The working principle and main structure of lead storage battery

The working principle of lead storage battery

The working principle of lead storage battery when charging and discharging is as follows. During discharge, both the PbO2 of the positive electrode and the Pb of the negative electrode react with sulfuric acid (H2SO4) to become PbSO4, so it is also called “double sulfide reaction”. During charging, the positive electrode PbSO4 is converted to PbO2, and the negative electrode is converted from PbSO4 to spongy Pb. The specific electrode reaction is as follows:

The working principle and main structure of  lead storage battery
Specific electrode reaction of lead battery

The main structure of lead storage battery

Lead battery is mainly composed of anode, cathode, electrolyte dilute sulfuric acid (H2SO4), battery shell, separator, liquid port plug (or safety valve), battery cover and other components. Its basic structure is shown in Figure 1.

The details of each component are as follows.

(1) Positive and negative grids. Lead-based alloys are used, and Pb-5% Sb alloys are generally used for ordinary lead batteries; low-maintenance batteries use low-antimony alloys (Sb content is less than 2%) to reduce water decomposition; maintenance-free batteries use Pb-Ca alloys. In order to improve the performance of the grid, other elements are generally added to the alloy for improvement, such as Cu, As, Cd, Ag, S, Se, Sn, A1, etc. The active materials in the positive and negative grids act as support frameworks and current collectors.

The working principle and main structure of lead storage battery
Figure 1 – Basic structure diagram of lead battery

(2) Positive electrode active material. Using PbO2, other additives are chemical short fibers, anisotropic graphite, conductive

Polymer materials, SnO2-plated conductive glass sheets, Bi2O3, phosphoric acid, cobalt sulfate, etc. As an active material, PbO2 determines the positive electrode capacity. The additives mainly improve the strength of the electrode plate, improve the conductivity and utilization rate of active materials, and improve the cycle performance.

(3) Negative active material. Spongy lead (Pb) is used, and other additives are carbon materials, short fibers, barium stearate, barium sulfate, lignin, humic acid, etc. Spongy lead (Pb) is the active material of the negative electrode and determines the capacity of the negative electrode. The additive mainly improves the strength of the electrode plate, improves the electrical conductivity, oxidation resistance, and inhibits the shrinkage and vulcanization of the active material during the charging and discharging process.

(4) Electrolyte. Dilute sulfuric acid (H2SO4), the general use concentration is 1.25~1.33g/mL. The additive is Na2SO4. Dilute sulfuric acid participates in the flow-forming reaction and can be understood as an active substance. The content and concentration of sulfuric acid affect the discharge capacity, and the additive can inhibit vulcanization and improve the service life.

(5) Separator. Starter batteries used wood separators in the 1950s, and microporous rubber separators dominated from the mid-1960s to the 1990s. By the 1990s, polypropylene (PP), polyethylene (PE) and ultra-fine glass wool (AGM) separators and composite separators appeared one after another. The separator mainly plays the role of isolating the positive and negative plates, preventing short circuit, and maintaining the ion migration channel of the electrolyte. In addition, the AGM separator and GEL also play the role of fixing the electrolyte solution from flowing.

(6) Battery slot. In the past, mobile batteries generally used hard rubber grooves, while stationary use used lead-lined wood grooves. After the 1960s, the plastics industry has developed rapidly. ABS plastic and polypropylene (PP) plastic are used for starting batteries, polyethylene battery tanks are mostly used for traction battery tanks, and modified polystyrene (AS) or ABS plastics are mostly used for stationary battery tanks. The battery tank is the container part of the lead storage battery, and accommodates the electrode group and the electrolyte.

(7) Working bolt/safety valve. There are acid-proof flameproof hydrants, closed hydrogen hydrants and safety valves. The main function is to discharge gas, inhibit acid leakage, and reduce water loss in the battery.

(8) Other lead-acid battery parts. There are mainly lead or lead-antimony alloy parts, iron, copper lead-plated parts, etc., which play the role of battery connection.