Leaf and hexagonal grid designs for lead-acid battery. An EIS analysis

This work explore the fabrication of two distinct metallic grid architectures of positive electrode, namely hex-agonal and leaf shapes, within the aim of improving the economic and the qualitative electrical performance aspects of lead-acid batteries in the automotive industry. By following a well-established aging procedure, Electrochemical Impedance Spectroscopy has been employed for their characterization by using different grid-acidic electrolyte interface changes. Two particular, parameters were investigated in order to predict the evo-lution of batteries lifetime performance: the resonance frequency single parameter, and time-dependent analysis of Constant Phase Element at 75 % State of Charge. Single resonance frequency fluctuations have been monitored at each PEIS step, in which we plotted the imaginary part of the impedance as function of frequency. An per-formance of battery lifetime has resulted for leaf battery than for hexagonal model, by comparison of the exponential-like increment degradation curve vs cycle number at SoC = 100 %. By using the effect of Q(1) linear decay in the equivalent Randle circuit at 75 % SoC, we obtained for both models a smooth trend of the linear decay slopes, in particular in the second part of their lifetime, in agreement with previous investigated cells, demonstrating that is a robust feature, present in all fabricated cells. A fitting linear regression analysis depending on cycle number was applied to both batteries, in order to highlight the degradation grade of these curves. Another linear fit calibration of the degradation speed was applied for the second sector of batteries lifetime, pointing out a positive correction for the Q(1) linear decay with similar to 30 % for leaf cell over the hexagonal model, but less than previous investigated rectangular models or the industrial type. This suggests that the current homogeneity on the rectangular models during the charge-discharge processes is better distributed in the lower and upper parts of the plates than for hexagonal or leaf electrodes, being spotted here by the effect of current uniformity on their Randle circuit. The homogeneity of the electric field is not ensured by the shape of individual sectors, rather by their size and orientation.

Automated summary

This study explores the fabrication of two different metallic grid structures to improve the economic and electrical performance of lead-acid batteries in the automotive industry. The characterization of these structures was carried out using Electrochemical Impedance Spectroscopy. The results showed that the leaf-shaped battery had better performance than the hexagonal model. The analysis of degradation slope and degradation speed indicated that the rectangular model had better current uniformity.