From the chemical reaction equation of lead-acid batteries, it can be seen that PbO2 is listed on the positive electrode plate and Pb is listed on the negative electrode plate. The conductivity and physical properties of these two substances change very little with temperature. Therefore, it can be said that the temperature effect on the discharge performance of lead-acid batteries is due to sulfuric acid, as only its activation performance (dissociation degree and ion migration rate) is temperature dependent.
The temperature of the sulfuric acid electrolyte in lead-acid batteries is high, resulting in more capacity output, while the temperature of the electrolyte is low, resulting in less capacity output. The reason for this situation is not only due to the decrease in temperature, but also because the solubility of lead sulfate in the sulfuric acid electrolyte will decrease when the temperature decreases, which will inevitably cause saturation of lead ions around the electrode plate, forcing the formation of dense lead sulfate crystals. This dense crystal hinders the sufficient contact between the active substance and the sulfuric acid electrolyte, thereby reducing the capacity output of lead-acid batteries.
If the temperature of the sulfuric acid electrolyte is high during discharge of lead-acid batteries, it will reduce the supersaturation of PbSO4 on the surface of the electrode plate in the sulfuric acid electrolyte, which is conducive to the formation of loose lead sulfate crystals, producing a coarse and strong PbO2 layer during charging, thereby extending the service life of the active material on the electrode plate. If the temperature of the electrolyte is too high during charging of lead-acid batteries, it will accelerate the diffusion of the electrolyte, intensify the corrosion of the plates and grids, and thus shorten the service life of lead-acid batteries.
Practice has shown that:
(1) During charging of lead-acid batteries, as the temperature of the electrolyte increases, the corrosion of the plates and lead alloy grids increases.
(2) In lead-acid batteries, the corrosion of the positive electrode plate lead alloy grid is greater than that of the negative electrode.