Electric Vehicle Battery Breakdown: Cells to Modules to Packs!

hello everybody Welcome to Monroe live my name is Tom pre I'm director of electrification for Monroe and if you don't know who we are we are a lean design consultancy where we specialize in new product development and we have a lot of focus on EV products and uh costing benchmarking tear Downs um today we're going to talk about batteries and uh we're going to get into the different types of batteries the different styles and their configurations as they are related to electric vehicle applications so behind me I have a table full of all kinds of good stuff to look at I'll start with the basic form factors of batteries um the ones that we see most popularly are of the cylindrical type as you see here they are called that because they're shaped like a cylinder we have a couple of examples of pouch batteries that are very popular and then we have the Prismatic cell that's an interesting sort of a combination of the two if you will so what do I mean by that um if you get inside one of these things you can tell that they're full of all kinds of unique features um I will talk about the smaller cylindrical cell first here and an important feature of that cell just so you understand what we're talking about so this is the anode which is one of the two parts of the cell that are most important and notice that it's got this little foil tab that comes off the end of it so this is the part that attaches to the bottom of the cell down here and it's also electrochemically the side of the battery that gets warmer if you will so it's a great place to take heat from if uh you look at the other side of the battery you'd find that this is the cathode so again here's your positive terminal here's your negative terminal the anod is the negative so this small tab if you take a look at Ohm's law you'll find that this is is a quite a restriction and because it's a restriction it has higher resistance than other components would have and it it becomes a hot spot because of ohms law so talking about ohms law take a look at if you're going to be involved with vehicle electrification under Stan ohms law it's a critical part of it it will keep you safe and it will certainly ground your understanding in how it all works so that said take a look at a so-called tablist design and this is what you find inside the 4680 cell you'll find instead of one tiny little piece of foil at the bottom you have several pieces of f of foil this goes around the circumference of it and gives you a much wider path for collection of the current so you can see that the Restriction isn't there with the tabless design like it is with the the tab type design we we looked at earlier so now what does that relate to out here these all have tabs in them so you have have the small 18650 that's uh very popular it's the type that's used in Model S's and X's you have the uh 2170 or 21700 as it's usually called uh again this is a function of the diameter being 18 mm here for the 18650 and it's 65 mm long along with a 21 mm diameter and 70 mm of length uh then you get up to the 4680 and this is 46 mm in diameter and 8 mm in length and you'll notice that the bottom of this thing is quite a bit different than the bottoms of the others these are flat um these again have the real small Tab and this becomes kind of a hot spot whereas this one has the tabl Lisk design that connects around the perimeter so it doesn't have that Hotpot the anode still gets hotter but it's a different approach to cooling that we'll touch on in a moment here but before we get too far let's look at the Prismatic so the one thing about the can of the cylinder is that the expansion and uh contraction that occurs during the charge and discharge cycle as well as over the useful life of the battery it tends to expand it's pretty well managed with the can you don't see much in the design of the pack that is uh relevant to the expansion and contraction of the cell because the can kind of minimizes the motion and manages it quite well the pouch not so much this pouch will grow in width and it will contract it grows when you charge it it contracts when you discharge it and um you have to manage that in the design you'll often find that there's uh polyurethane foam that serves as sort of a compression spring to keep the the big flat surface under pressure and managing the expansion and contraction so the Prismatic is kind of The Best of Both Worlds when you look inside here you can see that oh okay I've got a metal can on the outside so I'm managing a little bit that expansion contraction uh but it still grows enough where you do have to keep these under compression when you have an array of Prismatic cells inside the Prismatic cell find this interesting perhaps so what do you have you have what amounts to groupings of pouch cells without their envelope so when you think about the Prismatic cell it is truly a combination of the cylindrical cell that has the metal can surrounding it and the pouch that uh gives you a maximized um efficiency with your space I can fill this entire rectangular space with energy whereas with the cylinder no matter what I do when I put them together there's always that little spot in the Middle where you can't put anything sometimes that's used for cooling sometimes that's used just as a place for fire retardant foam other times as we'll see with these other batteries it's just air inside there so again that can become part of the risk mitigation strategy for thermal runaway in the uh cylindrical cell what you do with that little triangular space between them can be important so with uh the the pouches they're a little bit more difficult to manage with regard to Thermal runaway risk mitigation there's a lot of use of things like aerogels and other flame retardant materials that are used