Page 215 - Handbook of Battery Materials

184 6 Lead Oxides

An advantage of this plate design is the short distance that has to be passed by
electrons to reach the current conducting core; the disadvantage is the weight of
this thick core made of pure lead.
Negative electrodes in Plant´ e batteries are of the pasted type.

6.4.2
Pasted Plates

The plate support in lead–acid batteries is usually called the ‘grid.’ In most batteries
the grid has to provide both mechanical support for the active material and
electronic conductivity for the collected current.
Figure 6.5 shows the design of a grid and its horizontal and vertical cross-sections.
This figure indicates the origin of term ‘grid’ for this kind of plate support.
The network of lead wires must provide optimum mechanical support to the
pellets of active material that fill the void space. Sufficient conductivity has also
to be provided by the grid. Grids for positive and negative electrodes are usually
similar. In batteries designed for extended service life, the positive grid is made
heavier to provide a corrosion reserve. For very thin electrodes, a lead foil is used
as the substrate and current conductor.
The mechanical support of the active material is of minor importance when
additional support is provided, for example, by envelopes or tubes (cf. Section
6.4.3).

6.4.2.1 Manufacture of the Active Material
The production of the active material for positive and negative electrodes starts
with the same substance: a mixture of lead oxide (PbO) and metallic lead called
gray oxide or lead dust. It is a fine powder that contains 20–30 wt% of lead (Pb). The
size of the primary particles is in the range of 1–10 µm. Larger agglomerates are
usually formed.

Figure 6.5 Grid of a lead–acid battery with thicker walls
and a rectangular mesh. One corner and cross-sections in
vertical and horizontal directions (from Ref. [14]).