Although conventional lead-acid batteries are considered a rather mature technology, significant research and development efforts are currently under way to enhance their performance and operating life. These efforts are being driven by the demands of both the automotive and stationary (or standby) market sectors. Both major markets have need of lead-acid batteries with higher energy density or reduced size and weight; however, the automotive sector is also driven to mitigate the cycle-life reduction of its “starter, lighting, and ignition” (SLI) batteries that results from rising “under the hood” temperatures in modern automobiles.
The operating and cycle lives of leadacid batteries are limited by the resistance of the positive Pb-alloy electrodes to intergranular-degradation processes (i.e., corrosion, cracking, and creep). Figure 1 shows an example of near-through-wall cracking and some inter-granular corrosion (grain-dropping at surface) observed in a Pb-lwt%Sb positive battery grid following approximately four years of service. In addition to the breaching of grid electrical continuity by corrosion and cracking processes (as indicated in Figure 1), the relatively high homologous temperature of operation for lead-acid batteries (i.e., >0.6 Tm, where Tm is the melting temperature) promotes intergranular-creep processes that result in dimensional changes in the electrodes over time (i.e., grid “growth”); this causes adjacent plates to short, leading to reduced battery capacity.