| Lead acid battery is the most wildely-used secondary battery for its high cost performace, even though it is the oldest one. However, some failure modes such as sufation of negative plate and corrosion of positive grid lead to the end of service life of lead acid battery. Also, the rapid development of electric vehicles needs lead acid battery could be charged quickly. The aim of this thesis is to mine the relationships between the behavior during the electrochemical redox process of lead electrode and the performance of lead acid battery, probe into the essence of sufation and to find the restoring method, investigate the corrosion film of positive grid and some other relative phenomena, and find the simple and effective fast charging method through the investigation of electrochemical behavior of lead in sulfuric acid solution.The influence of the oxidative status and structure of the surface of lead electrode on the anodic peaks for Pb(?) to PbO2 and oxygen evolution was investigated via cyclic voltammetry. It was found that the source of lead sulfate on the surface of lead electrode has significant influence on its anodic peaks. When lead sulfate was from the oxidation of metallic lead, the overpotential of oxidation of PbSO4 to PbbO2 was so high and the characteristic peak of PbbO2 formation overlapped with the anodic peak of oxygen evolution. On the contrary, when lead sulfate came from the reduction of PbO2, the anodic peaks for oxidation of PbSO4 to PbbO2 appeared and the overpotential was reduced about 0.7V. Therefore, two types of PbSO4 with different reaction activity were found. The PbSO4 from the oxidation of pure Pb is denoted as PbSO4(O) and has low reaction activity; and the PbSO4 from the reduction of PbO2 is denoted as PbSO4(R) and has high reaction activity.The samples of PbSO4(O) and PbSO4(R) were prepared by electrochemical method and were characterized though cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The results showed that PbSO4(O) had compact structure, high ion-transfer resistance and low electrochemical reaction activity, whereas PbSO4(R) had loose structure, high electrochemical reaction activity and low ion-transfer resistance. The XRD results showed that the two types of PbSO4 belong to the orthorhombic PbSO4, which suggests that the significant difference in reaction activity of the two types of PbSO4 should not be attributed to the different crystal forms of PbSO4. It was proposed that during the discharge process, PbSO4(R) was formed on positive plate and PbSO4(O) with low activity was formed on negative plate, which is the essence of sufation of negative plate. It is sugguested that the inert PbSO4(O) on negative plate could be transformed to active PbSO4(R) via inverse charging. The restore test result showed that the new capacity after inverse charging was more than twice of the initial value. The discovery of the different reaction activity of the two types of PbSO4 provides the mechanism for the methods of the inverse charging or repeating redox process at positive potential ranges to reactivate sulfated negative electrode, and can also bring other novel recovering method, which means as long as PbSO4(O) is transformed to PbSO4(R), the sulfated negative electrode could be reactivated.The occurrence of "anodic excursion peaks "(AEPs) was investigated in detail via cyclic voltammetry (CV), linear sweep voltammetry (LSV) and low rate linear sweep voltammetry combined with potential step method. It was obtained that AEPs was closely related to the corrosion film of lead electrode formed at positive polarization potential, and the occurrence of AEPs depended on the passivated PbSO4(O) layer on the surface of lead electrode and positive polarization enabling the oxidation of Pb(?) to Pb(?). It was found for the first time that four AEPs occurred without reduction of PbbO2 to PbSCO4, which is in confliction with the conventional understanding that AEPs would appear accompanying with a large reduction peak for PbbO2 discharge. Therefore, we gave the mold for the formation of AEPs and proposed that AEPs corresponds to the oxidation of intermidate PbOn compounds which is the incomplete oxidation product of PbO. The compactness of PbSO4(O) layer and the electric field strength in PbSO4 layer determines the electro-migration rate of OH- through PbSO4(O) layer, which determines the oxidation degree of PbO and therefore determines the occurrence of AEPs. When lead electrode was polarized at high anodic potential, due to the inhibition of the transfer of OH" by passivated PbSO4(O) layer, the inner PbO was only oxidized to PbOn, and in the cathodic scanning, PbOn was continuely oxidized to PbO2, forming AEPs. Also it was suggested that the four AEPs correspond to the oxidation of PbOn compounds with different values of "n". About the phenomenon that AEPs is situated before and after the peak for reduction of PbO2, we propsed that it is attributed to the excursion of peak potential of reduction of PbO2 caused by the concentration of H2SO4, but which has no effect on AEPs.The effects of polyhydroxyl compounds and halide ion on AEPs were investigated through voltammetry. The results showed that polyol increased AEPs, but halide ion eliminated AEPs. When the amount of OH groups of polyols is less than 6, AEPs increased linearly with the increasing of amount of OH groups of added polyols. The SEM results showed that the lead electrode corroded in electrolyte containing glucose or sorbitol had a compact structure, which prevented the oxidation of PbO to PbO2, forming lots of PbOn, and therefore AEPs was increased. So, it was concluded that polyols such as glucose could be used as corrosion inhibitor of positive grid or the antioxidant of dry charged negative plate.The variation of AEPs with the concentration of added sorbtiol was investigated through CV and the inhibition of sorbitol on corrosion of lead electrode was investigated via Tafel polarization measurements. It was obtained that as the concentration of added sorbtiol was increased, the trend of the increase of AEPs and the trend of the decrease of corrocion current were similar, both of which varied linearly first and then became stable, which means that AEPs is surely relative with the inhibition of corrosion of lead electrode. Therefore, the measurement of AEPs could be applied to characterize the effect on additives on corrosion resistance of lead alloy grid, which means the additives that could increase AEPs have good anticorrosion effect. The coverage of sorbitol on lead electrode was calculated via the corrosion current from Tafel curves, and the adsorption isotherms was obtained from the coverage which obeyed Langmuir adsorption isotherm mold. The obtained adsorption free energy was a negative value, which means that the adsorption of sorbitol on lead electrode was a spontaneous process. It was proposed that the 2-hydroxy in polyols could be interacted with Pb resulting in the adsorption of polyols on the surface of lead electrode. So, the corrosion was inhibited and therefore AEPs was increased.The reversibility of Pb/PbSO4 electrode was studied through adding additives. It was found that tetrabutylammonium bromide (TBAB) increased the reversibility of Pb/PbSO4 electrode and shortened the reduction peak of PbSO4, which means that TBAB may shorten the charging time and could recover the capacity quickly. The result of charging test showed that the charging time of battery with TBAB was less than half that of the blank battery, which means that this simple method could be effective on fast charging and does not need complicated charging mode. This method would decrease the cost and energy consumption of fast charging. |
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