Improvement of the formation efficiency of the tetrabasic lead sulfate for lead/acid batteries

In the lead/acid battery manufacturing process, the formation of positive plates containing large needles of tetrabasic lead sulfate is very difficult to achieve. Today, the general solution to this problem consists in adopting a very long and expensive formation process with a large excess of Ah/kg. Even under these conditions, the extent of formation can be low. In this paper, we point out the difficulty to oxidize large 4BS needles because the crystal surface is covered by an insulating layer constituted of 0.2 μm interconnected PbSO4 nodular grains. The thickness of this layer is small (nearly 1 μm) and is slightly but not sufficiently influenced by external conditions such as long soaking time, higher temperature, and optimization of current profile during formation. In this paper, we present a calculation model to forecast the formation efficiency of 4BS plates taking into account the crystal dimensions, the thickness of the sulfation layer and the complete composition of the positive active material before formation. Then, after comparison of this model with experimental values, the role of each parameter is examined and new conditions for a better formation are obtained. From these results, we suggest several solutions in order to improve the 4BS formation efficiency, and the corresponding results are given.