Lithium Ion exploding batteries.

[BLACKPANTHER]

I've come across stories of batteries catching fire whilst in use on the bike. Is this just a Myth?

I'm aware that it's unwise to leave a battery on charge 'unattended', but is it possible for a battery not on charge, and not in use on a bike to catch fire? I ask, because I tend to charge my battery after a ride, and then keep it in a cupboard in the kitchen rather than with the bike in the garage. I also charge it in the canteen at work (on a 3 hour timer.)

 

[Streethawk]

I've heard of it happening in laptop and phone batteries, but really its so rare that i'd not worry about it. Its always been a rechargable battery risk, i remember a set of RC racing nicads exploding on me in the early nineties.

 

[flecc]

I've come across stories of batteries catching fire whilst in use on the bike. Is this just a Myth?

No, it's not a myth, it happens on a lithium battery using a plain cobalt cathode when the manufacturing standards are lax. The mechanism is that under some conditions the lithium, which is not present in metallic form normally, forms metallic crystals in the electrolyte which are jagged in shape as the grow. As such, they pierce the internal insulation and set up internal shorts. In high current batteries these set off internal fires and can lead to explosions, blasting out the contents as they expand and causing secondary fires in the environment.

As a result of this and one very serious case involving an e-bike, manufacturers dropped this battery type and changed to the much safer manganese based cathodes. These did not perform as well, but since then compound cathodes have been developed which are able to include cobalt and which are totally safe at all times.

That said, all high capacity batteries are potentially unsafe if abused and have been rightly said to be household bombs, so charging of these is best only done when present and awake.
.

 

[BLACKPANTHER]

That said, all high capacity batteries are potentially unsafe if abused and have been rightly said to be household bombs, so charging of these is best only done when present and awake.
.

.....but does that mean that the only time a battery could potentially turn into a 'household bomb' is whilst being charged?

In other words, is a charged (then disconnected from the charger) battery 100% safe to be stored in the house?

 

[flecc]

.....but does that mean that the only time a battery could potentially turn into a 'household bomb' is whilst being charged?

In other words, is a charged (then disconnected from the charger) battery 100% safe to be stored in the house?

Mainly yes, but nothing is unconditionally safe with large capacity batteries since the content has the potential to cause considerable damage.

Being chemical devices, the main potential for trouble is during charging since that is when a chemical reaction is active. At other times the potential for trouble is that of a short circuit arising as in those cobalt cathode types I referred to earlier. With that no longer present any potential is likely to be an internal wiring short through insecure terminations or chafing insulation due to on-road movement. This likelihood is extremely low, but possible.

So when off-charge and off the bike, probably something like 99.999% safe, off-charge and on the bike, 99.99% safe since the possibilities of a short circuit rise with the bike included.

Personally I ignore the risk of mine indoors on or off the bike, I just don't charge overnight or when out.
.

 

[BLACKPANTHER]

Cheers for that flecc. I'll sleep soundly tonight then. I know that many stories bouncing around this t'interweb thing are a complete crock, but it's still worrying when you hear of such possibilities.

 

[jbond]

Flecc, Blackpanther and I both have an Alien Aurora. This uses a 36v10AHr Phylion battery. Alien seem to sell several bikes and kits with the same rack mount battery. It's a 10s1p layout with a charge range of 42v-31v. I get the feeling a lot of other e-bikes use the same chemistry and electrical layout but in different packaging and it's been around for a while.

A typical "36v" LiFePo battery is bigger, heavier and 12sXp where X depends on the exact AHr. Our battery seems to be lighter and smaller than a Ping 36v10AHr.

What I can't make out is what chemistry it uses. Looking at the wikipedia page, Lithium-ion battery - Wikipedia, the free encyclopedia
It's unlikely to be LiCo for safety reasons. LiMn has the right voltage compared with LiFePo but the lowest specific capacity. The only other chemistry with the right voltage is Li-NMC but this is a very recent development. Even with 10s instead of 12s, the difference in specific capacity between LiMn and LiFePo looks like the LiMn should be heavier.

So I guess I'm asking what chemistry is the typical commercial packaged battery that's been used on E-Bikes for the last few years?

 

[NRG]

I recall Flec saying somewhere the explosive ones where based on Cobalt cathodes and the safe ones manganese but these did not perform very well so most batteries now use a compound cathode.

 

[flecc]

Yes, current Phylion batteries are lithium with either manganese, or compound cathodes which can now include some cobalt safely. Either have the same voltage that fits your measurements and are very safe.

The weight loss on current batteries is normally due to the polymer construction which uses soft plastic cell casing bags in place of the welded steel cell casings of earlier types. That can make well over half a kilo difference on a 36 volt type.
.

 

[jbond]

The cells in mine are rectangular with hard plastic cases. "Prismatic" ?

 

[flecc]

The cells in mine are rectangular with hard plastic cases. "Prismatic" ?

Maybe that's what's meant, but it indicates a probable plate type construction rather than polymer. It should also be a lot lighter than the strong welded steel cases I illustrated above. That particular battery's weight dropped from 4.4 kilos to 3.3 kilos when switched to polymer, a staggering amount while getting an increased performance.
.

 

[Lloyd]

I had a small lipo do this whilst sat stored at 70% charge in my bedroom

Very very lucky to have spotted it and got rid! I use these 7.4v packs for rc racing, and we are not allowed to charge them outside of fireproof lipo sacks, just in case. Fires are rare, but I have seen one or two go up, usually when charging or when shorted, and it's scary. My one was just being stored in between race meets and when I got it out it had expanded!

Needless to say my remaining 3 packs are all now stored inside my fireproof sack now just in case.

 

[pictsidhe]

LiPos tendency to swell under abuse cuts out a lot of the hazard, this effectively disconnects them internally when they gas, I once inflated a mobile phone LiPo with a cheap and nasty car charger AND bad BMS, oopsie. Hard case cells don't do this so well and can go pop. A large proportion of current fires now the chemistry has been tweaked are from abuse, a good BMS that measures every cell and prevents excessive over or under voltage will drastically improve safety, chargers should limit charge voltage, motor controllers limit discharge volage, but if one cell becomes unbalanced, a BMS is needed to catch it. In short, a quality pack and system is very unlikely to burn, go to the cheap end with cut corners and it gets much more likely. I have outhouses to charge in.