> The NiMH thread got me to thinking about a problem I've had with a couple of
> Lithium-Ion batterys that don't want to take a charge anymore

> I was wondering if some sort of high-voltage, narrow-pulse, low-frequency
> "zapping" methodology might (even temporarily) "repair" these things?  I
> recall hearing about something like that, but can't find the link (and I
> don't know if it was Li-Ion or other).

        The method you are referring to is used with NiCad cells when they
become shorted internally. Sometimes metal whiskers form in the cell between
the plates. These whiskers are produced electro-chemically as the cell
discharges and the chemicals change state. If the cell could be recharged,
the whiskers would be reabsorbed and the short would disappear. The problem
is that any charging current is shunted through the whiskers, bypassing the
chemical process which would cause the problem to go away. Discharging a
large electrolytic capacitor through the cell sometimes melts the whiskers,
allowing a charging current to complete the recovery process. As long as the
current flows through the short, there is little chance to dump energy into the
cell itself; if the short vanishes suddenly, the discharge energy could vaporize
the electrolyte and cause a steam explosion. This is why the process is not
widely recommended.


John N. Power

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