 Today we're going to take a deep dive into solid state battery technologies and we're truly delighted to be joined by two of the world's experts on the topic. We're joined by today Professor Linda Nazar from the University of Waterloo and by Professor Jurgen Yannick from the University of Gießen. Let me take a brief opportunity to introduce them. They are truly leaders in many aspects of battery technology. Linda comes from the background of solid state chemistry and for many decades she has been studying the structure-property relationship of ionic transport and over the past 25 years she has investigated many different types of battery chemistry ranging from lithium sulfur batteries, lithium air batteries, lithium ion batteries in terms of cathode chemistry. She started all the way from lithium iron phosphate to all the high energy density technologies that is very actively pursued today. Linda is a member of the Royal Society. She has won countless awards and mentored dozens of students and postdocs who are now doing their independent research elsewhere in the world and I've had the pleasure of knowing Linda since when I was a graduate student and I'm truly amazed at all the contribution that she has made and I'm delighted to hear from her today. Jurgen Yannick comes from the background of physical chemistry and it's very well known for developing many techniques both experimental and computational to understand fundamental processes happening in redox materials and in the recent 10 years he has made significant contributions to the understanding of solid state batteries whether they are based on sulfides or oxides and particularly understanding the importance of interfaces within those materials. Jurgen is the Dean of Biology and Chemistry at the University of Giesen. He also run a joint industry lab at the Carzwell Institute of Technology, the Bellad Lab, so without further ado I would like to ask Linda to start her presentation. Good morning everyone, thank you Will for that very kind introduction. So I'll be talking about design rules for solid state electrolytes and I put rules in quotation marks because they're not so much rules it's perhaps strategies and I would especially like to start off thanking all of the people in my group that did all of the work that made this, that is making this possible today. So there's been a lot of, I'm not going to talk about solid state batteries, that's Jurgen Yannick's position but I will just make a brief introduction to the topic and this is an article taken from the Julian Spector about why Toyota's next move is solid state batteries. Of course there's less risk of fire because they don't have flammable electrolytes, they also allow for fast charge times and in particular the technology will allow one to stack cells thus automatically improving energy density by a factor of as much as two to three. And the Economist in 2017 asked if solid state batteries will power us all, there was a nice article here and say optimistically assumed that electric cars powered by these could be on the road by 2020, well we're not there yet obviously but that's what happens when you're a little too optimistic. So solid state batteries rely on super ionic conductors and optimized interfaces and again Jurgen is going to be talking about those interfaces, I'll be talking about the super ionic conductors. So the concept is pretty simple, we have a positive electrode at some high positive potential which is indicated here by red, we have a conductive additive typically carbon indicated in black and at the negative electrode we have a negative electrode material indicated in blue again with some electronic additive and the electrolyte runs completely through that cell. So the problem is of course developing good solid electrolytes but it's also a problem of the interface the triple phase boundary where at the active material for example the positive electrode lithium ions and electrons have to be simultaneously transported to that active material and that requires very intimate interfaces. So while the electric the reactivity of the electrolyte is not a concern achieving this simultaneous transport is indeed a challenge and if one has large secondary particle aggregate that's also a challenge to obtain the the inadequate interface. So the more specifically there is also issues of chemical stability of the electrolyte with the positive electrolyte there is oxidative stability issues of the electrolyte in the presence of carbon and ultimately one really wants to use lithium or sodium it's one that using a sodium solid state battery one needs to want to use a metal metal anode and this presents its own problems because of course many electrolytes are not stable with lithium metal really only garnets are shown to be stable and and still dendrites will form and so that usually requires the incorporation of some sort of protective interface those concepts are summarized in this slide with just a little bit more detail on the challenges so the first point is that thick composite electrodes with a high active mass are really necessary in order to compete with today's lithium ion battery so that implies that we have high ionic conductivity of the solid state electrolyte in the order of five to 10 millisiemens and we have this stable interface that I mentioned and low redox activity with the additive the electrolyte itself the membrane needs to have good mechanical mechanical properties and that means that ideally it is a relatively ductile material that will enable dynamic pressure control to be established and again these criteria for conductivity so I won't get into these factors very much I've already explained that lithium metal is using it as a negative it's fairly crucial to really establish commercialization and a competitive edge for these batteries and just a point that I think you're going to discuss in great detail is the fact that one needs uniform density over that interface and I would just ask perhaps that glasses might be the answer but I won't have time to talk about