The following post was written as part of a question I asked regarding removal and charging of a deeply discharged e bike battery. That thread subject evolved into a question of the safety of charging a deeply discharged lithium battery and someone suggested to post it in this forum for a broader response. Thanks.
Safety of Charging Deeply Discharged Lithium Batteries.
- Thread starter JamesG81
- Start date
Do not use "lithium" thinking the many dozens of chemistries under that umbrella behave the same.
All these issues go away using LTO or LFP for example.
If you are talking about the rest, likely NMC (NCM), NCA, LCO/LiCo or LiMn varieties
yes massive concerns about thermal runaway, boom bad.
Regular capacity and resistance testing, benchmark when new or within say 20 cycles of commissioning, and track decline as they wear.
High C-rate and DoD use cases, EoL comes much sooner, even 50 cycles in extreme cases.
My standard is 70-75% capacity loss, or any signs of heating up at 0.4C rate charging, off they go to recycling, or sold off with proper warnings to thosesuckerspoor souls less risk averse than me.
All these issues go away using LTO or LFP for example.
If you are talking about the rest, likely NMC (NCM), NCA, LCO/LiCo or LiMn varieties
yes massive concerns about thermal runaway, boom bad.
Regular capacity and resistance testing, benchmark when new or within say 20 cycles of commissioning, and track decline as they wear.
High C-rate and DoD use cases, EoL comes much sooner, even 50 cycles in extreme cases.
My standard is 70-75% capacity loss, or any signs of heating up at 0.4C rate charging, off they go to recycling, or sold off with proper warnings to those
motomech
10 MW
JamesG81 said:
So, did you have a question?
There are several questions in the original post. You can pick any and answer.
Also I stated that I am open to getting more education on safety of lithium batteries so you can do that if you like.
Here is a specific question: why it is common belief that a deeply discharged lithium battery is much more of a fire hazard than a brand new one?
Thanks.
Also I stated that I am open to getting more education on safety of lithium batteries so you can do that if you like.
Here is a specific question: why it is common belief that a deeply discharged lithium battery is much more of a fire hazard than a brand new one?
Thanks.
It is not a "common belief" but objective reality. Keep pushing lifespan and fast charge rates and Boom becomes inevitable.
What ever gave you the idea there was any question about that?
Now if "deeply discharged" means never below say 3.4V, and the battery is still in its first 50 cycles, and charge rates are kept below say 0.4C
and temperatures are monitored, and charging is never left unattended.
Then yes still pretty safe.
What ever gave you the idea there was any question about that?
Now if "deeply discharged" means never below say 3.4V, and the battery is still in its first 50 cycles, and charge rates are kept below say 0.4C
and temperatures are monitored, and charging is never left unattended.
Then yes still pretty safe.
The issue is not just the SoC% of a given battery.
The real factor is, was that battery damaged by mistreatment, or just plain worn out past the EoL spec?
That is when increased risk of thermal runaway can get really dangerous, and especially during the charging process.
The real factor is, was that battery damaged by mistreatment, or just plain worn out past the EoL spec?
That is when increased risk of thermal runaway can get really dangerous, and especially during the charging process.
Once the battery cell itself (excluding the above protective mechanisms)
has been damaged by being allowed to go too flat
it is never the same, and cannot be "repaired".
It may continue to be used in more careful use cases, at lower charging voltages and lower current rates,
but it will continue to be a riskier unit than a newer / less worn cell, more susceptible to thermal runaway in a less extreme context.
This is wrt those chemistries in common use today, excluding LFP and LTO.
Obviously technology will over time advance, and the more dangerous formulations will become obsolete.
> Is there a way to verify that these are genuine Samsung cells?
Test its capacity and IR against a known genuine cell bought from a trusted source.
has been damaged by being allowed to go too flat
it is never the same, and cannot be "repaired".
It may continue to be used in more careful use cases, at lower charging voltages and lower current rates,
but it will continue to be a riskier unit than a newer / less worn cell, more susceptible to thermal runaway in a less extreme context.
This is wrt those chemistries in common use today, excluding LFP and LTO.
Obviously technology will over time advance, and the more dangerous formulations will become obsolete.
> Is there a way to verify that these are genuine Samsung cells?
Test its capacity and IR against a known genuine cell bought from a trusted source.
No one information resource can be "comprehensive".
Scientists are learning new things every day, including about battery chemistries in use for over a century.
Those formulated in recent decades will be obsolete long before we can ever understand everything about the physics and chemistry of how they operate.
Just regular cycling usage over time will cause a perfectly healthy battery to reach specified EoL, at which point it is **much** more dangerous than a new one.
No defects or contaminants, just regular wear and tear, no matter how well treated.
A CC load capacity test showing 90% or more SoH means you can safely use it for say another 50-100 cycles, ideally coddling it well below the maximum stress mfg specs.
If next test cycle it is at 80%, you definitely want to be more careful, treat it more gently.
70% is really pushing things, best to recycle, or sell on to some poor poverty-stricken ignoramus or person who lijes to live dangerously.
