Influence of fast charge on the life cycle of positive lead–acid battery plates

A criterion has been found for determination of the factor limiting the discharge of the lead dioxide plate. When on discharge with moderate currents, an arrest or a shoulder appears between 1.0 and 0.7 V (vs. Hg/HgSO4 electrode) in the potential transient, then the charging potential transient features a peak at the beginning of the curve. The capacity is limited by the interface. The life cycle of the battery is short. This phenomenon is known as PCL effect. When a broad maximum occurs in the potential transient on charge, this indicates that the electrode capacity is limited by zones of high resistance in positive active mass (PAM) near the interface. The capacity is determined by the lead dioxide active mass. It has been established that the life of the positive plate is proportional to the current density during the initial charge stage. A sol–gel–crystal mechanism of the charge processes is proposed to explain this effect of fast charge on electrode life. The high rate of the electrochemical reaction leads to high oversaturations of the Pb(OH)4 sol and to fast formation of gel–crystal PbO(OH)2/PbO2 particles, which not only form new agglomerates tightly connected to the PAM skeleton, but also fill in and improve the contacts between the agglomerates. The latter process has the effect of “welding” of the PAM skeleton. Moreover, the higher concentration of the Pb(OH)4 sol affects the macro- and microstructure of the PAM, which in turn has an influence on the electrochemical reaction. Impedance measurements have evidenced different values of the electron transfer resistance in electrodes charged at high and low currents.