In order to investigate the discharge/charge process of the active materials for the positive electrode in the lead-acid battery, a PbO
2 thin film was deposited on a piezoelectric quartz crystal by reactive sputtering, and then the in situ observations of the mass change in the PbO
2 electrode were carried out using the electrochemical QCM technique. The PbO
2 thin film produced by sputtering a pure Pb target in an oxygen plasma was identified as a mixture of α-PbO
2 and β-PbO
2. The discharge process by a very low current suggested that the reaction of PbO
2→PbSO
4 proceeded first and then the reactions such as PbO
2→PbO, PbO→Pb and PbSO
4→Pb occurred one after another. During the potentiostatic discharge/charge process, most of the discharge reaction of PbO
2→PbSO
4 was completed at the beginning of the process, while the charge reaction of PbSO
4→PbO
2 slowly proceeded. The conversion ratio of the PbSO
4 back to the original PbO
2 during charge was estimated to be only 52% or so based on the mass change. Right after the start of both the discharge and charge, the mass decreases in sharp intervals as the result of the dissolution-precipitation mechanism were confirmed by the electrochemical QCM technique for the first time. The repetition of the discharge/charge increased the ratio of β-PbO
2 to α-PbO
2 in the charged product. Moreover, there were PbSO
4 crystals of various sizes on the PbO
2 surface after discharge, and the small crystals in the lower part dissolved earlier than the large ones to be transformed into the PbO
2 particles of tens of nanometers during the charge. These results suggest that the refinement of the PbSO
4 crystals during discharge is an important factor to improve the charge of the active materials for the positive electrode.
抄録全体を表示