High energy density cathodes for lithium-ion batteries | Sun, Gasteiger | StorageX Symposium

good morning from stanford university i'm will chu i'm the co-director of the storage x initiative and together with my colleague professor itoy i'm very pleased to welcome everyone to the final symposium in the spring quarter for the storage act symposium we'll finish this outstanding quarter with a talk on cathode materials chemistry and electrochemistry is a topic that's very near and close to my heart i think it is a very rich playground for doing fundamental science and innovation and i'm extremely pleased to have an outstanding panel today with speakers and participants from three continents to uh to finish off the quarter joining us uh from germany is professor hubert gas tiger from the technical university of munich and i'll introduce him in in more detail in a bit and then joining us very late in the evening from korea is professor professor yonk son from hong yang university both of them have done seminal and significant work to advance the cathodes making what they are today um and let me go ahead and start introducing our first speaker so we can get started hubert uh is uh holds the chair of electrochemistry at the technical university of munich and he is truly a broadly trained individual he's done it all he started his career at lawrence berkeley national labs just right here in the bay area after receiving his phd at uc berkeley then he spent a decade working in industry at general motors developing electric catalysis and since 2009 a 2010 he holds the chair of electrochemistry in munich i cannot think of a more diversely knowledgeable person than hubert on anything electrochemistry and certainly his contribution extends beyond batteries but also fuel cells and electric catalysis we are really pleased to have him today to talk about the interfacial electrochemistry of cathode materials um huber if i can have you come to the stage okay there you go hubert we are very much looking forward to your lecture so thank you very much for this opportunity to present a talk at this wonderful symposium and thank you very much will and e for uh the invitation uh i'm also glad i'm the first one because it would be rather intimidating to be of the young cook so i'm glad that i can start uh so what i want to talk about the next half hour is about the different degradation phenomena in nickel rich cathode active material so-called ncms and so this is a talk we put together with three students of mine and is a little bit of a review of work we have done in this area so why nickel rich and cms of course at this symposium i think i do not need much of an introduction but essentially what happened in the last years was that the nickel content was gradually increased from 1.6 to 2811 and now even higher nickel content materials increasing the capacity and then in recent years also there has been attempts to gradually increase the upper cut-off voltage so it is of course interesting to see what the degradation phenomena of these different materials are at high nickel contents and anti-cathode potentials so the materials we talk about are these layered transition metal oxides with the very small excess of lithium and a theoretical capacity of 275 million bars per gram if you were to extract all of the lithium so if we look at the energy density so the energy density increases with nickel content so if we look here at the potential of 4.3 volts versus lithium so this would be 4.4 volts in the full cell 4.2 volts in a full cell so you go from the mcm 111 to 811. it's a significant increase in capacitance and the same is true of course at 4.5 volts where you can get significant gains so if we look at these different materials in terms of their cost there is a paper from the mantarin group which looked at a potential versus listing at 4.2 volts and then showed that the cost of the nickel rich materials is lower of course predominantly because of the reduced amount of cobalt however the drawbacks of these materials have to do with their higher sensitivity so when you increase the nickel content the stability towards the ambient towards moisture specifically decreases also the zono stability decreases so this was actually shown by professor soon in a previous seminal paper and then also the cycling stability decreases and so what we want to look at in this talk is what are sort of the different degradation mechanisms of the cathode material so focusing really on the cathode material uh during battery operation and so if we look at the different aging mechanisms with respect to the cathode active materials there is a few things which are pretty well known and so when we look at an electrochemical cell what we have is that particularly at higher potentials the ncm materials release oxygen we have a surface reconstruction and we create electrochemically inactive phase in addition during this oxygen release we oxidize the electrolyte our hypothesis was that it goes via singlet oxygen but there's of course other hypotheses in the literature but nevertheless what happens there is that you produce acidic species typically hf which leads to transition metal dissolution and migration to the cathode the other thing we have is uh depending on the cycling potential the time of cycling we see a cracking of polycrystalline ncm materials so what we get is a gradual breakup of the secondary dynamics into their primary crystallites and that in principle can lead to electronically isolated faces in the center of the secondary abdomen right and also of course at high potential we have the oxidation of the electrolyte which again produces protein species which get reduced on the negative electrode leading to hydrogen and then of course we have a third mechanism which is the so-called glycemical mixing particularly well known for lno and the hypothesis there is of course that these occupied lithium sites by the transition method lead to a slower diffusion so the question is how do we do a study where we exclusively focus on the cathode active materials and so what we do is we try to use we use a pre-lithiated anode so in order to eliminate constraints which come from the active lithium loss on the anode electrode we use a non-gassing anode in order to essentially eliminate the contributions from the anode to the gas signals and we use an excess of electrolyte in order to not have to consider the continuous consumption of the electrolyte um if we look at this what can we measure uh when we look at the formation of a surface reconstructed phase we expect an increase in the charge transfer resistance which in principle one would be able to measure in the case of particle cracking what we expect is an increase of the electrochemically active surface area meaning of the electrolyte wetted surface area so we would increase expect an increase in the charge transfer resistance actually a little benefit of this is that sorry in the capacitance a little benefit is that the charge transfer resistance also would go up a little bit and uh in case of lithium metal mixing of course we expect that we have a slower slower lithium diffusion coefficient in the active material in the bulk of the material so how do we decont impedance signals of course what we can measure is the impedance of the full cell but if we want to focus on the cathode active material we can either do impedance with a micro reference electrode so then we can collect the or acquire the impedance spectra of the cathode active material by itself the other thing is we can do gcr pulses in cells when we have a little reference electrode and then essentially get the impedance of the cathode uh or we can do impedance spectroscopy which i'll also show for a counter electrode which has a very very low impedance so that it can be ignored so these are the different approaches we use in our studies um so the talk is split in three sections one section relates to oxygen release and surface reconstruction the other one has to do with particle cracking and the third one with the potential lithium medium mixing so the oxygen release we typically measure with online electrochemical mass spectroscopy oems and the studies we had conducted in the past through this regards was a procedure where we increase the potential in a linear scan and we measured uh the you know cell the cell voltage the castle potential as a function of the state of charge uh this is shown here for three different materials a one one one a six two two and an eight one one material and as a comparison a high voltage swimmer and so what we see is that for the ncm materials we have the evolution of oxygen at approximately 80 state of charge and that is actually irrespective of the metal content when we look at potential then of course what you see is that the oxygen release on the different materials occurs later for the poor materials then for the little rich material right so this has to do of course with the slightly lower voltage of the nickel rich materials um the lnmo which here goes to as high potential as the ncm so pulled here so about five volts uh we see absolutely no oxygen right and so what we know is that the stimulus structure is actually stable against the oxygen release um when we look at other gases what we see is that whenever we have the onset of oxygen evolution we also have the onset of co and co2 uh evolution which we ascribe to the degradation of the electrolyte and as i said in our studies we ascribe it to the reaction of the released singlet oxygen with the electrolyte but as i said there's other hypothesis in the literature um of course upon oxygen release you get a material which is poorer in oxygen than the layered structure and what one finds for nickel rich materials is that it reconstructs into a rock salt-like face and so this is some data from the lab from jurgen yannick and bella of bsf for a nickel-rich material so 85-1005 after 500 cycles where they clearly identify rock-solid faces now when we look at the the material morphology uh what we know is that these polycrystalline ncms are actually composed of secondary agglomerates in the order of maybe five to ten micrometers in diameter and the secondary glomerates consist of primary crystallites which are in the order of 0.2 micro 0.2 micrometers so if we measure the bt surface area of these materials we get about 0.3 meters per gram this is what you would measure and if you use a surgical approximation you would calculate an effective particle diameter of about four microns on the other hand if the material were to crack during cycling work during other treatments into the primary crystallites which are about 0.2 microns in diameter the spherical approximations would say that the bet surface area increases to about six meters per gram right and so the truth of course is somewhere in between