Theoretical considerations
There is a large number of publications on the formation of lead/acid battery plates. These contain valuable information on the chemical and electrochemical reactions taking place during the operation. The discrepancies observed in the results and conclusions can be explained by: l the use of proprietary plates of so-called industrial quality l important changes in manufacturing methods, in particular as regards plate porosity and production speed, leading to high-temperature pastes. This is not a criticism, and general knowledge on plate behaviour during formation is well founded, but is of a proprietary nature, i.e., many factories and research centres have conducted extensive investigations; not all of this has been made available in the open literature.
Correctly, attention has always been focussed on the positive plates because: 0 formation efficiency is low 0 battery life is determined by the positive plates. In simple terms, in the formation of positive plates PbOz is obtained mainly from PbSO,, i.e., the active mass reacts with the sulphuric acid. This is a rate-limiting step. The sulphation depends on the diffusion of the acid which, in turn, depends strongly on the nature of the plate. The oxidation of the sulphate is very inefficient: the PbSO, is a non-conductor, while the presence of PbO, favours the evolution of oxygen instead of the oxidation of sulphate. Further, acid diffusion again exerts a significant influence.
The formation of the positive plates is more a complex technical problem of porosity and diffusion than an electrochemical one. Particle size and paste density play important roles, defining capacity and life. Laboratory work seeks for the best formation; industry is looking for fast formation and is satisfied with a practical, acceptable result. The basic electrochemical work generally tries to define an optimal current density, taking into account temperature and electrolyte concentration.
Moreover, the final product is identified by chemical analysis, spectroscopy (in particular for the amounts of a-PbO, and /I-PbO,), and measurements of the electrical performance.