The Toyota Prius has been around for almost three decades at this point. What that means it that there are thousands of older examples on the road with hybrid batteries that are on the way out. That tends to compromise the performance of the vehicle with the electric half of the drivetrain effectively becoming dead weight. The solution? A battery swap, and they just got more high tech than ever.
Early versions of the Prius were built using nickel-metal hydride (NiMH) batteries. These were fairly old technology even when the Prius debuted in the late 1990s. They were largely chosen for price reasons since lithium-ion batteries were much more expensive until recently (Toyota actually still uses NiMH on its hybrid trucks/SUVs). While cheap, they were relatively heavy for the amount of energy they stored, and the amount of power they could deliver. Plus, they don’t last forever.
So what is one to do with an old Prius with a dead pack? You could explore a lithium swap, as we’ve covered previously. However, the company behind those upgrades has taken another step forward in sophistication. Now you can refit your Prius with cutting-edge sodium power! Only, there is some drama going on…
Sodium What Now?
Sodium-ion batteries are a relatively recent phenomenon. Research began decades ago, but the greater potential of lithium-ion saw them ignored for some time. They later became a technology of interest alongside the rise of the electric vehicle. As EV production has continued to rise, there have been great concerns around extracting enough lithium and rare earth elements to produce batteries for these vehicles. In comparison, sodium is relatively abundant, being the sixth most common element on Earth. Thus, if it could be used to make batteries, there would be no problem in finding enough sodium to satisfy industrial demands. As a side benefit, sodium-ion batteries tend to require little or no cobalt, copper, or nickel in their construction—elements which can be hard to come by.
It’s only in the last year or so that viable sodium-ion cells have hit the open market. Sodium batteries aren’t quite as good as lithium-ion cells in the energy density stakes. Lithium-ion batteries can achieve energy densities anywhere from 250-650 watt-hours per liter (Wh/L), while sodium-ion cells currently land around 250-375 Wh/L by comparison. By weight, lithium-ion lands around 100-265 Wh/kg, while sodium-ion cells are in the 75-200 Wh/kg range.
Basically, sodium-ion cells are cheaper, but not quite as high-performance as lithium cells. However, they have other benefits, too. Certain formulations could be safer than lithium-ion batteries, presenting less fire risk. Plus, under the right conditions, the cells can survive over-discharge to zero volts without excessive damage.
The Prius Angle
NexPower, aka NEXcell, is a company that specializes in hybrid battery replacements. The company started out offering lithium-ion packs for various Toyota models, with older Priuses as the main focus. The idea was to replace worn-out NiMH packs with a more modern solution that offered better performance and lighter weight compared to the original batteries. As we explored in an article last year, users reported improved fuel economy after the upgrade thanks to the larger capacity of the aftermarket lithium-ion packs.
Unfortunately, NexPower found that its lithium-ion packs had some problems. The prices of lithium batteries fluctuated regularly, making it difficult for the company to keep costs under control. There were also durability issues. While some customers were able to make good use of the packs, others had major headaches, particularly in more extreme climates. One owner reported a fire, while other owners have reported less dramatic battery failures and concerns around the design fundamentals.
My Project Lithium Battery Caught Fire Yesterday
byu/sworzeh inprius
To that end, the company has turned towards sodium-ion cells, in a hope they will be safer and more resilient. In a video on the company’s latest packs, Nexpower founder Jack admits to the issues with the lithium replacement packs. Indeed, that has apparently been the instigator for the switch. “In the past four years in business, we have learned that the lithium replacement battery isn’t for everyone,” he explains.”On one hand, we have customers having the battery for more than four years, saving a lot of gas without any issue. On the other hand, we have a customer with the battery [that] can’t even last for four months.” He puts the problem down to lithium cells, which he says “are not designed to operate in extreme conditions.” For this reason, he says the company is switching to building its packs using sodium-ion cells instead.
The company uses 3D-printed housings for its sodium-ion replacement battery packs.
The company’s FAQs touch on the same points. It states that extreme hot or cold temperatures were responsible for issues with the lithium packs, as were driving cycles that completely drained the batteries. Corrosion in cell links was also cited as a major problem, which caused unbalanced voltage readings that confused the battery management system. However, the company claims to have solved these issues in its new sodium-ion packs, and apparently offers a 50% discount for former customers who bought lithium-ion packs and wish to upgrade.