you start out definitely with the low bt but what we find is that typically the bt area increases over the course of cycling and this is what we will look at in the next section uh which is about the particle cracking and in order to develop an in-situ method to follow the political tracking we first of course had to do some sort of method method validation and the method validation we did was by just simply compressing cathode active materials to crack it by mechanical force right and so what we know from fiber cm measurements is that these ncm materials are pretty dense have a few occluded volumes but in general otherwise they're rather dense on the other hand if you compress the material at high compressive forces you can see the cracking of the materials of course these are very high forces here as i say this was really just a validation measurement so the question is can we quantify this because of course the fibocm is beautiful because you can see the images and it is very visual and very clear but they cannot be quantified so what we try to do here is to develop a method based on bet but using krypton instead of nitrogen for the bet measurements as krypton is about two orders of magnitude more sensitive now when you measure powders that of course is irrelevant you can just use enough powder to conduct a nitrogen bt but when you use uh electrodes uh then of course your surface area your total mass is too little and so in our case it only works really when we use krypton bt so what we measure here is the krypton bt of the pristine powder when it is not compressed uh sorry of an electrode when it is not compressed and when we compress the electrode what we see is that the bt the krypton bt surface area increases now of course this is the total area of the electrode so this contains also the conductive carbon which has a very high bt surface area itself compared to the cathode active material so what we have to do is of course subtract the contribution from the conductive carbon and the electrode and so this was done by a model electrode which only contained a binder and conductive carbon and so what we can see is that the remainder here is the bet surface area of the cam in the electrode and this agrees actually very well with the powder here and as we compress this we see that the bt surface area increases as we crack these primary secondary agglomerates more and more so what we find right of course nothing unexpected compression reduces cracks and uh this increases the electrochemical surface area and so we use this to actually calibrate our new method which was trying to extract the capacitance of the cathode electrode using a transition a transmission line model uh with constant phase elements and when we do this we utilize so-called locking conditions and so blocking conditions can be obtained by either using a non-intercalating electrolyte which was done in this example here or by um going into conditions where the charge transfer resistance becomes very very large and so the typical impedance spectrum of blocking conditions is essentially more or less a vertical line not quite vertical so the constant phase element the exponent is 0.88 instead of 1.0 which it would be for capacitor and then you see here a little bit of a contact resistance so when we do this for all of these electrodes we can acquire the impedance data and um we can analyze the impedance data in terms of analyzer capacitance from the impedance data and then what we get here uh is it's actually the dashboards here and what we can show is that there is actually a very good agreement between the capacitance increase and the increase in the b t surface area so we can use the measure the capacitance of the electrode of the cathode electrode as a measure of the effective p e t area increase right of course we have to do the same subtraction of the capacitance contributed by the carbon so then we use this method to try to follow the particle cracking up on cycling so the first example here is done by xc2 utilizing krypton bet measurements so what we know is when we cycle ncm particles we have a significant change in the lattice parameters and then the let's is volume and so one expects to have a tracking of these particles due to mechanical strain which occurs uh particularly at the interfaces between the primary crystallites of a polycrystalline material so when we cycle the material and this goes to 4.2 volts what we can see after the first charge and the fiber cm is that you can now see the development of cracks in the material these cracks actually close again after the first few cycles when you go into the discharge state and when we so this this can be shown here you can see the close a little bit again of course very qualitative in this case and when we cycle for many cycles then of course even in the discharge state you see the tracking of the material quite clearly so the cracking is actually irreversible um if we now measure the bet surface area of materials what we can do is we can measure the bt surface area of the pristine powder as i said before it's about 0.3 meters square per gram for these materials we can also measure the bet surface area of a charged electrode that of course can only be done with krypton bt because you can not have so much active mass in your instrument and then we can actually follow the bet surface area of cycled electrodes uh over the course of cycling this of course is very tedious uh because doing fib scm is is a big effort plus also cannot be quantified and the krypton bt of course requires a lot of experimentation uh to harvest electrodes put them in the bt and so on so what we wanted to do is to see whether we can follow this with our capacitance based method and so this is shown here on the next slide for an in an ncm material uh six to two in cm and we utilize for this a gold wire reference electrode so something we published before where essentially we insert the micro reference electrode between the two electrodes and we utilize a pre-lithiated lto electrode because that allows us to bring the cathode electrode after each cycle into blocking conditions meaning completely charging the electrode where we know that the charge stencil resistance becomes very large so we get the almost similar infinite charge transfer resistance and this allows us to get again a blocking condition signal from which it is very easy to quantify the capacitance so this is shown here for the first cycle so if we then cycle the material um of course the number of cycles comes a little bit later this i believe 200 cycles uh what we can see is the change in capacitance this is just your marked by the 180 millihertz frequency point and um when we uh look over the cycling then what we see is that uh depending on the cutoff potential 3.9 volts versus less than 4.1 or 4.2 or 4.5 we get a stronger increase in the capacitance so again as i said before we have to subtract the contribution from the pristine electrode and so the ratio of the pristine electrode minus the carbon contribution which is this part here and the signal afterwards that is our increase in active surface area which we deduce from these capacitance measurements and of course what we see is that higher potentials you get more cracking you expose more surface area you have more side reactions and this we believe is the reason why when you go to very high potentials you have more capacity fading for one of the reasons than if you cycle at the lower potentials right so here the specific capacitance changes by maybe 10 20 um so this is of course well known and so the other effect we wanted to look at is what is the effect of oxygen released from the surface upon the surface area increase of the material and so this is shown here for ncm when we go to very high state of charge meaning beyond is 80 soc where we know we get oxygen release so this one first one here is a polycrystalline material six to two uh and so the experiment we conduct here is that we gradually increase the potential in 100 millivolt steps we measure the capacitance capacity and we monitor at the same time the capacitance right and so what we can see here for this material at about 4.6 volts or so we see a step change in the capacitance which um we can also see in an 85 85 1001 material however it happens earlier meaning it already happens at the lower potential and the reason for this is of course that we know that at 80 soc we have the oxygen evolution but this happens uh at different potentials for these different materials so if we now put everything on the soc scale in the x axis then you can see that these two plots essentially superimpose and relate of course very nicely with the oxygen evolution which we observed by mass spectrometry from these two materials so the oxygen release leads to a cracking or enhanced cracking of the material and increases the surface area uh due to particle cracking the other thing is when we use the single crystal material so this has the same composition these two materials uh the pc85 is polycrystalline the s 85 the single crystal and what we see there is that even when we go into oxygen evolution we see no particle tracking right and this of course also supports this idea that particular cracking mostly happens at the interfaces between the single crystallites in the polycrystalline material and since you don't have this single crystallite interfaces in the single crystals uh the surface area is quite constant and this is of course with the long-term stability which has been reported in full cells uh by the group of uh chef don okay so then the last the next part we will look at the analyzing some of these degradation mechanisms by using x-ray powder diffraction and when we do this we first have to ask the question sort of what are the different mechanisms now so we of course already talked a little bit about it but essentially this is a cross-section of ncm polycrystalline material and for a cyclic material what you can see is cracks around all these primary crystallites and so what we expect is that whatever electrolyte has access we will form uh a reconstructed oxygen depleted surface layer on the on the ncm active material and that should lead to two things an increase in overpotential uh plus also a loss-effective material if this surface area if the surface layer is inactive for lithium intercalation and de-intercollection the other thing is of course we know that we can get particle cracking so it can become extreme so that really single particles could be released and then we would have a possible overpotential increase because we have electronically now isolated particles sort of in the center of the secondary agglomerates and the third one is of course the nitrous mixing which in principle also should lead to an increase in the overpotential due to the reduced availability