What is Best Practice for preparing to dispose of Lithium Ion (18650) cells?

[wobbly]

I have a bunch of quite old Lithium Ion 18650 cells salvaged from laptop batteries over the years, they are all in good condition as far as I know.
I no longer need them so I want to take them to the local recycling centre.  Having them stored in my garage is making me nervous as they might pose a fire hazard ().

They are all charged (to about 4.0 V) and I think it's probably best to discharge them before I have them recycled.

I'm looking for guidance and perhaps a few good ideas about how I can responsibly dispose of these while not wasting all that stored energy!
The cells are all individuals, not ganged together in packs any more.

Question 1:
I reckon there's at least 300 Watt Hours of power in this collection.  Are there any ways I can somehow "decant" the energy from these cells into a single large cell or battery (perhaps a 12V one, that would be nice!)?
I'd be happy with doing this one 18650 cell at a time, I'm in no rush.  Is there something I can buy (inexpensively) off-the-shelf that can do this?  If not I'd be willing to build a circuit if one exists.

Question 2:
How low a voltage should a Lithium Ion 18650 cell be discharged in order to a) recover the most energy from it, and b) make it safest for the people doing the recycling?

The cells have been well cared for and never over- or under-charged.

What would you guys do in this situation?

 

[Gyro]

Question 2 first: I would think fully discharged (down to zero volts) would probably be safest. That way there is no danger of high currents and overheating if the cells get crushed or short circuited. Fully discharging would normally damage their capacity, but that's not something you will be concerned about if you are disposing of them. Do it carefully though, irrc, there is only a danger of metallic Lithium deposition if a cell is reverse charged. This can happen to the weakest cells if a series string is discharged. Metallic Lithium could, worst case, be a hazard if the cell is crushed and air/water gets in. The safest way is a resistor across each cell and leave for a few days. Something like 100R would be nice and cool for cheap 1/4W resistors. I'm being very cautious here.

Question 1: The cost of 300Wh of electricity from the mains is around 10p at current rates. Not worth your while - there's no sensible way of harvesting for that, even excluding your time. You could use a white LED and series resistor to harvest some reading light I suppose.

The only other thought, see if somebody trustworthy can make use of them, however if they are old and from multiple different packs, they probably have mismatched capacities making combined use not viable.

[armandine2]

Big Clive says (IIRC) at 3.0 volts these batteries have much less and safer levels of stored energy in them than at full charge - so I would not try to fully discharge them.

I think you have more batteries than you know what to do with - being worried about them is a form of procrastination. 

Do something prosocial 

[wobbly]

The safest way is a resistor across each cell and leave for a few days. Something like 100R would be nice and cool for cheap 1/4W resistors. I'm being very cautious here.

Caution is also my main priority, I've seen too many horror stories on the news of unexpected LI cell fires (e-bikes, public EV buses, Australian power farms).  I don't know much about the statistics of unused cells going bang while in dormant storage, but since I have no use for these things it makes zero sense to keep them.  Thank you for the tip about the energy being so cheap it's not worth saving -- I think I'd gotten used to using these cells for powering flashlights - where a little energy lasts a long time!

I'll build a little jig for connecting some suitable resistors (I've got a bag of 33 Ohm ceramic 3W chonkers around here somewhere) across some 18650 cell holders!

Many thanks. 

[inse]

What about drowning them in a bucket of saltwater outdoors?

[CatalinaWOW]

Step 1.  See if there are any recycling centers in your area that handle batteries

If there are, go to Step 2, if not, find recyclers on line and go to Step 2

Step 2.  Ask the recycler how they want you to handle these batteries.   Then do it the way they suggest.

Since most people who have end of life batteries Lithium Ion batteries don't have your level of knowledge or concern, I will bet that they will tell you to bring them in in their current condition as they are set up to deal with whatever comes in.  But no opinion from an on line forum rules here, the rules are set by those receiving these batteries.

I will second the notion that harvesting the energy is not worth any effort.  Just buying the appropriate parts will cost more than buying a small solar cell and generating an equivalent amount of energy over a few days or weeks and then continuing to harvest that trickle over the couple of decades of life of the cell.

[Geoff-AU]

https://www.sciencedirect.com/science/article/abs/pii/S0956053X18307840

For comminution discharging of Li-ion cells to an SoC of 0% is necessary.

https://www.sciencedirect.com/science/article/abs/pii/S2352152X22013779

Because the cathode and anode poles of the battery react electrochemically in solution, the ions in solution can exacerbate the corrosion of the steel casing and aluminum gasket surrounding the cathode and anode. This occurrence can cause the internal structure of the battery to be exposed to the solution, resulting in battery leakage and solution contamination.

So a salt water bath risks contaminating your water.

Safest method is resistive discharge to 0V.  The second link even proposes overdischarge (small reverse polarity) to avoid the voltage rebound effect, but this can be minimised by leaving the resistor attached for a decent amount of time (day or two).

[CaptDon]

I have a cell holder for the 18650 cells. I have a 47 ohm 2 watt resistor across the terminals. I take my undesirable worn out cells and discharge them for about 2 days one cell at a time. I then take them to the local Lowe's or Home Depot store, both of which recycle batteries. Their ONLY requirement is for exposed connections to be covered in electrical tape. They will take fully charged, no questions asked. The biggest risk of lithium cell fires commonly experienced is with battery packs that have 2 or more cells in parallel. When one cell shorts it must deal with its own heat developed by the short as well as the discharge current of any other cells in parallel. I know personally of 3 office fires started by parallel cell lithium battery packs. Two were laptop fires that occurred in the middle of the night while in charge mode and one fire was a 3 parallel cell camera pack that had sat dormant on a shelf for over a year!! I have converted a Heathkit modulation monitor, an Audio Technica wireless receiver and a DMX light controller board to run on internal lithium batteries. None of the cells have a parallel mate, all of the batteries are 4S (4 in series). 15.8 volts high cutoff for charge with an 80ma. charge current limit. (I don't mind the very long charge times) and I also have an 11.5v low limit discharge cutoff. The maximum drain on all of these devices is similar at around .15 to .2 amps. I do store these devices on metal shelving against a cinder block wall and concrete floor for safety if the worst should happen.

[Kjelt]

Wait till it gets colder use three batteries to power a pc fan and put the rest in series to a big resistor to heat your livingroom for one hour.