Overpressure vent mod idea

I have a couple of high drain flashlights which I consider modding with overpressure vents. I use fairly good protected li-ion cells in them but was thinking that an extra layer of safety wouldn't harm. Here are my current thoughts on vent placement and design:

I was thinking of placing the vent at the tailcap if possible, here is a ms paint drawing of what I had in mind:

I'd appreciate your input : )

Makes sense to me, but remember the cells will be hot and therefore larger so may tighten up in the tube when venting. I sincerely hope you never need to find out because the result is not likely to be fun.

Still, it is important to get the thing as far away from you as possible if you think it is going to vent. The gases produced when a lithium ion cell vents are extremely bad for you.

Hydrofluoric acid is the nastiest and can be produced in quantity.

Cribbed from here:

Update on the Navy's Lithium Battery Safety Program

A venting of a lithium ion battery may release

• Flammable organic electrolyte (e.g. PC-EC-DMC)

• LiPF6 -- this material is reactive with water; forms HF acid

• Carbon either as carbon or water reactive lithiated graphites

• LiNiCoO2 or other lithiated oxides and heavy/transition metals

• Metal foils and fragments (copper or aluminum)

• Methane, hydrogen, carbon monoxide (electrolyte decomposition


I knew that you should generally avoid contact with anything that leaks out of cells/batteries since it might be toxic and/or corrosive but I did not know that hydrogen fluoride is formed when li-ion cells vents. HF(g) and HF(aq) is seriously nasty stuff, eats through glass and causes severe burns and/or death on skin contact (just read their MSDS).

The vent is only for preventing or mitigating a catastrophic failure of the aluminum body. I know it probably won't have an effect on the amount of toxic emissions but my main goal with the mod is to avoiding getting shot with tailcaps by my flashlights like what nearly happened in the TK monster and the "Ultrafire 3000mAh exploded" thread. The cells themselves should not expand much unless their vents are blocked or defect, so I don't think that heat expansion would not be an issue.

Just modded a Romisen RC-M4 tailcap with a switch boot vent.

But really any flashlight (with tube form) has been exploited popping the body rather than the sides, like a pipe bomb?

I believe that the body will endure...and out through the threads, driver or head (More like a rocket than a pipe bomb).

I have curiosity about it. If you know about this history, please post the links here.

Holy crap they release HF? I've heard before that the vent gases are quite nasty but I never quite realised how nasty.

HF, burning lithium, probably burning lithiated graphite, noxious and inflammable solvents, shrapnel.

I mean, what more could one ask for from an explosion?

I remember being made to work out the energy of an ammonia/fluorine fuelled rocket. It was a lot, but I'd express a very strong preference not to be near the reaction products. I think the consensus in my class was, "Not on my planet!"

Have you seen the "interesting" chemistry blog at


Utterly hilarious.

The author on HF:

"Should some lunatic discover a wonderful reaction that requires the gas, I will respectfully pass. As will everyone else."

Exploding TK Monster

The cells were Sony's equivalent of IMR cells. They got badly out of balance and went boom.


Exploding 18650


CPF has a section on batteries getting frisky.