for and and reduced availability for lithium sites for intercollection so two effects also so of course what we find is that all these three contributions of course may play a role and we have in principle two effects uh over potentials an increase of overpotential which can of course be caused by all of those which would lead to a smaller soc window and thus to a loss of capacitance capacity and of course we can also have irreversible loss of material either by converting the surface into an inactive material by electronically isolating materials in the center of the secondary agglomerates or by having just less lithium sites available due to blockage by transition metal and so this capacity loss we want to examine by x-ray powder diffraction and the approach for this we set up a study where we looked at the long-term cycling stability of ncm811 at 45 degrees uh the c rate was 02 at a cathode potential of 4.5 volts so this is of course a rather high hassle potential so it was supposed to be an accelerated study so what we used were pouch cells where we had a lithium reference electrode and where the graphite electrode was pre-lithiated so to avoid any sort of contribution from active loss of lithium and where the working electrode the ncm-811 electrode was cycled against the potential of the reference electrode um and so we had six cells in this case uh which recited two different cutoff cycle numbers so six cycles hundred to fifty four hundred five fifty and seven hundred and what you can see is that the capacity fading of these six cells uh follows each other very nicely here at zero two and here at diagnostic cycles at zero ten the same is true for the voltage uh fading so you get the decrease in the average discharge voltage and an increase in the average charge voltage due to the buildup of uh impedances and if we look at the capacity loss for this uh experiment over 700 cycles and 45 degrees at this rather high cut of potential we lose about 68 milliamp hours per gram which corresponds to about 70 capacity retention roughly um and so then what we did is we harvested the the cathode active materials after these different numbers of cycles uh and in the discharge states and measured them in a capillary for ex very power diffraction and then in the charge state we use these electrodes uh charge them in a half cell and then repeatedly experiment in the capillary and so with this we want to investigate the fading mechanism so this is shown in the next slide where we have a calibration curve for the c over a lattice parameter ratio as a function of the lithium content of the cancer this is in the fully discharged state this is in the fully charged state and what we find is this sort of calibration curve of c over a and from the c of a calibration we can get uh the con the amount of lithium which is in the material of course you could do the same thing by let's say icp analysis and so these are the two uh in the two regimes in the discharged electrodes and then the charged electrodes you can get the relationship between the coa parameter and the lithium content and what we see is when we cycle the cells from beginning of test to end of test over 700 cycles in both the charge state in the discharge state we are narrowing the soc window and from that we can calculate the capacity which would be due to simply cycling between these two windows between the in the discharge state and in the charge state and so this delta lithium content multiplied with the total theoretical amount of 274 million per gram and then 1.01 accounts for this one percent listing access we can calculate the capacity capacity which we would expect based on these xrd measurements right and so what we record is the lithium content in the discharge state and in the charge state and here we can get the shrinkage of the soc window we can describe as a loss of capacitance due to overpotentials uh which is essentially the capacitance which we get the beginning of test minus that at the end of test calculated by this equation here um so when we plot this we can look at the capacity loss of course first the one we measure simply electrochemically that's this part here and then the capacity loss which we would predict based on the shrinking soc window detected by xrd right and so the difference between those two uh of course means that there must be a loss of cathode active material and we will try to a few slides later to quantify what this loss would be um so the other thing of course we looked at was was other possible capacity fading contributions one effect of course comes from lithium nickel mixing uh which we already discussed would induce higher over potentials and from a redfeld analysis which was conducted analogously to what we had done in a previous study we looked at the amount of lithium in the of nickel in the lithium layer and what we see over these 700 cycles we get an increase of about two percent to be honest we expected the much more significant changes so cons we considered this rather small so if you look at it what would this mean in terms of uh active material loss where you essentially blocking lithium sites that would be very little about 4 million per gram but of course what we cannot determine from here is what kind of overpotential this would induce so it is a possible but most likely a minor degradation mechanism the other thing is the cracking of the material as we've seen the material will crack over cycling and it is possible that we get electric electronically disconnected materials inside the secondary agglomerate where we have poor electron conduction but of course a very good lithium-ion conduction through the electrolyte in the cracks and this would result in a material loss from these isolated particles however if that were to happen what you would expect that in somewhere in the charged or in the discharge state you would have to see materials which have different lithium contents so layered materials which has different lifting content and so for that we recorded the x-ray powder diffraction after all these cycles in both the this church and the torch then this is just an example for the church that you cannot really see much here but i can assure you we never saw any two different faces in lithium content right so from that we conclude that we do not really have a material also due to isolated uh particles but of course we could still have a a slower electron transport path here and induce an overpotential uh so what we want to look at is well can we one part of the over potentials of course we can quantify that the charge transfer resistance of the cathode active material and this we measured by two ways one was by a dci or pulse uh versus the lithium reference electrode so in principle you measure mostly the cathode response and what we can see here is that the impedance increases quite dramatically over these 700 cycles if we do a experiment where we harvest the electrodes and we build them in a coin cell with a freestanding graphite electrode so this is an electrode which has very very low impedance so this is shown actually here so the total impedance contribution of the freestanding graphic would be half of what you see here so negligible then we can analyze the this is a contact resistance on the cathode active material and then this is the charge transfer systems so that one also increases and if we put it in the upper plot what we can see is it more or less follows the dc or resistance which really is what you would expect but what it shows is that the cathode impedance increase is mostly due to an increasing charge transfer resistance which we believe is due to the formation of a oxygen depleted surface layer on the cap okay so now last slide what is the active material loss how can we actually determine it and so we can look what is our capacity loss from beginning of test until a given cycle so from cycle 6 in this case to 700 cycles we lose about 68 milliamp hours per gram now we can calculate how much we would lose because of the shrinkage of the soc window which is due to polarization due to over potentials that is calculated from the xpd data as shown before and there we would lose about 31 of these 68 million powers per gram and then we can calculate what is the material loss this you could calculate from the difference of the capacity based on the soc window minus the electrochemical capacitance normalized by the relative utilization of the material so the details are really in the paper and that would come out as 40. now of course those two would have have to add up to this and as a matter of fact it's pretty good right so the sum of those two is 71 this is 68 so we have an error of about five percent uh the other thing we can calculate here is what is the percentage material so what fraction of our cam do we really lose and this would be calculate could be calculated quite simply for a given cycle this is what you calculate based on the soc window minus what you measure electrochemically and this is also consistent what you would measure at a very very slow rate or the rate test going to very slow rates also detailed in the paper and so we can calculate the relative material loss here and this is about 18 so that means over the 700 cycles at 45 degrees we lose about 18 of our hazard active material presumably due to the formation of a surface layer if that were true uh the estimated thickness of the surface layer sort of like a quartile particle if you want based on the bt area of a reasonably of attract material as we measured before uh would be about 1300 meter um so this is reasonably consistent what people find in the literature uh if we plot this here this is the relative material loss this would be the calculated surface layer thickness uh over the 700 cycles you see it sort of continuously increases and if we compare this to a previous data we have done with exactly the same material using the same process but at much lower temperature then you see that higher temperatures actually enhances this effect and so what we can see is that we have a formation of an inactive reconstructed surface phase that is more pronounced at the higher temperature and with this a little bit late but i am at the end so just to briefly summarize a few key points uh so we can monitor actually and see to the capacitance of an nc of ncm electrodes and use it to estimate the extent of particle cracking and what we see of course it increases recycling and up and oxygen release at about 80 percent ssc but that only happens for polycrystalline materials and not for single crystals reinforcing this assumption that the weakest point is really between the single crystallites in that primary and in the secondary glomerult the other thing is we see a surface reconstruction of an oxygen release which leads to an active material loss and an