The structure and working principle of lead-acid batteries

The structure and working principle of lead-acid batteries

Lead-acid batteries are mainly composed of positive and negative plate groups, separators, containers and electrolyte.

(1) Polar plate. The positive and negative plates of lead-acid batteries are made of pure lead, and effective substances are directly formed on them; some pole plates are made of lead-nickel alloy grids and coated with effective substances. The effective substance of the positive electrode (anode) is lead dioxide, and the effective substance of the negative electrode (cathode) is spongy lead. In the same battery, if the number of plates with the same polarity exceeds two, they are connected by metal strips and are called “plate groups” or “plate groups”. As for the number of plates in the plate group, it varies with its capacity (electric storage capacity).

(2) Spacer. In various types of lead-acid batteries, except for a few special combinations of plates with large gaps, spacers must be inserted between the two plates to prevent the positive and negative plates from contacting each other and causing short circuits. There are several types of separators, such as wood, rubber, microporous rubber, microporous plastic, and glass, which can be appropriately selected according to the type of battery.

(3) Container. The container is used to hold the electrolyte and support the electrode plate. There are usually four types of glass containers, lead-lined wooden containers, hard rubber containers and plastic containers.

(4) Electrolyte. The electrolyte of lead storage battery is made by diluting high-purity concentrated sulfuric acid with distilled water. Its specific gravity depends on the battery type and the electrode plate used, and is generally between 1:200/15°C to 1:300/15°C. The electrolyte (dilute sulfuric acid) used in the battery must be kept pure and must not contain any impurities that are harmful to the lead-acid battery.

Lead-acid batteries consist of two sets of plates inserted into a dilute sulfuric acid solution. After the electrodes are fully charged, the positive plate is lead dioxide and the negative plate is spongy lead. After discharging, small and soft lead sulfate is produced on both electrode plates, which is restored to the original substance after charging.

The theory of reversible reactions in the charging and discharging process of lead-acid batteries is more complicated. At present, the “double sulfation theory” proposed by Goldstein and Tlipp is generally accepted. The meaning of this theory is that after the lead-acid battery is discharged, the effective substances of the two electrodes and the sulfuric acid react, and both are converted into the sulfuric acid compound-lead sulfate; when charged, they return to the original lead and lead dioxide.

The structure and working principle of lead-acid batteries
Chemical reactions in lead-acid batteries