This chapter introduces the analysis of electrode load in lead acid batteries.
It can be seen from the charge-discharge reaction process of lead-acid batteries that the number of ions entering and exiting the positive plate is more than that of the negative plate, and the ions need electrochemical energy to enter and exit. Therefore, the ion reaction of the positive plate during charging and discharging is more severe than that of the negative plate. .
During charging and discharging, there are three reaction lines on the interface between the positive electrode plate and the solution. Each reaction line indicates that a corresponding chemical reaction is proceeding, while there is only one reaction line on the surface of the negative electrode plate. During discharge, SO42- in the solution enters the positive and negative plates respectively. On the negative plate, it combines with Pb to generate PbSO4; but on the positive plate, 4 H+ enters the positive plate and reacts with 2 O to generate 2 H2O, and then return to the solution. In this way, compared with the negative plate, there are 4 more H+ in and out and 2 O out on the positive plate.
In other words, during the discharge process, the number of ions on the positive plate participating in the electrochemical reaction is more than that on the negative plate. In the solution, the resistance to the diffusion movement and the speed of the movement of the same type of ions are the same, so because the positive plate reacts with more ions, the resistance is also greater when the ions move. The actual reaction rate of the positive plate controls the rate of discharge of the entire battery. In order to improve the discharge capacity of the battery, the positive plate should be provided with better ion diffusion conditions.
In the battery, if the positive and negative plate group adopts the structure shown in figure (a), the positive electrode on the side only participates in the reaction on the inner side, and the reaction on the outer side is very small, causing ion movement “crowding”, the internal resistance of the battery increases, and the positive electrode is active Material utilization is reduced. If the structure shown in Figure (b) is adopted, both sides of the positive electrode participate in the reaction, the channel for ion movement is increased, and the resistance is reduced, which is conducive to the progress of the reaction. In addition, the deformation of the positive electrode plate is greater than that of the negative electrode during charging and discharging, and the positive electrode can be deformed symmetrically and evenly when placed between the two negative plates, and the electrode plate is not easy to bend.
Therefore, a structure in which the negative electrode surrounds the positive electrode is often used in lead-acid batteries. In a plate electrode structure, the two outermost sheets are usually always negative electrodes. In a cylindrical structure, the positive electrode is always in the middle. The battery has a separator with a concave grid, and the concave surface always faces the positive electrode to meet the requirement of a large amount of acid required by the positive plate.
In some occasions, it is required to control the release of oxygen in the battery to the minimum. At this time, the battery plate group is made into a “positive and negative” structure. This kind of battery is commonly used in sealed batteries fitted with precision electrical appliances.
The above is the analysis of electrode load in lead acid batteries.
Principle and maintenance of lead acid battery,You can learn more about lead acid batteries.