Page 218 - Handbook of Battery Materials

6.4 PbO 2 as Active Material in Lead–Acid Batteries 187

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favored at curing temperatures above 70 C [23], which is of prime interest for the
later mechanical stability of the positive active material.
Single plates are usually cured in special devices (curing ovens or curing
chambers, cf., e.g., Ref. [24]) that control humidity as well as temperature. In
continuous plate production, the drying of the pasted ribbon is correspondingly
controlled. Furthermore, in continuous manufacture final curing can occur after
the plates are separated and inserted into the containers.
6.4.2.2 Tank Formation
Tank formation means that the cured positive and negative ‘raw plates’ are inserted
alternately in special tanks filled with fairly dilute sulfuric acid (generally in the
−3
range 1.1–1.15 g cm ) and positive and negative plates are connected, a number
of each, in parallel with a rectifier. The formation process means that the active
material of the plates is electrochemically transformed into the final stage, namely:
• lead dioxide (PbO 2 ) in the positive electrode and
• spongy metallic lead (Pb) in the negative electrode.
A survey of formation techniques is given in Ref. [25].
Because of the porous material in the raw plate, both substances are produced
in a spongy state with a porosity of about 50 vol%. Tank formation takes between 8
and 48 hours, depending on the plate thickness and formation schedule. When the
formation process is finished, the plates are washed and dried. They can be stored
and later assembled in batteries.

6.4.2.3 Container Formation
The fundamental difference from tank formation is that the battery is assembled
first, then filled with electrolyte, and finally the formation process is carried out
with the complete battery.
During the formation process, the battery is considerably overcharged and
generates both hydrogen and oxygen, with resulting water loss. The concentration
of the filling acid is adjusted in such a way that the desired final acid concentration is
approximated at the end of the formation, and only minor corrections are required;
another method includes dumping of the acid and refilling of the battery during the
formation step. These methods are known as ‘one-shot formation’ and ‘two-shot
formation,’ respectively (cf., e.g., Ref. [25], p. 17).

6.4.3
Tubular Plates

The tubular-plate design for the positive electrodes, shown in Figure 6.7, is
common mainly in European countries for batteries with larger capacities. In this
plate design, the conducting elements are separated from the components that
contribute mechanical support. The grid consists of vertical lead rods in the centers
of tubes that are formed by woven, braided, or nonwoven fabrics.