My Project Lithium Battery Caught Fire

"YOu DOn'T knOw whO I Am, BUT bUY tHeSE DoZEn eXpeNsIVe dOODADS to Get INcreASed MPg. USE my LInk tO SAve sOme CASh."
"Okay, I bought one and it caught on fire."
"LIAR!!! Tell Us WHo YoU aRE!!!"

 

See my proposed action plan in post #223 in your Signal Soother Test thread.

 

@Mr. F

Follow the troll train the link to my thread where I told old chapman who I have met from the forum.

Otherwise Im not sure what kind of personal info you want to know about me or why it matters to you.

Honestly it seems like you have mental issues typing like a keyboard warrior who would never meet anyone in the first place.

 

Seriously people, get a life. My NiMh battery caught fire FFS, I posted photos of it sometime back on this forum, yet I still had some members posting it was false
I have tortured a lot of LFP cells when I was initially designing our BMS and battery systems for off grid house batteries, and they simply do not catch fire .... they vent their more volatile parts of their electrolyte, it might look like smoke, but it is actually a dense cloud of vapour that settles very quickly, but they can't actually catch fire, they do not generate their own oxygen, so any fire would require oxygen from the air outside the cell casing and something to ignite it.

It requires cobalt in the chemical make up to generate oxygen inside the cell when over heated, then you have all the requirements for a battery fire, LFP, LYP and lithium titanate do not contain cobalt, Sodium ion doesn't contain cobalt either, so no chance they will catch fire either.

Sodium ion is a cell chemistry still developing and has been over 3 to 4 yrs, there are over 700 different combinations of anode, cathode, electrolyte mixes and more still in the lab.

Even though popular social media experts seem to consider the electrolyte is salt water, that was abandoned in the very early testing, the water breaks down and shortens the cycle life, the non active plate (anode and cathode relate to the direction of electron flow, charging or discharging) is not graphite, hard carbon and graphene are popular at the moment, but CATL is already on its second commercial version, so it's way too early to say what the ultimate combination will be .... but you can bet it will come out of China ... they are just so far ahead of the game in battery technology now the rest of the world would be some what foolish to even attempt to play catch up ......
Will sodium ion be the chemistry type to replace lithium ion ..... who knows, it will be the one that can charge the fastest, discharge at a consistent current rate from 100% SOC to 5% SOC without serious degradation of capacity or internal resistance over 10,000 cycles (that equates to 3 cycles from 100% to 5% every day for 10 yrs) yet remain cost effective .... sodium ion is up there with the best of them at the moment ......

T1 Terry

 

@T1 Terry
You sound like an intelligent person, which is refreshing. Thank you for taking the time to respond to my accusations.
Looking forward to continuing this conversation with another rationale adult.

A key difference is that you designed a BMS into your LFP system, whereas NexPower did not design a BMS into their LFP packs. So then all it takes is one cell overcharging and then it's game over. They added insult to injury by later creating the "Signal Soother", which masks cell failures to the one remaining OEM component that might otherwise detect said failure.

Would your company allow you to sell an LFP product that only monitors stack voltage every ten cells (e.g. 1-, 10+, 20+, 30+, etc)? Do you agree that is a recipe for disaster?

Please search youtube for several counterexamples. While fires are less common with LFP cells, they can and do happen, both directly & indirectly (e.g. due to heat spread into nearby combustibles). I have a few addenda below.

Yes, you have described the most common LFP failure mode. However, while LFP batteries are vastly less fire-prone than other lithium chemistries (e.g. NMC), they're not completely immune to fire.

I agree. Specifically, LiCoO2 is the primary catalyst for self-sustained oxygen generation in 'standard' lithium cells. The same precursor also decomposes into carbon monoxide and lithium oxide (the white crystalline solid that gets deposited on nearby surfaces during thermal runaway).

However, I must clarify that while LFP cells aren't self-sustaining during a fire, they are still capable of burning (i.e. producing flames during a thermal event). Yes, non-LFP lithium is more likely to run away, but the fact remains that LFP cells can burn if not properly monitored. Please consult your references online for numerous examples.

Taking a step back, do we really expect customers to care whether or not flames are emitted during an LFP thermal event? Either way they're going to have a bad experience, which is easily preventable by adding a BMS. Obviously having the car 'only' fill with smoke is a better outcome than also having it also burn to the ground... but are we really ok with a product that doesn't make even a passing attempt at preventing the thermal event from occurring?

Whether or not the cells sustain fire during a thermal event, engineering best practices require LFP systems to have a properly designed BMS system. That's why you designed a BMS for your system, right? The fact is NexPower chose not to add a BMS to their LFP products, which is unsafe because it leads to thermal events (whether or not there are flames).

