 Good morning from Stanford University. My name is Welchu. I am a professor of material science engineering and the co-director of StorageX Initiative at the Precord Institute for Energy. I am happy to be joined by the Precord Energy Director Itoi today to have our bi-weekly StorageX seminar. Today we are extremely happy to have two outstanding academic colleagues join us to talk about advanced electrolytes and aqueous chemistry for next generation batteries. This is an exceptional important topic and we are very happy to be hearing from the two of the world's experts. Our speakers today are Professor Tran Sheng Wang and Professor Yi Jun Lu. Professor Wang is from the University of Maryland and Professor Lu is from the Chinese University of Hong Kong. And I'm pleased to introduce Professor Wang in a little bit more detail. He is currently the Robert Franklin and Francis Rick's right chair in the Department of Chemical and Biomolecular Engineering at the University of Maryland. He directs the Center for Research in Extreme Battery and he is very well known for his outstanding work in aqueous batteries, advance electrolytes such as water and salt electrolyte and he has been recognized as a highly cited researcher since 2018. He has made many important contributions today and has many students and postdocs who are now working as independent scientists contributing to the battery and electrochemistry community worldwide. Tran Sheng, we are so pleased to have you today and we're looking forward to your talk. Thank you for the invitation and I really appreciate the opportunity and I will start to share my screen. Today I will talk about electrolytes design for high capacity batteries. First, I want to mention what is the current electrolytes and for the lithium environment. So this is the electrolyte potential reference to the lithium metal. I acquiesce electrolytes and normally have a 2.0 volt and because they cannot further extend one potential lower than 2.5 reference to the lithium and they will generate hydrogen and above 4.5 they will generate oxygen and so they cannot form, the water cannot form a solid face, passivated the electrolyte so that's the limited the window and so then because of the narrow window limited the energy density so then they switch to the organic solvent. Use organic solvent to replace the water the advantages of organic solvent when they reduce the form of polymer. So when the potential lower and also the salt has opportunity to also reduce the form of SEI. So in traditional ECBMC electrolytes all the lithium is salvaged by the solvent and PF6 they also associate but loosely associated with the lithium. When the lithium moves to the anode side they bring solvent and PF6 close to the anode and then they reduce both the solvent and the PF6 reduce and they form organic inorganic SEI passivated on the anode surface. If it is graphite and then the organic the SEI strongly bonded with the graphite make the columbic efficiency really high 99.98 that ensure graphite can achieve 1000 cycle because organic inorganic SEI is flexible strongly bonded with graphite can tolerate 12% volume change of graphite. So that make the lithium ion battery so successful but if we want to increase the capacity and use silicon or lithium replace graphite then we if we use the same electrolytes they also form the same SEI but since that this SEI organic ion also strongly bonded with the lithium metal and the lithium metal during plating stripping they have a huge volume change and if the bonding really strong the SEI also suffer similar volume change and then do many many repeated volume change they will crack. When they crack they have a self-heal and reduce the columbic efficiency to 95. So that will limit the cycle life. So the goal is how can we change the electrolytes make this number is high at least 99.9 above. Then what kind of SEI can tolerate the lithium? So we believe this bonding should be weak. If they are weak then if lithium diffuse through the SEI and become the lithium atom then the bonding weak they can easily diffuse along the interface. Second if the bonding weak means interface energy is high if the lithium by chance they penetrate into the SEI they will have a high very large energy penalty because interface energy is high and the additional increase the interface will bring additional large energy required. So in this case we think we need for SEI which has very high interface energy with the lithium metal. By calculation we find out that lithium fluoride has the highest interface energy with the lithium metal. So this is the calculated result we consider old ceramic and we find out that lithium fluoride has a high interface energy the also mechanical shear module is high if like these two numbers they are highest. Normally polymer normally has very high strong bonding with the lithium and so in that case we prefer ceramic in old ceramic we prefer lithium fluoride. And second lithium fluoride also has a really largest band guide the meaning is electronic conductivity is lowest and if electronic conductivity is lowest when they form SEI at everything the thickness they will block the electronics. Everything SEI translate into a very high first cycle Olympic efficiency. Third is if by chance we can form lithium fluoride on the cathode side and then you see the stability window lithium fluoride as high as compared to others. So in this talk we will not only mention the lithium fluoride on the lithium metal we also talk if we form a lithium fluoride on the high capacitive cathode like the MC811 they also significantly increase the cycle life. So in this based on the this justification we think the best way is form a lithium fluoride but how can we form a lithium fluoride? So the idea is we need to reduce the anion rather than solid because anion reduces the form lithium fluoride as yeah if they are fully needed the anion. If we want to reduce the anion the perfect largely reduce the anion we should bring more anion concentration also we want to solve and has a lower reduction potential what's anion has a higher reduction potential so they have a lot very large reduction potential gap. So first we talk about how can we increase for native anion concentration. So one is we put a lot of salt and either PL6 or FSI and if we put a lot of salt there and they can form CIP and AGG meanings when a little more to the anion side to bring more anion. So anion has more opportunity to reduce so they can form a lithium fluoride. So this is the the PNL also do a lot of work and we use the carbonate we put a lot of salt there and they really can increase the efficiency in 99.2 but when we put a lot of salt there viscosity is high and then we think we can reduce the viscosity by use the dilute and also PNL did a lot of work and called this as localized high concentrated electrolytes. We did the same thing we use the HFE diluted high concentrated electrolytes different is we use carbonate because carbonate has a higher reduction potential and they also had a chance to be reduced and then we use a full native carbonate so even the salt will reduce they still have all the humidity to form a lithium fluoride. So we can get the same putting big efficiency as high concentrated for the 99.2 still too low and then we think second method is increase the gap and we add either because either has a very lower reduction potential like a PHF. PHF will reduce at the point 2.3 but a PF6 at the 1.2 and 1.2 so they have a huge gap here and then in this case and we can have a high chance to reduce the PF6. Second also in the PF6 mixer we have a lot of CIP also a lot of AGG here but the SSIP very small so that means not only the concentration the reduction potential gap increase also the concentration and also high and so that is we use these electrolytes we can reach a high Olympic efficiency 99.8 in additional to reach this high Olympic efficiency we also put a lithium philic substrate this is a graphite and business we mix together this allow a little the nucleation uniformly so here a lithium philic and here a lithium phobic then the lithium metal can uniform distribute and bounded with substrate also block a lithium pharma dendrite so that's two reasons make this the high really high Olympic efficiency and this is not only for lithium metal any the anode with high the volume change they also work at the same principle and then we try micro size silicon silicon normally micro size everybody believe it's a really really challenge but we use this design we validate we use micro silicon we can reach 99.9 so micro size we talk about more than 10 micro even 20 and for the silicon we know when micro size silicon they have a crack right now traditional SCI if the SCI silicon crack SCI also crack electrolyte penetrate and then they form SCI separate the crack that silicon A4 have a lithium fluoride and the bond is so weak and if even inside the silicon crack if SCI can protect it electrolyte cannot penetrate then they still can contact each other so they're still working the same thing and right now everybody want to use high capacity kettle AMC 811 whenever you have a high capacity then you have a crack same principle hold also right if you form lithium fluoride SCI and even inside the crack electrolyte cannot penetrate they still can achieve very stable side life so we'll show some data and right now since we have a still have a sovereign even we use THM and but it's still have an opportunity to reduce because reduction potential is still higher than the the deterioration of silicon potential if we want totally avoid the problem another way to use a sovereign free ionic liquid so with them we synthesize some ionic liquid and we demonstrate that on the lead metal anode we make 99.9 even at a high error capacity to 5 million out of percent of the screen so from this we think if sovereign is really uh and it's not good for the high capacity the electrolyte because volume is really big and another way is totally get rid of a sovereign is solid state electrolyte solid state we can consider no sovereign it should be perfect but when we use aero zero and they bring additional challenge they have an electronic conductivity and second because in the liquid they might not have this issue they are they do not have any electronic conductivity in the liquid electrolytes second the issue is in the liquid electrolyte we can easily adjust the composition from a little fried but at aero