increased charge transfer resistance and from all we can tell is that the extent of lifting meter mixing even at 45 degrees and 700 cycles is really not very large um and so what i try to show you some diagnostic methods to try to deconvolute this capacity losses when cycling a cathode active material at some conditions so these were pretty extreme 45 degrees and a high cathode potential and what we see is that about 50 is due to impedance scan and about 50 is due to materials and with this i'd like to thank our sponsors so really most of the contributions most of the data shown in this uh actually through a project which we have had with bsf over the last 10 years and then some parts of it are funded by the german ministry of education and research and this report was also funded by bmw and then of course i'd also like to acknowledge my group who has of course done all the work and even help me make the slides and i thank you very much for your attention and i apologize for being a little bit longer than intended hubert thank you very much for the deep dive from degradation and diagnostics uh we have a couple of minutes for question before uh we move on uh to young cook so let me let's get started um i have a question if i may start first what is the relationship between the material loss the impedance and the impedance score so you talk about the bt surface area change at impedance scores but how about the the the cracking part how are they related or this is a bit separated material often impedance right so i mean the material loss we are pretty sure is due to the formation of this inactive phase which we know also will lead to an increase in impedance however to be fair from the measured transfer resistances we could describe approximately half of these capacity losses due to impedance from what we measure so the other half we believe must be due but we cannot quantify either due to the small increase in the lift energy mixing because of course it is difficult to say okay two percent more uh nickel and the lithium sites uh what effect does that have on the resistance uh and and or to due to uh you know higher electronic resistance into the inner part of the particle so i think a better a better idea one will get with these studies with single crystals because then at least you can ignore the cracking part right this will not happen and however the just a little mixing point will still be there right yeah absolutely agree hubert um maybe a quick follow-up on that one so what always has confused me a little bit um you know in terms of the bet surface area change in the impedance growth it's it's it's a little bit counter-intuitive right so through the cracking uh in the deliciated states you're increasing the surface area but yet the impedance is decreasing and and certainly um many yourself included have pointed out um the electrolyte reaction with the new surface but naively i also thought um nonetheless you're increasing the surface area can you speak to why i would not expect the increased surface area to drop the polarization resistance in other words if i plotted the bet normalized um charge transfer resistance it's growing very quickly right even more so than the on normalized value so i was curious yes i mean you're fully right right you would expect that this to create more surface area you have a lower polarization which i believe is also true the only thing is that most of the surface area gain from these very low 0.3 meters square per gram to let's say 1.2 1.3 happens within the first cycle then it sort of gradually increases but then you don't have the factor between point three and uh three anymore but you have the factor between i don't know one point two one point five and three right so so the i mean this to be honest is i believe the reason why the rate capability of ncms is reasonably high despite the fact that they have as a powder a very low bet surface area because the effective bt surface area after one cycle let's say after the formation and that's when our experiments really started is already much higher so most of the benefit of the higher surface area due to cracking you get in the very first few cycles agreed yeah so i think um the time scale of the resistance growth is also twofold first cycle and then later cycle absolutely very much so we have a question from our audience uh regarding the electrolyte chemistry so you discuss the um transfer resistance growth um can you maybe comment a little bit on how this would depend on the electrolyte choices so let's say the formation of this oxygen depleted surface layer we believe does not depend on the electrolyte choice it's mostly a function of the state of charge to which you polarize the materials but of course it is true that when you have a let's say industrial electrode a thick electrode the state of charge is not necessarily homogeneous across the electrode particularly at higher rates so that unintentionally some of your particles near the interface between the electrode and the separator may already be at a much higher state of charge than your average set of tertiary and so in that sense it does relate to the electrolyte meaning uh to the transference number of the electrolyte and the conductivity of the electrolyte but i think it's only secondary understood um hubert uh so although we are out of time um we did have one final question from uh yangshan horn at mit so i thought i would ask it and i would just read her question verbatim um young asks uh could hubert comment more on how the cracking occurs how the clocking occurs so what what we believe is so what we see for example for the single crystal material right which has a bt area of about one meters per gram so this corresponds to about 400 nanometers or so 500 nanometers we see no cracking even though we cycle it in the same soc range even though we go to very high soc in one of the experiments right and so we believe that the cracking that the intrinsic strength of the material is high enough to accommodate the volume change which you do have without cracking and that the cracking only occurs at the interfaces between the primary crystallites and there has i think it was from jeff dan's group that i believe there were some studies on this but essentially this is sort of the weakest point right because you have these crystallites which move independently and the junction in between this is the weakest part right and this is what uh what cracks otherwise uh in single crystals you would have to see the same tracking thank you very much hubert and uh we'll return back to you for our panel discussion uh after young cook's presentation so let me hand things off uh to e you can yeah turn the camera off right yeah thank you will thank you hilbert for the very nice talk very deep dive on to the uh the castle materials let me now invite professor yanko sun to the stage yankus is currently a professor of energy engineering and the han young university and seoul south korea uh he received his phd from saw national university in 92 and then he was later group leader and samsung at once institute of technology and contributed to the commercialization of the lithium polymer batteries um we all know yankov has been very actively involved in the uh research of all type of lithium related chemistry whether it's lithium ion lithium sulfur lithium air and also sodium ion batteries as well to highlight one of his major achievement is this design and of a new concept of layer concentration gradient mcm cathode materials for the lithium ion batteries young coot has published many many papers it's probably around the neighborhood of 500 papers right now with that introduction let me invite yanku to uh start his presentation okay uh thank you for introducing good introduction of you it is my big pleasure to present uh my my data and the person overall i would like to thank the prophecy and the prophet to invite me very disabilities prestige the comp symposium and i would like to talk today high energy canceled for next generation electric vehicles this is the this let me see yeah this shows variation over the earth's surface temperature between 1880 and the present and you can see the current earth temperature increased 1.29 nine degree celsius compared to late 19th century and is still continuous increase we suffered from the hot summer in the last year to suppress earth's of the temperature increase one of the best solution is widespread use of the electric pickers this is the development history of the electric vehicles uh at this moment we still use uh the generation two electric vehicles with the driving range between around 300 and 400 kilometers to further increase the driving range in more than 500 kilometers we should develop high capacity uh electrode especially nickel each ncmc ncm and nga cathode materials this is the map over energy density of the cylindrical 1860 region iron berries after the first generation of lithium-ion battery was introduced in the market and by sony in the 1991 the energy density of rhythm iron has been increased through 32 4 times for example as you can see here the grey metallic ended density increase around the three times the volumetric energy density increased four times the the optimization of the cell design to maximize the packing density is mainly contributed to such a increase in the energy density over course the multiplication of negative and positive material partially contribute to the in order to further increase any density we need a high capacity electrode especially in in the chest of the materials this is my content today's content i would like to introduce capacitive gating mechanism of can reach cancer the burst and this is the charge it is charge cause as you can see that with increasing nickel content discharge capacity almost linearly increase and uh the surprisingly you can see that here the pure nickel oxide material to leave the discharge capacity of around 250 million per grams on the other hand the cycling performance is decreased with increasing nickel content and as you can see from the dhc profiles with increasing the nickel content exothermic peaks shifted to lower temperature with higher heat generations this is the summary of the this start with increasing the specific capacity by raising nuclear content from the one-third to 100 percent summer stability and capacity retention is accordingly decreased however based on the uh based on this result we believe that it is impossible to develop ideal capsules with both high capacity and high safety just to adjust by changing the compositions however we need the test material at this point with high capacity customer stability and outstanding capacity tensions in order to develop the target capsules we should embed you should know the capacitive aiding mechanism on the for the nikkei rich ncm and ncaa