I agree, and will reiterate that only a few sodium chemistries will ultimately 'win' in the long run... time will tell who picked the right horse. Five years from now we'll likely have a similar conversation regarding the "NMC vs "MnO" debate ten years ago.

Yes, I agree, and time will tell. Two additional deliverable are volumetric & gravimetric energy density... sodium has a long way to go there... if it can catch up, it will leave lithium in the dust.

 

No sure how up-to-date you are on the latest sodium ion developments, but testing shows the charge faster with less heat generated and discharge much faster with less heat generated and very little voltage drop ..... but it is a tad more linear than LFP, so that needs to be factored in. Their real advantage is the apparent zero damage to being discharged to 0V, I'm not willing to attempt reverse charging them yet, where a cell drops to 0V but those either side still hold voltage and capacity, so the current is dragged through the 0V cell effectively reverse charging it .... fatal for LFP cells, I'll wait until I finish torture testing these cells before I subject them to that though, just in case :lol:

I've had LYP cells held at 4.5v till all the electrolyte had boiled off (they won't go over that voltage while they can boil off their electrolyte) but after that, the voltage is meaningless, there is nothing linking the plates together, the heat becomes so high the plastic separator sheet melts and seals each plate.

Care to link an LFP fire video that wasn't caused by aluminium cell cases touching one another or an outside metal component linked to the battery negative?
Unfortunately, I no longer have the time laps video of a cell on charge with a gas flame mounted 50mm above the vent ... it actually blew the flame out, second test was 150mm above the vent and the vapour stream can clearly be seen below the flame and a very weak flame above it, still not enough oxygen mixed with the vapour to create a decent flame. At $200 per cell, two was enough to sacrifice ....

You mention a vehicle filling with smoke, that indicates combustion, so not the correct term I believe, it is vapour and smells so sickly sweet that no one could stay seated in the vehicle well before it built up to cloud stage ...... from that one would assume the event of the vehicle filling with a cloud of vapour would not happen.

As far as batch testing cells, you do realise the Toyota NiMh module system in the genuine battery only voltage tests in batches of 12 cells (6 cells per module and 2 module testing) but I agree, every cell should be voltage monitored and a charging/discharging cut triggered when the upper and lower extremes are met .... but not even Tesla monitor that closely .... MG does, but I see they aren't part of the US market ......

Let's look at a battery pack that monitors 4 cells in each group, take a cell above 4v or below 1v and the safe range for the other 3 cells plus the over voltage or under voltage cell adds up to a voltage that could be monitored ... not that I consider that to be an optimal arrangement, but enough to avoid thermal runaway .... so safety level monitoring, not, not optimal cycle life monitoring .....

I consider that proper cell voltage monitoring, whether a single cell or multiple cells in parallel is the optimal method and temperature monitoring is not required, but if series group monitoring is used, them temp sensing is a must. The next essential thing is proper cell balancing, not milli amps but 5 amps min that switches on at 150mv out of balance and off at 5mv, so the unit isn't wasting battery capacity nit picking that last bit or trying to balance unnecessarily because different internal resistances were causing the voltage differential, not actually capacity related ... a hard yet not impossible task for Prius 228v battery, 16 groups x 4 cells with an average voltage of 3.56 volts. The nom. voltage for a traction pack is 201v/16 groups/4 cells = 3.1v per cell, the sodium ion can handle 4v high to almost 0v low, 3 x 4v = 12v x 16 = 192v if every group lost a cell yet it attempted to fully charge the battery ..... it wouldn't be that hard to set a min and max voltage regarding charging and discharging ..... better to monitor every cell, but .....

T1 Terry

 

@T1 Terry: Once again, thank you for taking the time to have a civil conversation.
@AzusaPrius: Look how we both take considerable time and effort to answer each other's statements.

I have seen lab data reporting the same.
However, I will hold off on further conjecture until I've reviewed NexPower's (allegedly proprietary) specific sodium cell chemistry in their V3 pack. Until then, let's continue discussing their existing V1.x & V2.x LFP designs.

IMO, sodium is more than a "tad more linear than LFP". In fact, LFP is known for it's nearly flat midband discharge curve, whereas sodium remains linear throughout the entire discharge range. For reference:
Typical LFP discharge profile.
Typical Na-ion discharge profile.

Using the above representative graphs, we can see the following rough voltages (I'm only using one decimal place for simplicity):
Vcell@25%SoC (LFP): 3.4 volts
Vcell@75%SoC (LFP): 3.5 volts
delta: 0.1 volts

Vcell@25%SoC (Na-ion): 2.4 volts
Vcell@75%SoC (Na-ion): 3.8 volts
delta: 1.4 volts

So then the sodium cell has a 14x larger voltage delta over the middle half of the SoC range.