zero you never from a little fried so that's two challenges make the Olympic efficiency even lower than liquid and for the so far we have one opportunity is we found we can put a chlorine in the electrolytes and then they form a lithium chloride in the liquid electrolyte lithium chloride will dissolve into the electrolytes but in the solid state now so this the the so far it will add a cooling up to now is better than LPS the reason is the inefficient energy lithium chloride is higher compared to traditional chloride free LPS solid electrolytes but they still the efficiency is still not high the reason is the reduction this is really not stable and the reduction is compared to aero zero they are most less stable so that's make this lithium chloride concentration is slow it's small so if we can add additional more chloride here it will really form the passivity of the lithium chloride maybe we have a chance to increase the cooler Olympic efficiency so today I will give a wide example talk about this and how the lithium chloride improved the cycle life of microsizing so this is the principle also suitable for aqueous because aqueous the limitation is water also the solid if we can avoid a solid reduction use the the knowledge we develop maybe we can also return the aqueous electrolytes window so now we think rethink the aqueous family aqueous the solid same as the organic the lithium solid with the water so they're limited the window if we put a lot of salt if they're the same as in organic we really can't turn the window because salt has the opportunity to reduce and then form sdm and another unique is if we put a lot of salt in the water and they are separated with some high order polysulfide or some really high hydrothelic salt the solution then they bring us a new opportunity for a new type of the gravity for example sulfur sulfur in organic the high order polysulfide is out but in the water itself and they are face separated because of this lithium sulfide also hydrophilic and the electrolytes lithium tf-sat 21 molar also lithium really they are really both attracted to water but they are face separated then we have an opportunity to charge discharge in a liquid reaction and without a shuttle also we can use the lithium chloride the lithium bromide and use the chlorine and bromide into insertly into the graphite because they are face separation and bromide chloride cannot diffuse back so this is a new opportunity but right now we are we further use this chemistry in the organic and we demonstrate that this chemistry also can work in the organic but we get this knowledge by by the water itself chemistry but this high concentration electrolyte they have a definitely have a some change is the cost so we have to reduce the cost reduce the cost of millions reduce the concentration for the salt if we reduce the concentration of salt and then we cannot form sei if we're not a form sei they cannot use time in the window so we have to add additional salt from sei and then we use ammonia otf and then we put the salt as otf as a salt we take an example of zinc we use zinc otf and put ammonia otf ammonia the tanyang large size and they absorb zinc surface and then why is that they can block the water second have opportunity to reduce so they can form a zinc fluoride sei even that same as a little metal battery if we have a zinc fluoride and they have a high interface energy a zinc it's not easy penetrate from land dry so we can get a really high membrane efficiency we will show some data and the same principle and we check ot ceramic and the zinc fluoride as in the carbonate has highest interface energy and then we develop on purpose develop a zinc the carbonate zinc fluoride sei on cover on the surface this is an in-situ form and also uh uniquely if you put the otf otf is hydrophobic when you increase the cathode potential and otf absorb our surface they block the water and then we find out if water not involved into the cathode oxygen reaction they really have a two electron reaction that will really fast so this is one way we we use this aqueous battery the knowledge and develop as in the air bag second is we also use add non flammable solvent into the water in salt then in that case we can reduce the salt concentration so recently we added non flammable solvent we turn the window the the cathodic reduction potential to 1.2 volt and we demonstrate that MMO LTO we can have a 2.5 million and our percent square high loading still cycle really stable so this is the date we put the power cell and we can cycle 200 so today I will take this as a example show the chemistry so the principle how the artificial energy and can provide dendrites of zinc so this is the first topic about the the lithium ion battery we use silicon so silicon I know we say micro size they crack silicon crack also the sei crack and the reason we just mentioned because they strongly bonded with seis strongly bonded with silicon crack as they are definitely correct so we have a tool if crack as you let's all i punish it then they are separated the city in this case that the the silicon separated each other and then we lost the capacity another way is to go to nano size i think usually it does so much work and the success of a diamond sheet this nano silicon is the the best choice but the city can nano city can also suffer for societal Olympic efficiency and the kind of kind of life will maybe also a challenge same principle mc 81 1 if high capacity they really have a crack and if you really use the same electrical artists they have a same problem if the organic organic sei bonded if a crack inside crack the sei maybe also crack also organic the component in the sei will be dissolved at high potential so we really also prefer leaving for so our idea design is this is actually material what i was sitting on mc 81 1 if we can form a little fly they have a high artificial energy bonding so weak when the volume change they swing and span it because the bonding is so weak the sei or sei they are stable we can fly it stable so we hope in this case if this is stable electrical i cannot penetrate so even they crack they still contact and then they're still working so this is we assume if we have a sei even product sei sei on the surface that even inside the crack it should keep a stable type of life and then we demonstrate first of all we talk about silicon silicon we calculate the oh this is the silicon at a different the the level we calculate artificial energy with the uh legal product they have a high artificial energy second we try to form high concentration for lithium-5 in sei so they depend on the concentration of the ion also the potential difference between the ion reduction potential for ion and solvent so this is where we demonstrate traditional electrolytes we have they have a lot of ssip and but in the the thf lithium tf6 we have a lot of cip in that case we can prefer to reduce the pf6 and so in that case specifically here we have a very small ssip in the traditional electrolyte they only have a small cip but we have a huge amount of cip in the mixed thf and agg also high here agg very small traditional electrolytes also the potential we just demonstrated traditional electrolytes the solvent and the ion reduction potential similar at one point uh one point but in the thf thf reduce potential very lower and the ion reduction potential very high and then we think the mechanism is this is a charge discharge for silicon and this is the stress the measure that uses the the thin film of silicon the concept is when the releaseation during the volume change you say at the beginning they are elastic deformation but after a certain releaseation level and then it becomes plastic so meanings they have a like a lithium at high concentration they are really soft so if we can block the sei block the silicon during the the elastic deformation if the electrolyte cannot penetrate it later even they crack they can self heal it because they are really slow so then we think the opportunity is if we have a silicon and when we decrease the potential meanings releaseation and at the beginning when they reach to the potential lower than pf6 they form a lithium fluoride and even to hear the volume changes very small because the releaseation among very small and also they have a they start to volume change when you have a releaseation we know at here they fully elastic deformation they may have a crack but if they bounding so weak and even they crack and as the the lithium fluoride can survive and then electrolytes cannot penetrate after that they have a plastic deformation and then they maybe they can hold and seal peel the the crack and because I hear the solvent and not reduce the the polymer not a form the only form that is a lithium fluoride only at the very end and when with the potential ratio to lower lithium pf6 potential then they can start but normally we already form a lithium fluoride so solubility is 0.3 reduce potential but if we have a lithium fluoride there they should have a potential this is only form at the end of releaseation so when we combine and because the bonding is so weak and then the lithium the silicon by a string they can easily untouch the the lithium fluoride so the sci is stable and then second cycle they are just continue the cycle so we demonstrate this concept this is the this is the silicon and then we check this really have a lithium fluoride or not we use the beam here we use the beam to check the surface this is we just snapshot and we want because the beam damage of a lithium fluoride really serious so at the beginning you see you cannot see clearly we believe it's a polymer and a lithium fluoride if we use a beam a little bit longer time we will see inside you see the silicon like a flow more clearly we just put this side at the beginning at the beginning just put continue the beam damage of the surface we will see gradually you see gradually and gradually clear meaning we decompose the polymer surface and the lithium fluoride we really can see inside the silicon flow so this is after many cycle you will see the silicon at the beginning particle right now it's like fiber because they have a chloride but they are not separated by the actual lattice at the end and then we check the surface it really has as lithium fluoride or not this is silicon particle and then we use the yields to mapping the lithium fluoride we really see the lithium fluoride covered on the surface and