Surface analysis of commercial lead/acid battery grids

Various lead, lead-calcium-tin and lead-antimony battery grids have been characterized using inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and metallographic microscopy. As-received, commercially produced grids are encapsulated by a thin film of lead(II) and/or lead(IV) oxide along with lead(II) hydroxide arising from atmospheric oxidation of lead. Alloy constituents (i.e., Ca, Sn and Sb) segregate to the grid surface during atmospheric oxidation; Sb(III) and/or Sb(V), Sn(II) and Ca(II) have been identified in the grid oxide layer. The influence of metallurgical structure on the oxidation-induced segregation of minor elements has been evaluated. XPS identified carbonate on the surfaces of as-received non-antimonial grids, while carbonate was not detected on antimonial grids. XPS analysis of grids aged in a humidified environment — to deliberately invoke the formation of lead carbonate — confirmed the formation of carbonate on non-antimonial grids, and the absence of carbonate on antimonial alloys. XRD phase-analysis of aged non-antimonial grids identified the basic lead carbonate hydrocerussite (2PbCO3 · Pb(OH)2). A mechanism is proposed for the antimony-free effect that is responsible for the premature capacity loss of batteries employing non-antimonial grids.