them today and ultimately good rate capacity and rate capability are necessary to compete so we might ask ourselves are these sorts of metrics achievable in a solid state battery comparable to that of a lithium ion so again the performance is limited by kinetics not so much by transport across the interfaces as I think you're going to be telling you and of course then we also have to consider the scalability of the of production of the solid electrolytes so I won't be talking about polymer electrolytes today not because they aren't a viable technology they tend to have conductivities that are a little lower than what are desirable but we work on the solid inorganic electrolytes this is just a comparison between oxides and sulfides and as you might imagine one obtains better conductivity with a soft anion lattice such as a sulfide with better stability with a hard anion lattice so examples of oxides include garnets, perovskites, nasocontite materials these are all relatively chemically stable like chemically stable at a high voltage they're compatible as I said garnets with metallic lithium but they do have this unfortunate um rigidity the very high Young's modulus in the order of more than 150 gigapascals and that makes them non-conformable and rather difficult to process into cells so in the case of sulfides um variety of different materials have been examined these are sensitive to moisture unlike the oxides they have high voltage stability limits they will react to the lithium metal oxide interface which means that sort of passivating layers are required but they are relatively ductile with a low Young's modulus in the order of 18 to 25 gigapascals and then a new player on the block are halides and so the halides um are also somewhat sensitive to moisture they're encompassed by materials such as li3 mcl where m tends to be a rare earth and also halo spinels which i'll mention at the end of my talk they actually are compatible with most cathode oxides although they're not stable with metallic lithium but they enable cathode aloxide materials to be used without a protective coating and they also have the advantage of good ductility and um the topic of today's talk will be sort of going over many of these materials but i guess one point just to remind you that all of these um solacea electrolytes have total ionic conductivity with negligible electronic conductivity and effectively that gives a transport number of one which is um offers real advantages over most liquid ion liquid electrolyte systems which will not have a transport number of anything close to one and often and a vicinity of 0.4 to 0.5 so in order to achieve good solacea electrolytes that we need to have a facile conduction pathway for the mobile ions that means a high number of carriers a somewhat flattened energy landscape which i'll be discussing we need to have disorder in the mobile ion lattice and weak interactions with the framework another topic of today's talk and a polarizable anion sub lattice and i'll be talking about the role of anion dynamics and in fact i'll pretty much start my talk with that so the first supraionic sulfide arguably is lithium germanium biophosphate this was reported by rio giocano in 2011 and it really opened up the field so this is often quaintly known as lgps because of its formulation and is reported to have ion connectivity in the order of 12 millisiemens at room temperature and so this makes that conductivity comparable to traditional liquid organic electrolytes and the solid electrolytes are not expected by viscosity at low temperature which gives them um good low temperature performance at least comparable to liquid electrolytes if not better so this is just a diagram from a recent paper by rio giocano and toyota nature energy in 2016 and this is what we call a ragoni plot of power versus energy and it compares all solid state batteries with a lot of other different technologies lithium sulfur magnesium lithium air conventional lithium ion batteries and you can see that the solid state batteries perform really rather well under these in this plot especially at high temperature but even under room temperature conditions they show advantages in both terms of power and energy this is what's um promoting all of the excitement in this area so a few years ago when we started uh looking at these materials we started working on some sodium ion batteries and we were aiming to find a sodium analog to lgps and we discovered this material which is not isostructural to lgps but it actually serves as an excellent model and i'll be using it as a framework to talk about anion dynamics so its formulation is na 11 sn2 ps 12 so you see the similarity in composition with the um lgps but it said it's a new crystal family and it has both it has ordered ps4 and sn4 tetrahedra shown here in teal and in cobalt blue and it has channels which contain different sodium ions there's actually six sodium ions the six sodium ion sites in this material and these form channels that run along the uh c-axis and also along the a and the b-axis so it's a three-dimensionally conductive material you can see that these channels are formed by face-sharing octahedra of the sodium that run in all of those three directions and here's a better depiction of that along the a-axis where you can see that this is the window the triangular window with which through which the sodium ions pass there's also an additional site which we call the sodium six site which is a cubic site um it's not so important so the point here is that the sodium one and sodium two positions are partly occupied these are the ones depicted in sort of a light rose color whereas the other three sodium sites in the lattice are about 95 percent occupied so we have a occupied partially occupied occupied partially occupied alternating type of system or arrangements but we teach them the lattice which gives rise to good conductivity in part because we don't there's we lower the energy for defect formation because of these partial vacancies the structure is reported by us in e-s