 All right, so today we're going to talk a bit about electrochemistry and how we use electrochemistry with Battery materials at least for battery research and the different types of tests some of the different tests We do I do in part with my battery research so electrochemistry, it's a It's a pretty broad field I I've only ever taken the freshman freshman chemistry courses as an undergraduate So before starting my research on batteries, I knew almost nothing about electrochemistry So all of this I had to learn on my own and there's not really any any good Courses within our department that covered the basics of electrochemistry Some of our classes do deal with the concepts of electrochemistry for example, there's a senior level corrosion class Dealing with the corrosion of different materials and that that heavily heavily relies on some of the concepts I'll share with you today, and I believe there's some other Metallurgy processing classes that also deal with these kind of reactions So my definition of electrochemistry, and I'm sure it's it's a shared definition is that you know It's the study of any chemical reactions that involve The electron transfer and so in other words if you have a metal ion or it could even be an organic Molecule that has a change in valence then you can assume it's going to be an electrochemical reaction So the basis of electrochemistry is a reduction and an oxidation reaction. Oh, I see it chat Could you tell professor McKensley how to edit the video lectures? Sure, I can I can I can give him some tips. I actually I'm not I'm not the best at it either. It is definitely a skill that you have to practice and acquire I was just using the Microsoft video editor, which is a very basic editor editor It doesn't it's missing a lot of stuff like you can't make any transitions between cuts So but sure I can I can send them an email So anyways back to it just a reminder reduction reaction is the gain of electron so for for example if you have a metal ion in this case of metal 2 plus ion and You gain an electron that goes from metal 2 plus to metal 1 plus. Okay, that's reduction on the other hand Oxidation is the opposite is the loss of electrons if you go from a metal 2 plus ion to metal 3 plus It's giving away an electron. It's increasing its valence state. So that's oxidation So in electrochemical reactions, you have to have both. Okay, so oftentimes we only talk about one Part of the reaction like a reduction or an oxidation separate But in every case, you know, you have to ask yourself where do those electrons come from if you're receiving electron There has to be an opposite reaction somewhere else in the system. That's giving away electrons. You can't just get electrons from nothing so here's an example of a Redox reaction is the oxidation of iron and metal into iron to oxide feo and so the reduction half reaction of this This chemical reaction is the oxidation Excuse me the reduction of oxygen gas. All right, so oxygen O2 molecule was a neutral molecule is giving away. Excuse me It's receiving electrons and becoming ionized. It's becoming a O2 minus ion And so the question is where does it receive those electrons from and that's the other half of the reaction is the oxidation reaction the iron metal which is a neutral atom is Oxidizing it's giving away its electrons and becoming iron 2 plus and then the overall reaction is the iron metal is oxidized by oxygen Becomes iron 2 oxide Okay, and of course there's this chemical reaction also depends on other factors like the oxygen content You know, we can get different different iron oxides depending on how how much oxygen there oxygen there is available the temperature for example presence of water and acidity and It can give you different chemical compounds like different types of oxides So iron 3 oxides iron 2 3 oxides different phases of those oxides So here's a anti example. This is not a Redox reaction if we remember last lecture I was asking you guys about this this type of reaction and we said it was a precipitation reaction It's not a it's not combustion. It's not oxidation reaction And the reason I said that is because well, we don't have any electron transfer So it's it's not going to be an electrochemical reaction. So in this example, we had a dissolved Species of iron 2 plus like iron chloride ferrous chloride for example and iron 3 plus like ferric chloride for example In solution and then so in solution iron 2 plus and iron 3 plus are at equilibrium. They have no problem being together Even though there's two different valence states of the two ions But then we would add a base such as ammonium hydroxide and we're shifting the pH the higher pH where these Ions are no longer Stable they're no longer at equilibrium in that solution. And so what happens is they precipitate out and in that forms this iron 304 also known as a spinel oxide this is actually Let's see iron 3 plus and 2 plus coexist in this solid material and in fact the crystal structure is a inverse spinel a spinel is a type of crystal we have a lattice of oxygen you have many different interstitial sites you have a variety of tetrahedral interstitials and Octahedral interstitials and so in this inverse spinel crystal the iron 3 plus Occupies tetrahedral sites which is given by these parentheses and then also it occupies Octahedral sites given by the brackets and then all the iron 2 plus also occupies the octahedral sites So that's an example of a precipitation reaction without electron transfer okay So how do we how do we? Find out what? What material oxidizes and what material reduces in the given a reaction? One way to look at it is the standard reduction potential these are empirically determined values of different species and their Reduction potential or in other words, you know what what's its potential to be reduced? so on this list the Species at the the bottom of the list have a higher potential of being reduced in comparison to the species at the top of the list so like lithium plus to lithium metal does not have a very high potential compared to Gold 2 plus the gold plus as far as reducing On the contrary lithium metal has a very high potential to become oxidized It's just the in the negative of this number and so the one thing I should point out is that this standard reduction potential chart is is Reference to the sh e sh e is standard hydrogen electrode It's just a reference electrode where you have a hydrogen reaction h plus Turns into h2 gas it's just a standard Potential so we we just arbitrarily may mark that as zero if we're going to reference it Every other reaction to that standard hydrogen reaction So I kind of made this kind of this diagram of different mountain peaks you could say you know So it depends on your perspective of where you are on the mountain You know you can either go uphill or downhill and then everything is relative to where you are So you know if we were to start at lithium for example, you know everything's uphill from us as far as reduction Potential and so you could easily say all these numbers are referenced to lithium Which we often do in lithium ion batteries Especially in research when we have our one side of the battery electrode is lithium metal And so you want to you want to measure your voltage compared to lithium rather than sh e So that's just an explanation of that Okay, but overall the species lower on the list have a higher potential of being reduced and compared us into the species above it So let's see Here's a kind of another explanation of this You know if we had a solution of iron 3 plus in the solution and we wanted to measure the voltage Between two electrodes platinum electrodes we use platinum because platinum is in an inert electrode There's not going to be any chemical change with the electrode itself So what we're really doing is measuring the potential of any reaction on the surface of the platinum So if we just have one Solution with two platinum electrodes and try to measure the voltage between it like with a multimeter We're going to get zero volts, right? There's there's no difference in chemistry between the surface of this platinum and the surface of that platinum It's all mixed together. So