Jack’s statements on the subject of lithium packs are somewhat concerning. The simple truth is that many automakers have managed to make lithium-ion batteries work relatively safely in vehicles that are used in all kinds of conditions. This obviously takes a great deal of testing and proper engineering, but it’s entirely possible to achieve. In contrast, Jack’s video seems to suggest that lithium cells are solely at fault, even though other companies manage to use the technology successfully.
NexPower has uploaded videos under its “Hybrid App” channel showing the upgrade process to install its new “V3” sodium-ion packs.
For the new NexPower V3 packs, Jack notes the sodium-ion cells are rated to perform from -40 F all the way up to 140 F. He also notes that the cells can even be fully discharged with “minimal degradation.” Referencing earlier issues, Jack also touts the benefit of the upgraded wiring intended to eliminate corrosion issues seen on cell interconnects on the company’s earlier batteries. As for testing, the company claims to have 81 beta testers for the V3 product worldwide, and that it has been testing since winter 2023.
NexPower says it has been extensively testing the new V3 packs.
The Autopian reached out to NexPower for comment on its existing packs, and its use of sodium ion batteries going forward. Jack responded to our questions on both the lithium packs and longevity:
Yes, after years of selling lithium-ion battery, several methods were discovered that could accelerate the degradation of the lithium battery. These methods include:
-extreme heat and cold environments (over 140F, under 30 F)
-keeping the gear in neutral for long periods (such as at a car wash), which drains the hybrid battery completely and damage the lithium cells
-bad installation with corrosion in the wire harness or a loose nut at the terminal, leading to an imbalance in voltage readings and triggering the computer to overcharge the battery in an attempt to balance the pack.
All the above issues have been solved with the new V3 sodium-ion battery technology. Even with a bad installation, the sodium-ion battery has such a wide voltage range that it won’t be hurt by the attempt of overcharging.
As for why the company is switching to sodium ion? “The sodium-ion battery is more affordable than lithium, and our sodium-ion cell has a much wider operating temperature (-40F to 140F) and wider voltage range (1.5v to 3.9v) per cell when compared to the lithium-ion at (33F to 125F) and (2.5v to 3.65v) respectively,” he explains. “The only drawback with the sodium-ion battery is the slightly heavier weight, however with the newly designed case with honeycomb structure, we were able to bring the weight down to the same [level].” He also notes that the company has been testing the sodium-ion cells since last winter and that the company has developed stress-testing methods to push the batteries to their limit. These have names like the cold-shower test, postman test, happy camper test, and diarrhea test, and are demonstrated on YouTube.
Jack also noted that the V3 sodium-ion packs will be available in two forms. The standard V3 packs will have cylindrical cells for “mild improvement on MPG,” while the V3 GT packs will have higher-performance pouch cells with lower internal resistance. This pack can achieve a “10% increase in MPG” according to reports from users and testers, Jack says.
Community Concerns
Still, there remain concerns in the community about the safety of the new packs, too. Self-declared “electrical engi-nerd” John Sullivan has made a number of videos on the topic, having come into possession of one of NexPower’s prototype sodium-ion packs. He’s cited issues around cell balancing, which can be critical to keeping cells operating safely. If voltages vary too much amongst individual cells in a pack, it can cause damage or outright failure in short order. While this is less dangerous with sodium-ion cells, it’s still important to manage the cells properly. In his investigation, John says he’s also found a loose wire, and found the glue holding the pack together was melting during his own tests.
John’s disassembly shows what is apparently a NexPower pack built with cylindrical sodium-ion cells.
The drama goes beyond YouTube, too. John posted a thread on the PriusChat forums regarding his findings, which devolved into a mess of legal threats from users who appear to be fans of the NexPower battery swap project. Perhaps most concerningly, the thread also reports his finding that the sodium-ion prototype pack did not actually have a functional service cutout, meaning that dangerous high voltages may be exposed during installation or service. A post from one “jacktheripper”– apparently the NexPower founder – appears to at least partially agree with this, while discounting John’s assessment due to the prototype he was able to obtain being “very outdated.”
For his part, John readily admits that as an engineer, he’s considered entering the hybrid battery replacement market himself. He also explained that he’d previously discussed working with NexPower on a Honda Insight product, but he decided not to take on the project. For now, though, he’s primarily been active in looking into the products from NexPower.
