thank for for this talk today it's really a pleasure for me to to give this seminar and i hope it it will be of interest to you so i will just share my screen and hope it is fine so uh the idea today was to give you a snapshot on what we did on non-lithium-based battery technologies with a special focus as christina mentioned on calcium and it's nice that she finished by showing this uh this figure from the batteries europe roadmap because i think it gives already the the view that there are many different technologies alternative to lithium and then they have very different levels of development and the timing for their development if it takes place may be very different so essentially uh as an introduction i would say that with a temporal perspective of course we all know about the past of batteries and the breakthrough of volta when building the first battery just aiming at showing that the the electricity did not have an animal origin and of course this was a breakthrough because one could generate electric current upon demand despite uh the performance was not uh very good if we look at it with with today's standards but anyway this was a breakthrough this was published in the philosophical transactions of the royal society of london volta was given awards was received by napoleon so pretty european already at that next breakthrough was the development of rechargeable technologies with the lead as asset technologies in france others came like nicole cadmium by junior in sweden and i guess all of us would agree that the present battery technologies by all means lithium ion this was uh commercialized in the early 90s it has boosted together with the with portable electronics market and and this development of portable electronics wouldn't never have been possible without the lithium-ion battery technology but then when we look at the future and i think that even if you asked a bunch of battery researchers or or or people working in in battery technology you may have very different answers as to what is the battery technology on of the future and the reason is that now the the field of applications for batteries has expanded a lot so it's not only uh for portable electronics where the amount of energy is in the range of what hour and the most important thing is to is energy density is expecting to know what our electric transportation and here energy density is relevant but safety is also very relevant and cost and durability and if one is thinking on the grid and for instance renewable integration then we can go to the megawatt hour um scale and of course uh here energy density may be less relevant for for stationary storage but of course cost and durability are very important and if we are thinking of a widespread deployment of of all these applications and and the use of batteries one should think of course of sustainability and and the use of of non-critical materials and this will likely also involve the development of new battery chemistries and this was already um uh seen uh in back in 2016 by the world economic forums in enforcement at davos where the next generation batteries made it number two of the top 10 immersion technologies just after the internet of things so when thinking at the abundant elements one can have a look at this uh periodic table which is really not very um uh i would say rigorous because the the area is supposed to be proportional to the abundance but this is not even true not even at the logarithmic scale for those here this would likely be a much more representative picture so you see that here um on this part of the periodic table there are very nice electropositive abundant elements which would make nice battery anodes and of course with those other compounds here one could make really sustainable technologies so when looking at those metals here here you see the abundance of the earth grass and the the cost of the raw material which may be the carbonate or similar and you see that there are many interesting alternatives to lithium sodium magnesium calcium aluminum all of them are abundant and lower cost and here one can think of two families of concept so first the family is the metal ion concept this is truly analogous to the lithium ion concept here the metal is just the charge carrier in this case we would be substituting lithium by sodium magnesium carbon etc and the issue here is that the the if the the charge of these ions is higher coulombic interactions would be strong both in the electrolyte and and in the solid electrodes and this will certainly have issues with respect to power and here i guess one could expect performances similar to those of lithium ion of course the energy density will depend on which are the specific electrodes materials that are being used knowing that the voltage limit for the operation of the negative electrode is the plating uh volt um the the potential for plating of of this metal and i think one paradigmatic case of the metal ion technology is sodium ion and i i will just mention it a little bit because uh i think it's a technology that has gone very fast to production and the trl level has grown a lot due to the analogies between lithium and sodium and accumulated know-how in the field of of lithium-ion and of course another concept would be to make uh batteries using a metal anode and in this case as you know for lithium there is an issue with dendritic growth which and there are a lot of efforts to try to solve this but one could think of other alternatives here you have a different metals and you have the gravimetric capacity in green and the volumetric capacity in gray of course nothing compares to lithium metal