I agree 0 volt tolerance is a huge benefit to sodium ion cells.
However, I'm more interested in what happens when these sodium cells are overcharged. If V3 doesn't have a per-cell BMS (very likely), that's the more dangerous condition; a cell at 0 volts has basically no energy inside, whereas an overcharged cell has all it can store... this is the reason pushing more energy causes rapid unscheduled disassembly.

Rest assured, I intend to test these V3 sodium cells on the bench.

Clarification needed: Are you actually referring to Lithium Iron Yttrium Phosphate cells (LYP), or did you mean to write 'LFP'?
When I tested V1 NexPower LFP cells to failure, they failed well below 4.5 volts.

It's more boring, but here are some more scientific academic research papers that performed real-world tests:
https://scijournals.onlinelibrary.wiley.com/doi/full/10.1002/ese3.283
Thermal runaway and fire behaviors of lithium iron phosphate battery induced by over heating - ScienceDirect

Less academic, but more approachable sources:
Can LiFePO4 Batteries Catch Fire? Unveiling the Science Behind the Flame

And for those that just want to watch videos:

(this is a puncture test, but I reference one observation below)

Note that half of the off-gassing from an LFP cell is hydrogen gas, which is of course explosive. So then when you contain this gas inside a vehicle, the interior space is highly susceptive to ignition. One potential ignition source is the overheating module itself, which we know can occur with NexCell's V2.x product (see OP's pictures in this thread).

...

If the above sources aren't authoritative enough, let's take a step back and ask ourselves "does a commercial LFP battery require a BMS"? I think you'd be hard pressed to find a reputable engineering team that would sign on shipping an LFP battery product without a BMS that can disable the system if even a single cell voltage is out-of-bounds.

I hesitate to ask the hypothetical question "name one commercial LFP product that's shipped without a BMS", as someone would likely state "NexPower's V1.x & V2.x Prius Batteries do! Checkmate!"

Note that in an enclosed space (e.g. the vehicle interior), the ignition source doesn't need to be in the outflow jet stream.
Were you testing for ignition in an enclosed space, which gives the 50% hydrogen gas outflow time to mix with atmospheric oxygen?

Based on the pictures @sworzeh's posted, we can probably both agree that a layperson would call the particulate matter inside their cabin "smoke".

This semantic differentiation isn't particularly relevant to the layperson. However, I agree that we should strive to use the correct terminology in our discussions. In general, I prefer the term "thermal event", because it's much more inclusive to any possible condition where things overheat (e.g. fire, smoke, meltdown, burns, etc).

FYI: Both @sworzeh, myself, and my wife described the smell as "strong permanent marker". I did not smell anything 'sweet' in the NexPower V1 cells I tested to failure on my front porch.

I agree, and they should do everything they can to leave the vehicle immediately. However, consider the hypothetical where someone drives the car to a state where a cell is about to fail, and then parks the car in their garage and goes inside... minutes later the cell fails, filling the car with explosive hydrogen gas. Meanwhile, the cell is rapidly heating, and can easily achieve temperatures that would ignite properly mixed hydrogen gas.

This is likely what occurred in the third video I linked above: When the person stabbed the cell with their pick, they briefly inserted enough oxygen into the cell that the hydrogen inside the cell was then able to ignite due to proximal contact with the red hot internal cell structure. This same condition could easily occur over time in a sealed enclosure.

Absolutely. The OEM Honda NiMH systems are the same, too. This is acceptable with NiMH systems, due to their vastly different chemical reaction properties. I will go into details if I must, but I would think you could spend 20 minutes exploring the interwebs. Do let me know if you want to debate this further.

This is the most important point, and I'm glad we agree on it.
Given that NexPower doesn't monitor every LFP cell voltage, and doesn't have a charge/discharge inhibit method...
...do you agree with me that their LFP designs are unsafe?

Maybe I'm misunderstanding your statement, but Tesla certainly monitors every intermediate stack voltage on every product they sell. For example, a 124S24P pack containing QTY2976 cells doesn't need QTY2976 'BMS' measurements, but does require at least QTY124 'BMS' measurements. A properly designed system (with high current interconnects between cells at the same voltage) only requires one cell voltage monitoring circuit per 'layer' in the stack. Note that for safety reasons you'll typically have two separate measurements per 'layer', but that's outside the point of this discussion.

Note that within a given parallel cell group, no cell in that set can exceed the single voltage measured unless it physically disconnects from the pack. This is the reason why Tesla has per-cell fuse elements built into their battery tabs. If a single cell goes bad and wants to operate at a different voltage, its fuse will open and it will disconnect from its neighbors. Once disconnected, the cell is no longer allowed to charge, which drastically reduces the risk that it will vent.

Other manufacturers don't have visible per-cell fusing in their welded tab matrix, but instead opt to use internally fused cells. They achieve the same result, albeit with slightly less efficiency.