cancel the materials this is the pq debris curves and the volume variation of various ncm capsule materials as you can see that the ngm 90 and 95 and the pure adreno exhibit four distinct redux peaks due to multi-phase reactions from the h1 and the moroccan h2 and h3s and the redux peaks became polarized and reduced in the height with the cycling especially in the h2 h3 phase transitions on the contrary these results of peaks of the 622 and 811 hardly change during the cyclings the this is as you can see this is the unit cell volume variation versus the volt charging voltage the unisa volume decrease monotonously up to 4.1 volt and then decrease rapidly above 0.2 volt corresponding to apex of the h2h3 phase transitions the the unit cell volume variation decreased increased increase decreased with the increasing nickel content for example this value is 4.3 percent upon 6 to 2 and almost 10 percent for the pure uh rno particles and these are the close sectional scm image charged to 4.3 volt at the process cycles and as you can see that observed the micro cracks in the cycle the 622 and 811 and cms ah were arrested before reaching to particle outer surface uh however the upon the the ncm-95 and rno exhibit increased amount of the microclick which propagated the two particle outer surface this is the degradation mechanism of the ngm cathode in the case of the nickel contains more than 80 percent the formed micro crack resulted from the h2 h3 phase transition propagated to a practical outer surface facilitating electrolyte infiltration along the grain boundary into the particle interior which excellate surface degradation of primary particles by reacting unstable tetraborate nickel with electrolyte to form a nickel oxide like the impurity layer which leads to gradual capacity fadings in order to overcome the international property of the capacity intelligence property of the capacity aiding of the nicole each ncm and the ncaa castle we developed two approach for last 20 years one approach is conscientious gradient the other approach is microstructure controlled cathode let me introduce uh concentrate gradient cathode uh this is the development history of the conscientious gradient capsule materials in 2005 we report core share or material called generation ones as you can see this is the concentration profile of transmetals and the the in the case of nickel concentration in the case of nickel content relation is kept at very high levels and then suddenly decrease the at the particle surface in the 2005 we developed the core shell with the consensual gradient materials and in 2012 we developed a pool concentric gradient material nuclear concentric profile like this and manganese and cobalt concentric particle like this one and in the three years later three years later we developed advanced full concentric gradient with the two slabs this is the schematic diagram of synthesis of the concentric gradient the hydroxide precursor by the co-precipitation and we can use the same possibility in synthesizing conventional hydroxide prequels additional facility is one solution give a tank as you can see that in this figures nickel poor solution in tanker 2 is slowly pumped into nickel leach solution in tank 1 where the mixed solution is fed into batch type reactors leading to smooth consensual gradient of trench metals during reading the particles during the co-precipitation process concentric gradient canceled material have unique pictures distinguish distinguished from the conventional capsule the active materials first as you know has explained concentric gradient capsule material consists of nickel rich lichtkowa and nikhil poor shared part uh as you know post uh the the as you know that the castle the third piece of composition compromising high nickel content is very reactive to electrolyte attacks the nickel-rich conventional cattle of the surface is easily damaged by the electrolyte attacks forming the thick impurity layer whereas the nickel poor surface of the concentric gradient the cathode is much stable electrolytes much stable from the electrolyte attacks as you can see here and the second secondary concentric gradient chest consists of long large shaped planet particles where this conventional cathode is composed of rods each exit the polygonal type shape the prior particles as you can see the cross-sectional same image the conventional capsule material easily developed developed significant micro crack induced by the internal stress during the charge however the larger shape primary particle of a concentric gradient can effectively dissipate internal stress and thus minimize microgrid formation within the cathode particles this is the one example of the the consensual gradient we synthesized the two cathode one is fcg full concentric gradient with a nickel content over 61. the another one is one more percent aluminum dope the fcg material called alfcg and then we compared long-term cycling performance of the two cathodes this is a microstructure of the poor concentric gradient material as you can see the epma mapping image the nucleus stability depleted at the particle surface and became gradually increased toward the particular centers epm lines can also verify successful synthesis of the fcg capsule the actin materials and epma as you can see from the tm images surprisingly fcg cancels the particle composed of the long large shape prime particle aligned towards two aligned towards particle centers their lengths estimate to be around 2.55 micrometers another unique picture of the fcg material is that all of the observed prime particles have their c axis aligned in normal to av plane providing best channel for the legendary field this is the comparison of the cycling performance of the commercialized ncaa 82 together with the aluminum fcg cancer materials the long-term cycling performance clearly demonstrates the superior risk intercalation stability of the aluminum fcg castle as you can see from the same image nearly all over the particle from the cycle the ncaa chest was completely popular published in comparison in the cycle the fcg castle the original spherical morphology were well preserved in addition composition line scan confirms that the original concentration gradient were well maintained even after 3000 cycles we did a safe test one is uh one is the nail penetration the other is overcharged test we fabricate uh pouch type cells in our laboratory using the synthesized fcg cathode with the capacitor over 250 million per hour absolutely and then after the fully charged 2.2 volt and then nail was penetrated after nail penetration if the nail penetration test the highest cell temperature uh over the cell was uh 70 degree celsius uh we also did the overcharge test overtime test was carried out charged to either 250 soc or 12 volt as you can see that the the pouch cell was slowly swelling due to electrolyte evaporation after as you can see here after the overcharge test the cell voltage increase only 5.5 volt with the temperature remaining below 20 degree centigrade if the nail and the overcharge test both cell shows no smoke no thermal runways this is another example of the consensual gradient we prepared two ncm-90 castles one is the csg 90 fiat is a conventional cathode without a consensual gradient called gc90 and then we compare the structural and electro chemical performance over the two chest holders the as you can see from the long-term cycling performance strategy itself shows much improved the cycling performance with the capacity tension of 80 percent after one thousand cycles compared to sixty eight percent for the uh uh the shishi in ninety capsule as you can see from the uh the closest section same image after 500 cycles the micro crack and the particle pressure was observed in the cc 90 cathode and furthermore after 1000 cycles the 690 secondary particles nearly propolized into the individual primary particles on the other hand the in the case of the 6090 capsules no visible micro crate was observed up to 500 cycles and only heroin cracks heroin microclicks observed within the particle interior after 1000 cycles in order to understand the phase evolution the decomposited three reflection of the h2 h3 phage as a function of state of charge are studied as you can see the 003 reflection for the cc 90 capsule shows shows whole existence of the h2 h3 phase is only detected around only 4.2 volt indicating sharp play sharp phase transition from the h2 and h3 in the case of the cfg90 the h3 stage began to appear above 0.2 volt but the 82 phase was observed up to 0.3 volt moreover the csg 90 capsules less support from the volume radiation compared to cc 90s this is a time image over the two castles after 500 cycles uh cfg90 part cathode particle exhibited nickel oxide like the impurity layer over five nano five nanometer on the particle surface on the other hand surface damage of the cc 90 is more severe than the death of csg cathode because of the nickel-rich outer surface showing the impurity layer of the 30 nanometers in addition to surface damage the interior primary particle also suffer from severe surface damage due to electrolyte attack through the form formed through the formed microclips to compound the outstanding mechanical stability of the csg cathode stress distribution was calcul uh calculated this is the shishi 90 cassos this is the shishi csg90 castle encapsulation encapsulating shell compress the core and lead to slightly smaller potential stress in the core than that in the cc cc particle to reduce potential stress suppress the micro crack formation and thus improve the mechanical stability as you can see more importantly how to share exhibit with a much more homogeneous stress field compared to fish cathode fish suppress correct growth ins growth inside the shells this is the the capacitating mechanism for two cathode based on this result we conclude that outer shell is very effective in suppressing micro crack growth within the shells our consensual gradient capsule the material already penetrated into the eb market the this technology was licensed to three korean companies and this in 2018 kia niro ev used these materials in 2020 in the hendai khona e kona eu and akafox mica 5 from the beijing motor cooperation also use the concentric gradient capsule materials and we are expecting the concentric gradient chest of the bacteria for the enter into eb markets i will briefly introduce microstructure-controlled cathode inspired by the concentric gradient cathode materials we modified the nickel-rich capsule the material without concentric gradient the conventional capsule the conventional nga and the ncm castle composed of randomly oriented polygonalized shaped primary particles and the microstructure can be modified by the x dopings the doped the modified castle consists of radially oriented rod shaped primary