we get zero volts On the other hand if we were to replace one of these platinum electrodes with a standard hydrogen electrode Which kind of looks like this. It's encapsulated in its own It's a cell where this is a glass cell and then at the bottom. There's this Micro porous frit. So it's a very very small poor porous Ceramic which allows ionic diffusion between the two. So you'll have a some kind of standard electrolyte in this solution That's different than this iron two or three plus But over time if you leave it in here for like a couple days, you'll have some some some Exchange between ions between this frit. So it's not good to have it for a long time and you'll have to Constantly be cleaning this and refilling it Anyway, so if we use a standard hydrogen electrode now we have a different chemical process happening at the surface of this This electrode all right and that will now we can measure of potential between that So that we're measuring the potential of the iron three plus to be reduced to iron two plus But I should I should make a note that when we measure potential like using a multimeter Ideally, there's no electric current going between the two electrodes If we were to short circuit this with a wire, then yeah, definitely the hydrogen here Would be oxidized the H plus and the iron would be reduced to Two plus though the reaction would go forward because there's that that thermodynamic driving force where the iron three plus has a higher Reduction potential than the hydrogen gas being oxidized or excuse me the hydrogen ions being reduced but that's not good especially for a Hydrogen standard reference electrode You don't want to change the chemistry because if you change the chemistry inside that reference cell Then you're changing the reference potential and you'll you'll see that this this potential would change So ideally when you measure voltage across a use like a multimeter, there's very little little current. I not only Might as well be zero very little current that goes through it That wire so it's we call this an open circuit voltage. Anyways So back to this list of standard reduction potentials So again, like I was saying, this is this is done. These are measured in the standard state so it'd be like a one atmosphere room temperature and then you know the standard The activities of these are at equilibrium so at equilibrium the concentration of the reductant is the same as the concentration of the Oxidant okay, so that's that these are equilibrium potentials in other words. So if you change if you change the amount of Reductant or oxidant you're going to change the voltage So here's an example, you know, what if we have iron 3 plus an iron 2 plus and Zinc 2 plus and zinc metal in solution. So we have four different species in the same solution. I Thought I meant for this to be Just going so you could think about it. But I guess I forgot to add the animations. Anyways, so you have iron 3 plus iron 2 plus zinc 2 plus and zinc metal And the question is which one of these species is going to oxidize and which one of these species will be reduced in this solution. So if we look at the chart, we see that iron 3 plus iron 2 plus has a higher reduction potential than the zinc 2 plus the zinc metal. So iron 3 plus is going to be the species that's reduced and Zinc metal is going to be a species that's oxidized All right, so nothing is going to happen to the zinc 2 plus and nothing will happen to the iron 2 plus We're just going to be we're going to be making producing more iron 2 plus and we're going to be producing more zinc 2 plus in our solution And those have their standard reduction potentials right for these different these separate redox reactions The overall reaction is given here The zinc metal is dissolving into the solution and the iron 3 plus is reducing in the solution So you're going to accumulate more zinc 2 plus and more iron 2 plus the solution. You have an overall cell potential The electric potential is related to the Gibbs free energy change of the reaction So you guys know that if you have a negative Gibbs free energy change, then the reaction is thermodynamically It will go forward as well. There's a thermodynamic driving force for the reaction to proceed So the same idea if you have this cell potential, which is positive Then there will be a thermodynamic driving force for this reaction to occur. All right, so it's just a simple It's negative Z is the number of electrons that will leave f is Faraday's constant which is the number of coulombs per mole of electrons and then E is the standard reduction potential or that will be calculated for the reaction Excuse me the reaction potential Okay, so let's look at this a little bit more so This is like the setup that we just described where we have a single beaker of Solution that contains these ions and this metal and I said well the potential the potential for this reaction is 1.5 volts But you know, how do you measure that? Physically, how can you measure that in a single solution and the answer is you can't measure that It's it's the potential between the surface of the zinc and the ions and solution right at the interface Right, so you just can't can't measure that and this will have this reaction will proceed And it proceeds at the interface of the zinc where the zinc dissolves in the iron 3 plus at that interface of receive those electrons and Turn in the iron 2 plus Let's see moving forward. However, we can measure this potential using like a multimeter If we separate these two cells or the these these Two sets of species into two cells, okay and separate electrolytes So in one cell we have iron 2 plus and iron 3 plus species And the other cell we have zinc 2 plus and zinc species. Also. I want to point out I have I'm not including any counter ions such as chlorine or Any whatever salt that these these cations came from those can also affect the redox potential and act Activity of these ions but just for simplicity. I'm leaving them out of the equation. Those ions don't won't change their balance We're just kind of folk. We're just interested in the metal ions in this these reactions And so here we have our iron species our zinc species our zinc metal as an electrode And we want to measure the potential between the two solutions. We have to add an extra electrode for our iron Iron solution, which is platinum again because platinum is inert and we don't want it to Influence the chemistry of the reaction, but it's acting as a catalyst So it's we're measuring the potential at the surface of the platinum and we also need to include what's called a salt bridge So salt bridge is just Something that can balance the charge in both of these solutions. So in It's it's the golden rule For all these systems that you must maintain charge neutrality if we take an electron away from one of these beakers We have to we have to give it. We also have to take a Positive ion away or in other words or if we add a positive ion to a solution We also have to add an electron to the solution, you know that overall charge must must maintain zero Okay So for example, if we're if we're reducing iron three plus to iron two plus and we're receiving an Electron from the platinum. Okay, but now our solution has just become less positive or more negative because we've reduced the number of Three plus ions. So we have to balance that solution by adding in some counter ions or taking away counter ions That and that's achieved by the salt bridge. It's just it's maintaining Ionic Continuity so I will learn later that the essential things for a battery or you know, the cathode anode and electrolyte But also we need electrical continuity through the circuit and then ionic continuity between that anode and cathode and this is achieved by the salt bridge Anyways, so at this point what we can do is put a voltmeter between these two electrodes the platinum the zinc and that voltmeter Should read the standard reduction potential of our reaction 1.5 volts Okay, again, these these two solutions by themselves are at equilibrium. Okay, but Compared to each other There's that thermodynamic driving force of 1.5 volts for them to for the zinc to Oxidize and for the iron