The Autopian has reached out to John for comment on the matter. He has a number of misgivings about the product, primarily concerning safety. He also raised concerns about the suitability of sodium-ion cells for use in the Prius:
-Based on my several NexPower product reviews (V1/V2/V3 prototype, Signal Soother), I do NOT recommend purchasing any product designed by NexPower. Their products do not meet numerous ASIL C (SIL2) safety requirements for safe operation in automotive applications. I have found major safety issues with every product they’ve designed to date. Even worse, their designs aren’t improving over time, despite my continued feedback.
-Specifically for the prototype V3 NexPower pack I reviewed, the sodium cell’s voltage discharge curve is much steeper than the OEM NiMH cell voltage, which means that only 1/3 of the total sodium pack energy is usable in the Prius. NexPower’s V1 & V2 packs used LFP cells, which have a similar discharge curve to the OEM NiMH cells, hence they were much better suited for this application. In this regard, the V3 sodium cells are a huge step backwards compared to LFP.
-The V3 NexPower pack continues to lack a per-cell BMS, which means there’s no per-cell supervisory control… which is a fundamental requirement for ASIL C design. Jack still maintains that reusing the OEM NiMH computer – which only monitors the sodium cells in groups of 5 in series – provides said safety circuitry, but that is absolutely not the case. If you know an automotive EE, ask them “is there any way to safely design a lithium/sodium pack that doesn’t monitor every single voltage in the stack?”
John’s full comments are too long to express here, but we can cover them in short. He raised concerns about the bypassed service disconnect on the V3 hardware, which is supposed to de-energize the battery when the service disconnect is removed. He also alleged the company’s “Signal Soother” devices were designed to mask failing lithium batteries in their earlier pack designs, and that the company is continuing to rely on circuitry in its new packs that simply isn’t fit for purpose. Beyond that, he cites issues with the product’s thermal management, busbar designs, and even the company’s shipping practices.
Writer’s Note: The engineer gave me WAY TOO MUCH information. Here it all is, the vast majority too granular and esoteric to be of interest. You’d have to explain second-year college electronics to even graze some of this stuff and there’s about 1000 words of it. Skip ahead if this is too geeky:
As an engineer myself, I can definitely see where John is coming from. In particular, the concerns around a non-functional safety disconnect are enough to raise my hackles, severely so in fact. His assessment raises an interesting question. Obviously, we rarely expect an aftermarket manufacturer to meet the same standards as an automotive OEM. But what constitutes good enough?
Ultimately, the situation is not the prettiest. On the one hand, you have a company developing a product with some significant demand. People with older Priuses want functional hybrid batteries, and many would love to have fresh, new packs using modern battery technology. On the other hand, it seems apparent that some of NexPower’s products have failed in the field, and that’s left a sour taste in the mouth of some. Furthermore, the company has individuals raising questions about the engineering of both its past and future products, and there are ugly flamewars on the topic on community forums.
via Priuschat
In any case, at this time, NexPower’s “SodiumHybrid.com” website indicates it will be shipping V3 packs in September. Facebook posts indicate that some packs are already shipping out to customers. The Autopian has reached out to individuals who have claimed to have received early packs for comments on their experience.
At this stage, it’s too soon to tell whether these sodium-ion packs are a game-changer for older Toyota hybrids. On paper, they should offer improved performance versus a NiMh pack, particularly an old one of reduced capacity. At the same time, they may be inherently safer than existing lithium-ion packs purely based on their cell chemistry. However, until packs end up out in the wild, and we see genuine instrumented testing, we can’t say for certain that they’re a safe and viable upgrade. In the meantime, plenty of barbs are being thrown around the community on this very topic.
There is little love lost on the Priuschat forums.
Fundamentally, if you’re trying to repair your Prius, OEM parts will generally be the safest bet. New aftermarket upgrades may be tempting, but they’re comparatively unproven, and there does appear to be some controversy around them at this point. We’re eager to know more about their performance out in the wild and will keep digging into this story. There’s a lot going on in the Prius modding community, and it’s exciting to see these older vehicles kept operating at their peak. Ideally, everyone involved wants to see that happen as safely as possible.
Image credits: Hybrid App via YouTube Screenshot, NexPower, PriusChat via screenshot, John Sullivan via YouTube Screenshot, Tycorun
I have one of John’s products in my 2001 Honda Insight, his “LiBCM” kit that uses 3rd-generation Insight lithium cells and provides interconnects and a battery management system that interfaces with and maintains the cells and presents the car with, for all intents and purposes, what it thinks is a bone stock very healthy battery.
