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Dr Bob

Safety of LiFePO4s in canal boats

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There have been a few comments on another lithium thread re lithium battery safety and I thought it would be useful to start this thread to be able to get peeps to pull together all the info that is out there so we can arrive at a position that it easy to understand. We all talk about the issues of using lithiums and talk freely about overcharging (which can your wreck cells) but we very rarely (if ever) talk about the likelihood of cells exploding or going on fire. Yes, LiFePO4s are safer than other Li -ion batteries but there is still a risk. Yes, there is a risk with LA's (hydrogen explosion/strong acid) but the effect on a boat could be far worse with an Li explosion or fire.

Where can we get information from? The internet is full of stuff but can you believe it? So many sites seem to give totally opposite 'facts'. We need to be searching out the papers and articles from solid sources! Lets try and use this thread to find the relevant stuff – my head is hurting from 5 hours of searching! I have a bit of an inside track as the company I am involved with (an independent test house for polymer materials) is part of a European funded programme – SABATAIR (Safe Battery transport by air) – supervised by EASA. A few years ago, ICAO ( International Civil Aviation Organisation) approved a temporary ban for Li-metal and Li-ion batteries to be transported as cargo in passenger aircrafts. ICAO is now working on the development of performance standards for packaging for safe transport of Li's in passenger and freighter aircrafts. This task has been assigned to a European sub group - SAE G27 – their first task in the SABATAIR programme is to come up with suitable test methods to test appropriate packaging. My company is therefore testing Li-ion batteries to destruction under varying conditions to identify suitable test conditions and our tech director sits on the SAE G27 committee.

To start the ball rolling then it is worth discussing the 'how do Li's explode' and 'how likely is it they will'.

There is a really good paper given last year in the committee by Charles Chanson on the hazards of Lithium batteries. https://ec.europa.eu/jrc/sites/jrcsh/files/claude-chanson_characterize-lithium-batteries-thermal-run-away-reaction.pdf

Charles is one of the lead members of the SAE G27 committee and this doc is one of the docs in their public domain folder. He is one of the biggest 'noises' in lithium hazards. It takes a bit of time working out what he is saying but after multiple readings you can get a sense of what is going on. One of the main threads seems to be that Li's are not that dangerous and are actually much lower energy in a thermal runaway than an equivalent amount of paper or plastic! What he doesn't say is that these Li's weigh far more than paper and plastic and I wouldn't have that much under the bed! Slide 4 is interesting in that it looks at the energy available in a run away breaking down the anode, cathode and electrolyte as separate energy sources. At the end of the day, there is a lot of energy in an Li bank and you have to take steps to stop it catching fire.

That is the purpose of the SABATAIR project and they are learning how to minimise tragic mistakes. The current thinking is that having batteries at 30% SoC is the best compromise for flying ie 100% definitely not...and 0% carries the risk of destroying the batteries. All the testing is being done at these two levels, 30% and 100%.

The 'how likely' is longer than a long piece of string. From the other papers from that meeting it is clear that most fires/explosions come from thermal runaways originating from micro short circuits in the affected batteries. See pic below. Not so much a micro problem – but what can happen if the manufacturer gets it wrong! Don't buy cheap Chinese copies! Micro shorts are mainly due to a variety of spot defects like: dendrite formation, defective or torn separators, misaligned electrodes, tab burrs, cell contamination, tab weld splatter, …etc. These give rise to intense local heating which then progress to thermal runaway. The work in our lab showed it was very difficult to get even an Li-ion battery into thermal runaway with a blow lamp or 'overall heating'. The only consistent way was to use a point source of temperature ie the tip of a soldering iron, to heat up a cell very locally. All these cells have inbuilt protection in a cap that will melt on high temp allowing the electrolyte to escape (normally as a gas). If general heat is applied to a bank, the caps will melt and the electrolyte will escape thereby reducing the ability of the anode and cathode to ignite. I think we see this when we are looking at the 'Chinese' video.