three plus to reduce. Okay, so if we were to put a wire a short circuit this Reaction then this this reaction would go forward But like I said before the multimeter ideally there's no current going through the multimeter. So this is an open circuit voltage That we're measuring and it also again Want to emphasize that we're measuring the potential at the surface of these electrodes, right? So these ions in the middle of the solution there's nothing it's going to happen to them All right, they have to be at the surface of the electrode in order to receive Electron and to be reduced and the same with the zinc the zinc at the surface is dissolving into the solution Okay, so this is an example of like a two electrode cell Oftentimes in electrochemical work. We use what's called a three electrode cell Where we'll have a working electrode and that's that's where the reaction that we want to study is happening at This is a half reaction. Remember, so just it's only oxidation or it's only reduction happening at that interface And then we have a reference electrode that we're measuring the voltage Against okay, so like in the previous example, we had a the reference electrode, right the voltage of the iron three plus Iron two plus reduction compared to the sh e raised point seven seven volts. So that's what this Circuit is is just measuring voltage. No current is going through there And then we have a counter electrode to provide the necessary electrons for this redox or this reduction or oxidation reaction Either giving electrons or taking electrons away So there's another reaction that's happening at the surface of this platinum if we were going to proceed, you know Drive this this reaction forward or backwards By changing the voltage There's a there has to be a counter reaction remember I said you can't just get electrons from nowhere So there's has to be a reaction happening at the counter electrode That's either providing or taking electrons, but you don't measure the voltage of that reaction So you don't really care as long as your solution is large enough You have a large enough quantity of this electrolyte that whatever reaction is happening here does not influence for example the concentration or The the pH of the solution then it's it's it's fine. It's negligible Okay Here's some different diagrams some phase diagrams are useful to electrochemistry ones the poor Bay diagram So I've used this quite a bit kind of shows you what's the stable species at a given pH So this is this is primarily just for a aqueous work So a lot of the battery research I do is also a non aqueous battery So this is not relevant too much, but you know different pH for a different different Species that are stable and what their reduction potential is and so it also useful for the you know predicting different chemical reactions in solution And then the other one is the Ellingham diagram, and I think you guys have seen this before It's like the first or second page in your kinetics textbook I believe that you've used the last quarter and I hopefully you've done some calculations using it If not, I think later this quarter when we do thermal properties lab We might take another look at this because we talked about the oxidation of different metals But basically you can you can use this diagram to show you know what species you would need to reduce metal oxide, so it's very useful for You know smelting of ores or refining of metal oxides All right, so most cases you're using carbon or carbon monoxide as a reducing agent to reduce a metal oxide such as iron oxide or aluminum Aluminum oxides a different process, but like iron oxide to reduce it into iron metal Okay, so let's talk about batteries now Like I said before I started any research on batteries. I hey, I knew very very little about batteries So I've had to learn everything on my own These are kind of like the the basics of how batteries work and specifically I I I say ion batteries But I mean all batteries need ions. I at least I haven't found any batteries that don't use ions But there's three essential parts of all batteries and that's the cathode the anode and the electrolyte All right, so there was going to be a Potential difference between your Cathode and anode just like in that cell we saw before, you know, there's this potential difference between this Solution and this solution because of this redox reaction Because of the reduction potential between the two Okay, and then the electrolyte is the medium that allows ions to transfer in and out of your of your electrodes a common I wouldn't say common, but Sometimes it's Misconceived that you know you have an ion that's in your cathode and when you when you dis or you when you charge the battery You're taking an ion out your cathode and it goes into the anode and oftentimes I see these diagrams where it shows the ion moving all the way from the cathode all the way to the anode It's the same ion that goes back and forth and reality That's that's very unlikely that you're gonna have the same ion go all the way to the anode in reality All these ions that come in and out of these different materials are probably going to be really relatively close to the surface and not travel too far In distance to go to all the way to the other side another Misconception that I've seen is that all lithium-ion batteries commercial lithium-ion batteries that are rechargeable like your cell phone battery or your computer battery or the batteries in electric cars They do not contain any lithium metal They instead for an anode they they all contain graphite Okay, lithium metal is just too dangerous of a material to be using in a lithium a rechargeable lithium-ion battery Right as the more cycles you you charge or charge and recharge The lithium metal will start precipitating Dendrites and those dendrites can grow and over many many cycles these dendrites grow Eventually they touch the other side and that's when you get a short circuit Right. So if the cathode and anode are touching each other Then you're gonna have a complete short circuit and you can't have any electron You won't have any electrons go through an external circuit. They'll just go straight to each other And so that can generate a lot of heat It's very high current and generates a lot of heat and that can cause problems and so in order to Prevent that in in all batteries. There's a permeable separator is another important part That's often left out of these diagrams the permeable separator can be for sodium ion batteries We use like a glass fiber So, you know allows the diffusion of liquids through it, but it prevents it prevents the anode and cathode touching and lithium-ion batteries We use a polymer Porous membrane so it has Very small micro pores that still allow the liquid electrolyte to diffuse through and you allows Ionic continuity But no Electrical continuity because when commercially when you make these materials you want to make them as compact as possible And so the anode and cathode are gonna be very close to each other And but you don't want them to be touching so there'll be a separating material in between and then I think for the Most of the work you'll see is gonna be for non aqueous ion batteries But both is they're all it's the same same Concept for both for aqueous and non aqueous Okay, so here's some definitions before I go forward about You know different definitions of the things we use in batteries such as capacity of the battery So capacity is equivalent to how many electrons are transferred You know between the anode and the cathode or between the reduction and oxidation process it's Exactly equivalent to the units of capacity are coulombs So one mole of coulombs is 96,000 Sorry, one mole of electrons is 96,000 coulombs and that That that is called Faraday's constant is this this relation However, the conventional unit for capacity and you'll see this written on you know Lithium ion battery If you have a cell phone that you can still take the battery out It'll probably say how many amp hours of capacity it has and So they use this convent this unit and one amp remember amp is a coulomb per second So one amp hour is one coulomb per second times at one