Operando Investigation of Lead-Acid Batteries

Title: Operando observation of internal structural changes of a lead-acid cell by synchrotron X-ray micro computed tomography
Authors: Kim, et al.,
Journal: Journal of Power Sources Link

Lead-acid batteries remain an attractive option for rechargeable cell technology due to their low cost and good durability, despite having a lower energy density compared to Li-ion batteries. In this study, the authors successfully demonstrated the chemo-mechanical behavior of a lead-acid cell during formation and cycling using operando characterization. They employed X-ray microtomography and energy-dispersive diffraction with a custom-designed cell that mimics real testing conditions.

X-ray microtomography, with a voxel resolution of less than 1 μm³, enabled visualization of structural changes within the cylindrical electrode containing a Pb wire. Crystallographic changes associated with phase transitions were captured using energy-dispersive diffraction during 180° tomography acquisition. The diffraction results during formation aligned with the widely accepted mechanism: PbO first converts to PbSO₄, then to PbO₂ in the positive electrode, while PbO is reduced to Pb in the negative electrode. A decrease in normalized peak areas indicates low utilization of the cell during cycling. Tomography revealed that void formation and growth caused by paste pulverization during formation led to surface changes relative to the internal volume of the positive electrode. In the negative electrode was observed void formation distinctively different from and a volume decrease as opposed to that of the positive electrode, reflecting the phase change and possibly highlighting the role of generated gas species. Further, a corrosion behavior around the Pb wire was different between the two electrodes.

The work provides real-time insights into the structural evolution of the lead acid battery electrodes during the early operation, with sufficient detail to capture the intricate process of phase transformation and gas generation. However, the analysis in the paper focuses mainly on the formation stage rather than the actual cycling of the cell - not elucidating the structural origin of the continuously reducing capacity utilization. Nevertheless, the combined use of X-ray microtomography and energy-dispersive diffraction represents a powerful approach for non-destructive analysis of commercial cells.