Long Term End-Of-Life for NiMH cells?

[MrAl]

Hi there,

As i realized in another thread, even as little as 100 discharge/charge
cycles can lead to a very long cell life if we only look at the d/c cycles,
but what else affects the life?

For an example, say we have to recharge a cell once every 60 days.
After something like 16.4 years we reach the 100^th cycle, and we
might figure we have another 400 cycles to go, but i am
now wondering if something else about the chemistry might end
the life of the cell first after maybe 10 years.

 

[bfg9000]

Electrolyte is probably one of the most closely held trade secrets for capacitors and batteries, and those are probably continually being tweaked, so the chemistry is likely very stable by now for the big brands. Competitors can analyze the composition of the electrolyte and try to guess the sequence of steps that would produce a replica, but the recent failing Taiwanese capacitor fiasco showed us it's not so easy to guess right even when you hire away some of their engineers

There's been some discussion here about insulators failing and generating internal shorts, especially on the highest capacity cells (supposedly those compromise on insulator thickness to make room for more working material). Apparently each cycle causes some mechanical wear as sharp dendrites form.

The only mode of failure I've experienced with NiCds is leakage from failed seals. Even 30 year old NiCd cells here still work fine if they haven't leaked, and they are a lot less likely to leak if kept charged up with some pressure.