hour. There's 3,600 seconds So that's one amp hour is equivalent to 3,600 coulombs. Okay, but this is the conventional You'll see this written a lot amp hour mill amp hour is another that we'll use So that's capacity. So again, how many electrons are being transferred and energy is The capacity of a battery times the voltage that the redox reaction is occurring at right so for like in our previous examples Well, I'll make it simple if you if you have a redox reaction and it happens at one volt versus Versus that zinc metal right and you're you you It lasts for one hour and the current that you're discharging it at is one amp So one amp of current for one hour the capacity is one amp hour And if that redox potential was one volt then it'd be a one times one to be one watt hour of energy Right, so the units of energy is jewels, but the conventional units that we use is watt hour So remember a watt is a form of is the unit of power Which is the current times the voltage so watts are jewels per second So current is coulombs per second volts are Joules per coulomb. Okay, and so that makes a watt So one watt hour is one joule per second times 3,600 seconds is 3,600 joules That's energy. Okay, so again energy has to do with voltage and capacity Another another thing to watch out for is the term capacity versus Capacitance capacitance is is different the units of capacitance is a Farad I believe F Farad and those are used for capacitors, and I believe capacitance is a coulombs divided by volts The the the I guess capacity divided by the voltage I'm not too familiar with capacitors actually although capacitors are very similar to batteries In fact, some super capacitors are basically just batteries that discharge and charge at very quick rates is the the point of the capacitor so here's an example calculation for Theoretical capacity so theoretical capacity is you know if we were to reduce all of the Material the valent change the valence state of all the ions in this material, you know what? How much capacity would that be for that material as a battery? So here's the example of this material vanadium Penta-oxide v2o5 So the you know the first question asks is there what's the starting valence of this material? All right, so the starting valence is of vanadium 5 plus And the next question is you know, how much are we going to? Reduce it by the vanadium is a very unique material Ion it can have multiple valence states there in this very stable So it goes from vanadium 5 plus vanadium 4, vanadium 3, vanadium 2 I don't think there's a vanadium 1 is very stable But all those four valence states 5 to 2 are stable forms So you could you could reduce this material all the way down to 2 I'm not sure if it would retain the same crystal structure if you did that because there's only a limited number of space for For ions to get inside but anyways, so in this case, let's just say we're going from vanadium 5 plus to vanadium 4 plus Okay, so the first question is how many moles Of electrons are transferred if we reduce all the vanadium 5 plus to vanadium 4 plus I'm going to go grab myself a coffee actually you guys spend the next five minutes trying to calculate the theoretical capacity In milliamps amp hours per gram. All right when I come back, we'll see if anyone's Progress from there. I'll do the next slide. So the answer here is 2 The next question will be two moles of electrons is how many coulombs of charge. All right I'm gonna pause the recording actually and I'm just gonna go grab myself a coffee five minutes. I'll be back Let's see if anyone's come up with an answer And if not, I'll get it Is that did anyone come up with a answer for the theoretical capacity of v2 of 5 if we reduce all the vanadium 5 plus to the name 4 plus Okay, I Don't think anyone did it That's okay. All right So hopefully you guys are still listening because I have no way of knowing if you're listening or not anyways, so We've we've determined that there's gonna be two moles of vanadium or two moles of electron per formula unit of v2 of 5 They're transferred for this reduction process So how many coulombs is two moles of electrons? I remember we use fair days constant right we use This number here fair days constant. So one mole of electrons 96,000 coulombs. All right So now we have the number of coulombs of charge that's been Transferred in this reduction process per mole v2 of 5 and then we can convert that to milliamp hours per gram Okay, so one Coulomb divided by let's see how did I do this? I already forget Coulombs All right, so one amp hour of Capacity is equivalent to thirty six hundred coulombs, right because one amp is a coulomb per second and an hour is The thirty six hundred seconds. Okay, and Then you multiply by or the inverse of the molecular weight and that will give you Actually, it'll be an amp hours, but you multiply by a thousand to get milliamp hours per gram Okay, so the the theoretical capacity per gram of this material for just one one electron transfer 295 milliamp hours per gram as a pretty good capacity for one electron transfer for a electrode material anyways Okay So one more definition is definition of power for batteries So the power is the amount of energy transferred divided by how long it takes to transfer that energy, right? So we could have a battery that is The current in the battery if we're drawing current for the from the battery very slowly at a really low current So it takes a long time for that energy to deplete they have you could say that that's a very low power Okay, on the other hand if we take if we can discharge that battery In a very short amount of time then it has very high power the problem is as typically in battery materials as we increase the The current or in other words if we're decreasing the amount of time to discharge the battery or increasing the current the increasing the number of Coulombs of charge per second Oftentimes that that The consequences that we have lower voltage of the battery and then also lower capacity of the battery which results in lower energy So as we if we try to discharge the battery faster our power density tends to go down And so that's a kind of a big problem with with batteries and it's what separates batteries from super capacitors Is that super capacitors they might have very low energy? But they can they can discharge and charge very quickly and so that they should have a higher power Where batteries are more limited by kinetics like for example the kinetics of ion transport within the material You know you have to rely on the diffusion of ions within the solid or also electrical conductivity a lot of these battery materials have very poor Electrical conductivity not only do you have to transport ions in the material? But you have to diffuse the electrons of material and so if you try to do that too quickly You're going to result in the in the higher visit higher impedance and so that's going to decrease your your capacity in energy Anyways the units of powers watts of course Jules per second So it what's nice about these conventional units when we took energy in watt hours and we just divide it by the amount of time it takes To achieve that energy, then we just get watts So I'll briefly talk about the three Mechanisms of charge storage in a battery So the first Mechanism is called intercalation Intercalation if you were to look it up in a dictionary, I believe at least at least maybe 20 years ago. It would say Something about taking a day out of the calendar year Or putting a day into the calendar year. So it has to do with the calendar and particularly it's talking about the February 29th A leap day year where we're taking a day out of the that calendar and then every four years we put it back into the calendar intercalate But we use it the same idea for for materials that we're inserting an ion into the material or we're taking an ion out of the material But the overall structure of the material the crystal structure remains the same or relatively unchanged So just like we're changing the calendar year the calendar structure doesn't change anyways So basically we're yeah, we're this happens You know a lot of different types of crystal structures But primarily