to try to keep these big blocks of energy self-contained in the event that one of them tries to let loose we'll save what is the cause of thermal runaway for some other discussion so so then let's look at some of the different types of modules so when you start with a cell this is the fundamental building block and what you end up with in the end there is an array of both series and parallel cells so in other words when they're in parallel they're electrically tied together like this with the cathodes tied together and the anodes tied together and as soon as they're electrically tied together they behave very much like one cell not unlike the way this Prismatic works with what amounts to four pouch cells uh in parallel and still giving you the same sort of terminal voltage that you would expect with the smaller cell so that being the case the U the cooling subject is a very important part of battery design the parallel combination turns it into a big block of cells that acts as one and you'll hear this in terminology in terms of s's and P what are the P the P's that's a parallel cell group in the case of some batteries this might be 22 cells or 40 some cells in parallel depends on the application and how much power you need and what the size cell it is uh and then there's the series configuration how many do you put in series this is a little bit like your D cells in a flashlight if you have two okay I've got two one and a half volts in a alkaline situation for a total of 3 volts these are much higher in voltage nomally 3 .6 Vol so okay I put two of these together and I get 7.2 volts and if I keep putting them together in a series array I get higher and higher levels of voltage so that's basically what the module does normally the majority of the packed designs that we see are cell to module module to pack so here's a module this one's out of a lucid air and it's an interesting topic because you can read a lot about this thing if you go searching on YouTube you'll find a lot of interesting information about this one of the things I wanted to quickly show is that underneath you have wires that are attaching the cells to these uh bus bars that we call current collectors so you'll notice if you look very closely that these Tabs are both wide and small and that is different than what you'll find in some of the other ones uh that we'll show here in a minute that use Bond wires so here's an example of bond wires these are small wires that interconnect the current collectors to the cells and they do it with the same size wire and that wire in both of these cases serves as sort of a fuse uh in the Lucid example the smaller one becomes diff fuse and the other one is larger specifically so that it doesn't have the voltage drop because of the bottleneck that it represents as a as a fuse wire so you'll notice that Tesla has moved away from the bondware concept they are a little bit frail they can break away they can cause malfunctions um so you'll find the most recent uh Tesla modules if you have a module they'll have laser welded collectors instead so quick look at these two almost identical looking modules these are from Model S and x uh but two different evolutionary steps you'll notice on this one that you've got two rows of cells with a a big gap in between them two more rows with uh another Gap and in that Gap if you look very closely you can see it at both ends there is a coolant channel that runs down the middle and just picks up the tangent of all the cells it's a straight piece of pipe quickly they learned though that they could gain more of the side space of the cell by making it a serpentine shape shaped like a snake and that's what you see with this module design if you look closely here all the rows are equ equidistant from one another and what that means is that the coolant Channel snakes through and picks up more of the surface area of the side of the cell so this was an evolutionary step that improve the cooling for the model S and X so from there I can take you to the latest versions of those modules all right so the model 3 and the model y if you look closely at them there's not a lot of difference between them they do have have Bond wires most of the these have been removed but again the little small wires that interconnect the cells with the current collectors uh if you dig through this plastic you would find the bond wires are covered in this and again that was to address both you know the need to have that as an electrical insulator and the foam serves as sort of a vibration damper against those wires breaking loose so the cooling system on these if you look at them this has a manifold on one end that represents say the inlet where the coolant comes in and then on the far end you have the outlet so that means that you are in a cooling mode and you're bringing cold water in and the hot water comes out the other side after it's cooled the battery creating a gradient that means that the inlet side has cells that are cooler than the outlet side does so that's kind of problematic the hotter cells that run that way most often will have a shorter useful life because of that and you'll see that the three amp and the Y have the same basic Arrangement Inlet on one End Outlet on the other and they all have this sort of serpentine cooler that I was telling you about that we saw with the snx module originally then came the Plaid so here's the plaid and you notice that they did something unique here the inlet and the outlet are on the same end of the module so what that means is that the serpentine cooler has been split down the middle the cold water goes in one side goes all the way down to the end returns and comes back to this end creating a situation where every cell has both a cold water and hot water connection creating a uniform temperature gradient across the array and