Development of positive electrodes with an SnO2 coating by applying a sputtering technique for lead-acid batteries

In order to prevent positive grid corrosion and to obtain a long life for positive electrodes of lead-acid batteries, a conductive and corrosion resistant SnO2 (tin dioxide) layer was formed on a Ti (titanium) substrate by a conventional dip-coating method. However, it is impossible to apply this method to a Pb (lead) substrate, because the dip-coating method needs a calcination process, at a temperature higher (conventionally from 450 to 600°C) than the melting point of Pb (Tm: 327°C). For this reason, an SnO2 layer to protect the substrate against passivation and/or corrosion was formed on Ti and/or Pb electrodes by applying sputtering, a method which is often used in the production of semiconductors. This improved electrode, with an SnO2 layer, was not corroded at all, even though the thickness of the SnO2 layer was only about 15 μm. The biggest problem of the SnO2 layer is that it dissolves in sulfuric acid when the positive electrode is polarized below 0.5 V (versus Pb/PbSO4). This suggests that this electrode should not be subjected to deep discharge.