layered crystal structures It's easy to do this because you're just inserting an ion in between the layers for example graphite Which is a layered crystal structure you can easily in insert ions And that's why why we use a graphite as a anode material because the the potential to insert ions into like lithium ions into Graphite is relatively low. So it makes it a good anode material You want to have a low redox potential for anode materials and then metal transition metal oxides that are layered like vanadium oxide or manganese oxide these these have relatively higher Redox potentials for these these transition metal oxides. So we use those as cathode materials So this is just an example again the v2o5 if we intercalate to lithium's and also we add two electrons then the the snooze formulas Lithium to v2o5, but it retains more or less the same crystal structure But we're just expanding or and sometimes it contracts actually the inner interlayer spacing and So obviously, you know if you insert an ion in between layers you you can conceptualize why it would expand right? We're putting material in between but in some instances You will actually see a contraction of the layers and why could that be and the reason is that these layers are Layers of like vanadium and oxygen or a different transition metal and oxygen the oxygen is negatively charged, right? So you have two kind of negatively charged planes Kind of against each other and then you insert a positive ion in between and that the Coulombic forces of the positive ion bring the layers closer together So they actually get smaller even though you're in putting putting material in Yep so intercalation is one of the main mechanisms for for lithium-ion batteries in fact the Nobel Prize winner for lithium-ion batteries Dr. Whittingham and amongst other others but dr. Whittingham got it because of his discovery of the intercalation process for modern lithium-ion batteries And actually another note on that dr. Whittingham Made this discovery while working at Exxon The gas company so they were doing a lot of research into Lithium-ion batteries. They're just kind of kind of funny that a big gas. It's not just gas It's a entered an energy company, you know is investing in the lithium-ion batteries That was that was during the 70s though So the the next Charge storage mechanism is called conversion So this is just like we're breaking down the bonds of a of a material and we're we're significantly Changing the crystal structure of that material So for this example, we have tin oxide or any kind of metal oxide like that adding lithium and electrons and Then that turns the tin oxide into tin metal So it went from tin four plus to tin zero or neutral metal and the lithium becomes a lithium oxide a solid So this this is this tends to happen At lower voltages. So a lot of anode materials that are being researched So if I go back to the this standard this standard, right if we look at these these materials Right, we're turning them into metals, right? So like where's the tin tin tin two plus to tin metal tin four plus those ten two plus So these often happen at lower voltages. So they're they're more prevalent for anode materials If I actually go back The highest one the highest voltage would be copper So there has been a bit of research of trying to utilize copper two plus to copper metal as Part of different materials to help increase the capacity like if we could if we could make copper two plus We would copper one through intercalation and then copper one plus to copper metal that could increase the capacity even further But the problem is you're you're just significantly Changing the structure of the material and that's going to make it more difficult for a reversible reaction if we want to you know We can discharge the battery, but the question is can we charge the battery and retain the same capacity? So oftentimes in conversion reactions capacity cyclic capacity Over many cycles the capacity gets smaller and smaller and smaller because you're you're losing material or the material is you know, it's The you're losing continuity electrical continuity, for example with the electrode So you have the crystal completely changes and then the last form of charge storage is alloying so in this case You might have a metal that can make an alloy with lithium for example or whatever ion you're using so in this case again tin metal can Can be lithiated with lithium and so in this case we're going for metal But then we have lithium ions the lithium ions is what's changing the valence state and so now just have a neutral metal This can this had these reactions these alloying reactions They can have a very high capacity and also very low voltage Which is it was just good for anode materials if you want to increase the energy density of your battery The problem is that there's very significant volume change in these materials Tin for example has a very large volume change another material that has been a lot of research is a silicon as an anode material because Silicon can can absorb a lot of lithium But again the volume change is very significant. I forget the exact number, but like over over 500 percent Change in volume so you can imagine if you're changing that much of your volume You're gonna have a lot of mechanical deformation and so over many cycles you get significant loss of capacity because Because of the mechanical deformation that's occurring in your electrode that the pieces are breaking off perhaps and Yeah, so there's some some research that's looking at you're making very nanoscopic particles of tin or of a Silicon or nano wires so they they can they can take they can have space for that volume change without breaking And then another thing to consider is The selection of your electrolyte and I don't talk about too much about the electrolytes and the solvents that are used But the electrolyte also has a limit of you know If you have a cathode inside your electrolyte It's going to have a limit where it starts to reduce or it starts to oxidize and contact with your cathode or anode And so it's depending on the loom oh the lowest occupied molecular orbital in the homo highest occupied molecular orbital of your electrolyte solvent And so if your cathode has a lower energy or excuse me Yeah, lower energy than the homo then you'll have a reduction And if it has the higher energy than the the loom oh the anode has higher energy than loom oh they don't have oxidation So for example for aqueous batteries this this severely limits the the Selection of materials in electrochemical processes for aqueous batteries because you have to deal with what's called the h-e-r The hydrogen evolution reaction That's where water breaks down into hydrogen ions and the hydrogen ions turn into hydrogen gas So that happens at a pretty low voltage and then So that's about point it also depends on the the ph of the the The solvent as well And then on the other end you have oxygen reduction reaction. So that's when water breaks down and You get oxygen ions that turn into oxygen gas So that's one of the limits for working with aqueous ion batteries And also non aqueous ion batteries. So There's some common electrolytes for non aqueous at least the solvents. So I should say the electrolyte is made out of a solvent And a a salt so the solvent for non aqueous electrolytes are typically a different type of carbonates like propylene carbonate ethylene carbonate diamethyl carbonate So these organic materials they have a very high working potential So we can allow for higher voltages or voltages as low as the lithium Without it breaking down and even even then some of the materials do break down And it forms what's called a electrolyte interface. So on the surface of your material you'll have a like a thin layer of a Byproduct of your electrolyte that's broken down on the surface But that that creates like a passivation for further breaking down but still allows ions to diffuse through that layer But in some cases that doesn't happen. So then you're you're constantly breaking down the electrolyte Which is not good and then the salt that's used is also important the salt determines, you know What what ions