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BATTERIES 347

Table 7.14 Advantages and disadvantages of the Leclan-
ch´ e cell
Advantages
It is cheap to make
It has a high energy density
It is not toxic
It contains no liquid electrolytes

Disadvantages
Its emf decreases during use as the material is consumed
It cannot readily deliver a high current

anode. We sometimes add starch to the paste to provide additional stiffness. The
juxtaposition of the zinc ions with the zinc of the casing forms a redox buffer,
thereby decreasing the extent to which the potential of the zinc half-cell wanders
while drawing current.
Table 7.14 lists the advantages and disadvantages of the Leclan-
ch´ e cell. Alkaline manganese
cells are broadly sim-
ilar in design to the
The lead–acid battery Leclanch´ e cell, but they
contain concentrated
KOH as the electrolyte
The lead–acid cell was invented by Plant´ e in 1859, and has remai-
instead of NH 4 Cl.
ned more-or-less unchanged since Faur´ e updated it in 1881. The
lead–acid cell is the world’s most popular choice of secondary
battery, meaning it is rechargeable. It delivers an emf of about
2.0 V. Six lead–acid batteries in series produce an emf of 12 V.

Table 7.15 Advantages and disadvantages of the lead–acid battery

Advantages
It is relatively easy to make, and so can be quite cheap
It has a high energy density, producing much electrical energy per unit mass
It can readily deliver a very high current

Disadvantages
It contains toxic lead
Also, since it contains lead, its power density is low
The acid is corrosive
Furthermore, the acid is a liquid electrolyte
Given time, lead sulphate (which is non-conductive) covers the electrode. Having
‘sulphated up’, the energy density of the battery is greatly impaired. To avoid
sulphating up, it ought to be recharged often