How To Ruin Your Electric Car's Battery - 3 Common Mistakes

electric cars have many advantages which have helped lead to their Rising popularity such as requiring a lot less maintenance however the battery is still very expensive and if it ever needs to be replaced it's a huge expense luckily there are practices you can put into place to make the battery last a really really long time and there are things you really shouldn't do which can dramatically shorten that lifetime my goal for this video is to not only explain the best and worst practices but actually explain why at the microscopic level why these are good or bad ideas now before we get into these practices it's worth mentioning this video is about nmc batteries meaning batteries made up of nickel manganese and Cobalt oxides it's a chemistry that gives you a lot of range and it's commonly used in the automotive space now if you don't know what chemistry your electric car's battery uses and why would you well much of these are good practices regardless we'll get into exceptions later so we're going to have three main rules number one don't store your car's battery at 100% for long periods of time especially when it's hot out now leaving your electric car in the hot sun for months at a time sounds like an edge case and it is but it helps lay the foundation for this video now if you haven't yet seen my video on how a lithium ion battery works that is certainly worth checking out but the big question here is why do batteries lose capacity over time and I've Illustrated many of the reasons here there's a lot of reasons why batteries will lose capacity over time the important thing to keep in mind is that if the battery is hotter and if the battery is at a higher voltage which occurs when it's at a higher state of charge these reactions are more prominent and they happen more quickly so you get more degradation when you have higher temperatures and at a higher voltage in other words a higher state of charge so one example I want to look at is called the solid electrolyte interface formation which occurs on both the particles in the anode as well as the particles in the cathode where it is then called cathode electrolyte interface so very simply what happens when you're originally creating the battery and you add the liquid electrolyte and you put it through its very first charge cycle well this solid electrolyte interface forms on these particles and this formation consumes the electrolyte it consumes lithium it consumes materials from the cathode and anode and so you're consuming useful materials from that battery and as a result you actually lose about 10% of the battery's initial capacity on that very first charge now you as a consumer never see this because this is done at the factory long before you ever get a product using this battery but it is worth mentioning because this continues to grow and so as long as this electrolyte interface continues to grow and consume other materials it means it's taking away from the usefulness of your battery now there was a really cool study done where they found that if you store a battery at a higher temperature it has more degradation but they also found that if you store a battery at a higher state of charge it also has more degradation so what did they do well they took a bunch of batteries and they stored them in a room at 50° C so very warm and they stored these batteries with a different state of charge so one of them at 100% state of charge one at 90% one at 80% and so on and what did they find well the battery that was stored at 100% state of charge had less than 60% of its original capacity after less than 200 days so it had degraded a ton versus the battery stored at 30% state of charge was only down to 85% of its original rated capacity after about 400 days so significantly more capacity and much longer duration than it was in the test so heat and voltage are both bad for battery degradation now there's an Incredible video by Professor Jeff Dawn a lithium ion battery researcher with seemingly endless knowledge in this space who also had a 5-year research partner partnership with Tesla for battery development he provides specific advice so for each of these three rules I'm going to share his advice for what you should do all right so say you're storing your electric car for a long period of time and it's going to be in a hot environment what should you do well he says you should Target a 30% state of charge for that duration now if you're storing it in the cold even for a long period of time there's no worries because of the cold temperatures you'll have very little reactivity so storing it at say 70% is no big deal number two don't wait until the battery is low to recharge it unless necessary now the critical part here is that you have a relatively low depth of discharge meaning say keeping your battery at 80% and only discharging to 60% before charging again it's fine to use the whole battery when you need it but after a short trip plug it in a bunch of small charges is much better than in frequent F depth charges okay so why well let's look at the particles that make up the cathode and if we zoom in on one of these electrode particles we can see that it's made up of many many many small crystallites and each one of these small crystallites has its own structure that's repeated so you've got oxygen metals and lithium that's moving to and from the anode back to the cathode back to the anode and so as this lithium leaves this crystal structure well this formation expands in One Direction and it shrinks in another formation and again the orientation of these are all over the place so you've got a bunch of different crystals all with different orientation that are expanding and Contracting in different ways so you can imagine that as that keeps happening you start to have cracks form within this particle as these particles are getting bigger and smaller they're creating these cracks within the particle well as these cracks form you have that cathode electrolyte interface formation so again you start consuming more materials more useful materials within the battery from the electrolyte the lithium things like that and so you have battery degradation okay so why does depth of discharge matter then well the growth of these crystals is roughly proportional to the depth of discharge so for example if you're just going from 60% battery to 40% battery well that's only 20% of your total battery right versus if you're going from 100% to 0% 100% of your total battery so that 60 to 40 has about a fifth of the effect of this growth and contraction that you have Within These crystals meaning if you use these smaller