When we consider LiFePO4s, these are considered safer than other Li-ion batteries as the oxygen molecules in the phosphate material have a much greater bond strength compared to other metal oxides and so are much harder to ignite. Wotever posted the Wikipedia link in a previous thread which looks very accurate! Also they have a much lower specific energy which means if ignited then there is less energy than normal Li-ion. LiFePO4s however still suffer micro shorts and can ignite if handled incorrectly. Dendrite growth is a key failure mode as with other Li-ion batteries and needs to be avoided. This link seems quite instructive:

http://ecst.ecsdl.org/content/41/39/1.full.pdf

Dendrite growth is clearly linked to overcharging and that is an area that we ourselves can do something about. In the last month there has been a lot of discussion on charging with @nicknorman designing a suitable charging system, MtB going for a cup of tea and leaving one of his cells to get to 4.2V and Richard  now charging his cells to 3.8V to balance. We do need to be mindful of charging too fast or at too high a voltage at very high SoC in that its not only the battery cells that might be damaged if we blink and it goes too far. Keeping my batteries away from 100% SoC is one risk mitigation that should work for me.

Two other random quotes:

Note that consumer concern about the safety of Lithium batteries tends to be focussed on the Lithium cathode materials, whereas in reality, thermal runaway is initiated at the anode, NOT the cathode

and from

http://ecst.ecsdl.org/content/41/39/1.full.pdf

Although, the LiFePO4 cell is much safer than other Li ion batteries, the safety of LiFePO4 cell is still a critical issue in its application such as portable electronics and transportation.

Overall then, there is a risk of thermal runaway in LiFePO4s but a big risk mitigation is to NOT overcharge and keeping them down below 80-90% SoC is another factor of safety.

 

 

 

 

 

 

 

 

Screen Shot 2019-12-04 at 13.43.55.png

Edited by Dr Bob
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My insurance company were not in the least interested in the fact that I had removed my diesel engine and fitted an electric drive unit, they seemed happy that I had LifePo4 batteries as well, only time will tell if it makes a difference if I have tp claim

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1 minute ago, peterboat said:

My insurance company were not in the least interested in the fact that I had removed my diesel engine and fitted an electric drive unit, they seemed happy that I had LifePo4 batteries as well, only time will tell if it makes a difference if I have tp claim

A bit like flood cover, after an area has flooded, it becomes excluded from a standard policy.  So far they don’t have any fire data for lithium batteries, if a few boats self ignite expect lithium battery fires to become either a very expensive extra, or just excluded in the policy.  Time will tell...........

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4 hours ago, Dr Bob said:

Although, the LiFePO4 cell is much safer than other Li ion batteries, the safety of LiFePO4 cell is still a critical issue in its application such as portable electronics and transportation.

So, has @Dr Bob’s company or anyone else actually forced a LifePo4 battery into thermal runaway by intentional over-charging or is this simply a theoretical risk?

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10 minutes ago, WotEver said:

So, has @Dr Bob’s company or anyone else actually forced a LifePo4 battery into thermal runaway by intentional over-charging or is this simply a theoretical risk?

At the price of them no!  I just did some research and mine turned up as very safe job done 

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3 minutes ago, WotEver said:

So, has @Dr Bob’s company or anyone else actually forced a LifePo4 battery into thermal runaway by intentional over-charging or is this simply a theoretical risk?

We havent but that last link I posted showed that 11 cycles of overcharging created dendrites which then causes shorts in the cells which would then rapidly heat the cell locally. I dont think it is then just theoretical if the spot heat wouldn't do more damage. Yes the phoshate part of the cathode may not yield its oxygen quickly but the electrolyte is combustible (and so is the anode - and the short will put heat both into the cathode and anode). All of the sites seem to be saying LiFePO4 is safer - where the 'er' are the key letters! It's not safe....just safer.

Are any of the videos on Youtube done with LiFePO4s....too many to look at.

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Just now, peterboat said:

At the price of them no! 

But the company is attempting to get them into thermal runaway. They’re trying really hard (they have loads of funds) and from what @Dr Bob says, finding it difficult to achieve. So I wondered if they (or any developer/university/testing house) had actually achieved it by over-charging of if that scenario is only theoretical. 

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Just now, WotEver said:

But the company is attempting to get them into thermal runaway. They’re trying really hard (they have loads of funds) and from what @Dr Bob says, finding it difficult to achieve. So I wondered if they (or any developer/university/testing house) had actually achieved it by over-charging of if that scenario is only theoretical. 