in 2018 and at about the same time or just very shortly thereafter by um Sophie uh Stephanie Damon and Bernard Rowling's group so we carried out AMID uh admonition molecular dynamic studies to understand sodium transport in this material and you can see this is the sodium ion probability density you can see that um there's isotropic conduction shown by this probability density in all three dimensions and you can furthermore see that the experimental conductivity of one point four millisiemens um is rather very good agreement with that predicted by the AMID theory which is two point four millisiemens and similarly the activation energy by theory of point two electron volts is very similar to what we obtain which is about point two four electron volts from experiment so this is as I said a three-dimensional super ionic conductor and the diffusion coefficient that we obtained from AMID is about two times the standard of the minus eight centimeters squared per second at 300 kelvin hundreds in all three three crystallographic directions and that makes it somewhat similar or very similar I should say to LGTPS but just in the LGTPS in the the basal plane so one of the um as we started to look for other analogs to this system one of the materials we discovered was the antimony analog which is shown here it was reported in chemistry materials about the same time and we expected this to have better conductivity because of its larger cell volume a smaller because of its larger cell volume I have those numbers can switched um compared to the phosphorus so this actually this has the um the smaller cell volume this has the larger cell volumes you have to switch those numbers the point here is that the conductivity is about half that of the phosphorus analog and the activation energy is much higher than that of the phosphorus analog and this is also borne out by your theoretical calculations and you can see that the either the sulfide or the selenide have a lower activation energy of about 0.25 compared to that of the of the antimony analog and the reason for this is actually shown in this these maps so this is these are maps obtained from neutron diffraction data these are called that this is derived from the maximum entropy method often abbreviated as mem and so this is effectively a map of the nuclear density it's obtained from extracting the structure factors from the neutron diffraction data itself and so what you see here for the phosphorus analog is the nuclear density for for example that for the sulfur around the ps4 groups so this is the red blogs here are the sodium ion density in the structure and this green density at 300k shows the rotational motion of the ps4 group about this phosphorus position and you can see that at three kelvin there is even disorder obtained in that ps4 group where is it 300k that is rapidly rotationally disordered and this is also true of course at 450k so we see this rotation at 300 where is in the antimony analog there is no motion whatsoever at 3 degrees kelvin at 3 kelvin whereas at 300k there is only some disorder but not actual rotation so there's a so this provides this is a real contrast between these materials which we wanted to look into in greater detail and that's shown on the next slide and it relates to this long this concept which was developed actually long ago and has been recently revisited which is sometimes called the paddle wheel effect and we actually prefer to make an analog more to a revolving door in which the motion of the framework is actually aiding the mobility of the cations just as one passes through a revolving door so just to put things in context the rotation of these anti-intestrihedral moieties and poly anion materials and for example sulfates or phosphates was implicated in high temperature rotor phases uh these individuals martin jansen in particular did a lot of work in this lung test as well so they were implicated in high temperature plastic phase of the sodium phosphate at 600 and in lithium sulfate and quasi-electron neutron scattering confirmed this orientational motion at 600k in work reported by jansen et al and more recently other using AMID and other complicated sophisticated techniques I should say have looked at other poly anions such as the closoboranes and also the borohydride Na3OBH4 so these are fairly recent reports but um there's it's hard to get direct proof uh for this coupling between the anion motion and the cation motion and uh that's um what i'll be talking about a little bit more today so our am so coupled with the MEMS which i already showed you this is the rotation of this kiosk four group so coupled with the MEMS we did these we carried out these AMID simulations at a variety of different temperatures that we're actually able to see the onset of this paddle wheel effect so this is just a snapshot a one picosecond snap shot that shows it as this poly anion is rotating the sodium is moving from one position to another in the lattice and so these two processes are coupled if one pauses or one artificially pauses the motion the activation energy for that transport the energy barrier goes up increases to 0.36 electron volts whereas without constraints it is significantly lower of about 0.2 electron volts now this is a little bit of an artificial imposition upon the calculation but still it it shows the point of of the importance of the poly anion rotation to enabling to lowering that activation barrier for transport and the reason for why that activation barrier is lowered is observed when one actually looks at the structure this again is the picture that i showed you before of the of the transport along these one-dimensional chains and the point is that as this poly anion in this case the ps4 rotates because it is edge bonded to these sodium octahedra in the lattice it literally turns and opens up that window for transport in a transient way so shown here is the antimony in blue and the phosphorus in pink and you can see that that window opens up as the poly anion rotates for the phosphorus compound but it does