ESTUDO DOS SOBREPOTENCIAIS E LIMITAÇÃO DA CAPACIDADE DURANTE A DESCARGA DE CÉLULAS DE BATERIAS DE CHUMBO-ÁCIDO EMPREGANDO MODELAGEM E SIMULAÇÃO

Abstract

This work aimed to employ an electrochemical model of lead-acid battery (LAB) cells to obtain, through computer simulations, information that contributes to the development of methods to estimate the state of charge (SOC) and state of health (SOH) of these batteries. After validating the model, the behavior of its variables during a discharge and the consumption of active material along the positive and negative electrodes, which is directly related to the capacity and to the SOC, were explored. The causes of the drop in LAB capacity with the increase of the discharge current were investigated and related to the overpotentials that are developed in the electrodes. Both the efficiency sensitivity of the use of the LAB cells' active material to the empirical and geometric parameters used and which one of these parameters has the most significant effect on the performance at different discharge rates were analyzed. Capacity estimates of LAB and its cells by the empirical Peukert equation, widely used for this purpose, and an equation presented by D’Alkaine et al. were compared and debated under what conditions their applications are valid. Three exponential decay equations, with the same objective, have been proposed and their results compared with Peukert's empirical equation. Due to the accuracy in estimating the capacity and low complexity, the presented equations can be easily used in battery management systems (BMS) for monitoring the SOC and, in two these equations, the distinction of the parameters obtained for different application LABs allow the characterization and categorization of batteries. The study of the amount of electrolyte transport in the positive electrode of LAB cells revealed two distinct exponential decays of capacity between the region adjacent to the electrolyte reservoir and the center of the electrode. These decays were modeled for cells under different operating and aging conditions and ion flow currents were calculated from the parameters of the two-phase exponential decay equation presented. The analysis of the behavior of these ionic flux currents makes it possible to determine which is the predominant aging mechanism and SOH estimate. In addition, a method to separate and quantify the overpotentials that occur in LAB cells during discharge is proposed and the result of three discharge rates is compared.