then we use the yields to identify and we check this is the the one two three four five and then we use the yields to the mapping we say at the surface is the polymer and in the second layer near five surface we have a lithium fluoride and inside it is a lithium lithium silicon so we really see clearly see the lithium fluoride and if you use the traditional electrolytes you never see the clear lithium fluoride surface the layer they always mix this carbon the polymer so this identify we really form lithium fluoride on the surface use THF solid so this is the the cross section of the silicon electron so we just bought the silicon from sigma of rich and 325 match we did not do any treatment and we just put the electrolytes and cycled so this is the THF electrolytes different cycles they are really stable but use the traditional electrolyte different cycles quickly decay and we also show high read because lithium fluoride always believe has a very lower lithium conductivity and maybe they have a suffer from read capability but I need to mention is lithium fluoride so thin overall we say ESR really really small so they even increase the read capability so this is the read performance we can reach to the 3C and 5C so 5C we still got the high capacity but the red one is a traditional electrolytes they quickly decay and very impressive cycle life microcyle silicon they can really stable and traditional electrolytes 20 cycles they quickly decay so lithium fluoride not only for silicon because lithium fluoride normally has a very high artificial energy to all the other chemical because they are bound so strong they cannot bond to the other element so we demonstrate it's a universal design principle we test the aluminum 20 micro and we charge the charge at a different read read capacity and cycle life so this is a 250 cycle and they are also stable microcyle 1st collimic versus C91 similar as a graphite and not only aluminum base mesh 17 30 micro and without any treatment and we just charge the charge this is charge charge curl read the performance because this is electronic and data so read even high the series even high cycle life so this we demonstrate this is a universal design and then we check the full cell THF the problem is the anodic stability is lower because it's a user we want to reduce the reduction potential also will sacrifice oxidation potential also so we first try the etymine phosphate so we use the IFP silicon mesh with a business and aluminum all of three they make the full cell cycle really stable so the nth pn ratio only 1.3 traditional electrolyte for silicon full cell quickly decay and we also demonstrate mc and nca but nca we cannot charge to the above 4.1 because that is the limitation of the thf so right now we develop a secondary two electrolytes so now we can cycle and mc811 to see it so we demonstrate we say this is universal not only for anode any high capacity electrolyte this should be suitable and then we check the kettle lithium cobalt side if we increase the the charge of potential to 4.25 we can get a high capacity 200 but a traditional electrolyte quickly decay if we use our high voltage electrolytes they can form a legal fraud it's really much stable than the traditional electrolytes cool and bigger versatility can reach 99.5 so this is generation one high voltage electrolytes so we have a generation two electrolytes we test the mc811 and this is a cycle line so it's 500 cycle cool and bigger versatility not enough for 99 same as verify really stable so we show this is a concept lithium fried but this lithium fried should be insidious form not just pre artificial because if they have a damage they can settle here so that is our guide and then we talk about equis equis and we take a sample zinc here so the we want to emphasize in equis if we put the ammonia otf they can form a sci also if we put a hydrophobic otf the salt they can when the charge they can block the water in the kettle side and then water not involved or less involved in the the oxidation reduction reaction that they can go through the two electrons reaction so this is the idea and hydrophobic otf when you have a charge they on the kettle side they block the water and then the water not involved the reaction and then they can easily form a zinc oxide this is the reaction we demonstrate that there are two electron reaction in a zinc otf and during charge discharge they keep reversible because two electron reaction must faster than four electrons so the keep the cycle life pretty stable and the weather fast charge and also when we put an ammonia otf ammonia can reduce the form the sci the zinc fluoride sci on the zinc they can block the zinc dendrite so they have when we check the sci on the zinc surface you have a really high the fluorine and also oxygen and then we we we we think it's that they have a zinc fluoride zinc carbonate on the zinc surface and we check the zinc plating stripping and the efficiency is 99.9 above when you reach this high efficiency you really can make the zinc anode free so we really make the zinc free cell cell they can cycle 100 i think that is the the talk i hope not you can too much time thank you and for attending my talk so i turn over to you transcend thank you very much for sharing that comprehensive and systematic body of work we have a couple of minutes for questions so let's get started maybe the first question is for me transcend you talk a lot about coulombic efficiency but i believe you also show impedance at the interface especially at the cathode is also strongly affected by the electrolyte due to the desolvation barrier and kinetics can you talk a little bit about the difference in the design rules for high coulombic efficiency versus low impedance on the cathode or the anode in terms of the electrolyte choice so the the impedance so when you have a high interface energy so we can make a cycle life is better but they also increase the impedance because the interface the energy high the binding we but if we form the c i or s c i has a very lower e s r the meaning resistance total resistance small for total impedance is not increased that we demonstrate they still have a very high read capability so the key part is we know the interface energy interface resistance and the increase because you you form the c i s e i we on purpose design have a high resistance so the key part if you want to have a total resistance small you need to reduce the s e i themselves impedance so that is we say even for right they are so thin because the electronic conductivity is so low so i have other concept i say for the s e i the criteria should be electron ionic conductivity divided by electronic conductivity even ionic conductivity is lower i think for right but they have a very very lower electronic conductivity so the reducer thickness really small significantly than the reduce on the ionic conductivity so this is really so still high this is really so should be linked with the e s r so that is a total error resistance so that is my point friends and this is very interesting maybe a related question is i know there's not a lot of data here so maybe this is just intuition for most of the inorganic s c i i believe the prevailing hypothesis in the community is that the bulk transport in the s c i is limiting hence the importance of ionic connectivity but how about the interfacial resistance between the inorganic s c i and the bulk electrolyte for example is that ever or do you believe that could be limiting in some cases yes this is a related to the by not a solid state of biography they say oh how about we put an organically electrolytes and a lot of people argue and when they transfer from organic ion to the ceramic what is the resistance they definitely have an additional resistance there and it's really i think it's depend on the interface and the interface between the ceramic and organically electrolytes and if they have a summer the lithium ion have a bonding with the ceramic and then they have a transition period very thin layer that will reduce the like activation energy so now they say you totally block the solar and go to the ceramic if we have an interface between them and the bonding is a transition i think that it may be not a critical issue that's a great point maybe let me segue into the ionic conductivity so one thing that has always been you know very confusing to me is the discrepancy between the bulk ionic conductivity of lithium fluoride and lithium oxide versus the apparent conductivity that we can infer from the recapability of the batteries as many orders of magnitude different what do you think the mechanism is that gives higher uh gives rise to the higher ionic conductivity in the deposited sci versus the bulk material yeah i think that the deposited one maybe they have a two possibility one is they deposit from solution they have a liquid when they form a solid they have to remove the liquid then they have a porosity there i don't think they are same as in the in a vacuum deposit they are really dense because they have to remove the liquid maybe they are not form a crystal maybe they're more like a nervous so in that case so that even if i'm crystal green boundary they have a chance they are not so dense but that can easily block a solvent and but it's not really dense so that case they can slightly increase ionic conductivity secondly in c2 form always thin because they are limited by electronic conductivity if the bulk is there are no limitation you just deposit they have a certain thickness but you see to form the electronic connect will be lowered when they form a very very thin this top so overall resistance still very small maybe we take one last question um this one has to do with the formation uh protocol so in your work uh transient are you exploring the formation as a way to alter the deposition of the inorganic sci um when you're screening the material or do you typically use a standard formation protocol what does your standard and because we think the little pride that they can form sci really quickly and let's stop and so that's easily from human just a few maybe five or ten sites they already form and stabilize when you have a organic inorganic then you have a large volume change then do you take a long long time because they grab it crack peel crack peel and then they take a long time and when they reach larger thickness then stable if a really little fried pure they can easily just stop stabilize