I’ve been an observer of the development process of this product on the InsightCentral forums and John is clearly an extremely experienced individual who puts safety and reliability first and foremost at every turn with his designs. The kid I received from him is insanely well thought-out, from the wire routing to the trace routing on the circuit board making sure that high voltage areas avoid the outer edge of the board so it isn’t possible to accidentally touch 170V DC when moving the battery around (even if you leave the battery safety disconnect connected while installing or removing the battery, which is obviously not recommended).
Beyond all of this, John has been incredibly transparent with the entire community through the development and sale of this project. Genuinely a world class dude. I’d take any criticism or advice he has as worth its weight in gold. Or lithium.
That said, it’s a shame this sodium ion product isn’t panning out. I’ve been incredibly intrigued in NaIon batteries, and intend on building a motorcycle or e-bike powered by them next summer for the heck of it.
When you consider that this is the only company producing new Prius HV batteries, it’s no surprise they attract a lot of attention, especially from critics. What’s interesting is that many of these critics have plenty to say but haven’t created anything themselves. Like with any innovation, nothing is 100% perfect, especially when you’re dealing with cars that are nearly 20 years old.
Personally, I not only have the lithium HV battery upgrade in my 2009 Prius, but I’ll be upgrading to sodium cells as soon as they’re available. I’ll be repurposing my lithium cells to build a powerwall, and shucking a few more to make batteries for my router and other electronics. My 2013 Plug-in with its larger capacity upgraded cells will also have sodium cells in the future.
It takes owners like myself, who not only has a lifted overlanding Prius but also swapped in the 2.0L hybrid motor from the UX260h and converted it to AWD with a motor that’s even more powerful than the rear motor of a Rav4 Prime, to push these so-called ‘boring’ vehicles into the stratosphere. The Prius is a seriously underrated vehicle—I’ll just leave it at that. I’m not like most timid owners, who seem afraid to experiment and try the new or even attempt what most said is impossible. Once we have more like me, you’ll really see advancements with this platform skyrocket! black.jmyntrn.com is where you can find me.
Temps under 30F are “extreme?” Lol.
I have an 11 year old Prius, and if my traction battery kicks it tomorrow, I’ll get an OEM one or one of the refurbs with a warranty.
I’ve read the “Project Lithium” threads on PriusChat and Reddit with interest over the years, but as soon as I saw one on fire, that was pretty much the end of that. A little better gas mileage isn’t worth it.
The Nexcell does not get better mileage, which I can say with confidence after owning two Project Lithium batteries. My first Nexcell was getting high 30s MPG in the mountains (RMAd under warranty), the second got around 45 MPG, and my new OEM Toyota battery is getting 50 MPG. Plus it hasn’t caught on fire so that’s nice.
“ In contrast, Jack’s video seems to suggest that lithium cells are solely at fault, even though other companies manage to use the technology successfully. ”
Well, EV manufacturers get to design the vehicle as well as the battery pack, so if there is a problem in one system, they can fix it in the other.
It’s sort of like each automobile manufacturer’s ICE car only functioning with their own formulation of fuel and their own size of tires, maybe only selling one use proprietary fuel tanks
Of course, the invisible hand of the market will only encourage more incompatibility and lack of competition.
In particular, BEVs integrate with the cabin climate control and actively heat and (for everything but the Leaf) cool the batteries. Of course, if the issues with the prototype were true of the production lithium packs the lack of cooling isn’t even the biggest issue.
I’ve had two GenII Prii and one GenIII, now have a Venza hybrid and a RAV4 PHEV. Long time member over at Priuschat, lots of DIY stuff but use maximum caution! Rule 1 for me is don’t mess with what works as in get the battery the Toyota brains recommend if needed which is rare. Bottom line is fairly boring vehicles but they just work and save you$$.
At least the instructions say “no chainsaw required”!
This stuff is so frustrating to hear about (but I’m glad it’s being spotlighted to any degree).
My Prius v is 12 years old with 155,000 miles. The hybrid battery is running fine for now and I’m still getting the advertised fuel economy, but I know sooner or later it might die, and if there’s any opportunity to “upgrade” the vehicle at the same time…I’d like to take it!
My Toyota dealership, when I offhandedly asked a tech, said it’s currently running about $3,000 parts and labor for a new pack for my vehicle (if no other problems are found). But apparently they only come with a warranty that’s a few years, max.