a much longer useful life of all the cells in the array so another big change occurred with the plat Evolution um and again you may find this in a lot of other places but the bond wires are gone now suddenly the current collectors are laser welded directly to the cells and the frail Bond wire is gone and then they've created details in in the current collectors that represent the fuses that the bond wires used to perform the function of so then you get to the structural pack and it's kind of the last iteration from Tesla to show you you'll see that they've done the same thing the inlet and the outlet are on the same end so it's the same sort of partition Serpentine cooler um much bigger because this is now the 80 mm cell so it's a a a wider connection and because this 4680 structural pack um had has the tablis design the side cooling I think makes it a clear winner with the smaller cells the 217s from the three and the Y and the 18650s from the model S and X um yeah the uh um the cooling function at the side becomes a subject of debate and whether one is better than the other I'll leave that for others to decide unless we get to do an experiment experiment one day to prove or disprove one way or the other so that said um let's take a look at how it scales up we had modules we had small ones in the beginning we had slightly larger ones the voltage goes up with these larger modules as well they could become inherently more dangerous it is still a difficult thing to get shocked by them but again HS law will save you if you know where to not touch then you will be safe uh so it's a matter of where are the voltage potentials and yeah this one could give you um you know 80 90 volts um even in the discharge State whereas the smaller modules are much safer to handle down in the 20 Volt range so that being the case sometimes there's no module at all that's what's happened in this structural pack here they've gone away from the ability to be able to replace sections of the battery uh and now it's all one big disposable piece of Hardware so again we call this sell to pack whereas the usual ual structure we see is cell to module and module to pack that said let's look at some of the packs so here's the model S and X I'm not sure which one this one is doesn't really matter for this discussion one unique thing about this design is the the cooling system has these little check valves in them these are normally pointed straight upwards it makes it very easy to remove this pack from the car it's basically just the perimeter Fasteners and some other Fasteners that hold it all in and um when you drop it this coolant Port disconnects itself and the little check valves keeps the coolant inside the battery pack which is a nice thing and you have the same sort of feature on the electrical connection side where all of these electrical connectors are pointed upward so that they just fall right out with the battery pack whereas a pack that's not designed for such an easy swap you might have several things that have to be manually disconnected and the coolant will probably make a big mess for you because it won't have the little fancy integrated check valve as part of it so SN x 3 and Y you can see the DraStic difference in the module size so that kind of takes me to some of the differences in how you manage these batteries in other words um we hear the term battery Management Systems uh or BMS as a term all the time what does that really mean so generally it is what keeps the lithium ion battery array safe and when I say array I mean anytime you have uh two or more cells in series they are independent devices that will behave independently from one another and they will drift apart from one another with regard to their state of charge over their time over their useful life so every charge discharge cycle might make them grow further and further apart in state of charge ultimately you would see this with voltage change so the battery management system has a number of different responsibilities first and foremost it monitors those cell groups so when we talk about cell groups we talked about the series and we talked about the parallel of cells and wide arrays of parallel cells I would call that collectively a cell group and that's kind of how we treat them here so you have to monitor the voltage of that cell group and that's one of the primary functions of the battery management system so in the case of this Tesla system here with the three and the Y you can see that there is a device that's local to the module that gives you that function of being able to measure those voltages if you look really close you can see that they use again some more Bond wires to connect each and every cell group to the battery management system so that you can measure the voltages in real time another purpose behind the battery management system is to measure temperatures uh a third purpose is to measure um or more importantly provide the balance function in other words I mentioned when they drift apart I want to move energy if I can and there's a type of balancing system called an active balancing system we don't see it much in automotive but it's very real elsewhere but that would tend to move the energy from the one that has the most to the one that has the least and that has lots of variant so I won't go into that but the passive systems that we normally see just simply take the ones that are highest in state of charge and it puts a resistor across those to bleed that off so that those states of charge come down to that of the others so the balancing function the temperature measurement the voltage monitoring it's usually handled by a satellite device like you see here where we have four modules and four of these little satellites there's also a battery management system that collectively brings this information