1. The generation of electromotive force of lead-acid batteries

After the lead-acid battery is charged, the positive plate lead dioxide (PbO2), under the action of water molecules in the sulfuric acid solution, a small amount of lead dioxide and water produce dissociable unstable substances - lead hydroxide (Pb (OH) 4), hydroxide ions in the solution, lead ions (Pb4) remain on the positive plate, so the positive plate lacks electrons after the lead-acid battery is charged. The negative plate is lead (Pb), which reacts with sulfuric acid (H2SO4) in the electrolyte to become lead ion (Pb2), which is transferred to the electrolyte, leaving two extra electrons (2e) on the negative plate. It can be seen that when the external circuit is not connected (the battery is open), due to chemical action, there is a lack of electrons on the positive plate, and excess electrons on the negative plate, as shown in the figure on the right, there is a certain potential difference between the two plates, which is the electromotive force of the battery.

2. Electrochemical reaction of lead-acid battery discharge process

When the lead-acid battery discharges, under the action of the potential difference of the battery, the electrons on the negative plate enter the positive plate through the load to form the current I. At the same time, chemical reactions take place inside the battery. After each lead atom on the negative plate emits two electrons, the resulting lead ion (Pb2) reacts with the sulfate ion (SO4-2) in the electrolyte to form insoluble lead sulfate (PbSO4) on the plate. The lead ion (Pb4) of the positive plate gets two electrons (2e) from the negative electrode, and becomes the divalent lead ion (Pb2), which reacts with the sulfate ion (SO4-2) in the electrolyte to form the insoluble lead sulfate (PbSO4) on the plate. The oxygen ion (0-2) hydrolyzed from the positive plate reacts with the hydrogen ion (H) in the electrolyte to form the stable substance water. Sulfate ions and hydrogen ions present in the electrolyte move to the positive and negative terminals of the battery respectively under the action of the electric field, forming a current inside the battery, forming the entire loop, and the battery continues to discharge outwards. When discharging, the concentration of H2SO4 decreases continuously, the lead sulfate (PbSO4) on the positive and negative electrodes increases, the internal resistance of the battery increases (lead sulfate is not conductive), the electrolyte concentration decreases, and the electromotive force of the battery decreases.

3, lead-acid battery charging process of electrochemical reaction charging
The current power supply (charging pole or rectifier) should be connected to the outside, so that the material generated by the positive and negative plates after discharge can be restored to the original active material, and the external electrical energy can be converted into chemical energy storage. On the positive plate, under the action of external current, lead sulfate is dissociated into bivalent lead ion (Pbz) and sulfate anion (SO4-2), because the external power supply continues to absorb electrons from the positive electrode, the free bivalent lead ion near the positive plate (Pb2 continues to release two electrons to supplement into tetravalent lead ion (Pb4), and continues to react with water. Eventually lead dioxide (PbO2) is formed on the positive plate. On the negative plate, under the action of external current, lead sulfate is dissociated into bivalent lead ion (Pbz) and sulfate negative ion (SO4-2), because the negative electrode constantly obtains electrons from the external power source, the free bivalent lead ion (Pb2) near the negative plate is neutralized into lead (Pb), and is attached to the negative plate with fuzzy lead. In the electrolyte, the positive electrode continues to produce free hydrogen ions (H) and sulfate ions (SO4-2), and the negative electrode continues to produce sulfate ions (SO4-2). Under the action of the electric field, hydrogen ions move to the negative electrode, and sulfate ions move to the positive electrode, forming a current. At the later stage of charging, the electrolytic reaction of water will also occur in the solution under the action of external current.
4. Change of electrolyte after charging and discharging of lead-acid battery
It can be seen from the above that when the lead-acid battery is discharged, the sulfuric acid in the electrolyte continues to decrease, the water gradually increases, and the specific gravity of the solution decreases. It can be seen from the above that when the lead-acid battery is charged, the sulfuric acid in the electrolyte continues to increase, the water gradually decreases, and the specific gravity of the solution rises. In actual work, the charging degree of the lead-acid battery can be judged according to the change of the specific gravity of the electrolyte. Use and maintenance of maintenance-free lead-acid batteries In recent years, with the deepening of the two-grid transformation of power systems, high-frequency switching power supplies and maintenance-free lead-acid batteries manufactured by switching power supply technology have been widely used. However, due to the lack of operation experience, the maintenance of DC power supply, especially the battery, is not in place, so that the reliability of DC power supply can not be effectively guaranteed.