your ion battery is so for for non aqueous lithium ion batteries a typical salt is lithium hexafluorophosphate lithium H, excuse me pf6 hexafluorophosphate is a common salt And then for sodium ion batteries non aqueous systems the sodium perchlorate is another common sodium salt So they they dissolve in the electrolyte. Excuse me. They dissolve in the solvent and that's what makes up the electrolyte Okay So some different properties of these battery materials and what they how they influence the different performance of the batteries Uh, so for the electro material, of course composition or in other words the chemistry of the material That will highly affect Things like the electrochemical potential So right, you know, if we're changing from iron ions to venetian ions that's going to change the voltage of our system um You know, even if we keep everything the same if we just replace that if we have the same crystal structure And we replace iron with venetium that's going to change our our crystal structure I'm assuming that's it forms the same stable complex, which might not um And not only that but you know, you can have the same transition metal ion like iron 3 plus iron 2 plus and change its local environment, you know, whether it's surrounded by Octahedral coordination of oxygen or a tetrahedral coordination of oxygen You still have the same transition metal But whether it's not whether or not it's octahedral or tetrahedral that will change the potential of your battery as well And it goes even further than that. It's not only the nearest neighbor, but it could be the next nearest neighbor So for example iron phosphate lithium iron phosphate compared to lithium iron sulfate so in both cases iron is I think uh I forget if it's octahedral or or tetrahedral, but in both cases The iron is surrounded by oxygen, but in one the oxygen is coordinated to phosphate Or phosphorus another one that is coordinated to oxygen Well, I say oxygen is coordinated to sulfur And so just by changing those next nearest neighbors You can also change the electrochemical potential of the battery or the discharge potential of the battery So it all has to do with the the energy levels of these of these transition metal elements and how near the local environment affects that energy And then like crystal structure can affect things like uh the cyclic stability Um, right it like I said if you if you have um Or capacity is a better example If you have a nice layered structure lithium ions or sodium ions can diffuse into the layer structure pretty easily But there's other crystal structures that are not layered or they don't have good channels for lithium ion diffusion So that can that can severely affect the capacity and or like things like power density because Uh, you're the if your diffusion is limited you're you're limiting you're limiting the kinetics of your reaction See you can't you can't just uh increase the current of your battery There's going to be a much higher impedance to that so that's going to decrease capacity and and power density Um morphology is also a big factor about uh with that like I said um Kinetics is a big part of of the performance of the battery You know, how fast can you diffuse lithium and also electrons electrical conductivity within your material? And just by changing the morphology, you know, say you're changing it from, uh Micro particle to a nano particle But you keep everything else the same the crystal structures and the composition is the same just changing the size of the particle Can change the the capacity and the power density because you're changing the kinetics I have an example of that Next the electrolyte, right? So what solvent you choose like I said that changes your electrochemical window Or whether you're using water or something else also some of the solvents might react with the electrode material And then the ion choice also so uh depending on what your ion is, uh, you know They were depending on what your solvent is some solvents can't dissolve certain salts and and so on Okay, so here's an example of changing the morphology Uh in titanium oxide. So titanium oxide is not a very good Uh, it doesn't have a very high diffusion of lithium ions and it doesn't it has a very poor Electrical conductivity, you know, it's it's a it's a wide band gap insulator, right? so If you you start with micro particles, you know, you can you can reduce the surface of a titanium four plus And titanium titanium three plus and interculate a bit of lithium, but it only diffuses into the surface So only the surface Is is reduced And so that severely limits the specific capacity or the the amount of electrons per gram of Material transferred But if you're to take the same material and make it on the nano scale now, you're really decreasing the Excuse me Really just decreasing the diffusion distance of the lithium. So lithium has no problem just diffusing a few nanometers and then you can fully Achieve the the full or near theoretical capacity in that case if you make very small materials and so there's an example of this from this paper And um where they have titanium oxide micro particles is about diameters about one micron And then compared it to a different type of titanium oxide particle They call this the the urchin particle. So it's basically a sphere, but it's been etched away. So you have A very high surface area. They're just kind of flat sheets that make up the sphere Um and nanowires and so it has very high surface area And then the thickness of the the sheet is very small. So the diffusion distance from like the lithium outside to inside is very small Um, and so you see just the difference in specific capacity You know for the high surface area Urchin type titanium oxide compared to just the bulk ti o2. So just by changing the morphology Making it smaller. You're increasing the capacity. Also, you're increasing the the performance I'll talk a bit about this type of data a little bit later So this is an example of how I make batteries in my research It's a bit different and like if you're making batteries from commercial applications, obviously In commercial applications, everything's Uh mass produced. You have these printers that print out the electro material very quickly, right? So just for research, we use these little button cells the coin cells And so we do we start with our material So either a cathode material or anode material It's whatever our active material is that we're studying We mix that material by weight These numbers can change but I use 70 percent and it's fairly standard and then you add carbon We use a black carbon. There's different types of carbon that have different like surface areas and You could also use some people use graphite That the purpose of adding carbon is because a lot of these materials have low Electrical conductivity for example, my my material here is a semiconductor And the purpose of adding carbon is to increase that electrical continuity of your electrode So you can help deliver the electrons throughout your electrode But the carbon itself does not participate in the electrochemical reaction Unless you have graphite And you're working at very low Potential then you could have at low potentials you can have low Lithium intercalation, but for my materials a cathode I work at higher potentials It's above the potential for intercalation. So it doesn't happen So it's inert basically it just added added to increase Electrical continuity and then we keep it all together using a binder So a common binder that we use is called a pvdf polyvime abbeam dive flooring Something like that basically it's a carbon chain and then You have flooring attached to each carbon and also hydrogen attached to each carbon So very similar to teflon which is a carbon chain with two fluorines attached to each carbon And so it's also chemically inert, but we can dissolve it we dissolve it in a solvent Called nmp. Nmp is a very it's very nasty solvent It's uh, it eats through a lot of different polymers including like Those the purple nitrile gloves that can eat through those purple nitrile gloves So we have to wear special gloves when handling it And so we we mix that together and either