so we normally ten sites and we can reach a stable capacity all right transcend thank you very much still many mysteries for scs as always but thank you very much for sharing your comprehensive body of work uh so now let me invite uh yi to come and introduce our next speaker uh louie jin yi yeah thank you well um transcend very very nice talk very strong dose on electrolyte i always enjoy your talk about that now let me invite uh professor eachon lou to come to the uh podium uh let me do a introduction about eachon um eachon did his her undergrad in the national xinhua university in taiwan then after that he went to mit to get her phd and material science and engineering so following by a postdoc in germany he she later joined um chinese university of hong kong as a faculty she's currently a social professor right there eachon has been doing quite exciting work in the past decade i have been following her research quite a bit now in her own research group she has a variety of the battery related projects ranging from redox flow to metal oxygen soft soft selenium battery solid state and so on her work has been widely recognized um she has won numerous awards including young research award 2016 the university education award in 2016 as well vice chancellor exemplary teaching award she's also a founding member of young academy of science of hong kong with that eachon i would like to invite you to start your presentation thank you thank you professor tray um hello everyone so first i'd like to thank uh professor tray and wealth kind invitation to speak it's a great honor to speak at the storage x symposium um me and my group members has been uh following closely to every lectures since the inaugurations of the symposium so thank you all very much so today uh i'd like to share our recent work in the area of aqueous batteries including lithium ion batteries and the redox flow battery so batteries are very important uh devices in our daily life and uh we actually need batteries from electric vehicles smart grid for the green cities and storing renewable energies as well as the large-scale grid storage so we are putting big batteries in our house in our cars therefore safety is one of the most important factors in battery design so currently commercial lithium ion batteries use flammable electrolytes which will cause battery fires and explosions ranging from cell phones laptops and electric vehicles and even in the larger scale when we connect batteries with renewable energy such as wind power and solar power plants so these type of catastrophic fire explosions are very serious things that we have to address therefore um using aqueous electrolyte in fact is a effective way to mitigate this type of fire explosion however water is limited by its stability window and traditional aqueous batteries are limited around two volts thanks to professor Wang and professor Xi's group work proposing a new concept of water and salt electrolyte using highly concentrated electrolyte to stabilize water by reducing free water molecules as well as forming stable sci layer their work has been widely applied and also in their work they show a working prototype of a full aqueous lithium ion batteries more than three volts and with very stable cycling stability as well so water and salt electrolyte has been widely applied and with many subsequent efforts in the field including hydra melt using about 20 molarity of lithium tfsi and or 42 lithium tfsi or 33 molarity li ptfs fsi so these highly concentrated electrolyte are effective in increasing water stability as we see that they provide wider stability window compared to pure water however they are also facing high cost and potential toxicity issues for future application in terms of commercialization and also sustainability so when we start thinking about this problem we were thinking how can we avoid using highly concentrated electrolyte but still stabilize water so we are inspired by a common phenomenon that in living cells called molecular crowding so molecular crowding essentially states that the activity of water can be significantly modified if we have a large molecule such as proteins present with high concentrations in the solution so changing water activity using large amount of molecular crowding agents could change activity so we were thinking could that be a path to reduce water decomposition using low cost and eco-friendly crowding agents so the idea is that to use the crowding agents which will interact with water molecules through hydrogen bonding and this type of hydrogen bonding is in fact weaker than water water hydrogen bonding but because we put a lot of it now we can reduce water and water hydrogen bonds and therefore we can actually strengthen the OH covalent bonds which then can discourage water splitting so in other words using a crowding agents such as water miscible polymers that we may be able to stabilize water in our aqueous electrolyte so in order to verify this concept we found a very common crowding agents for water this is a polyethylene glycol and it's a water miscible polymer which means that it can be mixed with water in any ratio and thanks to that we can make this type of electrolyte in more than 90 percent of the PEG mixed with water and PEG is not toxic and slow cost and you can see this material has significantly lower in cost compared to the lithium salt so in the electrolyte that we're going to use are going to have only two molarity for the ion conduction and will vary the PEG content to see the stability window of water so first we conduct the LSB to see the electrochemical voltage window so as you can see here the hydrogen evolution onset potential are significantly delayed as we increase the content of PEG from 70 percent all the way to 94 percent and with 94 percent of PEG we're able to delay the HEER to after 1.3 volts of lithium so with that we're able to achieve a 3.2 volts window with a low concentration of the salt and using the molecular crowding agents to stabilize the water so we use DAT to understand the water environment in the molecular crowding electrolyte and versus the electrolyte in the regular electrolyte so you can see the regular aqueous electrolyte we have a lot of free water running around and with the molecular crowding electrolyte not only we're reducing the free water but also waters are actually bounded with the PEG molecular crowding agents and therefore their environments are very different in terms of their property and their chemical environments so to further understand how the crowding agents change the environment of water molecules we use NMR and FTIR to probe as increase the PEG content how does that change water's environments so here we can see through NMR we see that as we increase the PEG content we found that the water actually become more shielded and which indicates a weaker hydrogen bond network around the water at the same time FTIR shows that as we increase PEG content the OH stretching has a blue shift through this FTIR spectrum and we can see that means that the OH stretching become higher in energy with stronger bonding so these evidence supports our hypothesis that with crowding agents we're able to strengthen the OH bond in the water molecules and therefore discourage the water splitting reaction so using this electrolyte through 4.5 volts all the way to 1.3 volts we are able to apply LMO as a positive electrode and LTO as the negative electrodes to see a full cell reaction in this electrolyte so before we cycle the battery we want to see whether the hydrogen evolution reaction or even oxygen evolution reaction is really suppressed in the full cell so we apply the online electrochemical mass by traspid to online monitoring the gas evolutions of this electrolyte in the full cell so you can see this is the first cycle of charge discharge profile and you can see that there is no sign of the hydrogen or oxygens or other type of parasitic gas evolution and this is the same even for the 10th cycle so you can see indeed not only the sickly photometry shows a stability window but using mass by trauma tree can still show that there is no signs of hydrogen evolution so with this electrolyte we're able to cycle this full cell about 300 cycles with about 80% capacity retention at 1C rates so we also want to compare the water stability window of our electrolyte with other type of highly concentrated electrolytes and we do that in identical electrodes just for the parallel comparison so you can see molecular clouding electrolyte in fact provide a wider stability window compared to the highly concentrated electrolyte to further support its efficacy for so stabilizing water also some of the electrolyte that may give you wide voltage window but in fact in the real battery operation you may still see hydrogen evolution so we parallelly compare the PEG molecular clouding electrolyte label in red and compare with highly concentrated electrolyte you can see that we can still see some of the hydrogen evolution in some of the electrolytes using highly concentrated electrolyte so these are the small side reactions that we need to further reduce but using molecular clouding it seems to be quite stable in terms of suppressing HER so what we compare so far is based on a pure electrolyte system with other highly concentrated electrolyte but we also know that there are other strategy that has been developed in the water insult type of electrolyte such as gel coating so we also applied the the coating that developed by Professor Wang and Professor Xu a fluorinated coating to enable a 4-volt full cell using the PEG molecular clouding electrolyte so therefore this is just a starting point for a pure electrolyte system that we can even add other type of strategy to make it better so and the flammability test also showed that the PEG electrolytes can successfully put up the fire and would be stable than the commercial electrolyte but also the PEG molecular clouding electrolyte is also more stable than the PEG itself and even some of the polymers such as PEO so we believe that the water play a critical role in the safety so so far the PEG molecular clouding electrolyte has been effective in providing wide voltage window with low concentration of salt however its ionic conductivity is not satisfactory it's around 0.8 millisiemen per centimeter which is much lower than the 21 molarity of lithium TFSI in water so and why is that so if you look at the viscosity of PEG