Balanced float charging of VRLA batteries by means of catalysts

The internal-oxygen cycle characterizes the VRLA battery as the main reaction during float charging. When it reaches a high efficiency, almost all the oxygen evolved at the positive electrode is reduced at the negative electrode. But, the two secondary reactions, hydrogen evolution and grid corrosion have also to be considered. With a highly efficient internal-oxygen cycle, the rates of these secondary reactions have to be equal. Otherwise, the basic law would not be fulfilled that equal currents must flow through both electrodes. As a consequence, the proportion between hydrogen evolution and grid corrosion determines the polarization of both electrodes. Only if hydrogen evolution and grid corrosion are well balanced, negative and positive electrodes are polarized sufficiently to keep their full charge. With the technical product ´battery´ the desired balance is often not reached, and if the hydrogen evolution rate is high compared to grid corrosion, partial discharge of the negative electrodes occurs during float charging. Incorporation of a catalyst into the unbalanced cell is a promising possibility to solve the problem. It also reduces the efficiency of the internal oxygen cycle, since the catalyst recombines a certain portion of the oxygen before it can reach the negative electrode. As a consequence, a correspondingly increased amount of hydrogen must be generated at the negative electrode. This again requires an adequate polarization and so ensures full charge. Simultaneously, the positive electrode is less polarized, and grid corrosion reduced