like in a moron pestle like this where we we kind of mix it all together Or we can put it into a little A little container and we ultrasonicate it with a very powerful ultrasonic probe It much more powerful than the regular like little container that ultrasonicates it And then we spread it out the slurry onto the electrode or what we call the current collector Now depending on if you are working with an anode or cathode You'll either use aluminum foil or copper foil as your your current collector The reason is for for lithium ion batteries and as well as sodium ion batteries If we use aluminum Lithium and sodium will alloy with the aluminum So it's an active material But it alloys only at low voltages that we would use like for um anode materials So for anodes instead of aluminum we use copper and lithium and sodium do not alloy with copper So we use copper foil for that However, at higher voltages copper will oxidize in the copper ions So we don't use copper for the cathodes. We only use it for the anodes aluminum on the other head Aluminum also oxidizes but aluminum has a passive oxide layer on it Which passivates it from being further oxidized at higher voltages So that's why we use aluminum foil for cathodes and copper foil for anodes anyways So we we doctor blade it onto this aluminum foil. I do mine just by hand I take like a glass rod and I just I put it onto the aluminum foil and I spread it out And then I let it dry and after it's dried like in this picture I'll cut out little little circles with a punch. We have a little like a lever punch that cuts out these circles And then we weigh those and then everything gets transferred to the glove box. This is a argon glove box so the atmosphere is Ultra pure argon. In fact, it's 99.999 percent argon and the expensive stuff and This glove box also has a filter system where it filters out oxygen and water Through if there's any leaks in there And so the oxygen and water content of this glove box is always less than 0.5 parts per million Every now and then it will kind of bump up to it'll start going up over time because the the cattle There's a in the circulation system of the glove box There's a copper catalyst the copper will will absorb the oxygen and water water from the atmosphere And turn into copper oxide and then over time that catalyst Depletes itself and it has to be regenerated and then the oxygen starts to go up So every every two months or so we'll we'll do a regeneration process where we we attach the the catalyst to Hydrogen so we have a 5% hydrogen argon mixture and we run hydrogen through the copper ox Which is now copper oxide catalyst and the machine heats it up And it reduces the copper oxide back in the copper And then it's it's good for another couple months before we have to do it again. So That's the regeneration process. There's a lot of upkeep that has to go on with this glove box Another thing about working with the glove box is that it's uh, it's not very comfortable because it's under It's under positive pressure Uh, and so it kind of feels like you're working underwater And also, you know along with the the lab coat We also wear like the purple nitrile gloves and I also wear like these chemical resistant sleeves Just keep my lab coat on and then we put that into these big rubber gloves Okay, and then on the other side inside the glove box. We also put on extra large purple nitrile gloves And so we got right already three layers of gloves and you can imagine during the summer it gets kind of toasty in there um, and then additionally If if we're working with sodium I work with sodium a lot and uh, the sodium Comes in chunks of sodium. I have to actually cut the sodium So I use a knife and we've had instances in the past where people accidentally cut the glove And then we start leaking argon out So now the rule is we have to wear these giant rubber gloves You see them in the picture these kind of yellowy pale gloves that go on top of these already big rubber gloves So it's it's very uncomfortable when you're trying to cut things and And um the lithium on the other hand the lithium we purchase lithium chips They're already in the little sort pre cut circles. So it's they're very convenient to work with sodium However, sodium is a much more reactive metal than lithium Um, and so it oxidizes more easily So there's I don't think there's a manufacturing method to make the pre cut Sodium to be able to ship out so we get the blocks of sodium or maybe there's no demand as well That could also be it But we get the blocks of sodium we have to slice the sodium and then we have a inside the glove box We have a pasta roller It's just like uh, you know making like pasta from scratch Rolling out the dough into a sheet and so we put the sodium chunk Uh in the pasta roller and we roll it out into a flat sheet of sodium And then we take a circle punch and we punch out the little circle chips of sodium Anyways, so then we assemble the the the battery inside the glove box We have the working electrode on one side that's connected to the top or bottom of this uh coin cell The coin cell is stainless steel So you need to make sure that whatever electrolyte you use some of these electrolytes are very corrosive You want to make sure that the electrolyte does not corrode the stainless steel And also you want to make sure that the stainless steel Does not react With your uh, you know when you're applying a voltage to it There might be some other chemical reaction happening at the surface of the the stainless steel and that's going to influence your results But the stainless steel it's you know has a chromium oxide passive layer So it's it's pretty chemically inert And then there's the separator that we add At this point we would add the electrolyte. So we have like a beaker of our electrolyte Some of them are pre-made that we purchase And then some of them we have to make ourselves So we have our solvent and our salt and we add the salt to the solvent and mix it up And then we pipette it into this uh this coin cell Then we add the counter electrode, which is probably just lithium or sodium And then uh in some of the cells we add stainless steel spacers and springs And then also importantly is that the top of the cell You need to make sure that the the counter electrode and the top cell does not make any Electrical connection with the bottom otherwise you short circuit the cell. So there's a a a plastic Plastic gasket that protects the two and then once you have that assembled There's a device inside the glove box That that's a press that crimps Crimps the the button cell so we put in the press and we we press it down and it compresses the button cell so everything's Sealed in and then it can be taken out So I'll talk, uh, I'll I'm about to wrap it up just a few more slides. I believe Actually, I think I might have added more so we'll go through it though Some of the different tests we do for batteries The machine we use is called a potentiostat or galvanostat And um, uh, this is an example of a galvanostat. We have the same exact one in our lab And so it has many different channels that you can put your batteries in and you program it So each channel actually has four wires, right? Like I said before for a three electrode cell Um, you know, you you have voltage between the working electrode and reference electrode And you have the current between the working electrode and the counter electrode Um, however for the two electrode cell like our button cell The reference electrode and counter electrode will be that part of the same same cell So we only have, uh, you know two two clamps Okay So this is one of the most common type of tests Cyclic voltometry or voltometry is uh, basically we're we're controlling the voltage of the system while we measure the current response at these different voltages Okay, so this shows, uh What at what voltages different redox reactions happen at so in this example, uh, we have a sodium vanadium phosphate material um Now when you make this material More very likely there will already be sodium inside the material when you synthesize it So let's say it starts with it probably starts in the vanadium Let's see you have vanadium 4 