not open up for the antimony because there is no poly anion rotation so the window remains effectively closed for the antimony where it opens up in the case of the phosphorus and this is what this is a large in large part what gives rise to the difference in the activation energy and so one can summarize this by saying that the anion rotation flattens the energy landscape for the cation transport through the structure and um as i said lowers that barrier we have also looked at this effect in lithium ion conductors specifically we've compared beta li3 ps4 which is a supraionic conductor but only at 200 degrees because the room temperature phase which is the gamma form is a very very poor conductor so it undergoes a phase transition at around 200 degrees or 250 in order to get to the to the beta form we've been able to stabilize a version of this structure at room temperature which has an equivalent roughly one millisiemen per centimeter conductivity with this is obtained by incorporating lithium and into the structure and adding silicon to replace some of the phosphorus so we're adding lithium and silicon into this ladder and that has the effect of effectively of splitting the lithium sites and so the lithium sites in the beta li3 ps4 structure each lithium site splits into two different sites and that is equivalent to effectively increasing the atomic displacement parameter by a large factor so all of the lithium sites are split by one angstrom which is equivalent to effectively increasing the atomic displacement parameter and this increases the lattice considerably the lattice volume and it stabilizes this effectively beta li3 ps4 type structure so this is an improperly stabilized lattice with a geometrically frustrated landscape and you can see the in the gamma form which is of li3 ps4 which is a very very poor conductor 10 of the minus 17 percent of meter room temperature there is a the mems map here show that there is absolutely no rotation whatsoever where as you can see that rotation in the high temperature the so-called beta phase at 200 this data was actually collected at 350 which you can definitely see the onset of that rotation and if you compare that with the silicon substituted form you can see the rotation is very evident in this silicon phase at room temperature which is also has about a 1 milli semen conductivity at 30 degrees centigrade so it is a similar effect to what I just described with the sodium we again have a transient opening up of this triangular window which is where the lithium ions pass in this structure and so when we pause the rotation the window disappear or diminishes when we let the poly anion rotate this is through amid calculations the window opens up and this is what lowers the activation energy barrier and we notice in the power spectrum that we see the same frequency range for that rotation for the rotation of the poly anion groups as we see for the lithium in the in the material so so that that again is evidence for the coupled mobility and the two-dimensional probability distribution of this phosphorus sulfur to lithium angle and the distance between the sulfur and lithium atoms in the first shell also shows the same sort of effect effectively that shows that the groups are highly delocalized which signifies a strong correlation between the poly anion and the cations if there was no correlation between poly anion mobility rotation and the lithium we would simply see this be localized in a discrete spot so the fact that this is delocalized is evidence of this this delocalized of this correlation so time is moving on I will switch to flattening the energy landscape this is just a picture of a golf course pointing out that we don't want to get into these little energy traps or the sand traps and I'll talk about the agiridite lattice in this material it is this or this material this is the diagram from Wolfgang Zier's paper you can see the poly anion tetrahedra the ps4 groups in this structure with these frank casper tetrahedra in which the lithium ions reside in all four corners of the cubic structure and these frank casper polyhedra have usually two different lithium sites called a 24g and 48h site this is the 24th g site here the 48 sites are here and this material is quite popular because it forms a passivating quiescent stable interface with lithium metal because these insulating materials form and are not and do not continually grow this is shown by Jurgen Yannick in a nice paper and he's going to be talking about that a bit more and this is also been is also been an anion dynamics which have been investigating which have investigated poly anion rotation so there is an intercage jump in this material which is thought to dominate long range transport so disorder on either of these two sites will determine the ion conductivity and if that if we have iodine in the lattice though the iodine is localized on the 4a site whereas sulfur is on the 4c site whereas in the case of chlorine and bromine there's delocalization over those two sites and that gives rise to very high conductivity so my grad student Lydongzo discovered that we could make highly conductive iodides using the antimenide version of this material and may have conductivity upwards of 10 millisiemens per centimeter this shows the diffraction patterns of the antimony the germanium and the tin analog the silicon germanium and tin analog and the supraionic conductivity is shown here as high as almost 15 millisiemens for this particular composition and so the point is that when we substitute antimony with the smallest aliovalent dopant which is silicon that gives rise to the highest lithium content as you can see here and that then gives rise to the highest conductivity and grain boundary effects are important this just shows some impedance data where we can separate the bulk from the grain boundary so in fact there is relatively considerably or there is considerable grain boundary effects in other words there's low conductivity especially when we get to higher values of silicon but at these conditions