gravimetrically but it's not very dense and in any case in lithium ion one uses graphite so you see that one could have interesting figures of merit for for all those metal anodes especially for aluminum considering that you would exchange three electrons for each ion and the energy density is the product of the voltage and the capacity so let's have a look at the standard redux potential and for aluminum is intermediate magnesium is somewhat lower but calcium has a very low value very close to lithium so in principle one could expect a very high energy density for for calcium negative electrodes and then one would have to look for for very good positive electrodes to match those capacities so with respect to the issue my to the sodium ion technology sorry which will be my first example as you know this technology is by no means new and in the early days of intercalation studies both intercalation of lithium or sodium or other metals were studying at the same time but there were prototypes of full cells full sodium ion cells using sodium caval oxide as a positive electrode and the sodium lead alloys negative electrode cyclability was not very good at the time but still and um of course all of this was was stopped when the lithium-ion technology was commercialized by this time but then the topic was somehow rediscovered uh later on and here you see it's from a review back in 2014 all the compounds which have been shown to be useful as positive or negative electrodes for for sodium ion batteries and an estimation of the energy density of full cells using those materials as positive electrodes and hard carbon as the negative one and comparison with graphite limin204 lithium ion and you see that that in some cases one will have a competitive um figures of merit and the same is the complementary graph thinking of different negative electron materials versus a layered oxide as positive and again comparison with lithium ion so as i was mentioning this concept has uh has witnessed a fast uh progress due to the similar chemistry with with lithium but of course uh there are also significant differences which need to be taken into account so in ionic radios which mean which will um induce difference in in coordination preferences and crystal chemistry so not not all the electrode materials which work for lithium will have a sodium analog which will work as well also the polarizing character which is um due to the higher radius of of sodium is different so this will affect both diffusion and kinetics solvation energy will also be different and then the solubilities of sodium compounds will be typically higher than for lithium compounds and this will impact the stability of the sei alloying behavior is is different and that's why sodium does not form alloys with copper electrochemically and aluminum current collector can be used in in both electrodes in sodium ion technology which is an advantage and another significant difference is that graphite does not interpolate sodium or at least unsolvated sodium and typically hard carbon is used instead and i i would like to redirect you to this paper where is there is really a nice constant resource analysis for soviet modern technologies and figures numbers are put into into these ideas and this will this will give you really an idea of how the technology has been progressing and also uh i would like to mention some of the european startups that are working in this topic at the moment first of all for avion which was the first one created and they have an interesting roadmap and they have they are now doing cells which are similar in performance to a graphite lfp lithium ion they use layered cathode materials and hard carbon they do these pouch cells and and this paper is very interesting where they uh describe all the roadmap since they they started to produce cells and how they were improving performance on on and by improving the different battery components later on uh tiamat was created in the north of france they are producing cylindrical cells and in this case the positive electrode is a polyan ionic one but i think they they are still doing also very well especially in terms of power and other companies for instance are altruists in in sweden who is looking at the prussian blue analogues as as oppression white as some as positive electrode materials for for sodium ion or even this other company in wales which has also recently uh built uh about cellular line so as you see there is a lot of activity in europe on this technology and the trl is quite high and has increased a lot in in very short time and now i will move to the main part of the talk with this with calcium metal batteries which is just the opposite extreme we were not the first to think about the calcium being an uh an interesting electrode for for batteries because it was somehow obvious that it is electropositive and uh abundant and so on and the first report of attempting to use uh calcium to the best of our knowledge was done in the 60s um as an anode for thermal batteries for for military applications there were also some attempts to use it with solid electrolytes but no major uh studies of the redox mechanism or or so were done at this moment just uh prototypes being assembled and and some performance measured but they did not develop beyond that then in the 90s there were studies by the group of emmanuel pellet and israel and stanky in in the us um aiming at substituting lithium anodes in the lithium tiny chloride technology by calcium as a safer alternative so calcium would have a higher melting point and also a higher conductivity and the main issue would be that upon cell reversal there