particle as you can see here and let me show the our typical example the first we developed bottoms of the nikolichi and shame cathode we prepared two castle the one is police team nga the other is the one more percent boron doped nga called the pnga and as shown in the this figures the microstructure of the b and c a uh cathode material notably change the two have a long large shape a prime particle with the length of the three micrometers accordingly the pnga cases shows much improved cycling stability with the capacity tension of the 83 percent at the 1000 cycles and as you can see from the cross-sectional scm image after 1000 cycles p and c h ethanol particles were nearly popularized into several segments whereas pnga chest maintained their original particle integrity the superior cycling stability of the bnca was further confirmed by the institute or xid measurement before and after 1000 cycles as you can see that the pnga cancels demonstrate smooth base transitions after long-term cycling whereas the h3 phase is not observed in pleasing pnga cathode after 1000 cycles in addition the change in the change in contour plot over the 03 reflection agree well with the agreeable detailed h2 h3 phase in peak intensity so h2 h3dox peaks for pnga castle disappeared almost disappeared almost completely after 1000 cycles while pnga canceled maintained the distinct the distance redux peaks at the same cycling period to estimate the extent of the surface damage over the on the surface damage on cycling nickel oxidation state was met by the typographic support x-ray combined with the x-ray absorption spectroscopies and you can see that in pleasing pnga capsule nearly all over the inter-particle boundary was completely saturated by nickel 2 plus phase in comparison although some region over the pnga support from the surface degradation along the grain boundary the distribution of the nickel 3 plus is uniform confirming enhanced cycling stability over the pnga canceled after verifying the microstructure modification effect we further investigate to find the optimum microstructure for achieving long-term cycling stability this figure shows the dopant effect on microstructure of the castle the primary particles as you can see the microstructure varied from large each axial polygonal type primary particle to bind needle-like fat particles the cycling stability as you can see is strongly dependent on the particle microstructure among the various dopant material shows the best cycling performance this is the cross-sectional sm image of the ncaa and the ngpa cathode material in the case of the nga the micro quaking becomes severe with the increasing cuddle potential and the particle was cracked into the several segments of the charging to 4.3 volts in comparison ngta cathode contains the fine microstructure which are rested within the particle course we fabricate electrode by mixing over nca and ncta canceled material and then charged the two 4.3 volt cross-sectional same image clearly demonstrate the superior mechanical stability of the ngta castle materials and indeed moreover aerial protection over the micro crack in the nga castle during the discharge rather than that the adults that larger than dodge during the charge at the same voltage suggesting that micro crack do not completely reversibly close however ncta canceled demonstrate reversible micro cracking opening and closing behaviors this is a mechanism that enables superior recycling stability of ncta and chester materials as you can see that compared to other ncx castles companion doppler castle the exhibit the best long-term cycling performance and the close sectional sm image compounds morphological integrity of the ngta cathode materials we found that microstructure or primary particle depends on the topic and conclude that there is the optimum microstructure such as aspect ratio and the parameter particle risk for achieving long-term cycling performance this is the high resolution and hadoop 10 image of the ncta capsule materials as you as indicate by the lead arrow we observed additional extra spot in the layered structure patterns in addition as shown in a high resolution pm image some region showing the extras part is also observed in the layered structure as shown in these extra spots comes from long range order the interchange of the legion and nickel ions so-called ordered ordered ordered ordering structures we believe that the interchange between legion and financial metal induced by high balance tantalum darkened heat which change charge distribution around itself this structure seems to enhance structural stability by suppressing inter-layer collapse at the highly charged state and we are further starting this ordering structures this is my conclusion it is impossible to develop ideal ncm and ncaa canceled just by changing compositions unlike ncaa castle aluminium wall cycle at the 100 percent dod for 3000 boron ncaa castles greatly improved cycling stability the tantalum substitute castle to produce readily oriented prior particles the superior cycling stability clearly indicate the importance of microstructure we believe that our strategy of optimization of the canceled microstructure can lead to rational design and develop of nickel rich ngm and nga cathode uh we thanks to the korean government bmw energy energy solution pssf cbmm for supporting this uh research thank you for your attention well thank you young kud for the very interesting result um let me ask you a couple of questions i think we have a little bit of time the first one yanku you show this very nice morphology control whether you go from a polyhedral shape to this more like needle nano rod shape kind of spiking going on forming these secondary particles what's the crystallography orientation if you have this particle this needle shape pointing out um and what's the a and b c s right particularly along the length of the rod what's that assets the reason to ask this question is um the volume change you show the unit cell when you take lithium out during deliciation the unit cells shrink then looking at abc lattice constant and which ones shrink the most then this morphology matching with the crystallography orientation whether there's a correlation you know how it arranged in these spherical particles that can help avoid the cracking i'm trying to establish that correlation i want to see your thought on this yeah that is a great question as you can see this is the highlighting pm image the large chain morphology has has the av orientation in this direction and the c direction is this g axis is aligned in this directions and the region therefore region can be easily intercalated or de-interpolated through the primary particles through the a towards av planes okay yeah okay so in addition she uh aji uh shown in the song before and let me see yeah in this case as you can see it's a stress distribution calculations uh as you can see right that this is the cheat directions during the charge and during charge she actually is expanded at the highly uh highly the ritual state and however the the stress is uniformly contributed only the shared legions therefore we cannot observe microclicking severely yeah so very good um so uh looking at hilbert's top right hilbert has this diagnostic tool you know during charging discharging looking at impedance change surface area change so the uh different composition and morphology control in your case some of them has a less cracking like the full gladium one has less cracking this neater shape has less cracking would you be able to do these impedance study yet like what hilbert just showed to see during this process how impedance will evolve and the surface area will evolve with charging in this charging cycle for different uh morphology of particles you have whether that correlates with the uh the performance yeah the food did a very nice research in the identified capacity dating mechanism in terms of the beauty surface area and the corrections and we did also almost similar experimentals the we checked the impedance variations uh during the charge uh in the during charge and with the cycling and then compare the conventional cathode with rather shaped morphologic cathode materials based on our the expected experiment the impedance of the conventional cancer the rapidly increased with the cycling however the hour the the the large shape morphologic cathode material shows a very stable cycling uh very stable charge transport impedance increase even though cycle irrespective of the cycling the charges transport is very stable which is much smaller than those or death over the conventional capsule materials and we also checked the specific surface area changed during the cyclings based on how result bt surface area not so or significantly increase with cycling compared to conventional cathode materials okay yeah so let me ask you uh one last question and then i'll bring uh will chu and also hilbert to the stage again for panel discussion uh from the audience there's one question about well how does the dopant affect the necessary sintering conditions such as temperature if you choose different dopant you know how does the sintering condition you will need to consider and also rather the effect of ammonium hydroxide content compared to the different dopant use you know what parameters have a really large influence and control the primary particle morphology yeah that is also very nice questions and yeah we are now studying uh the uh the research how to control the primary particle morphology by doping and other technology other things and we are based on the hourly sentence the some dopant is very effective to prevent the to prevent the sintering of the primary particles the in this uh the presentation i didn't tell didn't explain the morphology of the hydroxide flickers in the in our hydroxide precursors produced hydroxide particles have long large shaped primary particles and if the hydroxide cricut has a long large shape prime particles and if we add some dopant the concent the the large chain morphology is well preserved even at the high temperature calculations we are understanding uh intensively why this opened this opened prevent micro uh the prevent the shinton effect yeah that's great it's good to know the dopant has such a big effect and stabilize the morphology during sintering so we with this thank you yanku let me now bring a hilbert and we'll back to the stage um so this is for panel discussion you know this certainly questions freely flow so maybe the first one hilbert i'd like to pick your thought a little bit you have seen the young coast talk and yanku see your top i'll give the opportunity for both of you to mutually maybe you have one question to ask i see there's a lot of synergy you know between your your two talks do you want to mutually ask each other question yeah