Even an extremely mild boost to acceleration would be nice, but the boost to EV range (for what pittance it is) and overall MPG would be appreciated nonetheless.
Especially for $1800 (price last I saw it) and presumably a reasonable amount for a hybrid mechanic to install it, I’d probably be around the same. Sure as hell cheaper (by comparison) than a new engine if/when the head gaskets go.
i take the diarrhea test every time i drive to the local thai restaurant
“So what is one to do with an old Prius with a dead pack? “
The best bet is usually buying and swapping in a good used pack or getting a refurb pack with a warranty… which will cost more.
Ideally you want to replace the old pack with a pack using battery cells of the same chemistry because that is what the battery management system is programmed to handle.
Please pass the salt 😛
I purchased the v1 lithium then purchased an update to the tops John put out for high heat. I live in south Louisiana, so every little bit helps. They were installed in a gen 2 Prius that had OEM battery failure at 180k miles. The car now has close to 230k.
Since installing them 2 years and 40k miles ago. We’ve had Zero issues with the setup. I put in the effort to remove all corrosion, replace the bus bars, and wiring harness to the cells.
It is driven like a normal car. We don’t use the Prius as a weekend home, off grid our home’s electricity from it, or idle it for 24 hours in neutral. We drive it to work, and the grocery store, and drop kids off at practice, with a a couple 6-8 hour trips to the mountains or beach a year.
I have no dog in the fight other than being a customer 2 years ago. My opinion is that the lithium had so many issues because Jack failed to account for how stupid most people are and designed a product around a normal use case.
It’s comforting for me, a possible future buyer, to read other accounts like this, so thanks for sharing yours.
No Prob. I bought the nexcell lithium pack cause it seemed to be a better option that OEM, installed it, and like anything else that breaks on 15 year old car, never really think about it again. I had no idea there was so much drama going on.
I did the same, not realizing that Project Lithium wasn’t a fully polished creation. After taking it out multiple times for upgrades then it caught on fire, I realized I made a mistake. Now I have a new OEM battery and I am getting better mileage than my old lithium that caught on fire (50 MPG currently @343k miles).
Hey as the girl whose Prius caught on fire I just wanted to say that I also use my Prius as a normal car. I don’t use the Prius as a weekend home, off grid our home’s electricity from it, or idle it for 24 hours in neutral. My only mistake was moving to the mountainous west with a non-OEM battery.
That lithium battery was only a couple months old after my first one failed. All I did was drive it 15min each way from the university at the foot of the mountains then back to home. It hated the mountains; it completely confused the Prius’ charging system and overcharged it when it was already full then it caught fire. I’d definitely be careful with your mountain trips, but it did fine in the flat midwest.
This 100% validates my choice not to go with Project Lithium when I replaced my gen 2 battery. I thought they were awfully cavalier in their approach and seemed to lack understanding of some of the concerns that even I, a confirmed layman, could see with what they were doing. Knowing now that they consider “under 30 degrees F” to be “extreme” I’m extremely glad I didn’t put one of their batteries into my car that gets parked outside in Minnesota winters.
I’ll continue avoiding this company’s products and I appreciate the Autopian shining a light on what they’re doing.
Wow, it really gets that bad? Here in PA I dunno if it ever reaches that as the air temperature, although it’s probably hit that with wind chill a handful of times in my life. But I assume wind chill doesn’t count for this.
He said UNDER 30 degrees F, not negative.
Oops. Yeah, calling “below freezing” as extreme is…not great.
Very much agreed, seems rather ridiculous.
I don’t think that John gave too much information at all; I think it was extremely valuable to give that much detail. Major props to posting John’s response in its entirety. As someone who isn’t an engineer of any kind, I understood everything except point L.
Everyone is highlighting the lack of a functioning safety disconnect, which is indeed egregious, disqualifying, and unnecessary even for testing purposes. However what also struck me is that the bus bars are being soldered to the batteries. That is a major no-no, and battery-specific spot welding machines (not sure if that is the proper term) are used by many hobbyists, so the fact that an actual company doesn’t seem to have one is seriously disconcerting.
Assuming that Jack is indeed trying to attack the professional reputation of a forum member who is, at no charge, doing the community a great service, that’s another scary serious red flag. Put together, it seems like no one should buy anything from NEXcell. I appreciate what they are trying to do, but this is the wrong way to go about it.