we can by centering the pellets we can get conductivity upwards of 24 millisiemens per centimeter so improving the grain boundary contact certainly increases the ionic conductivity but the bulk is excellent and this is achieved with a very low degree of anion disorder between the sulfide and the iodine so comparing the structures of the of the pristine erudite with our silicon and lithium substituted material we see that we have four sites in the case of this new silicon substituted material where only two sites in the pristine material and these are indicated by these arrows and we again this is achieved with very little anion disorder so the the reason for this increase in conductivity is that we have these additional sites which lie between these franc casper polyhedra these are the cages that are shown here and so whether where we would normally have these jumps within the franc casper polyhedra and also some intercage jumps the addition of these new sites through a face-sharing tetrahedra it's a little hard to see um enable this initial pathway and so this allows a concerted ion migration path to take place because we populated effectively these high energy interstitial sites and this activates a concerted ion migration which was reported by effa mo also by garrod cedar and lowers this activation energy for lithium ion diffusion so we've also looked at just briefly at symmetric cells of this electrolyte together with with lithium and we're able to achieve current densities upwards of 0.6 milliamps per square centimeter over as much as a thousand cycles so this again indicates we have a quasi stable interface formed between this erudite iodide and the lithium likely due to the formation of lithium iodide and perhaps some lithium antimony phases and your gynec will be talking more about those interfaces in the next talk so i'll just end off on some halide materials also in a erudite starting from this chloro erudite when we with a different strategy here is to increase the halide concentration in this lattice which actually increases vacancy so whereas in the case of the intimidates we have a lithium rich erudite in this case we have a lithium poor erudite again as it said it creates vacancies in the lithium sites about 10 and it makes the material chlorine rich and you can see that the chlorine distributes on both sites before a and before c so we're not really increasing the anion disorder we're simply putting more halide into the lattice and so the activation energy drops as we add the halide and the conductivity dramatically increases so we are at about conductivity of about 9.4 for the highest chlorine concentration that we can achieve which is the chlorine 1.5 phase and that goes up to about 12 millisiemens for centered pellets and so this value of 12 is between the highest conductivity of the lgps phases either this material or this material which were reported in that nature energy 2016 paper that i referred to earlier and the reason for this are obtained from pfg nmr measurements where we actually quadruple the diffusivity these are experiments done in collaboration with jillian goward's group at the university of McMaster university and her grad student david bazak and so this is just a plot of the diffusivity obtained from these pfg measurements you can see that it's definitely the highest for the chlorine rich phase and the value of diffusivity of 11 times 10 to the minus 12 is actually higher than that in lgps and or in this lithium silicon lgps type or this other type of structure so diffusivity is about more than threefold and that basically correlates exactly with the increase in the conductivity that you see plotted here in this bar graph so the take home messages at the anion disorder and weakened interactions between the mobile ions in the framework lead to a quadrupling in the iron in the ionic conductivity and when we examine this material um when we found this material um by using cd we could see that there was much less current passed for the chlorine rich versus the pristine aguradite material especially after this is the first cycle and this is the second cycle so you can see that we're forming a passivating layer and we have better anodic stability with due to this higher halide content and so that inspired us to look at pure halide materials and so i remind you of this plot of um energy here where or redox potential that we're really trying to stabilize materials at these higher potentials halides are not typically stable with lithium metal but you can see that in this cd that we now have an onset of oxidation that is about 4.3 leases both versus the roughly 2.5 to 2.7 which is seen for a typical phosphate so this enables us to obtain coating free cathode solid state batteries and with development of a new lithium metal halide structure so i will skip over this slide just in the interest of time the point is that we're trying to develop not only solid electrolytes but also coating materials which can have advantages over things such as lithium niobate which are difficult to control the quality of as one puts coatings on cathode materials so lithium metal chlorides are relatively new player in the field they were actually investigated in 1997 1992 um and andy sun came up with some nice work on the lithium indium chlorides at about the same time that we published work and um all right there is a panasonic paper here cited in advanced materials um and but in this work we thought we substituted zirconium into either the yttrium or erbium structure to obtain conductivities upwards of a milli semen per centimeter so these materials this just shows that there are basically iso structural in the case of the yttrium and erbium this shows um x equals zero in other words the pure yttrium this shows the zirconium substitution and you can see that there's a change in phase as we add the zirconium to this lattice and that is concurrent with an increase in the conductivity up to about 1.4 milli semen at the highest levels of x of about 0.4 to 0.5 in other words zirconium concentration