Question House batteries

[Kevin D Pem]

It's been a while! Probably 2018. Some references were books, but some were online!!! I will spend some time looking.

 

[lostinfla]

Please do share links to such research on LiFePO4 batteries being a fire hazard as you describe.

Best,
-Mark

I too would like to see that.

 

[MemoriesByTheMile]

Ditto on wanting to see recent research.
Battery technology is quickly changing and with larger volumes of batteries in use, we now have the ability to have a larger set of real world data and not just theory based on lab sized sets of data.
I understand that Lithium Ion batteries have a higher risk of run away heat and is the battery that is seen in use in highly publicized pictures, but Lithium Iron Phosphate (LiFePo4) has been a much safer and stable composition. But LiFePo4 has a lower energy density than Lithium Ion.

 

[Kevin D Pem]

I know that the battery university website is shrouded by controversy, but the data is valid. This blog also has valid data, but is jaded with sales in mind!

Qnovo | WHAT HAPPENS AFTER 80%?

So much of my data came from research I did while experimenting and building my 90 ah 24v lithium-ion packs(2) for a pop-up slide in camper build, to use for a summer of traveling! Ion batteries were the choice for size and weight.

I tell you this as a preface to this subject. LiFePo4 were avaliable, as well as LTO, the hazards are much the same in all but the LTO, but that's another story!

That YouTuber that talks and tests lithium agree in the context that manufacturers can't make parts that don't vary. He points to quality as a measure that you get as a minimum what has been advertised. But in the world of quality, the cells must be classified through testing, not only capacity, but resistance. The parameters are grueling and extensive. Mismatched cells can be disastrous. So at manufacture date they are matched as precisely as humanly possible.

Over time imperfections in material start to show their ugly head. Cells become less matched and don't charge equally. BMS to the rescue!

Two types of BMS are produced, active(only the most expensive packs have them), and passive (most common)! To answer Neal's question 80% charge only works to save the batteries if the BMS is active! A passive BMS requires a 100% charge to equalize the cells.

BMS literally can claim savior status when we talk lithium. Without them you would not find lithium on the shelves! But they can't change the chemistry that makes them nessassary. Over time the unbalanced cells (we are talking physical characteristics) can't be overcome with balancing schemes. When the differences in cells become pronounced enough, we get to that 80% number, and quickly escalate.

So you ask, what happens at the 80% number that makes a fire Hazard?? The BMS is built to negotiate a new battery!

People, not educated enough to deal with the issue, continue bringing the pack down to 20% charge! They complain that their battery no longer makes it the expected duration.

BUT!!!

Internally some cells continue providing as usual, while those that are struggling with increasing resistance can never catch up! They try but to no avail. The enevitable gets closer, then on one cycle the slacker cell is brought to "0" volts. Then it reverses polarity!

Nice story Kevin! What's the point!!!

Well that cell becomes a dead short! Yes! and the entire battery works in unison to feed that new demand. One they can't fill. The shorted cell overheats to runaway temperatures and turns into a bottle rocket. But it doesn't stop there! The cell next door quickly overheats, and the chain reaction can't be stopped!!!

now I have seen LA and other chemistries short out and start fires. However nothing has matched the intensity of a Lithium fire!!! Literally fire departments learn to try and cool the fire because they are the fuel and will continue until there is no more power.

I gave you a few resources! My experiment told me what I needed to know! Lithium is far from new technology! If you're reading this likely the discovery was made before you could count! I know it was before I could! It simply was learned how it could almost be controlled.

Don't look for advancements that will make it truly safe. Not in yours or your offsprings life! Not going to happen!!!