Sophia Baucknecht

The dynamic charge acceptance (DCA) of lead-acid batteries has become one of the most important criteria for micro-hybrid vehicle applications to reduce fuel consumption and CO2 emissions by using regenerative braking [1]. Novel additive combinations, involving carbons in the negative active mass (NAM), have resulted in a two- to threefold increased DCA [2]. However, the properties of carbon that improves DCA require further investigation. It was found that the increase of the external surface area (SA) of the carbon increased the DCA of lead-acid cells [3]. Therefore, in this work, similar carbon additives with a distinct difference in the external SA were used as additives for the NAM to ensure that differences in DCA are remarkable. The main focus of this work is the electrochemical impedance spectroscopy which is used as a characterization technique to identify different processes within the cells due to different external SAs of carbon additives. Therefore, impedance spectra for the complete cell, the positive half-cell and the negative half-cell are measured at different state of charge (SoC), ranging between 50 and 95% SoC, different superimposed DC currents (0DC, ±0.5·I20 till ±3·I20) and different temperatures (xx °C). The correlation between the external SA of synthesized tailored carbon additives, the DCA and the parameters of the impedance spectra is outlined. Thereby, the electrochemical impedance of the negative half-cell in a Nyquist plot can be represented via semi-circles, which are smaller for test cells using carbon additives with high external SA (high DCA) and larger for test cells containing carbon additives with lower external SA (low DCA).

[1] K. Peters, D. A. J. Rand, P. T. Moseley, in Lead-Acid Batteries for Future Automobiles, 1st ed. Elsevier, Amsterdam, 2017

[2] E. Karden, AABC 2018, Mainz.

[3] J.Settelein, B.Bozkaya, H.Leicht, M.Wiener, G.Reichenauer, G.Sextl, J. Energy Storage 2018, 15, 196.