The work our lab is doing is based on the more volatile Li-ion batteries ie Lithium cobalt oxide etc as they are the bulk of the batteries being transported.

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1 minute ago, Dr Bob said:

I dont think it is then just theoretical if the spot heat wouldn't do more damage.

‘More damage’. Okay, but thermal runaway?

 

Just now, Dr Bob said:

The work our lab is doing is based on the more volatile Li-ion batteries ie Lithium cobalt oxide etc as they are the bulk of the batteries being transported.

Ahh, well, we all know that THOSE can result in thermal runaway. What I’m trying to pin down is whether or not LifePo4 can end up doing the same thing. So far it appears to me to be only theoretical. 

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13 minutes ago, WotEver said:

‘More damage’. Okay, but thermal runaway?

 

Ahh, well, we all know that THOSE can result in thermal runaway. What I’m trying to pin down is whether or not LifePo4 can end up doing the same thing. So far it appears to me to be only theoretical. 

I hope so Tony j really hope so?

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5 minutes ago, WotEver said:

‘More damage’. Okay, but thermal runaway?

 

Ahh, well, we all know that THOSE can result in thermal runaway. What I’m trying to pin down is whether or not LifePo4 can end up doing the same thing. So far it appears to me to be only theoretical. 

That's why I thought it a  good idea to post this thread. I cant see any data (or facts) showing more than just spot shorts in cells for LiFePO4s but there is a huge amount of info out there. Hopefully it will encourage peeps to look some more. Maybe you are right. I wouldn't like to think there is a short in one cell between the anode and cathode when at 100% SoC and 480Ahrs of 'power' behind it.

One of the last quotes in my OP was

Although, the LiFePO4 cell is much safer than other Li ion batteries, the safety of LiFePO4 cell is still a critical issue in its application such as portable electronics and transportation.

which came from that last link I quoted...but that dates from 2012 so is old.

What surprises me is that there doesnt seem to be a huge amount of data on cell destruction and the work we are doing included a lot of pretty basic stuff just to get to a position where we understood how to get consistant thermal runaway. I have a feeling that we are looking into an area with little data.

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36 minutes ago, Dr Bob said:

I have a feeling that we are looking into an area with little data.

Which of course could be, at least in the case of LifePo4, because it (thermal runaway) simply doesn’t happen.

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1 hour ago, WotEver said:

Which of course could be, at least in the case of LifePo4, because it (thermal runaway) simply doesn’t happen.

 

Well that's it, really. Three or four years ago I did a lot of Goggling on this subject having heard lots of scare stories, and concluded LiFePO4 really are a negligible risk based on the number of stories I found on thermal runaway, i.e. none for LiFePO4 specifically. ALL the runaway cases I read about were other types of lithium. 

 

And supporting this now, there have been no cases of thermal runaway cropping up on this forum or on the towpath telegraph that I have heard (so far).

 

If it turns out my bank is goosed from charging that one cell to 4.2v, I'm happy to donate it for a destructive test aimed at getting to thermal runaway.

 

I don't like it anyway because of the weird welded interconnects. One cannot separate the cells without using an angle grinder...

 

 

 

 

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1 hour ago, Mike the Boilerman said:

 

 

 

I don't like it anyway because of the weird welded interconnects. One cannot separate the cells without using an angle grinder...

 

 

 

 

Eeeek! Remind us what type of cells and post a pic.

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11 hours ago, Dr Bob said:

Eeeek! Remind us what type of cells and post a pic.

 

The whole bank is contained inside a rather complicated plastic case. One can take each end off the get to the interconnects but now the whole thing is installed in the cupboard under the bed and weighs about 40Kg, so I'm not taking it out just to take a photo!! 

 

 

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Yet every year you hear of a lead acid exploding, so they also have a risk, particularly if you leave the boat plugged in, or with large solar panels on.

I guess good practice with lithium, if leaving the boat, is to isolate the bank from all charging sources, because they don't like being kept full, but around 30-80%. for storage.  When aboard you can monitor alarms etc and take action.

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