We agree on this:
-A properly designed BMS must monitor each cell voltage level in an LFP stack (e.g. QTY48 circuits for a QTY48S pack).

I disagree.
Temperature monitoring is required on any LFP BMS, regardless of the cell voltage monitoring method.

We agree on this concept.
In addition, based on my testing, NexPower's V1.x & V2.x circuitry does not contain "proper cell balancing".

I disagree that high current balancing is absolutely required on a hybrid traction battery. You can achieve excellent pack balancing with even a low balancing current. Most lithium modules I've examined (including Tesla) use a relatively low current balancing circuit... typically this circuit is a simple passive discharge resistor, which can sink maybe 50 to 100 mA. I do the same on my LiBCM product, which can balance the pack at up to 52 mA. As long as your BMS system can remain on when the car is off, there's no reason to quickly balance a pack over its useful lifetime.

However, it wouldn't hurt to build an active stack-shuttling flyback converter that would shift energy from each cell, into a flyback transformer, and then back into the entire stack. LT (now Analog) makes some cool ICs that can cost effectively achieve these goals. In general it appears auto manufacturers shy away from this additional cost and complexity, as it only becomes worth the effort once the pack degrades to a state where the user should consider replacing the pack entirely.

Certainly there are mission critical applications wherein these active energy balancing designs make sense. Certainly I'd want redundant power sources, each with active balancing in a battery operated SIL3 and/or SIL4 product... but not in a SIL2 electric/hybrid vehicle application. It's overkill and adds unnecessary cost. I'm sure at least one car manufacturer has implemented active balancing, but I haven't seen it and certainly most companies don't.

Please clarify.
I didn't understand the point you were trying to make here.

Again, I'm holding off on sodium analysis until I get the V3 hardware.

 

Video 1, they show that the fire was actually deliberately lite using a propane flame. The fuel source for a lot of that fire is actually the plastics etc involved with wiring and cases etc, the smoke is the clear evidence of that. I haven't watched the 2nd video yet, I doubt it's much more than theatrics as well, but I'll make time to watch it when I can.
Video 3 & 4 are a visual representation of what I am saying, it is not smoke, there is no fire in video 3, video 4 the person doing the demo actually creates a fire by adding a second hole and a spark ignition to the venting vapour cloud.
Note to all LFP and LYP cell users, don't punch two holes in an aluminium cased cell, it might catch fire ...... :lol:

As for the claim the gas is 50% hydrogen ... where did you get that from? To start with, it is not gas venting, just like steam from an over heated ICE engine, if that broke down to the two elements and gassed, then you would have a mix of 2 parts hydrogen and one part oxygen ..... and that goes off with real bang.
The clouds of vapour above the fire in the 4th video also clearly show there is no hydrogen present, it would have created a huge fireball if it was hydrogen or even a small percentage present ... so please stop trying to spread that myth, it doesn't help and only muddies the water.

You asked about the cell chemistry, LYP, yes, they are Winston Lithium Yttrium Ferrous Phosphate chemistry, We used that chemistry because the upper and lower temp parameters are better than the basic LFP, and the quality varies so much from one manufacturer to another, impossible to do a comparison with any meaningful results. There is/was a brand that used square terminals as an example, looks like a great idea, but a square terminal is near impossible to seal to the case so the electrolyte boils off every time they are cycled ... the end result is obvious, very fast loss of capacity because there is insufficient electrolyte to keep a contact across the whole plate surfaces, half the plate saturated, half the capacity etc ....

As far as temp monitoring, think about it, what causes the temperature to increase internally in the cell? Then think about how useless measuring the external cell temp, where is the heat being generated .... that goes full circle back to why it is being generated in the first place ....
I'll leave the sodium ion debate until you have some hands on testing results to compare notes

T1 Terry

 

Maybe? Hydrogen burning in air is very hard to see if there are normal amounts of ambient light. See picture in Figure 6 here

https://www.imagesensors.org/Past%20Workshops/2017%20Workshop/2017%20Papers/P34.pdf

This is why most pictures of hydrogen burning have a black background. The photos are taken in the dark.

However, the heat from hydrogen burning can make other materials mixed in with it very hot, and the glow from that might resemble a fireball.

 

This does seem to take the thread in a less nyeah-nyeah direction. I still think it could get even better.

I like how mudder supplied a combination of research papers

and videos

So I would be happier if T1 Terry's reply had not seemed to engage only with the videos while leaving the papers unmentioned.

In fairness, only the first of those two papers (the Wiley one) just popped up in my browser to read. The second (the ScienceDirect one) only showed me the abstract and "section snippets", and I had to go through my library's web site to see the whole thing. Yay libraries.

