Archimedes-Based Glycerol Displacement for Electrode Porosity Measurement in Lead-Acid Batteries

Summary

Here, we present a simple and low-cost glycerol displacement method based on Archimedes' principle for measuring lead-acid battery electrode porosities. The method demonstrates good reproducibility and is safer than traditional techniques, requiring low-hazard chemicals and equipment. Combining the technique with microstructural analysis by X-ray diffraction provides information on battery electrode properties and degradation.

Abstract

The performance of lead-acid batteries is highly dependent on the structural and surface properties of the electrodes' active materials. Besides the importance of the material's phase composition at any given time in application, its surface area and porosity contribute to the overall performance of the battery. Mercury porosimetry, which uses a representative sample of the active material for its analysis, has traditionally been used to measure the porosity of battery plates. Apart from the possibility of inducing cracks and cavities in the material while taking the sample, many laboratories have moved away from the use of mercury due to its toxicity. The Archimedes-based glycerol displacement technique has the advantage of being a simple method that considers the porosity of the entire battery plate. Even though the method might not give detailed information on the material's pore volume distribution, reproducibility is achieved for individual plates as well as groups of plates taken from either a single cell or six cells from a battery. The method calculates porosity based on the material's absolute and envelope density, which makes use of absorbed glycerol volume to measure the average porosity over the entire plate. Lead-acid batteries are usually subjected to aging mechanisms that affect the active material's structural integrity and surface properties. This study describes the use of the glycerol displacement technique for the measurement of battery plate porosities, combined with powder X-ray diffraction material characterization to understand the degradation mechanisms of batteries that were subjected to capacity life cycling and calendar aging or shelf life, respectively. The results showed that the failure mechanisms of batteries are significantly different and that both the chemical and physical properties of the active material are interdependent; therefore, one cannot rely on a single analytical tool only to interpret a failure mechanism.

Introduction

The lead-acid battery is one of the oldest commercial rechargeable batteries. In 1859, French physicist Gaston Plante demonstrated the battery's working principle by submerging two lead plates in sulfuric acid. The potential for commercialization was realized only 20 years later, when improvements to the technology were made in using pasted plates that allowed the battery to be discharged and charged through a reverse current¹.

Even in the early stages of the invention, the significance of the exposed surface area and the porosity of the battery material became evident. It was understood that the larger the surface a....

Protocol

NOTE: The protocol is similar to the one previously described by Ferg et al.⁷. The equipment and reagents used in the study are listed in the Table of Materials. An image of the equipment used for the porosity measurement of the electrodes is presented in Figure 2.

Figure 2<....

Results

Capacity tests were conducted on three commercially purchased 12 V, 7.2 Ah VRLA lead-acid batteries at the C₁₀ rate to a lower voltage limit of 10.5 V. All capacity tests were performed at 25 °C. Upon receipt, the batteries were recharged at 14.8 V for 10 h, with a maximum current of 2.9 A. This was followed by two C₁₀ capacity tests with a standard recharge step at 14.8 V for 24 h at 2.9 A maximum. The results of the initial C₁₀ capacities are summarized in Table 1.

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Discussion

Capacity tests showed that Battery 1 delivered 92% of the rated capacity (6.62 Ah), Battery 2 delivered 50% (3.58 Ah) with only a partial recovery of 3.32 Ah even after a repeated recharge step, and Battery 3 delivered 91% of the rated capacity (6.57 Ah) (Table 1).

Variations in the concentration of H₂SO₄ within the PAM pores, resulting from chemical reactions that occur in the plates during capacity cycling, influence the structure and morphology of the .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Aeris benchtop powder X-ray diffractometer	Malvern Panalytical B.V., Almelo, The Netherland		For the microstructural analysis
Balance Attachment with crocodile clips			To allow for the weighing of the saturated and submerged plate
Battery cells (12 V, 7.2 Ah)	N/A	N/A	Any
DIFFRAC.EVA V 4.3	Bruker AXS GmbH, Karlsruhe, Germany	Version 4.3	Phase identification software
DIFFRAC.TOPAS V6	Bruker AXS GmbH, Karlsruhe, Germany	Version 6	Phase quantification software
Digital Electronic Balance	Dixon Science, China	EG5001-A	Digital Electronic Balance with a maximum capacity of 500 g and an accuracy of 0.01 g
Laboratory central vacuum line			To apply vacuum to the container to facilitate the infiltration of glycerol into the plates.
Laboratory Jack	Karl-Kurt Juchheim Laborgeräte, GmbH, Germany	2290	To raise the glycerol container until the top of the plate is just submerged
Powder sample holders	Malvern Panalytical B.V., Almelo, The Netherland		For holding powder samples for XRD analysis
Sample Preparation Station	Malvern Panalytical B.V., Almelo, The Netherland	9,43,00,17,70,101	To enable easy back-loading of powders into the sample holders for XRD analysis
Sturdy frame structure			Any
Suitable container with lid			Any
Telescopic crocodile clip			For submerging the plates in the glycerol
Vacuum Pressure Guage	WIKA Alexander Wiegand SE & Co. KG, Klingenberg, Germany	Model: 611.10	To measure the pressure of the applied vacuum