Comparison of Dynamic Charge Acceptance Tests on Lead-Acid Cells for Carbon Additive Screening

Including a certain amount of carbon in the negative active material is currently the state-of-the-art method to improve the dynamic charge acceptance (DCA) of lead-acid batteries. The DCA is a key parameter of batteries used in microhybrid cars where brake energy recuperation is implemented. To find the optimal carbon additive, it is essential to test the carbon both in short-term and long-term tests. This work investigates the long-term and short-term DCA of 2 V, 2.5 Ah lead-acid cells and correlates the results with the external surface area of the carbon. Five different carbons with tailored particle size (27-633 nm) and external surface area (7.1-159.3 m2 g-1) are employed as additives in the negative electrodes. The charge acceptance of cells according to the charge acceptance test 2 (SBA), the DCA (EN) test, and the run-in DCA test (Ford) is increased via an increase in the carbon external surface area. A correlation between the short-term tests and the first week of the run-in DCA test is established for the carbon impact. After several weeks of run-in DCA test, the carbon effect is diminished and only a differentiation between high and low DCA cells is possible.