and these are accompanied by a very low electronic conductivity of an order of 10 to the minus 10 and this data is effectively replicated for the for the erbium material so um this is a new structure and this just shows the lithium ion conduction pathway so we create a tetrahedral lithium ion site in this lattice shown by lithium three as opposed to the pristine material which just has lithium one and lithium two and so the pathway here is shown in these red arrows it's effectively a one-dimensional conductor but there is limited conduction in in the other planes and so this is a bond valence energy landscape map our energy plot and you can see this lowered energy barrier for act for conduction compared to that between lithium one and lithium two which is upwards of 0.6 so this lower energy pathway is what enables this conductivity of about what more than one milli semen to be obtained and we then looked at this material with lithium cobalt oxide as a positive electrode this shows the data for the erbium and for the yttrium and you can see that especially in the case of the yttrium we're able to obtain rather good performance electrochemical performance with as little as 15 percent of the electrolyte and especially you can see it in the impedance data the eis we have reduced charge transfer for the halide compared to a solid electrolyte we're using just lithium phosphate and that's less than uh one over 20th so that's really really decreased that interfacial impedance dramatically in the cell i might add to what we're comparing here is the cobalt oxide with either the halide in the cathode or the lithium cobalt oxide with the lithium li3ps4 in the cathode in both cases we're just using li3ps4 as the as the membrane in the cell so at rates of a half point five c and four point three volt window we're able to obtain stable cycling capacity and we since translated this to a new lithium disordered halo spinel which is i think the first in this class the structure is shown here on the left again conductivities of a new order of 1.5 millisiemens activation energy similar about point three and this shows the data for nmc 622 and for a high nickel nmc material uh nmc 85 concentration nickel and in this case we can actually cycle all the way up to four point six volts with reasonable stability over 70 cycles in the case of the high nickel material we're obtained we're able to obtain capacities upwards of about 200 milliamp hours per gram again over roughly um 70 cycles and this is in the window up to four point five volts so we're it even though these electrolytes have a thermodynamic stability window that seems to be about four point three clearly there's some kinetic stabilization that enables to take us up to four point five or four point six four so with that and two minutes left to go in my 35 minutes i'll just um briefly summarize by saying that we have some new descriptors established we have i would remind the audience of the need for high ionic conductivity to obtain high current densities the issue with lithium metal does need to be addressed and i've highlighted all of these points increasing the vacancy population strategies to increase conductivity and stabilize interfaces for example with halide materials controlling cation disorder and anion disorder the importance of anion dynamics and poly anion rotation which can enhance the conductivity by a factor of two and once all of the electrolytes um is unlikely going to overcome all of these um challenges and so bifunctional or dual electrolytes are probably necessary so with that i'd like to again thank all of the people that did the work um i'm just doing the talk and i'd also like to thank people at ornrl who helped us who got us helped us get neutron diffraction data our colleagues at basf my entire lab group showing here and uh basf and jc's are in particular for their funding and thank you for your attention linda thank you so much for that deep dive into ionic conduction and solid electrolytes and we have received more questions than we can possibly answer in the short amount of time so as um the moderator i have the difficult task of picking out the question for you so forgive me if i pick out um two difficult questions so let me start with a very high level question um one of our viewers is asking what has been the success in predicting new solid electrolyte via simulations you show some really beautiful work of administral md for understanding transport but could you comment on how that has led to discoveries of electrolyte well that is a very difficult question uh will and um i would say that there's a lot of hope for the predictive capability of simulations but at this point they have generally proven more as a guideline to interesting materials that may be super ionic conductors that turn out maybe not to be has they don't have as quite the conductivity that the simulations predict but it does give us um you know kind of a guideline in our in a an approach of strategy or target materials to target even though sometimes as they said the connectivity is not quite what was anticipated thank you linda and the next set of questions concerned the first part of your talk on the rotation uh and hopping coupling uh so the first question is can you expand upon the role of rotation on face stability relative to ionic conductivity i i think you showed a quick two figures on this so the question is on the role of rotation to face stability um that's a harder that well if we that's a very difficult question um because we don't really i would say that that answer is not clear in the case of the um there are lgps does not under seem to undergo any poly anion rotation and yet it's a relatively stable material in the case of the lithium and silicon substituted beta li3 ps4 we stabilize that rotor phase down to room temperature but that's really an entropic stabilization in large part because of the because of the fact that we have the silicon and phosphorus in the lattice but because we are sampling different um rotational states of the poly anion we