Investigation on Internal Short-circuit through AGM Separators in VRLA Batteries.

In VRLA(valve-regulated lead-acid) batteries with short plate-to-plate distance for high rate discharge applications, internal short-circuit through a thinner AGM(Absorptive Glass Mat) separator is one of the most serious problems. There, however, were no effective methods to observe such a phenomenon simply and evaluate the resistivity against the short-circuit of the separator quantitatively. We have newly established a simple separator evaluation method, in which a direct current is applied to an electrochemical cell consisting a couple of lead-alloy electrodes with a sandwiched separator in a PbSO4-saturated aqueous solution and the time until the abrupt voltage drop due to the short-circuit of the cell is measured. It was found that the smaller were average pore sizes and total pore volumes of separators, and the larger were their thicknesses and resistances, the superior were their resistivities against the short-circuit. Unexpectedly,the maximum pore sizes of separators were not related to the time reaching the short-circuit. These results exhibited very good agreement with those by actual batteries. It is expected that the improvement of separators will be accelerated by applying this method.