A detailed introduction to the working principle of lead-acid batteries

1. The emergence of the electromotive force of lead-acid batteries. After the lead-acid batteries are charged, lead dioxide (PbO2) on the positive plate, under the use of water molecules in the sulfuric acid solution, a small amount of lead dioxide and water will form a dissociable and unstable substance--hydroxide. Lead (Pb(OH)4), hydroxide ions are in the solution, and 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 the sulfuric acid (H2SO4) in the electrolyte to become lead ions (Pb2). The lead ions are transferred to the electrolyte, leaving excess two on the negative plate. One electron (2e). It can be seen that when the external circuit is not connected (the battery is open), due to chemical purposes, 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. This is the battery. The electromotive force. 2. The electrochemical reaction of the lead-acid battery discharge process. When the lead-acid battery is discharged, under the use of the potential difference of the battery, the electrons on the negative plate enter the positive plate through the load to form a current I. At the same time, a chemical reaction occurs inside the battery. After each lead atom on the negative plate releases two electrons, the generated lead ions (Pb2) react with the sulfate ions (SO4-2) in the electrolyte to generate insoluble lead sulfate (PbSO4) on the plate. The lead ions (Pb4) of the positive plate get two electrons (2e) from the negative electrode, and they become divalent lead ions (Pb2), which react with the sulfate ions (SO4-2) in the electrolyte and are on the plate. The formation of insoluble lead sulfate (PbSO4). Oxygen ions (O-2) hydrolyzed from the positive plate react with hydrogen ions (H) in the electrolyte to generate stable water. The sulfate ions and hydrogen ions in the electrolyte move to the positive and negative electrodes of the battery under the use of the electric field, forming a current inside the battery, the entire loop is formed, and the battery continues to discharge outward. During discharge, the concentration of H2SO4 decreases continuously, and the lead sulfate (PbSO4) on the positive and negative electrodes increases, the internal resistance of the battery increases (lead sulfate is not conductive), the concentration of the electrolyte decreases, and the electromotive force of the battery decreases. 3. During the electrochemical reaction of the lead-acid battery charging process, an external DC power supply (charging electrode or rectifier) u200bu200bshould be connected to restore the material generated by the positive and negative plates after discharge to the original active material and transform the external electrical energy. Stored for chemical energy. On the positive plate, under the use of external current, lead sulfate is dissociated into divalent lead ions (Pb2) and sulfate negative ions (SO4-2). Because the external power source continuously draws electrons from the positive electrode, the free two near the positive plate The valence lead ion (Pb2) continuously releases two electrons to supplement it and becomes the tetravalent lead ion (Pb4), which continues to react with water, and finally generates lead dioxide (PbO2) on the positive electrode plate. On the negative plate, under the use of external current, lead sulfate is dissociated into divalent lead ions (Pb2) and sulfate negative ions (SO4-2). Because the negative electrode continuously obtains electrons from the external power source, the free two near the negative plate Valence lead ions (Pb2) are neutralized to lead (Pb), and are attached to the negative electrode plate as flocked lead. In the electrolyte, free hydrogen ions (H) and sulfate ions (SO4-2) continue to appear in the positive electrode, and sulfate ions (SO4-2) continue to appear in the negative electrode. Under the use of an electric field, hydrogen ions move to the negative electrode and sulfate ions The ions move towards the positive electrode, forming an electric current. In the later stage of charging, under the use of external current, the electrolysis reaction of water will also occur in the solution. 4. The 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 increases, the water gradually decreases, and the specific gravity of the solution increases. 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. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous article: How to detect whether the lithium ion battery reaches the safety index