together and has the intelligence intelligence to know when to do balancing and uh it also adds the functionality of contactor control that is the electrical connection and disconnection of the battery pad pack to and from the vehicle so yeah there's your basic functions of a BMS you'll find different configurations with regard to whether you have uh the satellite configuration with a a central unit that manages it U primary and secondary is probably uh a good set of terminologies for that um there's also the concept of the spaghetti wire meaning you can have a BMS that's all in one piece but it's going to have a lot of wires that go to all the cell groups so here's an example of a battery management system that has the ability to do everything in one uh position if you will so you're going to go out and you're going to measure all the cell group voltages there's going to be spaghetti wires all over the place in this pack and you can take the same basic concept and you can bring it down to a more manageable level uh but it's quite normal that there' be a small plastic module plastic covered module that would be the satellite system that minimizes those spaghetti wires those spaghetti wires are very important because in the case of the cell group monitoring those are small wires you don't want to use big wires for that but if those wires ever touch together there needs to be some sort of current limiting function in that or bad things are going to happen so we find a lot of differences in different battery designs with regard to the current limit function on the cell monitoring wires and by having the the so-called primary and secondary design you minimize how far those wires got to go and you minimize the risk of routing those wires again you know any sort of a malfunction that was from you know shock vibration normal wear and tear or where she had a collision yeah those wires can come loose and they can cause a big problem if there isn't proper current limiting behind them cooling we've seen a couple of examples of cooling we've got the bottom cooling that lucid uh is very proud of and if you look at this U module when it's torn apart you'll find that there's a thermal interface material between the bottom of the cells which in this case are now pointed upwards um it's a a good cooling system design you'll notice that the cooling plate has this design in it that's supposed to provide a uniform uh distribution of coolant throughout the the module you end up with that same sort of temperature gradient that I was re referring to earlier where the cold water coming in might cool some cells more so than others um when you get into the pouches there's a mixed bag of ways that those are cooled um before touching on that we'll talk about the Prismatic and what is most common is that there'll be a layer of thermal interface material along the bottom of the cell sometimes you'll see some cooling at the sides but not very often in the case of prismatics but you will see that with the pouches so in the beginning first pouch cells that I looked at were from the Chevy Volt with a V and they had these plates that went between every cell and picked up the entire surface area of the cell and they even had little coolant channels that were distributed throughout the uh the plate that gave you a way to put actual coolant through there liquid coolant later the bolt with a bee ended up with a metal plate there that was kind of L-shaped that would carry the heat off the surface of the um the pouch cell and down to the L fold where there would be a a cold plate at the very bottom to take the heat away later we saw this happen that aluminum plate was too expensive so we went from an aluminum plate that had cooling channels in it to one that didn't to no plate at all and what they simply do in that case here is they use a thermally conductive adhesive at the very bottom of the cell and they use that to couple the The Thermals to the cold plate down below so you can imagine that this saves a lot of money uh and if it doesn't cause you a PO performance concern then it is a very inexpensive way to do your cooling so let's talk about the way pouch cells are cooled so this is an example of the ionic 5 battery module and you'll notice that at the very bottom of the cell much like what we were talking about with this cells here there is a layer of thermal interface material it's been removed but you can see the edge of what it was before it was removed and this is what it looks like when it's removed you'll see that it kind of follows the topology of the surface area of the multiple cells that it's trying to cool but you may also know a little bit about thermal interface materials the basic idea there you know a high school kid who does gaming knows that when he puts a big cooler on a CPU you want metal to metal and the thermal interface material is supposed to fill the micro pores of the otherwise metal to metal contact it was never supposed to be that thick the thermal interface material while thermal thermally conductive it still represents an impediment to transferring the heat you want the stuff as thin as you can make it so yeah not so thin in this case we find that allowed in in the pouches and again these are large format cells that have lots of energy in them and because of that it's pretty easy to get large amounts of power out of them and they can get away with thermal systems that are quite obviously challenged by things like thermal interface materials that are too thick then we talked about the space in between the cells often times we find them taped together it makes them difficult to get apart you can see some remnants of the tape in this case here they often have a foam like this as well that serves as sort of a spring that gives you this ability to manage the expansion and contraction of