i mean maybe maybe an observation from from his from young cook's talk and just to understand whether i got this correctly but from the analysis i saw the conclusion is in your case also note jungkook the particle breakage always occurs that the interface is between the crystallites right and that you can affect this by how you arrange crystallites in the secondary augmented uh whether you do it like this or you know in a spherical manner but it always occurs at the interface and not through a single primary crystalline is that correct did i see this correctly from the top uh actually yet i don't know exactly whether the prior particle is single crystal or not i think uh this is that is dependent on the nickel compositions uh we check the the the the crystal structure of primary particles uh uh reading uh secondary part of the nickel content the lower nickel content catalytic material for example nickel content of 60 percent we confirmed that the polio particle is was the single crystalline however we didn't check the crystal structure in detail of the prior particle in high nickel content such as 90 because as you can see that the primary particle morphology over the high nickel content is quite different from uh death of low nickel content in also of the particular shape and the particle thickness particle length and that is our the future homework to identify crystal structure and so on okay and then the other question i had was when you look at the effect of dopants right which then result in very different materials at the end is the effect of dopant to change the precursor material morphology which then carries over into the morphology of the callsign material or is the effect of the dopant affecting the way different morphologies are being formed during concentration yeah actually we are preparing the papers concerning this queen and uh based on our the agile i think the hydroxide precurse microstructure is very very important i mean that without a prior particle within the hydroxide precursors we cannot make large shape column structure the cathode active material and the calculations for example we prepared two different kind of the hydroxide prequels one is uh one is the one has the crisp long large shape prior particle the other is the conventional hydroxide precursor without the meaning that we don't consume without ladder shape morphologies after that we uh top the same dopant such as the container and the in some case in some case uh the cathode material shows the columnar structure a lot of the shape color of structure aligned structure however in some dope some the hydroxide particles cannot make the large chain based on this result it is necessary to make to synthesize hydroxide precursors with the bloodshed monopolies that's that that's great young could you have questions for hilbert or uh or should i pass to uh will if we will to ask you both of your questions yeah the hooves you did a very scientific and very nice uh analysis uh in terms of the initiative impedance and so on uh institute xrd and as you know there are a lot there are a lot of the uh the the variable for the capacitive fading potential acting material as well as such as the changing of the surface area and the surface changing of the crystal structure and the changing the change of the micro crackings and data you presented the capacity is mainly dependent on the three variables and micro cracking cattle mixing and increased surface areas however in the case of the micro quaking some isolated particles cannot contributed to to to the disinfect the effect such as impedance and xlv how to how can you differentiate differentiate among these parameters so i tried to briefly explain it but very briefly only but so essentially when we when we have significant particle cracking right you can imagine that portuguese inside may be electronically very poorly connected or disconnected and you know some people talk about these so-called fatigue phases or something like this right and in that case however you would have to see it in the diffractogram because you would have to see layered materials of different lithium composition right which is quite easy to distinguish and so that we never saw so from that we concluded that we didn't have you know perfectly isolated material you know you but however we could not exclude that you may not have a higher polarization uh impedance because of this right that cannot be excluded but you can exclude that you have completely disconnected particles that's for sure because if not if there were you would you would have to see it in the xrd so but overall right i mean it's it's of course very difficult to completely quantify the different contributions right i mean i try to say this i mean the the only contribution one i think can can quantify is sort of the material loss you have due to the reconstruction of the surface and the impedance of the charge transfer impedance but the contributions by let's say lithium nickel mixing which does increase over time right but still remains at a very low level i mean we cannot put into numbers i mean not quantify what effect it would have on the capacitance and capacity sorry so yeah so that we could not not determine i mean what we what we had hoped for to be honest because we had done this study at 25 degrees right and we didn't see any significant just in nickel mixing and so what someone had suggested was like well why don't you see it at higher temperature because there should be some significant mixing right and so that's why we conducted the study but we didn't see anything unfortunately i mean it was the same level as we saw at room temperature yeah you mentioned that uh you mentioned that at the capacity loss is a partly coming from the loss of the cancer act material did you measure measure the this amount from the anode side graphite another side or each metal side i think the because i think the capacity the mass loss is coming from the isolated particles within the particle centers well as i said i think we we excluded the isolated particle hypothesis because we would have expected that we would see it in the x or d either in the discharge or the charge state because they would have to have a different listing content so that we didn't see now any effects of the anode right in this study are completely eliminated right because you know we have a lto anode which was pre-lithiated we have a lot of electrolytes and so on right so this study really was just a sim only focus on the on the cathode active material um so and then the the amount of particle loss yes i think you can get that pretty conclusively because you know the soc window in which you cycle so you know what capacitance that should give you and we know the electrochemical capacitance we measure and the difference is the material lost and you get the same result instead of doing the i mean the extra d analysis is nice but this very cumbersome and actually you can get the same results by doing very very slow rate tests right so if you do a rate test from high rate to very low rates you can extrapolate sort of your material loss and that agrees with the xrd and this is admittedly much simpler experiment so material for sure is gone and we believe we can exclude that it's isolated material and let's say the amount you know of the material which you would grow as a surface space on the on the cathode active materials it's reasonably consistent with what people report in the literature in terms of thickness right but of course to really truly convincingly demonstrated one would have to do some detailed tm measurements right to measure those i mean that's for sure this this is very nice discussion where do you have a question you want to ask the panelists well the moderators are almost not necessary here so i think i have now found the recipe to have a great discussion as to have it you know friday midnight or friday afternoon and really the the blood gets flowing a lot so i'm really enjoying the discussion um young cook you you made a very important statement it was the first line in your conclusion which is it is difficult if not impossible to simultaneously realize safety and capacity and you made this point very clearly a number of years ago with the very famous plot showing the oxygen um release and the um temperature and also um the energy with the nickel content so i would like to probe a little bit deeper to the both of you uh hubert and young cook how as we go to these very very nickel rich compositions it seems that all the modification is only having a negligible effect on the oxygen stability of the system with regard to exothermic reactions and safety so how do we reconcile this too what is the strategy to getting the safety back in the system if there is a strategy or is it something that we have to do at the systems level maybe at the battery pack level or thermal management to combat this issue maybe jungkook can comment yes who would mentioned that he studied a lot of a large stud he studied evolution of the evolution mechanism of oxygen he published many papers and the based on the the i just focus on the cracking mechanism and i think the the quaking and oxygen evolution uh occurred simultaneously because the as you know tetravalent nickel is very very unstable at a highly charged state and the catalytic reactive and unstable category is changed automatically changed to more stable page such as nickel oxide laxative phase during this process this process oxygen is automatically evolved from the host structure and therefore in order to prevent the oxygen evolution from the horse structure uh the the meaning that other ways in meaning that the stabilization of the cathode material by preventing cracking is is that we should make we should synthesize columnar structure the catalytic material because even though the main capacity painting is coming from the inner particle in the prime particle within the secondary particles because the surface area of cathode material not so big not so high and however if particle cracking is happened the edge of the robot showed the surface area include dramatically increase which which increase the plastic reaction really with the electrolyte and therefore we should uh prevent micro cracking to creating and thus the uh morphological integrity should be should be maintained and i mean that otherwise if the micro quaking is a happens in the exposed surface area within secondary particle is huge and which induced nickel oxide nickel oxide laxative phage transport nickel oxide phase formation together with the simultaneously together with oxygen evaluations can i maybe before hubert you also share your thoughts let me just ask jungkook a quick question do you believe there is a way to delay the oxygen evolution exothermic oxygen reaction uh on heating right so to really think