I second the opening question—where did the 50% figure come from?—but the "to start with" part seems to be trying to argue there isn't H₂ gas, but simply other hydrogen compounds like the H₂O in steam. That would sure be a big difference, but here's an example where it would have been helpful to engage with the papers mudder linked, given that the second one measures the H₂ gas.

Now, I didn't happen to see anything in that paper to shore up the "50%" figure. What they reported was 0.53 grams of H₂ in their analysis of the total stink leaving the test chamber hood. That compared with 81.49 g of CO₂, 5.63 g of CO, and 2.61 g of HF. (All those numbers from the 100% SoC test.) So nowhere near 50% by mass. I haven't tried converting the grams to moles of those different substances to see what the proportion is by moles.

Importantly, the authors make a big clarification in the paper: they aren't saying they think the 0.53 g of H₂ they measured from the exhaust duct was all the H₂ that was given off. There was fire in there, and their exhaust gas analyzer only got to see the amount of H₂ that escaped unburnt. That came out to 0.53 g in the 100% SoC case, and none at all in the 0% and 50% SoC cases. The authors aren't saying there was no H₂ emitted in the lower-SoC cases, they're saying it completely combusted in those tests. The 100% SoC test sprays stuff out so violently that the combustion is less complete—that's also why there's more CO and much more HF in the 100% SoC case.

Anyway, as to the chemistry behind H₂ in the vented gunk, that paper cites this one: https://iopscience.iop.org/article/10.1149/1.1838287

I notice I mentioned the two research papers already, and the videos, but not this one:

Oh my stars, did you even read that mess? I'm not sure it does or doesn't beat the AI-generated spark plug treatise!

I haven't completely made up my mind whether this one's AI-generated. It might hang together a little bit too well, which would mean there's some actual human responsible for writing this stuff:

As above, we ignited your curiosity about the fire safety of LiFePO4 batteries. But before we delve deeper into their fiery potential, let’s crack the code behind their cryptic name: Lithium Iron Phosphate (LiFePO4).

Imagine a microscopic dance floor where lithium ions (Li+) pirouette between two partners – a phosphate (PO4) molecule and an iron (Fe) atom. This synchronized tango is the heart of LiFePO4 batteries. The unique chemistry creates a stable, thermally robust structure that sets them apart from other lithium-ion batteries.​

I've lately been reading more of the ongoing research into bullshitting, and see that researchers have come up with some useful categories like "pseudoprofound bullshit" and "scientific bullshit". ("Scientific Bullshit Receptivity" gets measured by "taking existing physical laws and changing their central words with randomly selected words from a physics glossary", such as “There are no transverse waves when the total magnetic sublimation through a stiff photon is equal to its scattered matrix”, then seeing who thinks they sound legit.)

This article seems to be something different: it isn't aping the sound of science, it's aping the sound of a certain kind of science popularizer, the kind who can come up with entertaining, breezy, punny ways of explaining something. Only that's the key: something has to get actually explained by the end.

In this article, after you've managed to drag your eyeballs across Li being "the energetic soul of the party", LiFePO₄ being "the sturdy duo forming the dance floor", and PO₄ being the "silent partner", and you've been told this "harmonious trinity imbues LiFePO₄ batteries with several advantages", you realize nothing has been explained at all. A real science popularizer with skill would at some point have brought it back around to say just how all the dance images correspond to the chemistry, and just how all that "imbues" the battery with those advantages, but none of that happens in this article. Maybe researchers into bullshitting need another category, "science pseudopopularization"?

I guess what I'm saying is it doesn't bother me that T1 Terry had the sense not to engage with that article.

 

Please watch the video in more detail. Yes, they are using a propane flame, but it is not directly contacting the cells. Instead, they are heating the cells to failure using a hot plate. The propane flame is there only to guarantee that ignition occurs once gases leave the overheated cell wall. You don't actually need a flame for the ignition source; overheated modules themselves can ignite the gas; this test just uses a flame to guarantee that happens.

Is this a fair test as it applies to the Prius? Absolutely! Since the NexPower V1.x & V2.x hardware has no method to limit regen energy into the battery, the battery can easily overheat (just like the heat plate). In fact, we see this exact failure in @sworzeh's pictures, so we don't even need to academically verify anything.

Obviously the plastic burned, too, but do you think plastic was the only fuel source? That fire burned for 90 minutes. I don't know for sure, but I suspect that on the low end at least half of the energy input is the LFP cells... I reckon it was closer to 90% of the energy input.

Let me know when you've watched it.

As I mentioned previously, a layperson is going to call particulate matter suspended in the air smoke, but fine let's call it whatever you want. It doesn't really make a difference for the purposes of this discussion.

Please see my previous post, wherein I specifically explained why I included that video.

The 50% figure I mentioned is both from my prior study (not an authoritative source), and is also mentioned in the 2nd video I linked previously.