is significantly higher than the pure electrolytes therefore we are developing a new type of clouding agents with significantly lower viscosity to improve this ionic conductivity to more than 2 millisiemen per centimeter and so that will help us to improve the electrolyte conductivity and also the contact resistance of the cell so here you can see that with the new it was a new clouding agents in blue we can significantly reduce the over potential that in the cell compared to the PEG molecular clouding electrolyte and using the spectroscopy we can also show that there is no sign of hydrogen evolution or oxygen evolution in this new type of clouding agent electrolyte so to summarize this part we believe that this is a new platform for designing high-voltage aqueous electrolyte using molecular clouding agents to break hydrogen bond network within the waters therefore we can strengthen the OH stretching within the water molecule therefore to widen the voltage window and stabilize the water going beyond lithium-ion batteries we actually learned from previous symposium lecture that if we want to realize long-duration energy storage we need to go beyond lithium-ion battery and low-duration is such as more than 10 hours of storage and that we will need something else than a lithium-ion battery so in fact redox flow batteries has a very good cost advantage for long-duration application so this is a schematic taken from a recent ITIF report very nicely schematically show for a lithium-ion battery two times durations means two times cost for particular application but for redox flow battery a two times duration will just need a small added cost on top of the original system thanks to its decouple power and energy and scalable durations also an important feature of flow battery is that it has much lower safety hazard because we actually separated the positive and negative electrolyte so they will not be short circuiting or self-discharge easily if we stop the pumping so therefore there are a lot more control over lithium-ion battery however flow batteries currently are still struggling with a lot of challenges including it's still expensive for short duration applications it has lower energy density and it suffers from crossover which then become a problem for cycle life of the redox flow battery so in our group to address this issue we're looking at a very low cost earth abundant element sulfur so polysulfide-based redox flow battery is very safe and cheap thanks to sulfur which is we know extremely low cost and with high capacity so you can see the cost per charge is significantly lower than that of vanadium that used in vanadium redox flow battery so using polysulfide in fact is a great option so in the markets they are polysulfide bromide flow battery but bromide could be a toxic gas when during the cycling so in 2016 we demonstrated using iodide as a couple with polysulfide and this system in fact achieved a lower chemical cost compared to the vanadium flow battery and promised higher energy density compared to the vanadium flow battery when we did this in 2016 unfortunately we were using a commercial naphyl membrane and we always observed decay starts at about 50 cycles and this decay is directly related to a few reasons first is the crossover of polysulfide and polyiodide across the membrane and this will lead to capacity loss and this capacity loss essentially irrecoverable and second is water migrations and also OH migrations through the membrane due to the osmosis pressure and so this become a critical issue if you want to pursue polysulfide base redox flow battery so recently we developed a new membrane and to help mitigate these type of questions so we developed a PVDF bounded catch and black coating and to put on the both side of the membrane and this membrane with a hydrophobic component of the PVDF which can penetrate into the pores and this can mitigate water and OH migration and this carbon phase could be absorbing the polysulfide on the negative side and absorbing a polyiodide on the positive side which then can further repel its identical ions from further crossing over to the other side so using this strategy we hope to alleviate this crossover issue in the polysulfide redox flow battery so to show its efficacy we first to check the self discharge so we charge the battery to a full charge state and discharge and then let it sit without charging or discharge and measure the ocv so you can see using the commercial membrane the self discharge it's very quickly and the battery basically go from full charge to almost zero volts over across of 50 hours but using the modified membranes essentially we can it can last for more than 900 hours with very small decay over the course of 900 hours and if you do the cycling of charge discharge you can also see that the profile of the cell using this membrane are very consistent over cycles over 1200 cycles but the one with just napheon you can see start to decay even at the 50 cycle so we first perform this static cell test to see the membrane efficacy so you can see that this type of membrane can reach more than 99.9 percent clube efficiency for polysulfide which is significantly higher than one piece of napheon or even two pieces of napheon and over the over three months it does not show any decay and at the end we start to see decayed after three months and you can actually calculate the final decay rate is about 0.005 percent per day or 0.0004 percent per cycle so you can see this is completely different from what polysulfide would have been in the commercial membrane and then we start using a fully flow two-sided fully flow polysulfide iodide battery and then we can see over the course of flow cycling we still see a very stable performance over again 3.1 months and at the end we use a 100% SOC to check the actual remaining capacity and we get more than 99.2 percent remaining capacity after three months so the decay rate for the flow battery is about 0.008 percent per day which is quite similar to that of the static mode which show that they are quite consistent stable without whether it's flow or not so we want to understand what makes it so different between this membrane and the commercial membrane so we perform the small angle x-ray diffraction to detect or to measure the water cluster size within the two different membranes so you can see the modified membrane has a much smaller water cluster size compared to that of the commercial membrane which is consistent with a much lower water uptake of our modified membrane as well as the much lower swelling ratio of the modified membrane so that is the key to the restraint the water migration as well as the polysulfide crossover we also perform an institute at TIR try to understand the water migration behavior through the membranes so what we did is we perform a hydration and dehydration process and try to measure the water content in the membrane through the time so you can see with the commercial membrane the water can go in and out through dehydration and absorption very quickly but that of the modified membrane has much restrained water migration and water mobility so that is also consistent with the stable cycling so lastly we want to know what is the economical analysis for this type of battery so we adapt a model from Schmid and co-worker to calculate the levelized cost of storage as you can see from here the polysulfide iodide that we use our bench top lab scale prototype you can see that it can be much lower in price compared to other emerging flow battery and even can be beat the well-established vanadium flow battery when the storage hour are more than 14 hours so this is really targeting for long duration application so to show that this is not only just the projection we actually did a validation test for the flow cycle for the flow cell of a storage time for 13 hours and 15 hours and to see whether they can really hold up to this long duration so you can see over 80 days there is no capacity that can be detected using this membrane for the polysulfide iodide redox flow battery so to summarize today we discussed a new platform for designing high-voltage aqueous latch light using molecular crowding agents and this is a way that we can really expand beyond lithium ion could go to sodium and potassium ion batteries where molecular crowding agent could be low cost and environmental friendly to improve the stability of water and second we showed that the membrane design is a deterministic factor of a polysulfide low-cost polysulfide flow battery and lastly for the audience who is interested in assessment method and performance metrics for redox flow battery you're welcome to also check out our recent perspective in discussing the redox flow battery assessment methods and performance matrix in the regulations to the working principles and the degradation mechanism so this really help us to put things together and also have unified performance matrix comparison for the community lastly i'd like to thank hong kong government for the funding agents rgc and the itc and the work presented today are mainly conducted by two of my students miss jinxia and dr jerjun li so um and thank you all for listening and i'm happy to take questions well each one thank you for the very nice talk and very nice work um let me uh start by asking you first questions um if i look at trance's work and your work about the uh you talk about this concept molecular crowding uh it's very very interesting um so this really made me uh just recall um about made more than 10 years ago about 2009 when ball parkings were still here working with me closely at stanford we started a a piece of work uh it's actually just increased concentration of electrolyte for the lithium system so the overall idea of whether is uh water in salt or molecular crowding is using something to hide out the water's activity reduce water activity so you can increase the stability window i remember 2009 we see go up to like four more or five more concentration of lithium electrolyte the stability window already increased but we didn't go to the level of like what you and trance have been showing so what i want what i mean right here this tide tide out the water activity is critical to expand the stability window by the same time um you see ionic conductivity actually drops quite a bit um aqueous solution typically you are looking into it's like 100 millisilium per centimeter square at that type of range right