The charge-discharge reaction of the electrode proceeds only at the interface in contact with the electrolyte. As can be seen from Figure 1, the reaction of the positive electrode must be PbO2 and SO42- contact, 0 and H contact, the reaction of the negative electrode must also be Pb and SO42- contact, no contact can not occur. The active material on the electrode plate is of agglomerate structure. When the sulfuric acid is injected into the battery, only the surface of the agglomerate is in contact. In the interior of the lead particle, since it is not in contact with the acid, it does not participate in the chemical reaction of charge and discharge, but only provides an electronic conductive circuit. In order to increase the contact area between the electrode plate and the electrolyte, the electrode plate is always made into a porous and loose sponge during manufacturing, but it is impossible for us to break the lead powder into a single molecule, and it is impossible for the electrode plate to have two layers of molecules. So thin, therefore, the utilization rate of lead in the battery cannot reach 100%, usually only about 50%.
During the charging process, the gas is generated, merged, extruded from the plate, and there is a process until it is completely separated from the plate. After the gas is generated on the surface of the electrode plate, it cannot quickly overflow to form bubbles, covering part of the electrode plate, reducing the area of the electrode plate that the sulfuric acid really contacts, and the area participating in the effective charging reaction is also reduced. At this time, although the charging current remains unchanged, because the part converted into chemical energy is reduced, and the part consumed in decomposed water increases, the charging efficiency decreases, and the temperature rise of the battery begins to rise. In order to use the power reasonably and protect the battery, the charging current should be reduced to adapt to the changes inside the battery.