However, given your doubt, let's look for more authoritative sources. According to UL's lab testing, they measured 36% hydrogen gas emission in their recovery apparatus. However, they have a footnote that says "Gases above combustible volume". In case that caveat unclear, UL is saying "36% of the hydrogen gas emitted from the cell didn't combust; we weren't able to recover all the gas because some of it burned". In other words, UL's lab test shows that empirically at least 36% of the gas emissions from a burning cell are hydrogen gas.

But let's dig deeper and see what academia says about this. According to this paper, the theoretical hydrogen gas emission from LFP cells undergoing a thermal event at 100% SoC is - drum roll please - 50.82%.

From that same paper, we learn that LFP also generates 4.5% (flammable) methane, 6.6% (flammable) ethylene, 9.3% (deadly) carbon monoxide, etc. So overall emissions are ~62% flammable compounds.

Again, I don't car what we call the particulate matter ejected from a venting LFP cell...
...but, the water vapor exiting a radiator is initially in a gaseous state. However, as soon as this hot vapor exits the radiator, the cooler surrounding air causes the gaseous steam to rapidly condense into tiny water droplets, which are no longer gaseous. If there's any uncertainty here, please refer to water's pressure-temperature phase change diagram.

To repeat, I don't care what we call the particulate matter. Continued focus on this is irrelevant to the safety issues I want to discuss.

I agree, but this isn't a counterpoint to anything I've mentioned in this discussion. Specifically, I haven't proposed that water is breaking down into hydrogen and oxygen.

It's impossible to deduce this statement simply from watching the video.
It's also incorrect both academically and empirically (see above).

Just to make sure I understand, you're proposing that none of the materials (I would call them gases) emitted from an LFP cell are flammable? This would disagree with both academia and empirical test results. Huge if true.

Thanks for clarifying that you were previously referencing LYP cells. The reason I asked for clarification is that I thought we were discussing LFP cells (I know I am), since that's the chemistry NexPower used in their V1.x & V2.x products. Thanks for sharing your LYP experience, but I'm not sure how it's relevant to this LFP-focused discussion. Let me know if I'm missing the point you were trying to make by bringing up LYP cells in an LFP discussion.

So to be clear, you're proposing that an LFP BMS without temperature sensors is safe?
Wouldn't you also want to know the temperature for things like Voc->SoC lookup, which is highly dependent on temperature? And also so you could reduce/limit charging current at low temperatures, and also to prevent all assist and regen at high temperature?

My LiBCM BMS has QTY12 temperature sensors... and honestly I wish I had designed in more. Knowing cell/ambient/intake/exhaust/PCB temperatures is really useful to safely monitor a battery.

Makes sense.

 

I agree. It's refreshing to have an actual scientific discussion.

See my previous reply.
Note that whatever the actual percentage is (I still contend it's 50%), the fact remains that at least some of the gases emitted from a venting LFP cell are flammable (I contend it's at least 62%).

0.53 g H2 = 0.263 mol
81.49 g CO2 = 1.850 mol
5.63 g CO = 0.201 mol
2.61 g HF = 0.131 mole

The difference between the paper you used, and the paper I used, is that in my paper the test apparatus was in a sealed chamber with inert gases. Specifically, since oxygen was removed from the test chamber, the emitted particulate matter (again, I would call them gases) was unable to combust. Hence in my paper we are measuring the actual unreacted gases emitted from the cell, whereas in your paper the gases are allowed to react with atmospheric oxygen. That's also the reason your paper measured much higher CO2.

Yes, this is a very important point... and I wish I had read it prior to writing the above paragraph . Specifically, it points out the primary difference between the two tests we cited.

Agreed... it's pretty bad. That's why I introduced it with the caveat "Less academic, but more approachable sources".

Maybe that article is for @AzusaPrius? .
I probably shouldn't have linked it to begin with. Fortunately, I did link actual research papers, which fortunately is primarily driving this discussion.

 

Every once in a while, there's something that's not worth approaching no matter how approachable it is.

Wouldn't even wish it on Azusa.

 

That'll learn ye to go replying to a post afore yer done readin' it.

 

I'm sorry, but after battling a "research engineer" for over 15 yr, I regard any paper that isn't peer reviewed as the work of someone or some group paid to come up with the response the finance is paying for ..... as an example, if there was interest in the level of hydrogen, the test would have been done using spectro analysis of the vapour, much the same way ore samples are analysed by microwave heating the sample till is gasifiers and looking at what is in the vapour cloud. I feel the papers were funded by those who wanted "scientific" verification that LFP, LYP and all lithium ion chemistries would burst into flame. I'm a believer that non peer reviewed "science papers" are just papers that have not been verified using the scientific principle by at least one other " independent" research team ..... some might remember the "scientific paper" circulated by the tobacco industry that tobacco smoke was harmless .......