will be no calcium plating so it would be safer and the the reason why no calcium plating takes place was thought to be that the sei in this technology is um consisting of calcium chloride and then this this does not enable transport of of calcium ions so uh then um i would like to show you uh some uh some back of the envelope uh calculations uh i told you that a priori um calcium loops is an interesting anode but uh could we pair this with with uh an interesting cathode are the numbers feasible so we took this uh excel spreadsheet from from this paper by eric berk and co-workers where they uh estimate uh parameters for for performance of of a single cell um consisting of um uh either two porous electrode or one forum's electrode and one metal and they take realistic values from the lithium lithium-ion technology with respect to porosity density of the electrolyte and so on so we took this and we just simulated cells using current collectors of aluminum on both sides using a cathode and then a calcium metal anode and this is what we got this is the volumetric energy density or the gravimetric energy density considering calcium and hypothetical positive electrode materials with the operating voltages between two or 4.5 and capacities between 50 and 300 and you see that for uh cathode with moderate i would say uh figures of merit we could be already on par with the lithium-ion battery technology so the prospects of of a good performance are real but uh unfortunately the the reports in the literature were not that promising and uh after the the the papers i mentioned to you there was a seminal work by the group of doran auerbach who who attempted again calcium deposition in organic solvents pretty much like those used for the lithium-ion technology and they concluded that it was not possible and again the reason seemed to be that the sei did not enable transport of calcium ion and of course then if there is not suitable electrolytes for plating this hindered a lot of the development of cathodes despite intercalation of calcium in some compounds was tested but that it was really a scattered studies and as this darpa adage in the us setting the six this technology is always limited by the materials available so i like to use this um this graph which is imported by uh from from patrick johansson uh who likes to show these ideas about why we do something and in this case well we were uh interested by the potential performance of these calcium batteries because this technology could be sustainable especially if for the cathode we would use abundant metals but also we were sparked by scientific curiosity so the first question was to know why is the electro deposition of calcium not feasible is it because the the migration of solvated calcium ions in the electrolyte is hindered or it is desolvation of calcium ions at the surface of the aci or or transport through the sci as was thought before or even nucleation and um we we realized that the issue was really formation of ion pairs within the electrolyte and that just by simply increasing a little bit the temperature using some specific electrolyte formulations we were able to achieve placing and stripping here this the electrolyte is 0.45 molar calcium bf4 and ecbc and you see the the cyclic voltammograms at 100 degrees c this is the calcium deposits and of course this is far from ideal because the efficiency is not very good there is quite a lot of electrolyte decomposition but still we we were able to see by creating fractions that this is calcium metal and here you see a symmetric calcium calcium cell you see that they are huge the polarization is huge this is 100 degrees c and just to benchmark this is lithium lithium symmetric cells at room temperature so really still uh a lot to improve but at least we showed that the position of calcium was was possible despite all the issues later other studies uh were done with with uh other alternative electrolyte formulations so then the group of peter bruce reported this formulation with much higher efficiency despite lower stability upon upon oxidation and uh in this case there is also formation of a sort of native sei between the the deposited calcium and the electrolyte and it consists of calcium hydride and then later on there were also reports by the group of linda nasa and the group of zidane zironga zhao karger and max figner in in germany with other assaults also containing boron and there is also work going on by the group of robert dominco in slovenia in all cases trying to look at new electrolyte formulations for the best efficiency in calcium plating and stripping so for the moment nobody is perfect but at least we start to have a bunch of formulations to work with so at that point we started to look for cathodes and we used the the the electrolyte with which we had been working because calcium bl4 is commercial and also because of the stability at high voltage and here we were facing a lot of issues with the experimental protocols because one cannot mimic what what is typically done within the lithium ion battery technology because ideally one would like to assemble um half cells with a calcium anode but i show you that calcium anode were very polarized so we need to know what's going on one has to to use three electrode cells and then the question is which is the best reference electrode to to use and we had to calibrate and so on so this took us a while but finally we developed a set of protocols which were reliable to test the potential uh positive electron materials and we were exploring a little bit the periodic table we were focusing on intercalation compounds with with transition metals