X-ray computed tomography for macropore analysis of cured and formed plates in lead acid batteries

When it comes to the properties of lead-acid batteries, macro porosity is seldom considered, even though it influences the active material loading, accessibility of acid into the active bulk material and the structural integrity of the plate. The porosity characteristics of positive and negative cured and formed plates were comprehensively analysed on the micro, meso and macro scale using a combination of BET N2 adsorption, mercury porosimetry and X-ray computed tomography (CT) respectively. Total porosity, pore size distribution, surface area, open and closed pores and surface-area-to-volume were included, where possible, with a plethora of additional data being obtained from X-ray CT analysis. Analysis from a single plate used in Starting, Lighting and Ignition (SLI) type batteries, which included three isolated samples per plate, revealed heterogeneity in macro-porosity across all regions analysed in the negative and positive cured and formed plates respectively. X-ray CT was further applied to thicker plates and a plate from an AGM type battery with a glass mat separator. The use of X-ray CT to study the changes in porosity characteristics can yield valuable insight into the properties of the active material since it remains intact within the grid support of a lead acid battery plate.