The microscopic model of discharging in the case of a lead-acid battery

August 10, 2015 // By Szabo Levente
The microscopic model of discharging in the case of a lead-acid battery
Szabo Levente explains a microscopic model of discharging in the case of a lead-acid battery.


Modeling of the operations of the batteries with electrical circuits has been developed in multiple dimensions from a simple capacitor to very complicated electronic circuits. These models take into consideration the state of the charge, the nominal voltage, capacity, aging, temperature, the discharging current, self discharge and other external and internal factors.

The purpose of this article is to understand the phenomena occurring at the electrode area by building a simulation model and its simple electronic circuit during the discharge of the battery. The voltage is the result of the accumulation of the electrons at the negative pole and the absence of the electrons at the positive pole. In an equilibrium state, when the external circuit is open, the charge and discharge reactions occur equally in both directions in the area of the electrodes.

When the external circuit is closed, the electrons from the negative pole will migrate to the positive pole through the external circuit, because the electrical field will act upon them. In the area of the negative electrode, where the reactions take place, the equilibrium is disrupted by the changes of the electron concentrations that occur. The system tends to equilibrium by increasing the quantity of the discharging reactions and decreasing the quantity of the charging reactions in both electrode areas. Initially the difference between the count of the discharging and charging reactions is at its  maximum. During the time when the primary elements decrease and the secondary elements increase in the electrolyte, the battery is discharging. Henceforth we study and model the electrochemical phenomena in the unit of the electrode area.
Processes inside a unit of electrode area in the reaction zone

We consider a unit of an electrode area in the reaction zone from the negative electrode to have the dimension of one molecule, and this area can release multiple electrons at the same time in a single reaction. For simplicity we

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