Lead skeleton

Fig. 3.48. Scanning electron micrograph of lead skeleton obtained during first formation stage [55].

The inclusion of the PRU grains in the bulk of the lead skeleton branches indicates that this carbon black type has high affinity to lead. During formation of the negative active material, the carbon particles are adsorbed on the lead surface of the growing lead branch. As these particles are electroconductive, the electrochemical reaction of lead ion reduction proceeds on their surface. The newly formed lead surrounds the carbon grains and thus the latter are incorporated into the bulk of the lead branch of NAM skeleton. 

Microstructure of parts of the inner volume of the current conducting branches of NAM lead skeleton after dissolution of the PbS04 phase. NAM contains 0.2 wt%, 1.0 wt% or 2.0% printex ... 

It follows from all above said that carbon particles interact with the lead active mass, being adsorbed on its surface and/or incorporated in the bulk of the lead skeleton branches. This results in macrostructural changes (reduced median pore radius and increased specific surface area of NAM). Thus, carbon additives alter the very nature of the lead electrode, converting it into a lead—carbon electrode, which will inevitably affect its electrochemical behaviour. The latter will depend on the affinity of carbon to lead, on the electrical conductivity of the carbon additive and on the electrochemical properties of the carbon surface. 

The lead skeleton has a double function it serves as a current-collector for all parts of the active mass and provides mechanical support to the lead crystals which participate in the current generation process. Based on this fact it can be presumed that the capacity of... 

Scanning electron micrograph of skeleton of discharged negative plate after dissolving PbSO crystals [2]. The lead skeleton is unchanged after cycling. 

FIGURE 2.2 Negative electrode structure (a) skeleton of interconnected lead crystals and (b) secondary structure of separate lead crystals deposited on the lead skeleton surface. (From D. Pavlov, and V. Iliev, J. Power Sources, 7, 153, 1981.)... 

During the second stage, reduction of PbS04 to Pb occurs and the lead crystals obtained are deposited on the lead skeleton surface in strongly acidic solution. 

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