INTRODUCTION
Electrochemical noise signals have been used in ,this work to assess the correct formation of porous electrodes of lead-acid batteries. The signals give good indication of the formation quality of the battery electrodes which will determine the performance of the product.
Although several new battery systems are being developed, the lead-acid system is still produced in great quantities and used worldwide due to its reliability, low cost and good operational life. For this reason, research is still carried out and even new designs have been developed to improve the performance of these type of batteries. Most of this research is focused on the main problems that limit the life of a battery and to understand the changes that this system suffers during service, nevertheless very little work has been published directed to the optimum formation of the electrodes in the battery and some way to quantify it. It is well known that the porous structure of the [l] formed electrodes will determine the overall performance of the product and that it is desirable to have reproducible properties of the finished good, which can only be achieved with a reliable production process. Characteristics that determine the performance of the active mass (the material1 that actually takes part in the electrochemical reactions, i.e. PbO2, spongy Pb and H2S0,) which delivers the charge to the load connected to the battery, develop during the formation stage. These include porosity (void volume), internal surface, chemical composition, pore distribution, crystallography, #etc. and as the formation current varies these features will vary too. The efficiency of formation will also change with current formation, low currents will result in less energy spent during the formation process and will allow slow processes to occur (e.g. mass transport). Unfortunately, economic considerations avoid the use of very slow formation current practices. On the other hand, batteries are often treated as units with certain electrical properties and during process & including information, these practices are carried out with little consideration to the electrochemical effects that they have on the fine! product. For these reasons, quality control is very often based on electrical parameters rather than electrochemical.
Electrochemical signals have been analyzed for many systems to obtain relationships that could be used to describe e1ectrochemica.l processes, for example using frequency analysis [2], statistical counting [3], fractal geometry [4], as well as some efforts have been made to describe electrochemical signal generation processes [ 51.
The present work is an effort to identify an electrochemical-based means to help producers have tools that can be used to ensure a good quality product, particularly the formation of porous electrodes. Electrochemical signals or electrochemical noise signals (EN) have already produced tools in practical applications such as in the case of corrosion monitoring in industry [6]. This has been possible thanks to the many works done to identity the origin and characteristics of EN and relate these to the different phenomena associated to the electrochemical system in study. It is now understood that there are electrochemical features related to the morphology (e.g. crystallography, porosity, roughness, etc.) and nature of the interface electrode-solution, including the positive electrodes of Pb-acid systems [7, 8,9].