the cells while they charge discharge and get larger over their useful life so yeah lots of variants of this foam are out there as well um sometimes you see the foam is is uh Complicated by other materials such as the aerogels mentioned earlier as a uh thermal runaway risk mitigation so that being the case we have covered I think the cooling we've covered the expansion and contraction we've covered why the bottom cell cooling is good for the cylinders uh except for the cylinders that don't have a bottom tab um and from there we go on to the spreadsheet so this is a streamlined version of a spreadsheet that I use a lot um it normally has a lot more columns and a lot more rows U but I've reduced it in scope here for our discussion today uh before I get too deep into it I'm going to cover a couple of quick terminologies uh capacity you hear this term a lot it's generally uh a unit in amp hours so I'm defining the cells at the top half of the spread sheet here and the amp hour rating of the cell is important for all of the energy and power calculations so um again what this means if in the case of a 5 amp hour cell that means if I draw five amps from this fully charged cell I can do that for an hour all right so that's just kind of a general rule of thumb so it's current uh over time for amp hours uh if you take that and again apply ohms law and multiply that amperage with the nominal voltage now I know what is the nominal energy if you will so you can see that in terms of Watt hours here so volts times amps is watts and if I include the element of time it becomes Watt hours again power is this instantaneous moment in time that decides what your acceleration performance could be in the discharge it decides what your regen performance would be in the the deceleration mode if you will or where you're trying to recover kinetic energy from the vehicle so from there another General grouping is the module definition you'll find in this spreadsheet I've got all of the batteries in question have at least one module um in even in the case of the structural pack with the 4680 it's still electrically group as as a module even though it's not a separate replaceable device within the pack so that said um not all of the batteries in question have two different module sizes but where they do in this case here I've got them clearly identified and then down further I declare how many of one type of module I have versus how many of the second type and then I don't have any of them in this case that have strings of those in parallel except for the case of the Hummer so we'll get to that in the beginning here let's start with the simple uh rivan I have a 5 amp hour cell this is a uh 2170 1700 depending on how you like to describe it it is one of the few where we had the luxury of having a data sheet that you could get from the original equipment manufacturer uh easily confirmed with what is the part number printed on the side of the cell so I'm able to get some pretty good information going into that it's otherwise um filled with information in the yellow cells that I've uh either calculated uh inferred from some other reference or gotten from some nefarious anonymous source so again accuracy isn't guaranteed in this but it gives you a great idea of how this works as a system now go to the energy of the cell to the energy of the module to the energy of the pack and you can see in this case here we've got 141 kilowatt hours we've got that number represented by What's called the the serial and parallel cell grouping so what we do there is we talk about how many cells are in series and then how many groups there are in series and by groups I mean groups of cells in parallel so we Define that in the module in this case here with the rivan there are 72 cells of the 2170 type that are all grouped together as a single cell group and then there's 12 of those in series to make a module so each of the modules has 864 C in it then we take those and put them in series and we end up with a pack and we can see that if we see how many modules there are we can see what the total amount of energy there is in terms of kilowatt hours now one thing i' i' I've avoided in this spreadsheet explanation is the subject of power and a very important topic that I hope to get into in a a a subsequent um discussion that is called C rate so if I have uh five amp hours and I have one C okay that would mean that I could get five amps out of it right if I can get one two c out of it I can get 10 amps out of it and again there's different durations I'll touch on that at a little a later point but you need to understand the importance between the amp hour rating that can tell you what the instantaneous um Power would be simply by knowing the C rate that is a very deep subject for another time so that being the case don't confuse power with energy we're talking about energy here and this is always power over time so again there will always be some element to it that says hours and uh sometimes you might see it expressed in minutes depending on what you're trying to do so that being the case there's always a difference between the kilowatt hour rating of a pack and what would be the usable energy so this is a little bit like your gas gauge in your car um when it's full there's usually something more than full you can usually put put a few extra gallons in on top of when it says full and likewise is the case when it's empty nobody likes to walk so there's always usually a couple of gallons at least when it says empty before it's completely empty and you walk so they've done the same thing in batteries and that is the difference between this gross energy figure that is function of the the physics and the parallel and series grouping of cells with a particular capability and the notion of um the usable energy and I've expressed that here