How safe are Li-ion batteries, specifically 10440's in an LF2X

[OrlandoLights]

In the current thread "Who got their LD01 Stainless Steel?", 4sevens had some warnings about using 10440s in the LD01, but also, from what he said and from my little research so far, it seems that Li-ions in general have safety problems.

I asked some questions there, but I don't want to take that thread off topic to find out more about this issue. Maybe someone can answer a few basic questions I have.

Does anyone know the safety record on Li-ion batteries, and 10440s in particular. Are there any actual statistics?

I have AW's 10440s and the Nano charger for them. I got them for and use them exclusively in the LF2X, which has a protection circuit. I have read that Li-ions without a protection circuit are dangerous; does the circuit in the LF2X completly take care of that problem?

I am careful to watch for the green light to come on when charging, and take the battery out right away, and every few days I check the voltage using the LF2X internal voltage reading circuit, keeping track of how close to 3 volts they are.

It seems that charging is when most Li-ions fail, should I do the charging outside?

I guess this is the bottom-line question I have: Are whatever risk there is with these batteries worth the amazing amount of light they provide in the LF2X (double the light from Eneloops)? I'd like to make an informed choice, so any help from the CPF community will be appreciated.

 

[mudman cj]

I haven't seen anything in the way of statistics for safe Li-ion use. It is very difficult to even find reports of incidents with Li-ion cells, though not with lithium primaries.

Even with a protection circuit in the light, that only prevents the cells from being deeply discharged by the normal operation of the light. If something were to cause a dead short of the battery, nothing would prevent it from becoming too hot and beginning a thermal runaway reaction which ends in . The thought of a Li-ion cell bursting within a sealed aluminum tube in my pocket is disconcerting to say the least. Even though it is possible, it is also unlikely that a quality light like the LF2 could short the battery. That said, I carry a cousin of the LF2 (Extreme III) loaded with an AW 10440 in my pocket daily. The smaller the cell, the less energy it has to release in the event of an accident, so from that perspective the 10440 is at the safest end of the spectrum for unprotected Li-ion cells.

Charging is most dangerous when the cell has been over-discharged or when charging continues past the nominal cut off of 4.20V. Unprotected cells are at the mercy of the charger to stop charging at the right point. A malfunctioning charger could cause them to , so caution is advised when charging them. Over-discharged cells should be very slowly charged back up to >3V before putting them into a regular charger to prevent dangerously high charging currents. Many members choose to charge them in some sort of protective enclosure, and also monitor the charging process.

 

[1dash1]

OrlandoLights:

For your edification:
The Welcome Mat
MDs Lithium Ion Guide
http://batteryuniversity.com

You've already taken some right steps: purchased high quality li-ion cells, using a charger that is dedicated for charging 10440's, pulling the cells as soon as the light turns green, and are applying the cells in an application with a discharge protection circuit. Most importantly, you are alert for the potential danger.

Other prudent measures:

1. Don't drop or otherwise physically abuse the cells. (One of the more obscure ways of abusing cells is via too-tight-battery-tubes. Tightening the head or tail cap can crush batteries.)

2. Periodically examine the cells for signs of damage, leaks, dents, bulges. (Just because the cell is dented doesn't mean that you have to throw it out, but it does raise a red flag and you should scrutinize it more often. On the other hand, if there are any telltale signs that the cell has vented, I'd suggest that you immediately remove it.)

3. Only charge cells when you are physically present, just in case something goes wrong.

4. Periodically, touch the cells in the charger case, to check that they are not overheating.

5. Periodically, check your starting and ending voltages to get a "feel" of how long it should take to recharge the cells from a certain level of depletion to full charge.

6. Install a cutoff timer to automatically turn off the charger, just in case you forget. (This is something increasingly necessary at my age. )

7. If you rotate cells, check the starting voltage of the cell that you've stored and are about to put into service. The voltage drop (other than rebound effect) from the time that it was freshly charged should be negligible.

8. Properly store the cells at room temperature. Plastic AAA cases are fine. (I store my larger cells in penny- and dime-size plastic coin tubes.) If you plan on storing them for extended periods, it is recommended that you discharge them to approximately 3.9~4.0 volts to maximize the their longevity.

9. Label your cells so that they are individually identifiable. (I number them with a Sharpie. If I purchased just one cell, I label it with a simple number, e.g., "1". If I purchased a set of cells, I label them with numbers and alphas, e.g., "2A, 2B, 2C, 2D".) Labeling ensures that I can keep track of inventory - particularly dates. I can easily tell whether two cells came from the same purchase or which one is older. Others keep track of the total number of cycles each cell has been recharged.

10. When using multiple li-ion cells in series, be careful that they are properly matched (voltages, capacities). Mismatched cells are a high risk situation that you should be aware of and avoid.

11. Do not throw Li-ion cells away in the regular trash. Turn them in to your local hazardous waste recycling center.

Except for the last two items, I don't expect you to do everything on the list. However, if you check them every once in a while, you'll soon become familiar enough with your cells that you can tell when they are misbehaving.

 

[OrlandoLights]

Thanks for the information and the links. Very helpful in clearing up some of my questions. I will take the precautions listed, and will charge the 10440s outside at a sheltered outlet that has a ground fault circuit interrupter.

I suppose if these Li-ion cells were blowing up frequently, we'd be some of the first to know about it at this site.

At one of the links I read that it's is best to keep the Li-ion above 3.5 volts. Am I reading that correctly? The LF2X protection circuit cuts off at 3 volts I think.
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[DM51]

Please post in the correct forum. It is obvious that this topic should have been posted in the Batteries section. I'm moving it there now.

 

[mudman cj]

The protection circuit kicks off at 3V under load. That would correspond to a higher voltage - somewhere around 3.5V - once the load is removed. Cell voltage 'rebounds' after deep discharges and can take several minutes to settle.

 

[torpeau]

You've already taken some right steps:

Thank you for putting so much advice in one place. It is tiresome for everyone to say to be careful with Li-Ion batteries, but making people do searches to find out what care is needed.

 

[mdocod]

I'm curious, how much current does this little pocket rocket pull from a li-ion cell?

If it's over ~500-600mA, then it's probably pretty hard on the cell, and would increase the risk of having a cell explode, especially while charging.

This is my biggest concern with miniature pocket rockets that use really small li-ion cells, like CR2 and AAA size. With low capacity comes low safe current limits, but from what I understand, a number of these designs completely ignore the safe limits of the cells.

Eric