Scientists are learning new things every day, including about battery chemistries in use for over a century.
Those formulated in recent decades will be obsolete long before we can ever understand everything about the physics and chemistry of how they operate.
Just regular cycling usage over time will cause a perfectly healthy battery to reach specified EoL, at which point it is **much** more dangerous than a new one.
No defects or contaminants, just regular wear and tear, no matter how well treated.
A CC load capacity test showing 90% or more SoH means you can safely use it for say another 50-100 cycles, ideally coddling it well below the maximum stress mfg specs.
If next test cycle it is at 80%, you definitely want to be more careful, treat it more gently.
70% is really pushing things, best to recycle, or sell on to some poor poverty-stricken ignoramus or person who lijes to live dangerously.
First, laboratory testing is a wonderful thing and can provide much information. However, very, very few products are exclusively used in laboratories.
Another way to look at this - if the weatherman says there is a 5% chance of rain, do you take your umbrella? How about a 5% chance of severe lightning strikes, and you need to carry a 10 foot metal pole, vertically?
The much greater degree of personal risk makes a difference, doesn't it?
Several members have personally experienced battery fires, some with severe property damage and even loss of life. Many more news stories of similar incidents have been reported here. Most, BUT NOT ALL, of these have been batteries which were being charged at the time. That IS the most dangerous time. BUT - it is NOT the ONLY dangerous time. Some have caught fire while in use, and a few have caught fire just sitting there. Battery fires are very energetic and have an abundance of toxic fumes.
As for the specifics of why a severely discharged battery is more dangerous, several reasons have been offered and it is clear that experienced members absolutely will refuse to use such batteries. I will take field experience over laboratory results every time.
Another way to look at this - if the weatherman says there is a 5% chance of rain, do you take your umbrella? How about a 5% chance of severe lightning strikes, and you need to carry a 10 foot metal pole, vertically?
The much greater degree of personal risk makes a difference, doesn't it?
Several members have personally experienced battery fires, some with severe property damage and even loss of life. Many more news stories of similar incidents have been reported here. Most, BUT NOT ALL, of these have been batteries which were being charged at the time. That IS the most dangerous time. BUT - it is NOT the ONLY dangerous time. Some have caught fire while in use, and a few have caught fire just sitting there. Battery fires are very energetic and have an abundance of toxic fumes.
As for the specifics of why a severely discharged battery is more dangerous, several reasons have been offered and it is clear that experienced members absolutely will refuse to use such batteries. I will take field experience over laboratory results every time.
CamLight
10 kW
One possible issue with deeply discharged li-ion cells is that the copper foil the anode (negative side of the cell) uses can start dissolving if the voltage is too low. This copper then plates itself wherever it wants to when the cell is recharged. Eventually this can lead to an internal short circuit.
These short circuits could just cause a small increase in the self-discharge rate of the cell or it could cause a temperature increase high enough to send the cell into thermal runaway...which is very not good.
This has been reported to start occurring at about 2.0V or lower for some cells but I’ve seen a research paper where the cells they tested did not start dissolving copper until they were brought down to below 0V, i.e., they were being reverse charged. It probably depends greatly on the cell chemistry and cell being discussed.
Basically, your risk increases if you start going below the cell’s rated low voltage cutoff but we can’t quantify the risks or tell you if it’s just a cell-performance-loss risk, a safety risk, or both.
These short circuits could just cause a small increase in the self-discharge rate of the cell or it could cause a temperature increase high enough to send the cell into thermal runaway...which is very not good.
This has been reported to start occurring at about 2.0V or lower for some cells but I’ve seen a research paper where the cells they tested did not start dissolving copper until they were brought down to below 0V, i.e., they were being reverse charged. It probably depends greatly on the cell chemistry and cell being discussed.
Basically, your risk increases if you start going below the cell’s rated low voltage cutoff but we can’t quantify the risks or tell you if it’s just a cell-performance-loss risk, a safety risk, or both.
Because it is. That's why pretty much all consumer devices (think cellphones) have a trickle charge mode for when the cell is below about 3 volts - to reduce the odds of damage, heating and fire. Generally you have to charge at below about .1C until you get back above 3 volts.JamesG81 said:
The copper plating issue seems to be the real problem with Li-ion cells that have been over discharged. Beside that, the internal resistance of most cells will drastically increase once you get close to zero SOC, so if you are running high charge or discharge rates, the cells could heat rapidly. This can be managed by limiting current when the cells are below a certain SOC like Bill is pointing out.
The guy from A123 Systems said for LiFePO4 cells, once they get below 2.0v, they will be permanently damaged and generally you will see excessively high self-discharge rates on the damaged cells. Not so much a fire risk, but the cells will not perform properly.
The guy from A123 Systems said for LiFePO4 cells, once they get below 2.0v, they will be permanently damaged and generally you will see excessively high self-discharge rates on the damaged cells. Not so much a fire risk, but the cells will not perform properly.
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