can see that in the phonon modes there is probably a contribution of that rotation to the overall stability so i would say that there is probably a contribution but it is not completely quantified or it is not well quantified thank you linda uh and on a related question um in terms of the rotation dynamics can you comment on its contribution to the temperature dependence and um specifically how does that contribute to the activation energy in terms of both um the rotation and the hopping so you're asking if the rotation the rotational dynamics contribute to the temperature dependence um effectively as things rotate faster does that does that help does that aid the conduction um we have not yet quantified and we would be doing this with amid so we have not quantified the the rotational speed so to speak with the effect of the cation diffusion so experimentally of course conductivity is going to go up as a function of temperature but i think what that question is really addressing is whether or not we have quantified this by amid and the answer is we have not okay i'm being told we are almost running out of time but i will squeeze in one last question your talks discuss a lot of the dynamics in terms of the hopping contribution and um to to the conductivity but can you also talk about the effect of carrier concentration so in terms of the amount of disorder and what type of dependence do you see of the ionic conductivity on the amount of disorder in the standard ionic conduction picture well of course carrier concentration is extremely important if only portion of the lattice is involved in that conductivity then uh in in the conduction mechanism um you don't end up with a very good conductor so the whole the whole approach of disordering lions and the lattice over many different sites for example in the antimony agiridide is to do just that to increase the carrier concentration so we invoke a larger number of participatory ions in the process and in the case of the halide we actually see a situation where again we by increasing that by generating new sites for lithium population and invoking those ions in the pathway we increase the carrier concentration even though in that case some of the lithium ions are are immobile and they just form an immobile framework so the short story is really important thank you linda and for our viewers the many who we could not address the questions we apologize but i'm sure linda will be happy to answer your questions by email if you reach out to her so linda thank you once more for the deep dive into the solid state chemistry of ionic conductor a crucial part of enabling solid state batteries here at stanford we're very concerned about all aspects of technology translation being in silicon valley so i will like to ask the first question on translation and the second question on policy i know this is a bit different than the technology focus of today's talk and the material science and chemistry so my first question to the both of you is about the cost learning curve so we know that the cost of solid state battery is not known today it is difficult to estimate but if you i can ask you to assume sometime into the future commercial activities are becoming more mature commercial products are delivered how do you think solid state battery can compete with the cost learning that is in the incumbent technology in lithium ion batteries so as the costs begin to fall for solid state battery so does lithium ion battery and that is a very severe and rapid learning curve and you know there is a cost floor for lithium ion battery but there is still considerable room so i was wondering if the both of you can talk about for technology like solid state or maybe other energy technology how do we compete with another technology that is incumbent that's a 50 billion dollar industry that is also learning at the same time well i think this is the same as probably in all other technology fields i think new new solutions always have i think difficulties in competing with the existing ones of course so we see currently the fight of the electric vehicle with the auto motor which is more than 100 years in operation and is being further improved so i think in fact i think once the solid state battery will not have substantial advantages it will be difficult i think really to have in in in sufficient time the sufficiently steep learning curve to to be also economically competitive i think in the current least materials cost of batteries the cathode is the most expensive part and the electrolyte is only taking a small share of the cost if a solid electrolyte would change that picture too much then this is already a significant disadvantage so the solid electrolyte should not be really more expensive which so i think this this is an important point so and i think in the in the fast but cluster in germany the cost issue is in fact something we also deal with we try to understand in fact the cost issue well i'm not an i'm not a specialist in techno economics so probably i'm not the best to answer these things i try to find good solutions and try to understand which route one can go but as i said uh it's not i would say it's not a simple automatic route for the solar battery but we are really in an early state and of course industry is always impatient i would say but um we still need some time but we should of course in order i think to understand economic potential success we should not forget the cost of it i say cost issues yes uh and i'm happy if people make solid i would say techno economic models that are reasonable but upscaling changes things so for example i remember that the the solid power guys and i really like their work in the u.s uh in last year on the conference they were worried about the price of lithium sulphide because that is a and was an important part of the cost of preparing tyrophosphate and the recent conference that was not anymore changed was not anymore mentioned so that must simply means there must have been now there must be a cheap source of lithium sulphide which