once this water get tied up the ionic conductivity also drop down to single digital millisilium and maybe around that range so what what will be the balance and thinking about that you know what do we need uh and ionic conductivity and this all balanced with water activity reduction so i want to see your your thoughts on on this question yes absolutely this is one of the most important balance in this in this line of research so so first of all i think ionic conductivity is very important i think we need to at least get to five to ten or even 20 millisilium per centimeter to be to be more competitive and i guess practical so i guess right now uh using the PEG molecular clouding electrolyte it was below one millisilium so the approach we are using right now is to reduce the viscosity of the polymer itself so finding those polymers that uh even much lower viscosity and in in our recent experiment this shows that you can increase about to about three to five millisilium and that is one direction is is for whatever tidying up the water molecule we want to make sure that is not very viscosity very high viscosity so that's one thing and also i guess salt is always a the reason for higher conductivity right so maybe now we are only used to molarity maybe slightly increase but just to increase the ionic conductivity there are other school of thoughts that in the in the research paper that people may be adding organic electrolyte that has lower viscosity to the water and salts type of electrolyte to increase the conductivity but also that says disadvantage of safety right so so we are looking at safety uh conductivity and the voltage window so in my opinion i think since we are working on this for the safety so i think the the safety is first right otherwise we just use non-aqueous electrolyte uh so with that uh the voltage window we want to go through maybe right now we are looking at 3.2 to 4 volts so uh now we can enable lto but can we enable graphites right so if aqueous type of electrolyte can enable graphites then that would be also very good um i think ionic conductivity for practical maybe around five midi semen could be already practical but of course better the higher the better but again we are looking at the the balance here so it's it's tough yeah yeah yeah um second question um so these uh uh clouded molecular clouding electrolyte uh you look at the HER side it's suppressed uh so OER do you want to comment on OER side this is also a question from an audience you know uh you know what's the suppression effect on the OER uh it's do you get more suppression or what do you get so little suppression if uh we're a little yeah yes actually this is a very critical question uh in the in the beginning when i discuss this idea with professor uh county uh you also actually point out uh from our data that is a very asymmetry suppression so we suppress a lot of HER but OER is actually pretty similar to every other type of electrolyte uh and we actually kind of figure out a little bit why um so the reason we improve HER is because we strengthen the OH bonding of the of the water but if you look at OER process the rate-determining step of OER is actually not OH bond breaking but the rate-determining step for HER is the OH bond breaking but the rate-determining step for OER is more like the say the uh OH uh OH desorption or the old desorption to form oxygen so because they have different rate-determining step this molecular clouding methods can affect HER a lot but not much of the OER so in order to do that then you need to look at the rate-determining step for OER so it's really the desorption uh or the adsorption of the water then I think modifying electrolyte surface would be more effective for the OER so that's also something we are uh doing right now is try to see different type of electrolyte modification to to see how much we can suppress the OER side yeah so this is great um so the next question uh related to your redox flow I mean very nice what you exploring uh polysulfide chemistry as annual iodine as a cathode and we know in the redox flow battery is always you want to come up the right pairing having the right potential right solubility and and so on so first question is is iodine can see the uh attractive uh I see your cause analysis right go down to about 80 dollars per kilowatt hour of materialist cost is is that limited by iodine right that's my assumption also yeah um so so it will be great to come on another redox couple that's much lower cost that's one question I want to pick your thought the second question is this iodine side and the polysulfide side right I think this audience is also a person asking the question great question looks like it's a pH mismatch right it's my understanding correct they are a different pH condition yeah would that cause a quite bigger problem to handle you know uh during the operation yes so so let me start with the second question so yes that the pH is slightly different so one is the neutral uh and one is uh more on the alkaline side so therefore the OH migrations and water migration associated with the OH migration is very critical therefore without membrane modification you can see we can't do more than 50 cycle so that is why the membrane is so important when you have the membrane modification you can do it right um but the first questions iodine is definitely the cost limitation we're looking at here um and I mean there are there are options with lower cost like a bromide right so polysulfide bromide is actually a commercial uh almost commercial system that's available in the in the in all the star company uh so I think this membrane can also be applied in the polysulfide bromide system it's just we didn't do the bromide because we don't want to deal with the toxic gas uh and etc so but that doesn't prevent uh this membrane applied in the lower cost of the bromide system so you're absolutely right I think the iodide um it is the cost limitation but it is already better than vanadium so uh I think that could be a something that we should keep searching yeah yeah uh that's great um each one uh next question is um well there's a person in the audience asking so the solution you know uh is the key you're playing right now uh so what about coating on the electrode I can't you you can't already mention that already maybe giving you a little bit more time to expand on that how does the coating on the electrode in conjunction with with electrolyte can improve uh the uh the performance suppress the cyclical reaction even further just expand on that a little bit of the effect of coating yes so uh this is a great question so after we kind of not figure out but have a hypothesis on why OER is not changing as much so we immediately thought okay that's surprise is great determining step so first let's maybe have a hydrophobic coating on the on the electrodes especially on the positive side um and so that can help to prevent water get closer to the electrodes and and that also applies to say we can have hydrophobic coating on the carbon particles uh so that's actually something we are working on right now to in conjunction with the molecular crowding and the electrodes modification to see if that can bring both OER and HER together so I think hydrophobic coating is one path um also it could be an oxide a lithium ion conducting oxide uh that is not electrical conductive but ionic conductive right so these two paths could uh could really help on OER sites uh in my opinion so yeah so maybe one last question then we'll bring uh both will and turn some back to the panel discussion um the redox flow you show the iodine and the polysulfide with this uh incredible performance this new paper you have this year and nature energy um so in the redox flow we all know um you know one major e-special right is a crossover between redox species once you know it crossover even your crossover just one percent and over the cycle this will degrade fast because of mixing now the species for most redox couple they are not allowed to mix except very few redox system that that that could be fine kind of people like mixture or ion chromium you know different concentration so I don't need to go go into the detail um so I'm thinking you're looking in your uh data uh have you done the measurement just after cycling these flow this liquid in and out for number cycle measuring using maybe ICP right elemental analysis on different analy or catholic and that will give you the quantified concentration of crossover yeah uh would you be able to see the two crossover rates uh like 0.1 percent per cycle or less you know right you want to see hold on this yeah yeah that that's an excellent point um but so yes I think that would be important maybe very much more quantitative way uh just kind of do the ICP on both side of electrolyte we haven't done that um and so I think that's something we we were definitely uh looking to do that and but basically through the estimation from the capacity loss over the course of say three or four months that's what we are currently using but uh I I agree with you I think uh uh to go to that even just 1 percent or 0.1 percent over cycles it will be a lot so uh that's something we were definitely looking to yeah great Yichun thank you so much for your great talk um and let me bring Will and turn some back to the stage as well we can have a little bit of discussion maybe Will I just throw out one question for both of them then you can ask your question so so Chunsun I enjoy your at the beginning the two slide over Will kind of generation by generation of electrolyte design you know you know my talk I like to use generation that's uh indicate as the understanding progression so you are showing that slide very nicely um this uh idea of using high concentration eventually get to you know water and salt or salt and salt have a concept there's a local diluent you you are doing Jason Zhang is doing in Piena Niao right um these all this idea coming in you know um so it looks like you are changing number one is also Yichun's talk the solvation structure uh quite a bit the solvation structure you tied up a solid molecule so you enhance the decomposition of the anion together with your lithium building that stable interface uh with all this idea coming in what will be your you know favorite idea for both of you to say that's the path I can go down to because this parameter space is so big you need to consider a b c d e in order to have