Coin Cell Battery Assembly – When to Worry About Shorting

batteriescoin-celllithiumshort-circuit

At work I assemble coin cell batteries (lithium metal) inside a glovebox. I'm a bit confused as to when I do and do not have to worry about shorting. For example, say I'm making this battery:

Cathode: LCO

Anode: Lithium metal

There is various advice online that states to be careful touching the battery to metal because you could short the battery. However, I am still confused about when exactly I need to worry about it. For example, if I drop the lithium metal on the stainless steel floor of the glovebox, it's ok, But if I have partially assembled the battery and touch the stainless steel tweezers from the lithium metal to the LCO, a short occurs? Or if I have 2 coin cell batteries assembled, and they touch each other, they both short. Can someone explain what is the the underlying explanation behind this? When do I need to worry about shorts?

Best Answer

As soon as there is a piece of metal (or other conductor) connecting the 2 poles of the battery (+ (top and side) and - (bottom)), you get a short circuit, which is bad.

The good thing is, that the side (connected to +) is not going down totally to the bottom, so if the coin cell falls flat on the bottom, there is no short (because side and top don't touch the floor).

Basically, there is no position on a flat (conductive) ground where the coin cell can be shorted, excepted if it falls diagonally, where there is a slight risk : but this position is unstable, so the short circuit will last no longer than a fraction of a second (which is not good, but will probably not cause any significant damage).

There are other situations where continuous short might happen (and that's really bad) :

  • the battery ends up on the "border" of a metallic box, with the bottom (-) of the cell on the bottom, and the side (+) touching the wall. This is not very likely (but possible) on a flat metallic box, but becomes very likely if the box is tilted (the battery will slide down until touching the "vertical" wall (that is now a bit inclined)
  • you connect both poles with a conductive object (ex : tweezers)
  • you hold the battery in such way that you cause the short (depending where you try to put it, it can happen quite easily if you tilt the battery too much

So to summarize : it is not a problem if the coin touches a metallic object, as long as the metallic object don't touches the 2 poles at the same time (still, avoid to let it touch any metal excepted the connectors of its final destination)

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