Failures of SLFBs are believed to be associated with PbO₂ deposition/dissolution at the positive electrode. Although failure mechanisms are not well understood, passivation and shedding of PbO₂ are suggested to decrease efficiency of SLFBs. Formation of a passivation layer of non-stoichiometric PbOx is found to be correlated to proton activities. PbO₂ deposits of poor adherence and low quality are also observed to occur when the electrolyte is high in acidity. We therefore employ sodium acetate (NaOAc) as electrolyte additive, and successfully extend the cycle life of SLFBs by over 50%.

In this study, effects of acetate additive on electroplating of PbO₂ are investigated. Surface morphology and mechanical strength of electroplated PbO₂ via electrolyte with and without NaOAc are examined by scanning electron microscopy (SEM) and nano-indentation, respectively. Acetate-assisted electrolyte is found to substantially enhance deposited film strength and leads to a more integrated and smoother surface. Crystal structures, grain sizes, and grain orientations of plated PbO₂ are analyzed via x-ray diffraction (XRD) and electron back scatter diffraction (EBSD), and very different phase distributions and grain orientations are observed for electrolyte with and without NaOAc. Electroplating and oxygen evolution kinetics are further investigated by rotating disk electrode (RDE) experiments. Our findings elucidate acetate additive effects on electroplating of PbO₂ in SLFB systems and shed lights on battery life extension.