In Situ Characterization of Metastable Pb 3 O 5 and Pb 2 O 3 Phases During Thermal Decomposition of PbO 2 to PbO.

Nonstoichiometric lead oxides play a key role in the formation and cycling of the positive electrodes in a lead acid battery. These phases have been linked to the underutilization of the positive active material but also play a key role in the battery's cycle life, providing interparticle adhesion and the connection to the underlying lead grid. Similar phases have previously been identified by mass loss or color change during thermal annealing of PbO 2 to PbO, suggesting that at least two intermediate PbO x phases exist. Using multiple, in situ analysis techniques (powder diffraction, X-ray absorption, X-ray photoelectron spectroscopy) and ex situ nuclear magnetic resonance measurements, the structural conversion and changes in the lead oxidation state were identified during this process. Isolation of the PbO x phases enabled confirmation of Pb 3 O 5 and Pb 2 O 3 by diffraction and the first 207 Pb NMR measurement of these intermediates. The thermodynamic and kinetic stability of these intermediates and other reported polymorphs were determined by density functional theory, providing key insight into their origins and variation of PbO x structures found in previous studies.