This was a concern I questioned Jack about in a couple of the screenshotted Prius threads in the article. Soldering is more expensive and labor intensive, not good for the cells, time consuming, subject to operator error, and not good with vibrations. Why on earth would they bother with soldering if you can pick up a cheap battery tab welder.
Solder joints can carry more current. Proper bus bar design fixes both of these problems.
I’m not sure there’s any way to do proper business bars with off the shelf cylindrical cells, no? Afaik you’re basically limited to tab welding, ultrasonic tab welding, or soldering. The current limitations are a good point, but I’d have to see it tested in the Prius application to see if it would even matter.
I’ve seen two solutions that I don’t *totally* hate. One of them is soldering thicker gauge copper to the nickel strips and then welding those tabs. The other solution is mechanical bus bars, like wildly over-built cell holders.
Hahahahahahaha fuck no. You build in more safety cutoffs to a prototype, not less (or possibly none?). There is no conceivable reason for a disconnect bypass to exist in the first place, other than some very specific tests of alternative safety cutoffs, and those test conditions should never, ever, ever make it to the public. Assuming this is an accurate description of the battery pack, NexPower has basically welded it’s circuitry open with no fusing. Just a fire waiting to happen.
A fatality waiting to happen. I don’t care what else they get right, any company that bypasses a fundamental safety feature like this is automatically out of consideration as a supplier for me from then on.
What a marvel of a nerdy article! Thanks for all the detail and explaining it in a way that my dumb ass can understand.
I was willing to grant the benefit of the doubt towards hobbyist as opposed to conman, but those “raised on the Internet” snappy comebacks (that, you’ll note, carefully dance around addressing any issue actually mentioned and incorporate a litany of logical fallacies) plant this flag firmly in conman camp. He might even be a True Believer conman, but “keeping the gear in neutral for long periods (such as at a car wash), which drains the hybrid battery completely and damage the lithium cells” clearly indicates this person has no concept of what fit for purpose means or is catastrophically deluded into a useless definition (see also “alternative facts”).
I’ve been sat at a standstill in traffic longer than some car-washes take, so that’s definitely an issue.
(Although in those circumstances I’d usually turn my engine off)
That’s not a problem. The engine will run to recharge the battery if it runs down while you’re sitting still in gear. The issue is if you put the car in a mode where it can’t charge the battery from the engine, but the battery is still being drawn down. I know putting the car in On but not Ready mode will do that. I suppose neutral might too since presumably that decouples the eCVT in a way that might stop it from charging. I think reverse is similar, or at least I’ve noticed that when my car is in reverse it will slowly drain the battery even though the engine is running.
TBH, doing that to any battery (including the stock NiMH ones) is a bad thing and can kill the battery prematurely. That might be the least of their sins in my book.
It’s not necessarily a problem with the Lithium battery, it’s just the design of the hybrid system. With the transaxle in Neutral, the engine is disengaged from everything, there’s no way to charge the vehicle. On the factory setup, it’ll flash up a red triangle with a warning about having no way to charge if you leave it in neutral for too long, put it in neutral while the battery is low, etc.. I don’t have the older Lithium hardware to confirm for myself, but the Signal Soother that they tried to implement essentially lied to the car’s factory Battery Control Module about the voltages… wouldn’t surprise me if some users didn’t get the dash warning before it was too late and the lithium cells were drained.
So the “Signal Soother” is like the “LiBCM” they both feed fake values to the cars computers….
I would never thought Li-ion batteries would be suitable in a regular Prius due to how hot the Li-ion batteries get when being charged/discharged there there is little to no cooling installed in the Prius from the factory. There are vents but no active cooling. The Nissan Leaf has had major battery degradation in southern states with excessive heating and lack of adequate cooling.
Also how will this affect your insurance if this thing catches fire? Parked it in your garage at home? Home insurance? Parked in a garage at work? Downtown?
Yeah the factory cooling system in the Prius isn’t great. Not unusual to see ~130-135F temps on the pack when driving in the summer. I just rebuilt my old pack, used tape to create a better seal on the factory fan ducting for the battery, and my batt temps seem to be doing a lot better now (it’s cooler outside, but I haven’t been able to get it above like 101F)
As far as I have read and seen, there has never been a fire with the Lithium battery in question. There was an issue where a customer had smoke and melted modules but no fire ever happened.
This came down to a Quality Control issue in which the owner Jack explained what happened.
