Improved lead alloys for lead/acid positive grids in electric-vehicle applications

Currently, the excessive weight of the positive grid is a limiting factor to the increase of the specific energy of the lead/acid battery. With present alloys, a thickness of a few millimeters is a pre-requisite in the processing of a positive grid which is submitted to heavy corrosion during the charge and deep-discharge cycles usually encountered with electric vehicles. The search for a lighter battery approaching the ALABC's goal of 50 Wh kg−1 therefore requires the development of a new set of alloys that are able to withstand mechanical stress and corrosion experienced by a positive grid during the service life of an electric-vehicle battery. The work reported here shows that tin addition (to a level of 1.2 wt.%) or combined tin (to a level of 0.6 wt.%) and silver (to a level of 0.05 wt.%) additions increase considerably both the mechanical properties and the corrosion resistance of a Pb-0.08wt.%Ca-0.013wt.%Al alloy. Gravity casting trials reveal that the tin-rich alloy (1.2 wt.%) and the silver-rich alloy (0.05 wt.%) could be used directly in the industrial processing of batteries that use gel technology. Information is also given on the performances of these batteries when submitted to the international TC69 cycling test, as well as indications of the minimum grid thickness that could be achieved with these alloys without sacrificing battery cycle life.