before that was just a fine chemical so with upscaling often things change and that has to be taken into account and uh this is my comment maybe linda has uh another uh view on that i think you've um described it pretty well you're gonna i think my view would be that the the rate of drop in the cost for traditional lithium ion batteries is flowing to some degree whereas it's in that rate of change that the drop it's in other words the rate of the crop is going to be much higher for solid state batteries and at some point one assumes or one hopes that they may cross over because there's so much more to be learned in solid state batteries and indeed um upscaling of the solid electrolytes is very important and i think we're not at the stage yet of even having defined the ideal solid state electrolytes so i i see that coming down that the drop in costs especially with processing costs coming down very rapidly whereas i think we're we're coming down in lithium ion but at a much more gentle level now sort of scaling out so i think that would be my only additional comment to what you're gonna say linda and you're gonna thank you for painting this cautiously optimistic picture of course um highlighting the role of chemistry behind all that in the few remaining minutes i thought i would turn your attention to the policy side of things and i'm sure there is not a single participant here and our viewers there are free from the pandemic and we have seen some very encouraging and exciting reports where the response to the pandemic is also being coupled to the response to issues of energy and sustainability the european union for example has announced major initiatives in this area as many other countries i was wondering if the both of you can talk about looking forward what would be your recommendation to the policy makers how the two can be coupled in a way to accelerate the recovery and also our advances for clean energy so maybe now linda may start asking is it the more difficult question you're in well you know as mark kerney has said you know eventually covid will be controlled but climate change remains the real pandemic that's on the horizon and so to speak so um in in terms of in terms of establishing sustainability for the future there is obviously no question amongst policy makers i think and scientists alike that electrochemical energy storage is is part of that solution and that is ever going to be more important whether we're in a day and age of covid or not i i mean i would say in fact perhaps even increasingly more so um we're going to have to think about obviously things are going to change at least in the short term and perhaps in the long term but in any case um energy policy and sustainable energy policy has to be part of the solution that's uh that goes without question so i don't know if you're gonna have things to add yeah maybe oh it comes to my mind yeah did i answer your question will or were you asked for something else no no this is great linda thank you for sharing uh jirgin yeah i think what comes to my mind is first of all that i think that uh it may look that that the covid let's say period helps but i think on the other hand i think at least in europe we have this very strong trend towards public transportation and even discussion for free public transportation to or say reduce individual transportation that of course is worth with with respect to carbon dioxide or the carbon footprint and i think the covid period of course is is a it's a strike back because people have the tendency for more individual transportation so i think in europe we see maybe even in the us we see more bikers e bikers and so i think that's that's not very supportive so i think the trend of more public transportation electric buses i think is a big wave coming with interestingly solid state batteries entering into that with polymer electrolytes um i think it's not so simple with the covid it it looks as if that helps to advance uh alternative things but partly it also leads to strike backs i think jirgin do you get a sense uh within the the e you that there is an injection of funds and resources as a way we start the economy specifically for uh technology like uh like batteries and future technology like solid state battery yeah absolutely this is the case i think the these big programs that are currently being advanced uh i think uh europe as such uh so um they had the idea really only in principle to uh put i would say really substantial funds uh into the support i would say of well environmentally benign uh technologies and things and i think in germany also i think the i think there's a electric cars are being supported and there is the idea to support i think environmentally friendly there's of course always a struggle uh because of social issues uh have to be uh considered but by and large i would say that there is a strong sense for that in europe yes well i think that goes and that that that will also that will definitely also i would say be trans translated into funding yes i'm sure so sounds like there's a combination of push and pulls uh as a result of the pandemic yes um but i think we're all hopeful um that the the two uh can be somehow a couple between the recovery and also um uh progress for clean technology so we are out of time uh linda and jurgen i'd like to thank you once more for joining us from canada to germany and entertain our viewers with exciting results a six course meal and really a wonderful journey for the past hour and a half so thank you both very much so just a quick announcement we will have our next symposium uh also on friday june 12th the same time seven a.m pacific and uh we will be joined by professor claire gray uh from the university of cambridge and also professor uh gurus sader from the university of california berkeley and they will continue on our excellent theme so far of understanding materials and chemistry for energy storage technology and on that note like to thank everyone again for participating and we hope to you uh see you on june 12th thank you very much