about ways to improve the safety so in other words if you have a particle that doesn't crack at all do you think you could substantially raise the um the oxygen release critical temperature yeah i don't know how exactly the uh these are the questions maybe who would you so uh who knows uh vietnamese because he studied he studied oxygen evolution reaction intensively to be honest i would i would go back to your your data because you published this beautiful data right that showed very clearly right that the higher the nickel content the lower is the temperature at which you release oxygen you know at about 200 degrees or something like this for a really nickel rich material right so that problem i think will not go away so when you say safety right there's always a question what what safety is it overcharged or is it overheating or whatever but let's say overheating that problem i think with the nickel rich material for sure will be there right because and it's kind of funny in history now because people had nca and they said well nca is a little bit unsafe so then people came up with ncm so they used the ncm111 which was quite safe but then they said oh but it doesn't have enough capacity so they made a ncm85105 or whatever right and now it's safety is the same right because it's just the nickel content so i think in terms of intrinsic safety i mean you i mean there is the high voltage spinel right that doesn't release oxygen neither electrochemically nor thermally unless you go to really high temperatures and the other material is lithium and manganese manganese-rich material right so i think both would have intrinsically a much higher safety huber i really resonate with your point it is a trade-off right between performance and safety and right now this is really driven by market requirements um and you know it really depends on how much you value each uh exactly but this goes look i think could be a segway for me if if you don't mind i can ask one more question which is given all these trade-offs what should the road map be for cathode chemistry i think this is the you know literally the trillion dollar question uh that people are asking everywhere uh academia industry and the like uh you know certainly we are already approaching almost completely uh lithium nickel oxide surely there will be a little bit of dopants and such but we're getting very close to the maximum capacity what's coming next um maybe i can provoke the both of you to comment a little bit on this and try to forecast where the next generation cathode would be i mean there was a recent discussion with some oem's car manufacturers right to where it was like well you know what about safety and do you compromise safety and they said we never compromise safety right and i think it is really true right you can control even this very reactive chemistry but it is additional cost to your system right you have to have additional safety features in your system you have to cool the battery you have separate sensors and whatever but it can be done right and so at the end it's just the question well how cheap can it be and what is the cheapest system and so of course if you can make a material which is very safe you can save a lot of systems cost right on the other hand well maybe you have a material which is not so safe but very cheap you can afford it on the other hand right so i think it's not the question one can look at uh in an isolated fashion right because at the end it's the cost of the entire system and at the end it is for sure true that i mean this was a person from volkswagen who said that right that we do not put cars on the road which we do not consider said uh not in the millions right i mean that would be crazy and so i think yeah so i think it's been demonstrated right that the safety of these materials can be maintained it's just always a question at which cost right and so i think if you if you look at sort of the energy targets people have and you know for electric vehicles 60 kilowatt hours is almost standard right and they want to go to 100 i mean at the end then it's cost right and then when you look at cost then i think it's pretty clear you have to get rid of nickel because only manganese could meet the cost targets right and so i think the two chemistries which are intrinsically safer maybe the manganese rich chemistry be the spinel or be it the you know the list of manganese-rich materials i mean they of course would if if one can make them work to the extent that they meet all their lifetime requirements they would of course hit both targets so that's why i think it is quite important to to look into these materials because i think this is the only way to uh yeah realize cars with large batteries right even larger i mean to a normal cost thank you hubert all right that's uh answer to the trillion dollar question uh young cook yeah i think the there was a two way to develop the uh cancer vector materials one way is like running is a continuous increase in the nickel content to deliver high capacity and we should make the make the good material at a as a as as possible as we can and for example the uh as i told you as i told its edges presented and we should synthesize why we can show the dji in nucleation material with columnar structure without without the micro questions which increase the stability further as well as the cycling behavior and if we make the the best cathode acting material with the nickel content even though even though even though which shows the shows the possible stability cell company cell make will optimize the the lithium ion battery by a combination of the anode material and the electrolyte and all and other other materials that is the one way and another way is to develop the mangan manganese rich layered cathode materials and as you know lithium rich and the main rich material is the even though one strong candidate however there are a lot of research for more than 20 years nobody's achieved in overcoming these issues another way is my opinion is that we should develop the manganese rich manganese rich layered materials the the question is how to stabilize the crystal structure lay the crystal structure for manganese chest x material and my question is that we should do topping and making the making the morphology such as columnar structure something like that and that we should we should deeply investigate this way because this research was not intensively before and people say that manganese we cannot make the we cannot uh synthesize the layered many rich cathode materials and we did it we didn't intensively study this material that is my my my opinion to develop good cancer materials so so i think our time is getting close i have one last question but i'm going to ask the question you guys don't need to answer i'll let bill to wrap up the whole day and also for the audience to consider so so will all this discussion change right dramatically when we go into the solid state better is regime i know it's very early solid state batteries um maybe it is hard to have a detailed discussion right now but if you want to have you know 30 seconds each to say what you want to say about solid state whether that will change the whole thinking hilbert looks like you will have something exciting to say oh uh the solid state well i mean in general right i mean the solid state batteries still use the same cathode active materials right i mean maybe slightly different morphologies or whatever but the chemistry of the active materials is not any different right and i mean one of the big advantages of course potentially would be that you could use a lithium metal anode right but it's not so straightforward either because the solid electrolytes are not so solid right i mean dendrites can still grow through and um but yeah so in terms of you know there may be some advantages in terms of temperature stability or so but as far as the active material degradation per se by itself is concerned i think you would have exactly the same the same phenomena right you would have the same oxygen release and you would have if you have a deliciated a strongly deliciated ncm it would release oxygen if it gets warm right so that i think wouldn't change anything you know i think it has many advantage potential advantages i think but as far as just reducing it to the cathode material i think it's very similar yeah well young 30 second there are a lot a lot there are a large number of huddles to develop the solid stability in terms of the capsules and electrolyte and anode material too and we should develop we should solve one by one step by step and as you pull the cathode material cathode material should the requirement of the cathode act material for solid stability is very very the resistive material to the high pressures because you know in order to make the solids the good solid stability we should we should in intensive uh threshing between uh electrolyte and the cathode echidna within under this circumstance the cathode activator very digestive for the problem the pressure and that is the cathode material active material the requirement in addition in addition surplus should be very stable from the reactive sulfide or hydride electrolyte yeah as for the electrolyte we should develop the more stable more reliable electrolyte rather than sulphide electrolyte and we should in order to mass production of the solid stability we should use the region ion battery facilities in order to do that we should we should develop the very stable very stable solid electrolyte and the adipose rich metals each metal still has dendrite problems even we use the solid-state electrolyte and we have a lot of hurdles that's probably for another day well we thank you young thank you but wish that we'll back back to you yeah let me add my thanks for a very illuminating uh and uh provocative discussions uh both technically and on a broader note um so thank you both again and um with this we are wrapped up for the spring quarter seminar series we will return um after the 4th of july holiday in the united states with our summer series of seminar so please stay tuned for our announcement on the next series of speakers ah i see uh we we also have a um a rescheduled talk so some of you might remember that um tim holm from quantumscape um was to speak in june but was unable to so we have rescheduled tim to july 30th so um we'll announce uh the talks for the next um quarter uh in the next couple weeks so with that like to thank everyone for tuning in this spring uh and hope everyone will enjoy my mostly pandemic free summer and hope to see you in july thank you very much you

Channel: Stanford ENERGY

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Rating: 5 out of 5

Keywords: Stanford, Stanford Energy

Id: 4aIswRfopnQ

Length: 121min 24sec (7284 seconds)

Published: Thu Jun 24 2021