battery ranges you have much less cracking occur within these particles and the battery lasts significantly longer so again a really cool study looked at how a battery's depth of discharge impacted its normalized capacity over time okay so for this study they're putting the same amount of energy in and out of all the batteries but they're using a different percentage of the battery to do it so for example if you're just going from 40% to 60% well you're going to have a bunch of small charges versus if you're going from 0 to 100% you're going to have fewer charges but the same amount of energy cuz you're using the whole battery and so what did they find well they found that going from 0 to 100% constantly the battery only had about 50% of its capacity after less than a 100 days versus going from 40 to 60% constantly the battery was at about 85% after 400 Days okay well what does this mean as far as context so going from 60 to 40% constantly was the equivalent after 400 Days of about 3,200 full cycles of that battery now if you were to have a battery uh on an EV that had a 250 Mi range well that means this battery would last about 800,000 miles before its degradation reached about 85% so that's incredible right now the catch is that means you're only using 20% of the battery so you'd be limiting yourself to 50 m trips personally I don't stress about this one the easiest way to think of it is to just plug in your car after every trip rather than waiting till the battery is low to recharge it all right so what does Professor Jeff Don recommend he says stick to low stateof charge ranges 25% is great now obviously if you can't charge at home this is tough to do which is fine if you follow the next rule he says your battery will still very likely outl last the life of the car number three don't regularly charge to 100% okay what the heck shouldn't this be the car Maker's problem not mine yes absolutely that's why warranties exist and there are real engineering solutions to these problems so to understand number three let's look at the engineering Solutions now once again looking at the particles that make up our cathode there's a very clever solution here we're instead of using a bunch of many small crystals you use a single crystal structure for the entire particle so what this means is you have uniform expansion and contraction of that entire particle rather than having a bunch of crystallites at different orientations which as they grow and contract they create all these cracks so you avoid that cracking using this single crystal structure this is used in some Modern EVs and it has much longer capacity retention another Trend you're tending to see is batteries that are using higher nickel content all right so if you use a battery with more nickel it has better energy density seems like a smart thing to do so what's the problem well here we're looking at two different graphs with different nickel content in these batteries this one has about 50% for the cathode this one has about 80% for the cathode so using that higher nickel content you can see the voltage curve looks a bit different where we have this Plateau at the end for that latter portion of the state of charge from about 75% to 100% you've got this Plateau well this plateau toe is associated with a large volumetric change so you want to avoid that especially if you're using these uh you know many small crystallites as the structure for that cathode so you avoid that region you help avoid that micro cracking well what if you use a single crystal structure and also what if you use a lower nickel content well you don't have that Plateau you don't have to worry about that as much no problem you can charge up to 100% the same is basically true for lithium iron phosphate batteries which use a different chemistry all right but even if we're using a higher nickel content as long as we're using a single crystal structure we don't have to worry about cracking right well yes unfortunately this Plateau is also associated with a very small amount of oxygen being released during that portion of charging so you want to avoid this even if you're using a single crystal structure if you have a high nickel content battery because that relates to gas formation within the battery which means you're going to have degradation over time all right what's what's the Dr Don recommendation charge to 75% that way you have plenty of range daily and say you have a long trip coming up well charge the night before to 100% to have the extra range if you need it now obviously if you live in an apartment without charging going out and only charging up to 75% sounds very tedious and repetitive and personally I'm of the mindset that if you can't charge your electric vehicle at home well it really doesn't make sense for you yet to those who do it hats off to you but it's certainly not very convenient so I think the simple message is don't stress about it charge to as low as a percentage as you feel comfortable charging yeah 60% is better than 90% but if you need 100% use It ultimately it's the manufacturer's job to address these challenges and modern chemistries are doing exactly that I also want to make sure that it's clear that these best practices are so that you ensure your battery lasts a very long time hundreds of thousands of miles so that you don't have to worry about battery degradation for the life of the vehicle even if you do everything wrong it'll still very likely last a very long time hence EVS tend to have long battery warranties oh and what about fast charging this is probably worthy of its own video but Dr Dawn says it's not much of an issue typically it won't make much of a difference and this is because the vehicles themselves will control the charging current when you go to a DC fast charger so that it won't charge faster than the battery can handle so drive your car how it's convenient for you and for the best practices that are easy to put in place do it your battery capacity will remain better as a result also this video is basically a shortened summary of a presentation that Dr Don gave which is absolutely fascinating and it deserves more views so I'll include a link to that video as well as a link to my video on how lithium ion batteries work if you have any questions or comments feel free to leave them below thanks for watching

Channel: Engineering Explained

Views: 393,673

Keywords: electric car, electric car battery, lithium ion battery, lithium ion battery health, battery health, tesla, ev charging, tesla cybertruck, hummer ev, engineering explained, dr. jeff dahn, best practices

Id: w4lvDGtfI9U

Length: 12min 54sec (774 seconds)

Published: Fri Jan 26 2024