This is all talked about in the forum where this guy “mudder” a so called “expert” tries to trash talk Nexcell and gets a hold of products and “prototypes” in which he was not intended to be a tester for.
Even Toyota still puts NiMH in the current AWD Prius as they expect those will go to colder climates where the Li-Ion won’t do good.
To the question of how other companies are using Lithium ok in these more exteme temps, for full evs they have entire cooling/heating systems for the pack, most hybrids don’t have as much infrastructure around their packs, which is why most were using NiMH for the longest time.
My question is, was he actually using LFP? Cause those are more resilient to catching fire and draining. And if he wasn’t using LFP, wth not??
I mean, yes this doesn’t have the kind of comprehensive cooling that a full EV would, but does it matter as much if the pack weighs all of 40 pounds or so?
Looking at like Nissan Leafs, the early ones that had smaller packs, and bad thermal manaagement, I think it does. Modern Leafs use LFP to try and be a bit more rugged but still without needing extra thermal management.
Yes the Lithium packs were LFP. If they’re not being properly monitored (i.e. being overcharged or failing and not derating and going into limp mode) they can still experience a smokey “thermal event”… Plus, they’re inside of plastic housings, so…. Things can still happen if they’re not being properly monitored and controlled
Jack did make his batteries LFP, which is why my fire was not as severe as any Tesla fires which burn to the ground. I am grateful for that decision.
My reading of this is that it is definitely a ‘hobby’ level product. Jack’s main issue is that he is trying to change the battery chemistry used without access to the full control system. The Prius system is designed around a NiMH battery, so it assumes things like acceptable operating voltage and operating temperature based on that chemistry. Lithium or Sodium may be superior for weight/density/longevity, but they need a control system that recognizes other limitations.
I think he’s trying to fit a (superior) square peg into a round hole. He’s also doing it on a shoe string budget that leaves a lot of details well below OEM levels.
Newer Toyota hybrids use different battery chemistries based on whatever was available that day. Sometimes it’s NiMH, sometimes Li-ion. I think Jack is missing something. Clearly Toyota designed their control system to be modular – is it a software setting? Is there a control board that needs to be swapped out? And if it’s a software setting, did those settings exist in the older Prius’s?
Toyota clearly found a way, and given the plugin Prime was available as a Gen2 Prius, I suspect the stock control system can be made to support multiple chemistries even in an older car.
The newer Toyotas get NiMH vs Lithium depending on where they’re being shipped to, and trim level/configuration. On the Gen 4 Prius, the two base trims got NiMH (because it was cheaper), while all trims above that got Lithium (and got a sizable economy benefit). AWD trims got NiMH by default because they assumed you’d be using it in a colder environment, where NiMH is superior.
As for how they control them, they’re completely different. The battery case is different, the internal wiring is different, the BMS system is completely different. The Gen 2 only ever got NiMH, regardless of where it was, it has no provisions or systems for anything else. The Gen3 was the first to get a Plug In system with Lithium, no the Gen 2 like you mentioned. The only real way to design around this is by doing something like the LiBCM for the insight, where it does per-cell monitoring and basically feeds “fake” values to the factory computer to make it happy… Until it detects something is wrong and relays that to the factory computer to make it act differently (derate), throw a code, trigger limp mode, etc for safety and longevity purposes.
So…the LiBCM feeds fake values to the factory computer to make it happy?
Sounds like what “mudder” says and you repeated about the “Signal Soother” lying to the cars BCM.
So both of these products do the same thing right?
I guess mudder’s product should be called Lie2BCM.
The article references Li-ion but the Engineer states LFP.
Are the weights and energy density’s provided for Li-ion or LFP?
Hopefully the writer knows the difference between Lithium Ion (Li-ion) and Lithium Iron Phosphate (LFP). Ion and Iron do sound the same, so he wouldn’t be the first person to make the error, nor the last…
LFP cells (to the best of my internet reading / YouTube watching knowledge) also have no cobalt, can be charged to 100% without harm
Very likely these packs are LFP, and the differences between LFP/Li-Ion are generally that LFP is less temperature sensitive, albeit struggles at lower temperature, is less energy dense, but more resilient to 100% SOC cycles, and generally has higher longevity at lower cost. Higher-end EVs tend to have lithium Ion because the potential for more power and higher range per battery volume/weight is justifiable on a premium priced product.
