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The negative electrode supplies
electrons to the external circuit (or load) during
discharge. In a fully charged lead-acid storage battery the
negative electrode is composed of sponge lead (Pb). The positive
electrode accepts electrons from the load during
discharge. In a fully charged lead-acid battery the positive
electrode is composed of lead dioxide (PbO2 ). It
should be noted that the electrodes in a battery must be of
dissimilar materials or the cell will not be able to develop
an electrical potential and thus conduct electrical current.
The electrolyte completes the internal circuit in the
battery by supplying ions to the positive and negative
electrodes. Dilute sulfuric acid (H2 SO4
) is the electrolyte in lead-acid batteries. In a fully
charged lead-acid battery, the electrolyte is approximately
25% sulfuric acid and 75% water.
The separator is used to electrically
isolate the positive and negative electrodes. If the
electrodes are allowed to come in contact, the cell will short-circuit
and become useless because both electrodes would be at
the same potential. The type of separator used varies by
cell type. Materials used as separators must allow ion
transfer between the electrolyte and electrodes. Many
separators are made of a porous plastic or glass fiber
material. The above components are housed in a container
commonly called a jar or container.
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