Electrochemical Evaluation of Pb–Ca–SnSr alloy for Positive Grid of Lead–acid Battery

Optimizing the electrochemical and mechanical properties of the positive grid of lead–acid batteries exert a profound influence on their performance. High content of calcium in a Pb-Ca-Sn alloy causes premature capacity loss, while reducing its content brings about losing hardness and casting ability. This issue can be solved by using strontium as the fourth element in the positive grid alloy. In this study, we prepared four different alloys with Sr contents of 0.012% to 0.060% and the same Ca and Sn values for comparison  with a reference sample without Sr. Cyclic voltammetry, potentiostatic coulometry electrochemical impedance spectroscopy and hardness tests were conducted on all samples. The results indicate that adding Sr improves the performance of the grid alloy in all the mentioned tests.  The best results were observed when Sr was used in the range of 0.012% to 0.020%. Based on hardness and electrochemical tests results, the best sample was chosen for preparing a 66 Ah battery  to undertake  tests according to PSA standard, including capacity, CCA, charge acceptance and cycling to compare with an alloy without Sr. The results showed that employing 0.020% of Sr in the grid alloy resulted in four-time lower passive current density, 41% lower PbO formation peak, 70% lower O₂ evolution rate, 55% increased electrochemical impedance of the oxides formed on the electrode surface, and 16% increase hardness — all compared  with a reference Sr-free alloy. The battery performance results were also in line with the electrochemical ones. Strontium  improved the CCA of the battery by 10%, enhanced the  charge-acceptance by 37%, prolonged the  battery cycling test 44, %, and resulted in a 57% lower residual capacity loss after cycle life.