Modeling of Effect of Double-Layer Capacitance and Failure of Lead-Acid Batteries in HRPSoC Application

Lead-acid batteries fail faster in partial state-of-charge start-stop technology than in SLI application. Accumulation of lead sulfate on negative electrode's surface has been identified as the cause. It is also known that life can be enhanced by increasing capacitance of negative electrode. A bench-marking test cycle is used to explain these observations through a one-dimensional model. It is shown that, at the large discharge current densities used, faradaic reactions in the electrodes are spatially inhomogeneous, and charging is unable to reverse its effects. Consequently, lead sulfate deposit is larger on electrode's surface than at its center. Model uses a rate expression for charging modified to include diffusion of Pb2+, and predicts that sulfate continues to accumulate with cycling. A portion of electrode becomes inactive when volume fraction of sulfate reaches a critical value there. Battery fails when inactive area becomes large. It is shown that double-layer capacitance suppresses the non-uniformity in the faradaic reaction and alters the pattern of accumulation of sulfate. Negative electrode does not benefit from this since its capacitance is low. Sulfate accumulates in positive electrode also, but does not reach critical levels since positive electrode's capacitance is large. This explains the life enhancing effect of capacitance. (C) The Author(s) 2017. Published by ECS. All rights reserved