Effects of lead foam on structure and characteristic of negative active materials in VRLA batteries

The surface morphology and composition of negative active material (NAM) both on the cast grid and on lead foam grid at the state of charge and discharge, in valve-regulated lead acid (VRLA) battery, were characterized by SEM and XRD, respectively. Moreover, the specific surface area and electrochemical impedance of the negative active material for both negative electrode grids were studied by chronoamperometry and EIS. The result indicates that after lots of cycles, compared with the cast grid, the sponge lead of the lead foam negative plate is smaller; the specific surface area increases by about 16%; the residual PbSO ₄ on the surface of the electrode is less at the state of charge. At the state of discharge, PbSO ₄ crystals on the surface of the negative plate of lead foam are smaller, and the specific surface area increases to 209%. EIS analysis shows that compared with the negative plate of cast grid, no matter what state the negative plate of lead foam is at, the electrochemical impedance of the material is lower.