Application of Inelastic Neutron Scattering to Understand Lignosulfonate Stability and Lead Battery Failure Mechanisms
The purpose of this research was to leverage inelastic neutron scattering to evaluate the stability and persistence of lignosulfonates in lead battery negative electrodes, and establish the technique for enabling the rational, hypothesis-driven approach to designing next-generation battery organics.
2V flooded lead batteries were prepared and tested per SAE J537 followed by the Dynamic Charge acceptance test of ILNAS 50342-6 and 17.5% DoD endurance in cycle test. Negative electrodes were harvested following formation, prior to the 17.5% DoD endurance test, and at end of life. Grids were analyzed on inelastic neutron spectrometers VISION (Spallation Neutron Source, Oak Ridge National Laboratory, USA) and MAPS (ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, UK). Peak intensity was used to quantify the lignosulfonate retained in the negative electrode, while concentrations in the electrolyte were determined through UV-vis spectroscopy.
Low-energy spectra (VISION) displayed dramatic changes in peak intensity as the electrodes evolved during testing. Initially interpreted as indicating dynamic lignosulfonate migration between negative electrode and electrolyte, this was disproven UV-vis studies. These features are putatively due to formation of lead hydroxide moieties either in situ or during harvesting.
High-energy spectra (MAPS) revealed a definitive feature attributable to the C-H bonds of the organic expander. Surprisingly, we measured no meaningful differences in the C-H feature intensity between the electrode samples, indicating the lignosulfonate concentration remains unchanged in the electrode throughout the life of the battery.
This finding thus contests a historical assumption about lead battery failure and suggests lignosulfonate decomposition is not a root cause of negative electrode sulfation.
Future work includes evaluating stability of additional organics, as well as electrodes that have failed under conditions known to accelerate sulfate formation. Additional experiments should also be performed to understand the interfacial behavior of the organic and its stability.
Keywords: Lignosulfonate, Vanisperse, Sulfation, Negative, NAM
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