Ask A Scientist Chemistry Archive

     
name         Carol P.
status       educator
age          50s

Question -   What are the reasons that batteries go dead?
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Batteries, as you know, are nothing more than oxidation-reduction reactions
wherein the cathode (reduction) compartment is separated from the oxidation
(anode) compartment so high potential electrons will have to travel via a 
wire
from the anode side to the cathode side - and so that the potential energy of
these electrons may be siphoned off for work.

In theory then, some of the ways batteries can "die" are if one of the
reactants in the anode or cathode side get depleted, or if the concentrations
of the solutions within the compartments become so high that they inhibit
chemical reactions from taking place.

In practice however, batteries are very complex systems of 
oxidation-reduction
that it is very difficult to actually pinpoint specific chemical reactions.
So, many things can happen. In wet-cells such as those in cars, breaking the
connection points (the lead honey-comb structure may fall apart), will cause
the battery to die. In dry cells that are not sealed properly, the production
of gases as a result of the oxidation-reduction reaction result in the 
battery
not being able to be recharged. Side-reactions may occur which deplete the
starting reactants.

Roberto Gregorious
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Batteries contain chemicals that supply electrons (electric current) from
one "pole" of the battery to the other. The substances differ depending upon
the particular type of  battery. When the chemical substances are "used up"
they no longer can supply the electrons and there is no longer an electric
current. That is, the battery is "dead". Some batteries (for example car
batteries) can be recharged. Recharging involves supplying electric current
to the battery from an outside source to regenerate the original chemicals
in the battery. Other batteries CANNOT BE RECHARGED. In fact trying to do so
can cause the battery to rupture or explode. It is potentially dangerous to
try to recharge those. The small "coin-shaped" batteries used in calculators
etc. cannot be recharged. Rechargeable batteries are usually clearly labeled
as such. Do not attempt to recharge any battery that does not specifically
state that it is "rechargeable" and even then one has to have the correct
recharger.

Vince Calder
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Consumer alkaline batteries go dead because they are used up.
All the oxidizer-fuel inside is satisfied, having received the electrons 
it wanted,
and a corresponding amount of the reducing-fuel has donated those electrons.
If you never allowed any current out of the battery, but it died from 10 
years aging anyway,
one could say it had "internal leakage currents" that used up its capacity.

Battery capacity is measured in Ampere-Hours.
A typical AA cell has roughly 1 ampere-hour of charge.
It will be used up by running 0.25 amp for 4 hour (a penlight).
or by internally leaking 1/100,000 amp for 100,000 hours (ten years storage).
Or any trade-off in between.

Those batteries are "primary" batteries.  People make fuel-chemicals, put 
them together, get some electricity, then it is dead.
It's not rechargeable, because of a combination of
   a) chemistry barriers in way of charging,
            which makes charging require a higher voltage than the battery 
 gives when discharging, plus,
   b) there are alternative chemical reactions which start to happen at 
 those higher voltages,
            using up all the charging current, disintegrating the battery, 
 or making dangerous gasses.

Rechargeable batteries are reactions which just happen to not have those 
problems.
But then they become disabled when recharging recreates the original 
chemicals, but at the wrong locations.
The reducing-fuel is usually a metal.
If this metal gets re-created in the shape of a wire from one electrode to 
the opposite electrode,
the battery is shorted out all the time, for both charging and discharging.
This happens to NiCad's and lead-acid car batteries.

A similar problem happens to car batteries.
The reducing-fuel is lead, the oxidizer-fuel is sulfuric acid, and the 
"Ash" product is lead sulfate.
If the ash shakes off the lead plate where it formed and falls through the 
liquid bath to the floor of the battery case,
it then is out of the stream of recharging current (from plate to opposing 
plate), and it cannot get back to where it can be used.
One fix is to turn the liquid into gelatin.  This is the "Gel-Cell", or 
gelled-lead-acid battery.
(Believe me, they do not use "Jell-O" or "Knox".   Silica gel or 
waterglass is more likely.)

I do not know what goes wrong with rechargeable lithium-ion batteries.
But I am sure there is something.
Batteries seem to be a tricky job.

Jim Swenson
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