The effect and mechanism of bismuth doped lead oxide on the performance oflead-acid batteries

Flooded automotive and motorcycle lead-acid batteries were manufactured fro m three kinds of lead oxides including electrolyzed pure lead (99.99 wt.% P b) oxide, electrolyzed pure lead oxide doped with Bi2O3 (0.02 wt.% Bi2O3) a nd bismuth-bearing refined lead (0.02 wt.% Bi) oxide. The first cranking an d cold cranking curves of the automotive batteries show that there is no ob vious difference among the above lead oxides. Bismuth in lead oxide does no t affect the water loss of flooded batteries. However, bismuth results in t he improvement of capacity and charge-acceptance capability. In discharge, the positive voltage versus cadmium of plates with bismuth decreases more s lowly than that of plates without bismuth. In order to investigate the mech anism of the function of bismuth, three other kinds of test electrodes were prepared from electrolyzed pure lead (99.99 wt.% Pb) oxide, electrolyzed p ure lead oxide doped 0.02 wt.% Bi2O3 and electrolyzed pure lead oxide doped 0.06 wt.% Bi2O3 The cyclic voltammetry curve shows that bismuth has no sig nificant influence on the electrochemical behavior of the positive active-m aterial. There is an opposite result concerning the cathodic polarization c urves between bismuth doped in the electrode and Bi3+ ion doped in the elec trolyte. Bismuth doped in the electrode results in a decrease of the hydrog en overpotential. Conversely, Bi3+ ion doped in the electrolyte results is an increase. The chemical analysis confirms that a trace of Bi3+ ion exists in sulfuric acid solution (e.g. plates soaking, after formation, after cyc ling). A higher porosity is observed in the positive active-material contai ning bismuth by SEM technique. SEM morphology shows that needle-like crysta ls begin to occur after a few cycles. X-ray diffraction phase analysis prov es that the amount of alpha -PbO2 is increased by doping bismuth in to lead oxide. The existing forms, chemical characteristics and electrochemical re actions of bismuth during manufacture and are of lead-acid batteries are de monstrated clearly. The mechanism of the function of bismuth improving capa city, prolonging cycle-life and reducing water loss has been elucidated in detail. (C) 2001 Elsevier Science B.V. All rights reserved.