BCI separator oxidation testing

The lead acid battery separator serves to prevent electrode shorting while providing high ionic current conductivity for battery operation. Normally the separator must provide this service for years in the hostile, oxidizing environment of a lead acid battery without being the life limiting component. For low cost polymeric materials with highly porous structures this can be a major challenge. Battery and separator manufacturers have long desired to predict the life of a particular separator without merely installing the separator in a battery, placing it in service and waiting for failure. The results could take years and require many samples to cover the extremes of conditions. Even accelerated battery life tests require long testing periods. While laboratory accelerative bench tests are obviously needed, they should be tempered with the understanding that different batteries are exposed to a variety of conditions that can alter the mode and rate of separator degradation. As a further complication, each separator type may have unique failure mechanisms. The BCI Subcommittee on Separator Testing concluded that a single test, or set of oxidation tests of a fixed duration, cannot fully predict the degradation of all separator types in all batteries under all conditions. Therefore, while not embracing any particular test method, the committee has agreed to offer several basic methods consolidated from its members that can be modified or adapted for a particular separator or battery condition. The author summarizes the oxidation effects on separators of several of these tests as conducted by GNB Technologies and Daramic Inc