terms of this might be what the manufacturer advertises if they advertise it at all and it might also give you a number that's important to say that in this case here 95.7% of the gross energy is available to the user so yeah these will be somewhat subjective elements this could mean everything from the simple thing that nobody likes to walk uh so you don't ever um go below empty if you will although in most cas Cas you can you get to uh zero miles of range you can go negative in most cases to your own detriment perhaps um and certainly lead to the batter's dislike so that being the case yes Um this can also be the function that the OEM decides they can change on the Fly because there's an over there update that's possible they can change the amount of usable energy that's available to the user either through some sort of a paid uh subscription upgrade or in the case of uh some situations maybe there's an a disaster or an emergency where they want to have uh more range for the electric vehicle customers they have so again that can be managed uh with a software aspect then you know lastly we take the number of series cells and the number of parallel groups and we put them together in what we call S's and PS this is a very common uh terminology 12s 72p is because because I've got 72 cells in parallel and 12 groups of those in series and if I take that pack wide I know that with nine of those modules I end up with the same 72 in parallel because I didn't change that but I now have 108 cells in series and that gives me what is the ultimate voltage that I can work with at the Pack level so it's quite simple I take what is the max voltage up here at the cell level and the Min voltage at the cell level and the will vary a little bit depending on technology and then i' simply multiply by the number of series cell groups that I have in the array and I end up with a maximum voltage and a minimum voltage that you can expect to be what would be the physical limits in this case not the ones that the user has access to in other words you may or may not be able to discharge all the way down to 270 volts um but something above that is quite normal and again that would be a function of how much of that energy is is usable to the user going across the top here and I'll wrap this up there's lots of different shapes and sizes um one of the more interesting ones here is the Hummer this is one that can dynamically change itself um it is normally a 400 volt system but it can rearrange itself for 800 volts to make it easier to do DC fast charging so it just kind of shows you that the voltage range varies quite a lot and finally the notion that um it is simply changing what is the s and P arrangement for the pack you'll notice that at 800 volts it's a 192s 3p and at 400 volts it's a 96s 6p so again it can do that dynamically and as a function of whether it has a real 800 volt charger to work with or not so other ones that stand out here um you'll notice the nominal voltage of the lfp cell is significantly lower than that of almost the all the others um again that's what we hear about a lot with lfp it has less energy density it also has a nominal voltage that's considerably lower and because of that you'll need more of them in series to get to the same sort of ultimate voltage operating range that the others all enjoy so that pretty much rounds up this spreadsheet and how it works uh again um I add to this C rates and what the instantaneous currents can be for both short durations of say 2 seconds or 10 seconds as well as the continuous performance of what I expect to be able to do uh from Full to empty uh without interruption so again we'll talk about C rates and power at another time for today we've covered how we calculate the energy content of a pack and we've talked a little bit about how the user always has some uh subset of that available to them all right so to wrap this up let's talk about how packs are rated we hear a term a lot uh kilowatts and one thing to keep in mind is that that terminology is often misused or misrepresented uh when you talk about a pack in terms of kilowatt more often than that they're referring to kilowatt hours which is a unit of energy um where kilowatts is a unit of power and we've gone through what the difference is there so uh a Tesla pack might be 70 80 90 100 kilowatt hours and you'll find people who call it 70 80 100 kilowatt so don't let that confuse you again what makes the difference um Power is an instantaneous Mo moment in time and how much power you can get is a function of both the series array how much voltage you have as part of that series array as well as each parallel element of that array every cell group how much current can it provide as a cell group so that current over time is energy um as long as you take voltage into consideration so again mes law is your friend there with that um we covered kind of just the tip of the iceberg here if there are other things that are interesting to you that you'd like us to uh look at as a follow on here please let us know give us the comments that we need to guide you further and we thank you for your time today and um we hope to see you back again [Music]

Channel: Munro Live

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Keywords: EV, BEV, Sandy Munro, Munro, Electric Vehicle, Benchmarking, Electric, Insight, Lean Design, Design, MunroLive, MunroLive.com, ElectricCars, Review, Car Review, Automotive, Automotive Review, Teardown Titan, Tesla, video review, Elon Musk, Munro Live, Technology, Luxury, Electric Car, Electricity, Automotive Engineering, Automotive Technology, Innovation, Battery, EV Battery, Batteries, Battery Cell, Battery Module, Battery Pack, Munro Battery Teardown, Electric battery, Battery Technology

Id: hBbhevHZZ5E

Length: 37min 38sec (2258 seconds)

Published: Tue Feb 20 2024