idea electrolyte so what really give you the very exciting path to go down to you say I can have all these parameters within a range I could tune to become practical electrolyte so right now because this is really a balance of different parameters so we want to get in our organic reach ICI or CI in that case for ICI we have to reduce the solvation solvent reduction potential if you reduce select the solvent has a lower reduction potential and then the high voltage you have a mission and so that's reason when you go to the subcase and then you have to make a decision solvent really really uh impact have a big impact for ICI or CI so that's reason two years ago we think we should go to the ionic liquid that one we do not have a solid but ionic liquid right now still cost is high another option is use in organic that the eutelic the salt so that in case we also going to have a solvent and only some eutelic they own their melting point is 50 so we can go to the 80 we demonstrated some some really good performance and another case solid state they also know solid but that case we need to consider how can we form from lethal fraud ICI or lethal chloride which has high artificial energy with either silicon or the lethal metal if you use you have to use a solvent and then we need to consider the balance the the voltage and also can ionic conductivity so the trick is right now we think the direction maybe you go is the solvent has lower like the bonding with the lithium but they still have a reasonable solubility and they also have a high like ionotic stability this kind of at the beginning we think it's that contradicted with a different performance but they were recently really has kind of this kind of solvent like the Zhang Qiang in the Qinghua University he published one paper that they have a solvent biometric the number is really small but they still have a solubility meaning the solvent bonding with the lithium is really weak but they still have a reasonable ionic conductivity then we still have a conductivity and also they are not reduced so this we need to have a new criteria what what is the limit critical parameter control the solubility also the reduction potential the solution energy is weak but they still have a solubility so this the region is only a few papers that is the region in my group we signed student we tried this the direction say overall comprehensively what is the parameter really can control you still have a high solubility reasonable high solubility but solvation energy might be small and so they can when little more solvent it's not a move but the lithium it's really carry the anion to the anion side so this is a little bit complicated but they still have a room to go there yeah each one yes so for us the first criteria we think is whether we can put this into market so it has to be low cost and it has to be eco-friendly so that's why we we pursue the molecular crowding with the polymer so but then now we are limited by ionic conductivity and we are still want to further expand the voltage from lto to potentially graphite so i think there are a few parameters we are looking at so the viscosity of the polymer and we also want to increase the water content so right now it's below 10 percent so we want to increase the water content to 20 or even 30 percent at the same time that basically guarantee the safety but also increase the conductivity but then the key is whether we can also expand the voltage and i think the molecular crowding agent the ability to lock down the water is something we are looking into so we believe i mean we don't have to go to super high conductivity so something that's practical but we guarantee safety then i think there will be a space for this type of system in the market so that's something we are exploring right now and of course including the electro modification in conjunction with the electrolyte modification so we are very excited about this and i think so this a lot could be done and there's something we are working on in in tuning different parameters that we including viscosity voltage window and the voltage window actually relates to the crowding ability through the agent and then also water content we want to go up and that will help us to achieve the target yeah so that's our approach yeah maybe i add one additional point for the high concentration electrolytes you see the ionic conductivity is low but they normally increase transverse number so they if you increase transverse number overall the conduction is not too bad so it's really depend on how can you the the balance the the total we say total conduction not only use the conductivity to divide it if a transverse number really increase a lot let's you can balance some reduced ionic conductivity thanks will thank you so trance and ijun i found a very strong link in your presentations today is that both of you are guided by chemical intuition and also chemical design rules which i think is very exciting much better than just trying a bunch of things i have noticed in both of your work your focus on sort of one or two major descriptor that governs your design for electrolytes for flow battery chemistry i'm a little bit curious because i think from a design perspective having more knobs is even more powerful right to vary more things but of course as he says makes it more complicated so i'm wondering if you can expand beyond the descriptors you have talked about for example and transition in your work you talked about the reduction potential you know are there other sort of up and rising descriptors that you are considering that could be interesting knobs that the community should be thinking about to give some additional freedoms to tune the chemistry this is a little bit too big so but i want to say based on my thinking i really think right now really mature battery is verified little cobalt side right now everybody want to move higher energy so you have to increase the little cobalt side capacity use mc and verify you have to use the silicon and then a little metal so right now the the right now we use the mature experience to design high capacity cathode and anode and looks like based on my experience we cannot just copy improve and because in when the volume change largely you have to think in a different so right now we have a big gap at a verified we already identified for the legal matter and silicon we just have a limited experience is there any really continuous guideline we say when volume change from 12 percent verified to silicon 300 percent to lithium is finitive and when volume change how it link with the artificial energy the funding how it link with as your mechanical property if we have a continue this kind of model and then we can systematically design it and also the cathode the same thing cathode we need to consider also right now everybody is modified coding the surface that is really uh input performance but that kind of capability at ci cannot sell heating many many cycles they will lost the capability and a lot of people they crack and they think that they steal the crack but if the same principle if can sell form ci before it they definitely can block the electrolyte concentration then they are sure we find the same principle and what is the volume change and interface and bonding between the ci to the to the cathode that also critical for next generation of leading one battery so we if we have a general design principle not just pick up a chemistry one chemistry another one and then we'll have a whole community have an overall knowledge for next generation battery what is the design principle if we know the fcf design principle and then we go for the design intellectual audience so if that happened then that will help the community not just try and even some principle is not perfect when you modify to experiment you can further refine the principle the principle may be bought high so that is my comment chun sun i agree with you i think this new material adding the very important dimension is this so materials change volume change reading so coupled together with ci and ci that dimension is so many things so complicated that how do i require new thinking yeah i just want to resonate with what you just said yeah so some will you mentioned about what other knobs that we can do i think uh where i'm looking at is how can we improve the safety of the electrolyte right so water is one route and so when we go to the water routes then you have to find all different way to stabilize water right so then you can go into a watering song or a crowding and so on but there's another routes to improve the safety is the fire redundant agents right so you can put into things that you can put out the fire and or even not never go into fire but those small molecules can also have negative impact impact on the cycling stability so stabilizing water or stabilizing the fire redundant agents is two things that we all want safety and that's i think i mean like professor trace work on the the current collector you can actually encapsulate the the fire redundant agents and release at the the time where you need it right so i think there's a lot of space and design rules that we can targeting a good safety it doesn't have to go to the water routes i think there are a lot of different parameters we continue now just electrolyte but also current collector structures the membranes right so i think to to improve and achieve safety i think that's well we will need a lot of options and together with electrolyte electrodes and separator to make it a safer options for our future battery application so that's my my belief that we need to encourage different type of thinking and approach to to achieve that as a community together well it's a very rich playground for sure e back to you yeah thanks well let me ask you just brainstorming with you guys right i want to see your thought of this question will and i have been talking about this a lot you know in the past the storage acts and podium this discussion topic on long duration storage each one of you you know your paper today you talk about that now can we really look for the battery system that can get us to the cost right and talking about in the order of ten dollars per kilowatt hour i'm talking about roughly about orders of magnitude lower than lithium higher um what's the possibility right here so i think lithium iron will go down to the past in the cell level of course you're going to see 80 60 