(1) Positive and negative plates
In order to increase battery capacity, the internal structure of lead-acid batteries contains multiple sets of positive and negative plates. Each set of positive and negative plates is welded horizontally to form a parallel set of positive and negative plates. The positive and negative plates that make up the set of positive and negative plates are interlocked (the positive plates and negative plates are arranged alternately). The active substance on the surface of the positive electrode plate is lead dioxide (PbO2), which is dark brown in color (therefore, the positive electrode of the lead-acid battery casing is marked with a dark brown "+" sign), while the active substance on the surface of the negative electrode plate is sponge like pure lead (Pb), which is blue gray in color (the negative electrode of the lead-acid battery casing is generally marked with a "-" sign). Insert partitions between the positive and negative plates.
In each individual battery, the number of negative plates is one more than the number of positive plates (to ensure even discharge on both sides). The more effective the amount of surface active substances on the electrode, the longer the discharge time, i.e. the larger the capacity, under a certain discharge current.
The thickness of the domestic negative electrode plate is 1.8mm, and the positive electrode plate is 2.2mm. Lead acid batteries produced abroad often use thin plates with a thickness of 1.1mm~1.5mm. Thin plates can increase the specific capacity of batteries and improve starting performance (personal understanding: starting performance refers to the starting performance of internal combustion engines).
(2) Partition board
In order to reduce the internal resistance and size of the battery, the positive and negative plates of the battery should be as close as possible. In order to prevent short circuits caused by contact between adjacent positive and negative plates, a partition should be used to separate the positive and negative plates. The separator is also a carrier of electrolyte, capable of absorbing a large amount of electrolyte, and has many micropores, which can make the electrolyte flow smoothly.
(3) Electrolyte
During the charging and discharging process of a battery, the electrolyte not only conducts electricity but also participates in chemical reactions. The electrolyte of lead-acid batteries is prepared by mixing pure sulfuric acid and distilled water in a certain proportion. The electrolyte density of lead-acid batteries is generally between 1.24 and 1.31g/cm3, and the selection of electrolyte density varies slightly depending on different regions and climatic conditions.
(4) Overflow valve
The overflow valve is located at the top of the battery, providing safety, sealing, and explosion-proof functions.
