Temperature-dependent formation of vertical concentration gradients in lead-acid batteries under PSoC operation – Part 1: Acid stratification

In micro-hybrid vehicles, the starter battery is subject to heavy cyclic loads. Results of these cyclic loads are vertical concentration gradients (acid stratification). For this study, it was analyzed systematically how different temperatures influence the formation and reduction of acid stratification. To this end, flooded lead-acid batteries were cycled during a cycle test with 17.5% depth of discharge at −5 °C, 3 °C, 27 °C, and 60 °C. To determine the extent of acid stratification caused by the cycling, the acid density values of the test batteries cycled at four different temperatures were measured using acid density monitoring. The acid densities were measured hourly in 0%, 15%, 30%, 45%, 60%, 80%, and 100% sections in the direction of the perpendicular z-axis of the battery. The measurements showed that the extent of acid concentration gradients is dependent on the temperature, with acid stratification caused by an uneven distribution of current over the height of the plates. Furthermore, it was established that battery discharging as well as battery charging causes an inhomogeneous acid density distribution in the battery electrolyte.