as redox center either having or not calcium in the crystal structure because of course if we have a calcium metallano there will be excess of calcium in the cell and also we were exploring oxides sulfides nitrites etc and among these we explore traditional intercalation costs like v205 or tis2 but also i would say new horse or potentially new costs which were calcium transition metallanox traditional metal oxides sorry so one of the compounds which we thought was interesting was perovskites because this is a very rich family of calcium metal oxides and amongst them uh molybdenum compounds seem to be very interesting and we were able to prepare it but there was no way to electrochemically extract calcium from the crystal structure which we um understood with the help from elena arroyo at universidad completence de madrid who did the dft calculations and was able to to realize that the the migration barrier for calcium in this crystal structure is huge is two electron volts same we were also interested the by calcium and 204 and for this stoichiometry there were calculations by the group of christian persons the christian person in the in the us uh she considered the the spinal polymorph which is not known because calcium is not that stable in tetrahedral position but if it was uh possible to prepare this compound apparently the migration barriers for calcium would be very low especially because calcium as i was mentioning is not that stable in in this um would not that be stable in this coordination so uh instead we looked at the stable polymorph which is the moroccan one which has this double through dial chains and these these tunnels along the crystal structure which look very interesting but again when we prepared it and we tried to extract calcium from it it was not possible we saw a huge oxidation which resulted to be only electrolyte oxidation the iterative fraction pattern of this compound did not change and the calculation of the migration barriers yielded also a very high voltage so this time we decided to revisit the is2 and there was precedence of interpolation of calcium in the ios2 by jean roccell in the in the 70s in mount in france and they did this with um using a calcium dissolved in liquid ammonia and they were able to intercalate the calcium in between the layers of tis2 uh still coordinated by ammonia and then by gently heating they were eliminating ammonia so this is uh what we got when we tested it electrochemically there seems to be a reversible behavior but the polarization is huge so really not really a practical interest so when we did the diffraction xc to a different point since it was what we see there is always a significant amount of tis2 which has not reacted so there is likely an issue with kinetics despite the 100dbc but we see the formation of of different phases as you can deduce from those uh peaks at low angles in in diffraction and uh we were able to identify uh some of them so for the first one the one with the highest interlayer space we believe that this space has a solvent coin intercalated so it's solvated calcium that intercalates then phase number two would be the same phase with naked calcium that john rook cell had had prepared in liquid ammonia and then about phase three it would be maybe a stage two phase and as you can imagine with these patterns it was not possible to to refine the calcium occupation and uh in this crystal structure so we turned to complementary characterization techniques to make sure that really these structural changes were related to intercalation of calcium and we were able to do transmission x-ray microscopy at the calcium lh at the alva synprotron we were using uh different compounds as standards and here is an image of what we get this orange shell has a similar calcium density as calcium carboxylate so it's likely produced by electrolyte decomposition in red this would correspond to calcium fluoride which we also see on diffraction also due to electrolyte decomposition but then these pink bubbles would indeed correspond to calcium inside the tis2 particles of course polarization is huge and as i was telling you calcium anodes are not the best so at this moment we were thinking of separating issues and just not importing problems of calcium animals when looking for cathodes and trying to decrease the temperature because the testing at 100 degrees is also a guarantee of electrolyte decomposition so we're looking at other counter electrodes and the first obvious choice is activated carbon and this is what we did the main issue here is that the balancing of the cell needs to be carefully addressed because the capacity of activated carbon is very small due to the capacitive mechanism but but still if this is taken care of one can have a successful results and this is what we did in this case we use calcium tfsi which is also commercial and much easier to dry than calcium bf4 and we saw that uh at uh at 100 degrees we we have the formation of of the same phase as we saw not phase two surprisingly even at 60 degrees and we can also see the formation of this phase even at room temperature which was quite interesting then we were following this intercalation mechanism by operando diffraction and this was done at alva this is a cell an operando cell which enables circulation of a fluid to increase temperature and this is what we got at 65 degrees and we are still investigating this because the redux mechanism seems to be much more complex than what we have thought and in fact the position of those peaks seems to be evolving in in the course of cycling so the the mechanism is something that we still need to understand better so