plus Is that right? Yeah starts out as vanadium 4 plus with one sodium in it I'd say so in that case if you were to take this material And it's freshly made and it's inside your battery and you were to measure the open circuit voltage of this battery This material is in the vanadium 4 plus state the open circuit voltage would say it's around this this would be right here So right there's no current going through the battery. You're just measuring the voltage It'd be right in between here. And so that's it's at, uh, the equilibrium state at that potential Okay, and so what this test will do is it sweeps the voltage for example It's we start with decreasing the voltage and as it decreases the voltage you start to get a reduction reaction If it's negative current that's reduction So we're giving electrons to the cathode of this material and we're taking electrons away from the counter electrode So in this case the counter electrode our voltage is v versus sodium Metal so the counter electrode is just the sodium redox reaction So we're taking electrons away from sodium sodium is dissolving into the electrolyte and the vanadium 4 plus is Reducing the vanadium 3 plus at the same time. We're intercalating sodium ions into the crystal structure Okay, so that's what this current this peak represents. Okay, and then and then after that peak, uh We we keep on pushing the voltage and there's nothing no reaction happening because we haven't met that uh redox potential yet for the next Uh reduction reaction, which is vanadium 3 plus and then the same thing happens So we we intercalate another sodium ion into the structure Okay, and then at this point now we've fully reduced vanadium 4 plus into vanadium 2 plus So you could say this is the discharged state of the battery And then we reverse the voltage sweep and then the opposite happens the oxidation potential The oxidation reaction happens on the cathode so now sodium is sodium ions in electrolyte are plating onto the sodium metal so they need to receive an electron and the cathode The sodium vanadium phosphate is is oxidizing it's giving away an electron All right, and that's given that's indicated by the positive current All right, so basically what this shows is which uh what potentials what reactions are happening Although you have to have a bit of knowledge on like what you know What species is being reduced and what species it doesn't tell you obviously but it can tell you a bit of information on like the kinetics Like how how high the current is um The reversibility so this might happen over many cycles and see if it's repeatable or if the chemistry changes You know after if you cycle the battery many times Perhaps the local environment of the vanadium might change and what you would see is that these peaks begin to shift And in potential you say, oh, it's not it's not stable It's not a reversible reaction because things are shifting around right which is not ideal for a battery if you want to put in the consumer electronic So that's the kind of information you can get So cyclic voltometer again controlling voltage measuring current I had some examples of cycle cycle of a telemetry. I think we might skip through it because uh We're a bit over time on this lecture and my voice is starting to go So i'll just briefly introduce the second most common test is galvanostatic cycling So if cyclic The latometry was controlling voltage and measuring current galvanostatic cycling is Controlling current and measuring voltage response. Okay, so this is the same example with a sodium vanadium phosphate And this this type of test you'll say discharge at a certain current. So for example 10 milliamps per gram All right So you you you know the the amount of material in your battery because you weighed it before you assembled the battery So you can calculate what 10 milliamps per gram is for that that battery right and give it a current Oftentimes we use what's called a c-rate So this symbol here one c one c is equivalent to the current density Needed to it's completely reached the theoretical capacity of the battery in one hour. That's so that's one c So zero point one c or c over 10 would be Let that be six minutes. So it that would be it would take six minutes to Reach the theoretical capacity at whatever current that is. Anyway, so c-rate is often used And the other common Current rate is milliamps per gram is also the common. They're they're basically equivalent Um So in this type of test, you know, let's say we start with our material and it's in the charge state All right, it's fully charged. That means it's fully oxidized vanadium 4 plus So as soon as we start the test, you know, then the voltage will will under it'll reach it's uh, this is the The this plateau the voltage of this plateau is equivalent To this peak this voltage, right? So you see this is the redox reaction happens at this voltage vanadium 4 plus of the vanadium 3 plus That's essentially the same as what this plateau is showing is that this is the reaction happening And then capacity this x-axis is essentially the same as time So remember we're discharging at a constant current And so for example, uh 100 milliamps And then this is just measuring the time and so you just multiply by time as milliamp hours and that's capacity So this kind of shows how much capacity there is in that material and then it reaches a certain voltage and This is a bit arbitrary. We we decide as a user when to stop the test You know say like oh this this person could have stopped the test at 3 volts or it could have stopped at 3.2 volts And it would have been more or less the same Although this this uh study didn't go to the further Reduction state of vanadium 3 plus the vanadium 2 plus So that's and this is the fully discharged state just from vanadium 4 of the vanadium 3 And then what you'll do is you'll reverse the current So if we this was negative current to discharge Then you'll reverse it the positive current to charge and so you'll you'll go back to the origin And it'll go up and this is the the charge potential the plateau Representing the vanadium 3 plus the vanadium 4 plus reaction And then again, it's arbitrary when you want to stop the test So that's a galvanostatic uh rate stability is another uh very similar test where you're changing the current rate That you're discharging or charging the battery at so that's again the c rate representing the current rate So like I said before as you increase the current rate The you're you're re you're bumping into certain kinetic limitations of this Electrochemical cell for example the lithium diffusion in your material or the electrical conductivity of your material or perhaps the the There's an energy barrier for electron transfer between your your electrode and the material So if you try to increase the current Higher and higher you're reaching those kinetic limitations, which is going to start dropping the voltage All right, because there's going to be a voltage drop if you have a resistance It's essentially the same as v equals ir if you have a resistance and you increase current the voltage Drop in this case a voltage drop increases So if we were to take this plot and increase the current We would expect this plateau to get smaller and smaller and smaller and smaller And then also the the capacity would get smaller and smaller and smaller as well That's what we see exactly here as we increase the current our capacity is getting lower and lower Okay, um, yeah, I think we'll stop there We covered a lot and now it's uh Some of it's a bit complex, but I I hope you guys kind of get a a broader understanding of Kind of battery materials energy materials and electrochemistry. Is there any questions? Um about what we covered All right, if there's no questions, uh, I'll see you guys thursday Um, I haven't planned out exactly what we're going to cover. There's a lot of slides. I haven't included About some of my own research in the the battery Results some of it's kind of interesting, but I still want to talk more about maybe the The data analysis, um a bit so I'll find something to talk about on thursday Um, and if there's no questions you guys are good to go. I'll see you on thursday