For reference, NMC (Nickel-cobalt-manganese) and NCA (Nickel-Cobalt-Aluminum) are both Lithium-Ion chemistries, but the abbreviations are for the differences in cathode chemistry. To explain my above example, the Model 3 Long Range, NON-Performance usually uses a LFP battery, while the Performance uses (I believe) exclusively an NCA chemistry. This all ties into the article published last week about EV battery chemistry being weirdly obtuse to figure out on the variance in battery chemistry for even a single model due to supply chain shenanigans.
“An LFP battery, also known as a lithium iron phosphate battery, is a type of lithium-ion battery.”
LFP is just one of many li-ion chemistries. It’s quite distinct from the others, yes, but it’s still Li-ion tech.
The drama here seems very warranted. It seems like NexPower is doing their best with the limited resources on hand, but issues like the soldered cells, bad cooling design, and poor case design are all deeply concerning. The case design and 3D printed nature for the sake of weight is extremely concerning. Not only is it highly exposed due to being skeletonized, but it is absolutely not strong enough to handle the heft of a pack in any sort of medium or high speed collision.
I have no doubt their lithium packs encountered issues, Li-on is far more temperature sensitive than NiMH, and the Prius only has provisions for air cooling. To switch to a higher output chemistry opens the door to overheating problems that are only compounded by poor cooling design. This is similarly problematic with a less energy dense Sodium chemistry that occupies a larger volume, leaving less room for air flow. Gluing cells together without room for forced air cooling, especially with an open case design that removes any and all channeling, will not help the longevity of the packs.
While I commend the company for trying to innovate and improve the performance of aging Prii, it seems like there are serious issues with the designs of their packs and that they certainly do not conform to the design requirements I had to comply with for undergraduate design team research, which was a pure development/prototype vehicle use case, much less a full production, daily driver level.
Production versions are injection molding not 3D printed, those are prototypes.
Am I the only one who liberated some sodium for ‘further testing’ during HS?
Yeah, little squeamish about suggesting my septuagenarian parents replace their gen2 Prius battery with this given the results I saw. I know it’s not rational, but, that shit went boom.
If you think the sodium booms, you should try lithium some time (from further away)
I hear you—but I’m nowhere near as adventurous as I was decades ago
Pfft, I take lithium everyday!
To be fair, Sodium and Lithium are both Alkaline metals, which are both highly reactive to water, which is exactly why lithium EV fires are a mess to put out, and can reactivate without any warning.
Paging Toecutter. Toecutter, please pick up the white courtesy phone. Mr Toecutter, please pick up the white courtesy phone and explain this to us non-engineers.
What do you need explained? The above article and forum posts explained the situation well, IMO.
I do know how to make battery packs. Here’s a 46.8V 10.5AH pack of NCR18650GAs, LiIon, and has received a 30A BMS with temperature sensing.
https://i.imgur.com/CEzH0nK.jpg
A lot of people don’t know this, but you can design a safe LFP battery that doesn’t even need a BMS. Keep it a single string of large AH cells, with care placed on the installation of all interconnects and fasteners, where each individual battery was bottom-balanced to 2.650V before installation. Never do this if you have any parallel strings, and never do this for any other lithium chemistry, ever.
Don’t feel like you have to explain to this level, but I do regard electricity as one step removed from magic…
This is a huge problem though. From reading the forums, a lot of people who DIY replace their Prius battery (i.e. the target market for this company) don’t even bother with a torque wrench. With the stock NiMH battery this causes errors and might make the car undriveable until it’s fixed, but it’s not especially dangerous. It sounds considerably more hazardous with the other chemistries that they’re pushing.
So as long as you have a safe LFP battery you do NOT need a BMS, wish everyone knew this.
This design choice only works if the LFP battery is a single series string and all connections have equal resistance. Its a trick used by a number of hobbyist-built EV conversions to avoid the complexities and issues associated with adding a BMS(sometimes referred to as a Battery Murdering System), a number of which have gotten six-figure mileage out of their packs.
Make sure the charger used to charge them is precise to 0.001V, and make sure all batteries were initially bottom balanced to 0.001V of each other before their first charge cycle.
The advantage of this setup is that replacing a bad battery is as simple as fully discharging the pack, locating the bad cell, disconnecting and removing it from the pack, finding a replacement cell of identical make/model/size/chemistry, discharging the new cell to match the remaining cells, and installing/connecting the new cell. Doable in hours with a power supply, battery discharge tool, and a ratcheting socket drive, without having to take the entire damned car apart.