then when looking at the at the other group of compounds so calcium transition metal anodes uh transition metal oxide sorry um we we were interested in this uh compound which is a derivative of the hexagonal peroxide and its crystal structure is made of columns of alternating cobalt uh octahedra and and prismatic coordination which are sharing faces or one in some cases one can have also manganese and there is calcium between these columns and the our idea was that maybe uh this crystal structure would favor calcium uh mobility through this through these columns we prepared this compound it is really easy to prepare this family of compounds has been has been uh studied a lot for its magnetic properties with the intron inter couplings between the chains and so on and we were able again to do operando diffraction at the alva synchrotron using these coin cells at room temperature and um this is somehow the electrochemical curves that we get so we get the oxidation and then we get the reduction and then we were able to further reduce again xc2 the cell and and take some patterns at the end and the result is the same for the global than for the cobalt manganese compound this is what we get so upon oxidation in red what we get is that the pristine phases start amount to starts to decrease and a new phase a new oxidized phase appears but then upon reduction as you see there is nothing going on and i don't have the blue pattern here but it's exactly the same one as the greens so the thing is that we were able to elucidate the crystal structure of the oxidized phase and we were able to refine the the amount of of the occupation of calcium and it's clear that we have electrochemically extracted calcium from the crystal structure but somehow this does not seem to be reversible so this can lead to intrinsic uh structural constraints maybe the migration of those calcium ions in this oxidized crystal structure is more hindered than in the pristine one or it may be due to the fact that to intercalate calcium you need to dissolve the ions from the electrolyte and maybe the desolvation energy has a role to play here so this is something that we're um still uh trying to to address and finally i would like to uh to mention uh other two cases which we investigated again in collaboration with helena royal in madrid who did some screening of different calcium transition metal oxides to look at possible migration paths for calcium in the crystal structure and when she found the low energy barriers she came to us to to pursue the uh the experimental uh study so the first interesting compounds is calcium 2 mno 3.5 this is a derivative of the huda slam popper phase calcium 2 mno4 which has some oxygen vacancies which as you see one can see very clearly on the iv plane and in this case the coordination of manganese is not octahedral because there are those oxygen missing is in some pyramids so she calculated the migration barriers along different pathways and you see that in this av plane where the vacancies are the migration barriers i would say tolerable about one electron volt and of course uh when uh one consider a migration along the the c direction and these uh uh pair of sky's labs then it is the various are very high but still this was considered interesting for experimental investigation and another uh compound with which she came with calcium b2o4 which is uh has a very similar crystal structure and the manganese phase that we have been studying before and in this case um she found that the migration along the tunnels uh has very low uh barriers about 0.5 electron volts and if
you were able to extract almost all calcium from the crystal structure then the barrier would be a little bit higher but still those were considered interesting for for electrochemical investigation and also uh in parallel works by the group of pero piero canepa in singapore came with with similar values so we prepared those compounds and we oxidized them electrochemically and the first thing is that the oxidation the potential at which the oxidizes is huge is equivalent to five volts versus calcium metals so we will for sure have a lot of electrolyte decomposition here but when we did diffraction of those materials we saw that there were changes in the diffraction pattern so really there is something going on in the in the material so this is the pristine calcium panelium oxide and this is the oxidized phase and the same for manganese so again this is operando diffraction in this case for the manganese compound and what we see is similar to what we saw with the cobalt compound so we see some evolution of the diffraction pattern upon oxidation here you see this process and then after oxidation when we reverse the sense of the current despite we get some electrochemical response there are no changes in the diffraction pattern so this evolution seems to be irreversible the issue is that when we were trying to refine the uh occupation of calcium in this oxidized phase we ended up with the same calcium amount of the pristine phase which means that the the charge compensation mechanism must be different so if it's not extraction of calcium it could be intercalation of anions and in fact when we did the fourier map we were able to see some electronic density in this position which was the oxygen vacancies which we saw before and also on this plane in which the rather slim copper compounds are known to intercalate fluorine so we we did some attempts to confirm whether there was fluorine interpolation it could have been oxygen maybe as well we confirmed the presence of fluorine by yields and anti-x and we were able to even estimate the amount which