Formation of negative plates

The electrochemical reactions that proceed during formation of negative plates can be represented by the following equations. represents the equilibrium potential... 

Fig. 3.47. Scanning electron micrograph of crystals within Pb + PbS04 zone during first stage of formation of negative plate [55].

The secondary lead structure of the completely formed plates with or without expander is shown in Fig. 3.57. In NAM without expander, the secondary lead structure covers the skeleton in the form of a smooth layer, whereas the secondary lead structure in the NAM of expander-containing plates comprises individual Pb crystals which are located over the skeleton structure. Hence, organic expanders regulate the processes involved in the formation of both types of structure in the lead active-mass during the formation of negative plates. 

Fig. 3.55. Polarization curves during second hour (first stage — I) and seventh hour (second stage — II) of formation of negative plates with or without expander [66].

Negative-plate formation. The stages in the formation of negative plates have been determined in terms of the zonal processes as presented in Fig. 3.45. The reactions involved in each of the formation stages are presented schematically in Figs. 3.43 and 3.44, and are summarized in Fig. 3.59. The formation can be divided into the following stages. 

The above sequence of reactions indicates that formation of negative plates will proceed in two stages. The difference of 300mV between the equilibrium potentials of the PbO Pb and 3BS Pb... 

Fig. 3.42. Changes in phase compositions of paste and active mass of negative plates during formation [55].

Fig. 3.45. Photographs of cross-section of negative plate during formation (a) prior to formation (b)-(d) during different formation stages, dark regions are Pb- -PbS04 zones (e) completely formed plate [56], Plate thickness is 1.8 mm. This is a vertical cross-section of the plate.

Formation of the plates containing expander is completed within 10 h, while those without expander require 12 h of formation. Hydrogen evolution starts on plates with expander at an overpotential which is 160 mV more negative than that on plates with no expander. 

Fig. 3.59. Schematic of cross-section through structure of negative plate during the formation stage when Pb- -PbS04 zones have covered the whole plate surface.

Processes During Formation of Negative Battery Plates 483... 

Evolution of Pore Structure of Negative Plates During Formation... 

An example of inhibitor treatment of negative plates to prevent oxidation of the sponge lead in the active mass after formation is as follows the washed plates are immersed in a 10—12 wt% solution of boric acid with addition of 1.0—1.5 wt% salicylic acid. The plates are left in this solution for about an hour and are then dried in a drying oven at a temperature of about 130 °C. 

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