. And lithium is the other end of the spectrum these long scales. And so, yeah, I really didn't want to get involved with it. But Nancy Dudney kind of sucked me in and then a colleague here at Michigan Tech, fellow named Steve Hackney, he had some really good ideas and instead of running 25 indents per sample, we started running 100, 200. And then it was, okay, maybe we can start to do something from a statistical standpoint and figure some of this out. But it was, like you said, it's just an extremely rich material from a scientific standpoint, but wow, is it difficult to work with? The experiments are hard, the data analysis is hard. And so, if I hadn't had people to work with like Nancy and Steve Hackney and Steve Visco and other folks, I definitely would have given up. So it's just been really rewarding. At the beginning of my talk, I said, without these collaborators helping me out, I wouldn't be here today. I literally meant that. You got to have that cross-disciplinary help and people that are just excited to explore that space and try to figure it out. So, yeah, that's what comes to mind for me. Well, I really resonate with the message here. Be adventurous and try new things and work with new people. And I really resonate with that. Well, on behalf of Stanford, we really appreciate the time and Steve, especially for your early hours here with us, really appreciate it. And thanks for all of your contributions to the field. If I can have the closing slides, please. I believe we have aqueous energy storage on our schedule. And then two weeks after that, we will have one on sodium ion batteries. And forgive me, I may have flipped the two. So these are both tackling the issues of low-cost energy storage for decarbonizing the grid. So please join us for those two events before we come to the end of the year. And again, thank you, Steve. Thank you, Eric, for the time. Thank you all. This morning, we really enjoyed it. And good luck in tackling these super reactive, high homologous temperature system. Thank you. Have a good day. Thank you very much. All right, you too. All right, bye-bye.