would be about 0.6 which would be an agreement with not only this position being filled but also a small amount of fluoride there and the definite proof that this was fluorine due to electrolyte decomposition was that we performed different electrochemical oxidations in other electrolytes containing or not fluorine and for instance when we do uh when we use lipo which does not contain any fluorine we don't see any changes in the diffraction pattern but when we use seeds which contains fluoride or even cesium fluoride we do see these oxidation so indeed what happens here it is that when we oxidize the compounds we we get intercalation of fluorine so this will not be useful as as a positive electrode for calcium batteries and finally the last compound again this is calcium b2o4 this is operando diffraction data at alba we see again evolution upon oxidation but in this case upon reduction we do also see an evolution of the integrated from the diffraction pattern despite the pathway seems to be different and this is something which we are still investigating so we seem to to have a two-phase process here and here we seem to have the formation of a solid solution and this oxidized phase was found to uh to um to have a stoichiometry of calcium point seventy two o four so it's really not that much that we have been able to extract and we are already at a very high voltage versus calcium this is just the phase uh fraction of the pristine and oxidized phase which uh of course one decreases and the other increases upon oxidation and upon reduction you see that the the the amount of each phase of each phase becomes uh stays more or less constant despite we increase the amount of calcium in this oxidized phase in agreement with the formation of a solid solution so we did some attempts to to to build the um cells which would uh which would attempt to to cycle in different conditions the the profile does change upon cycling and of course again there is a lot of electrolyte oxidation so it's something that we are uh looking at it more more closely and there is still room for for improvement but at least this is the first time that we have shown that calcium can be extracted and re-integrated in the crystal structure of an oxide compound so to sum up a little bit we were studying uh positive electrode materials and we show we saw all types of behaviors reversible intercalation of calcium but together with uh with a solvent molecule for tis2 some irreversible behavior some electrochemical oxidation in some cases involving indeed extraction of calcium in others involving intercalation of fluoride but irreversible but also uh for the case of the vanadium compound the behavior seems to be reversible so at this point i think that the role of of the calcium interaction with solvent is crucial and there is the the need for for more electrolyte research for sure and another uh take-home message which i wanted to give was the need of uh use a complementary characterization techniques when looking at multivalent battery chemistry so one does have to do blank experiments this is just aging in the electrolytes so this particular compound was reacting with the electrolyte this one has to know the need of three electrode cells the need of complementary characterization techniques because there is no real standard there is no standard electrolyte the anode also has issues there there can be many side reactions going on as you so for instance here with fluoride intercalation so one has been very has to be very careful when interpreting results so nothing can be taken for granted you need to to make sure that your electrochemicals set up is reliable and there are many issues that one one should look at and also for the positive electrode materials a care has to be exercised when when interpreting just an electrochemical response and uh this is a a table of all the compounds for which calcium intercalation was reported so already uh two years ago and in some cases you see that there is only the electrochemical response so then one has to have a critical view because some of these interpretations may be maybe biased because all of these phenomena and side reactions then that can take place so overall the the message is that the the development of of new battery chemistries can be very slow especially if there are not uh preliminary technologies or knowledge which one can import with and this is the case for for calcium this is a graph which which was usually been given by ralph brought with different steps in the development of a new technology and in each step you need uh more staff and more amount a higher amount of material and so on but finally it would take between 10 and 20 years to reach the market if successful because for some concepts you may not just be able to go from one step to the next one because the performances would not be as good as expected so just to finish with a quotation by walt disney because of course all this matter is complex but i have always been an optimistic person and just i want to acknowledge all the people that contributed to this work very so the map team especially alexander who did all the studies on on the um calcium plating ashley black who worked a lot on the cathodes and of course long-term collaborators like elena royo or patrick johansson and uh the alva team patrick rosia silly matt and and fannia bardea the possibility to start with this topic because the initial project was funded by toyota and then we had um funding from the from the european uh commission and so this is all on my side and if you have questions i will happy to to take them and thank you very much for
2022-02-24