I'm sorry that my time is very limited, so I don't have the luxury of reading and re reading sections, then cut and paste and reply ... plus I've lost my mouse somewhere in the motorhome, and touch screen tablet type computers seem to defy any attempt I make to do that sort of thing .
Even when I get back home, I doubt my time will be my own, I'm married :lol:

Some where in the last lot of replies, there was something about the vapours self igniting purely from the heat, yet in one of the videos, the glow from the shorted plates is clearly visible, yet it requires the second puncture to establish a flame, possibly spark ignition of the hot vapour ... but just an assumption or guess to put a more accurate label on that bit.

The difference between adding yttrium to the LFP mix affects the flammability how exactly? The flammability as far as I can determine is related to the make up of the electrolyte, and that is different for each manufacturer (not brand) and the climate is designed to function in, cold climates require more volatiles in the compound, hot climates less volatiles to avoid boiling the electrolyte causing it to separate into its basic compounds. I gathered most of this knowledge from watching Jay Whitacre's lectures some 12 yrs ago when he was at Carnagey Melon university.

Regarding the need for temperature measurement and the value that might be, the heat is in the electrolyte, how are you going to measure that, case temp won't produce an accurate and timely warning, the "horse has bolted" by the time the whole cell temp has reach the point the case gets hot enough to reach and alarm level.
In all lithium ion chemistries, internal temp is generated in the electrolyte can no longer move all the lithium ions from one plate to another .... this is always associated with an instant voltage shift in either the cathode or anode to the point it is outside the stable voltage operating range, monitor and respond to the voltage at the terminals of the cell and the temperature will remain stable .... the only time cell temp is of a benefit is when the absolute extreme current discharge is needed instantly and for a short time duration, drag racing is a good example, keeping the temp at that magic point is a very exacting science and closely guarded "secrets"
Life cycle is not in the equation at all ...... if the cell lasts for 10 secs then that is more than enough to include both the "burnout" and run time ..... they are unlikely to vent, the vent valves are sealed and the pack very heavily strapped to stop expansion of the cases that would lead to a cell rupture.

There are probably a lot more points I need to address, but time limited, the wife says it's time to get back on the road and I have no intention of challenging that authority

T1 Terry

 

Now I can't help wondering which of the two papers mudder linked you are describing that way. The one funded under National Key R&D Program of China, Grant/Award Number: 2018YFC0809500; Changzhou Sci&Tech Program, Grant/Award Number: CE20185001; Open Project Program of the State Key Laboratory of Fire Science, Grant/Award Number: HZ2015-KF13 and published in Energy Science & Engineering? Or the one funded under Science and Technology Project of the State Grid Corporation of China (Development and Engineering Technology of Fire Extinguishing Device for the Containerized Lithium Ion Battery Energy Storage Systems, No. DG71-19-006) and published in Journal of Energy Storage?

Would deliberately including semiconductor H₂ gas-analyser sensors in the experimental setup, as the second research group describes, be any indication that there was interest in the level of hydrogen?

This about their funding sources is something you feel?

I had begun to think things were looking up for this thread....

 

Seems like a cop-out, but ok. Our discussion was fun while it lasted.
Having already provided QTY3 separate papers that show that explosive materials (I would call them gases) are emitted during LFP venting, I'm not sure that providing half a dozen more would change your mind... fine.

FYI: The inert measurement paper's authors are:
-College of Locomotive and Rolling Stock Engineering, Dalian Jiaotong University, Dalian 116028, China, and;
-State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China

Why is spectrography required? Before dismissing the extensive time and effort this research team performed, I encourage you to re-read their paper, which provides several pages of context on why they selected the particular test apparatus used in their testing. Here's their opener:

I agree with skepticism, but in this case I think you hiding behind unwarranted doubt (FUD). Whether or not that's true, I'll reiterate that there are likely half a dozen more independent tests that have been performed using various testing methods... that ultimately all come to the same conclusion: some of the exhaust particulate matter (I would call it gas) that vents from LFP cells is flammable.

I'm sorry you've chosen to no longer participate in this conversation, and have instead chosen to exit it in a dismissive way. My time is very limited, too... everyone's is. I respect that you no longer with to participate in this conversation, but I don't think sowing doubt on your departure is the best way to do so.

Same.

I don't believe anyone made a claim that the vapours would spontaneously combust. I've been clear that an ignition source is required, which could be the overheating modules themselves, a nearby spark or flame, someone lighting a match in the car, etc. Most flammable materials require external ignition sources. Regardless, they're still flammable, hence they warrant additional safety measures.

I just didn't understand why you were talking about non-LFP cell chemistries. If parts of these different chemistries are identical, then it might be relevant, but I would think it would be worth explaining in context. Thanks for the clarification now.

Carnegie Mellon.
Great campus.