dollars per kilowatt hour probably in the next five years also in the cell level right and then below 50 than lithium iron probably very very challenging and then we need to think about completely different chemistry ten dollars per kilowatt hour like let's how do we do that what's what's the thinking about is it a quick system or is it you know still organic system what's the you know end of chemistry catholic chemistry that's possible to get us there otherwise we cannot have this weekly like monthly energy storage if you haven't talked about seasonal yet i mean seasonal maybe even ten dollars per kilowatt hour is not sufficient so let's brainstorm on this topic a little bit we'll certainly feel free to chime in as well i think this is panel discussion we can all chime in so my question of thinking i mean if we really reduce the cost one is you have to increase energy density and also material cheap that is a foundation if you can do not have this tool then the chances are low and then energy density and then we consider you have to use the air in that case it means we're not carrying the oxygen so that is a metal air but metal air if you consider lithium organic that is really hard and then we measure it to the aqueous aqueous and then aqueous stable also cheap maybe zinc so i'm thinking maybe zinc air battery if you really can make design aqueous electrolytes they can tolerate like a carbon dioxide and they will not evaporate because that one high concentration can do it but a high concentration the increased cost but we need to find something they can stabilize the water not evaporate and so they cannot they will not react with carbon dioxide and zinc they form sci and they will not have a dandroid all this combined together maybe has opportunity and if you really sealed you saw organic even you use really really cheap material and normally cheap material they have a energy density is lower so like we use a little bromide that you can corrode that one may be cheaper and but you have to match with little metal if you use graphite it still cannot be really high energy density so on so two point one is currently organic one you have developer cathode because i know the city can maybe work but cathode really limited if we cannot find a breakthrough on the cathode really high energy density and that is really hard also this should be cobalt nickel free so that is the one direction but that is the improvement it's not you cannot expect a suddenly change but a chemistry zinc here maybe has an opportunity but let's still have a lot of challenges and but at least this open system maybe has an opportunity and to do that solid state air is still a lot more challenging there so we don't know that it's but it's still an option but the cost manufacturing are also a challenge so that is actually my personal point that's a good thought that you churn so yeah i think well ten dollar per kilowatt hour so i don't know if that's possible but i think if any any chemistry you're going to make it well i think professor donald southerway once said that if you want to make electricity the storage dirt cheap you want to make from dirt right so i think sulfur is already very cheap and so there's so you know irons so i mean in the free last flow chemistry you can involve irons iron could be some of the iron could be at a higher positive side so iron and sulfur and i think flow battery has really good advantage in long duration if you're talking about 24 hours 24 days or seasonal the cost basically go down to just chemical cost so the the membrane the stack will become very negligible so i think if we want to target ten dollar per kilowatt hour i think redox flow battery long durations um sulfur and irons will be something that we because the chemical cost is is is physically right there you have to you can not ignore them so that's something i would and of course aqueous system so that's something would be maybe a possibility one day so that's a good thought iron and sulfur the voltage is probably about 1.2 1.3 wall like because iron 2 plus 3 plus is what 3.4 versus lithium sulfur is about 2 2.1 so okay uh well do you want to chime in maybe maybe given that we are at the end of the hour maybe i will have the final award today this is a great discussion and this is a you know a really tough question so i will just share some of my my learnings and east job of course is to ask the the hard question you know if we look at the benchmark right what is a good benchmark let's look at in the lithium ion battery area lithium iron phosphate and graphite right both of this material the cost is dominated by shipping the raw material is nearly free right lithium iron phosphate now is close to five dollars a kilogram and will only become lower and if you can produce them locally use them locally it's it will be even less expensive so that's the benchmark right but when you put this into the whole battery the architecture determines the cost not the material nor the chemistry so i can already sort of imagine the future in which for lithium ion battery the chemistry is free then it's all about the manufacturing about the architecture so that's why i'm you know really thinking that if we can put substantial resources into new architecture like the new architecture for metal air new architect architecture for flow battery and really think about the cost of making the cell so i think this is my sort of realization lately that at least for lithium ion battery the chemistry is already nearly free if we are willing to accept say the performance attributes of lithium iron phosphate and graphite and and that is pretty good for grid level storage already so i think so i think my two cents is it really comes on a cell an architecture and upscaling and that's going to be a very hard problem just look at how much money has gone into lithium ion battery so if we can put the same investment in the new architectures i think there's great hope and great future hopefully some of our colleagues from government and industry are paying attention i think here is where massive investment will result in massive breakthrough so hopefully that could be an inspiration as well for all the great work that both of you presented today but before we close uh Chen Shen and and each one do you want to have any final advice for maybe the younger students and postdocs who are listening in what they should be thinking to do in the future to contribute to solving these problems okay so when i talk to my students i always encourage them thinking differently and because you right now so many people work on lithium ion battery and if you just follow improvement and then that is a slow process even if we think differently even we are not successful but if one time successful we really make a big change so i really encourage the student to somehow thinking differently and thinking big don't afraid of the fail because we expect from the field you learn and next time in a five or six year period in the PhD you'll maybe have a chance successful so that is always come more the technology forward so that is my explanation yeah i fully agree with professor Wang and i think one thing i talk to my students when they try to evaluate if something is worthwhile doing i always ask well what if let you would let assume you 100 achieve what you want to do in your proposal and and then you ask a question can you change the world even without even with 100 successful of doing what you are proposing and if you can't then don't do it because we may not do 100 but if you do 80 percent 60 percent so not not even a chance right so that's dream big and also kind of like resonant with professor Trey mentioned like well think out of box and just challenge 10 dollars per kilowatt hours why not what limits us and so i think we always are limited by ourselves and thinking big is something it's very important and not to be afraid to be to be i guess making failure but i think that is how we learn so i think we all are learned from a mistake and do not be afraid and that's something has been very helpful to personally and also my group so that's my it's my fault fantastic well you have the final word this is this is so inspiring i i need to reflect on your inspirational works and maybe copy them as well thank you both very much i think this is the first time we have a truly international symposium with ijun from Hong Kong and then Trenton joining us from Maryland of course Ian and myself in California so we have exactly 12 hour time difference i think so ijun very uh we're very thankful uh for you staying up until midnight in Hong Kong to join us but i think this is being a very uh international and global discussion in the literal sense so thank you both very much for doing this so i just want to remind everyone that we have four more symposium for our spring quarter um storage x events next in two weeks we have a very exciting session featuring uh tim home who is the co-founder of quantum skate and professor jennifer root from mit who will talk about solid state batteries after that we have uh diane guernich who is the former california utility utility public commissioner uh who will talk about building energy efficiency and energy storage um in june fourth we will have the head of batteries at boats wagon uh frank blown talk about their recent progress and then to close the quarter off we'll be joined by professor yung kook sung from hanyang university and professor hubert gas jagger from the university of munich to talk about latest progress and catheters so please mark your calendars these all will be 7 a.m pacific i also want to invite everyone uh to be connected to us we have a lot of exciting programs coming out um if you are a linkedin user um please consider joining our linkedin network um you can also uh participate in other talks we have a two technical talks by our current students and postdocs on april 30th uh next week and then finally uh for professionals joining us who are interested in learning more about the energy transition broadly uh stanford offers numerous online courses including uh technologies for energy storage and many other things and you can find this online um on our website and also as online dot stanford dot edu and with that um i will like to close the symposium today and thanks everyone for listening and have a great day and great evening thank you okay thank you thank you thank you very much thank you fantastic thank you