Page 219 - Handbook of Battery Materials

188 6 Lead Oxides

b

c

a

d

Figure 6.7 Section of a tubular plate: a, lead-alloy spine
(grid); b, active material (PbO 2 ); c, tube, (in this example,
fabric of polyester fibers); and d, bottom seal of plastic
caps.
The advantage of tubular plates is the comparatively high utilization of the active
material, which results in a rather low weight in relation to capacity. These features
have two causes, namely:
• The central current-collecting spine produces uniform current flow across the
active material.
• The mechanical support by the tube allows the use of fairly light active material.
This means high porosity and a high utilization factor.
A disadvantage for tubular plates is the fact that a minimum tube diameter
between 6 and 8 mm is required for economic production, but the tube diameter
corresponds with the plate thickness, and lead–acid batteries with such thick plates
are inferior for high-rate discharge.
The production of tubular positive plates is in principle similar to that of pasted
plates. A number of manufacturers use the same gray oxide as the basic filling
substance. Sometimes the portion of red lead or minium (Pb 3 O 4 ) is increased
above 25 or even to 100 wt%. The latter is more economic when the manufacturer
runs his own minium plant; then the expense of the chemical oxidation of lead
oxide (PbO) to minium (Pb 3 O 4 ) may be compensated by reduced formation cost.
Furthermore, curing is not required, because of the high oxidation state, and the
battery starts with full capacity when formed.
Different methods are in use for plate filling. The material can be filled as a
powder with the aid of vibrators. Other techniques use a slurry of lead oxide or
even a paste, as described above [26].