I absolutely disagree. Your hypothetical only considers a rapid failure mode.
Consider the numerous failure modes where the cell slowly overheats.
And of course, consider that charging and discharging at low/high temperatures can accelerate these failures (hence you can avoid them to begin with by disabling assist/regen in unfavorable temperatures.
The "horse won't bolt" if you don't agitate him into bolting.

Internal temp is generated by more than just the one contributor you mentioned.
You are focusing in on individual elements, whereas there are multiple contributors.
Also, I'll note that the voltage shift you describe is far from instant, although it does happen much faster compared to the rest of the chemical conversion process. I mention this because there are actually lab methods to detect this voltage shift as a last resort to avoid a thermal event.

I disagree with this entirely. Knowing cell temperature is extremely useful for numerous different cell state parameters. For example, I previously mentioned Voc->SoC lookup tables are strongly correlated to temperature.

I don't follow your line of reasoning here, or really understand what you're trying to say.
Honestly, at this point it just seems like you're just throwing things at the wall to see if anything sticks.
I worry we're getting stuck in the weeds, and drifting away from the one point we agree on:
selling an LFP product without a BMS is unsafe.

Not sure the context, but yes, this is how vent valves work.

I understand what limited time feels like. I'm standing by if you want to re-engage with this conversation (and have time to do so).

 

This was my feeling, too. Sigh.
Hey, at least @AzusaPrius has stopped posting. Bless their heart.

 

And there you've just @-ed him. I think you're lonely.

 

Didn't mean to sound like I was exiting the thread, just explaining why the replies are bit all over the shop without a lot of direct references made.
I believe this thread is about an LFP battery that caught fire. It wasn't punctured, so the staking is not particularly relevant, yet the fact that additional holes to allow air to enter so oxygen was introduced into the cell was required to get one of the test cells to actually catch fire.

The suggestion hydrogen was a gas in the vented electrolyte vapour, yet the testing was only carried out on burning electrolyte vapour, leaves many unanswered questions. Using that flawed methodology to assume hydrogen is 50% plus of the ejected vapour just muddies the water, more valid testing would be required.
The possibility that the hydrogen was not actually part of the vented electrolyte vapour but rather part of the by product of something within the vapour burning in a restricted oxygen supplied combustion situation causing an incomplete combustion, needs to be answered one way or the other .... one paper started with "Theoretically" regarding the hydrogen content .... we all know the difference between theory and the real world, in theory they are the same, in reality, they are often not even close .....

Hopefully once I get home and the dust settles, I'll have more time to do research regarding back up testing by the likes of Carnegie Mellon (sorry about my mutilation of the name) NASA etc, they had a lot of research work they conducted 12yrs or more back when I first became involved with LFP cells and their various construction designs and why that design was chosen. Paint me sceptical, but I don't trust any of the specs or testing from Chinese "research" facilities, very few of them have panned out to match my test results and when questioned, a whole different set of parameters were used to obtain the results they advertised ..... Winston was one of the exceptions, as was A123, but they only sold to major manufacturing concerns.

The 18650 for example is two long sheets sprayed on both sides with the active on one sheet and the graphite on the other. Designed for high C rates, not longevity or the storage and release over longer periods at a lower C rating. Prismatic, the type I prefer because of the multiple layers spreading the variations out that are inherent in mass production, a spring loaded vent, insulated case and capable of being compressed to minimise case bulging ..... the pouch cells came later and to be honest, not a fan, too many failures and poor heat dissipation potential. I'm intrigued by the new cylindrical cell sizes as to why? I'm guessing to house the increased capacity and possibly integrating the multiple layers found in prismatic cells with the long contact facing available in a cylindrical cell.

I am interested in your ideas regarding other reasons a cell would heat up, if the cell is cold enough to freeze the electrolyte, the wrong compound electrolyte was chosen and probably the wrong combination of elements in the active material. This is what directed me to the Winston LYP chemistry, all the benefits of LFP with an added minimum threshold of -36*C and upper threshold of 70*C .... I like the sodium ion cells I'm part way through testing because they stretch this a bit further with better under voltage and over voltage tolerances before they cease to function as specified ... actually, I'm still in the process or discovering if they meet the manufacturers specifications or just what specs they really have in regards to their expected performance.

I'm not really interested in supporting or rejecting anyone's claims against how someone else went about their BMS design, either it worked or it didn't. Did it catch fire? No evidence has been forthcoming that there was actual combustion involved. If the electrolyte vapour had been vented outside the vehicle cabin, would this circus have even got the tent up?
I know for certain the NiMh modules catch fire if over voltage charged, the insurance investigator backed that up, the melted modules and blacked steel cases just confirm there was combustion ... the flames licking out of the vent by the back passenger door was enough to convince me it was on fire :lol:

T1 Terry