Influence of paste composition and curing program used for the production of positive plates with PbSnCa grids on the performance of lead acid batteries

Abstract

The cycle life performance of lead acid batteries with PbSnCa grids is strongly affected by the structure and properties of PAM and of the interface PAM/grid. The latter interface is formed during curing and formation of the positive plates. The processes that take place on curing of positive lead acid battery plates produced with Concast or Conroll PbSnCa grids and 3PbOPbSO 4·H 2O (3BS) or 4PbOPbSO 4· xH 2O (4BS) pastes are discussed in this paper. The enhanced processes of Sn and Ca segregation in the alloy of the grids during plate curing lead to the formation of a thin layer of a new phase, composed of the intermetallic compound (Pb 1− x Sn x ) 3Ca, in the spaces between the metal grains or sub-grains. This layer makes the interface heterogeneous and exerts a detrimental effect on the cycle life of the battery. In order to suppress its effect on battery performance, the thickness of this layer should be reduced by reducing the content of Ca in the grid alloy. During plate curing, the heterogeneous surface of the grid alloy is oxidized under the action of oxygen and H 2O at elevated temperature and the alkaline solution in the paste pores. A corrosion layer is formed comprising a thin sub-layer (CL1) and a thick partially hydrated lead oxide sub-layer (CL2). The 4BS/CL2 contact surface is larger and more stable than that between the 3BS particles and the CL2 layer. Both 3BS and 4BS particles are bonded to the CL2 layer through their hydrated layers. When curing is conducted at temperatures above 80 °C, 3BS particles are converted into 4BS ones which contain water. It has been established that positive plates produced with 4BS plates cured at 50 °C have the longest cycle life and adequate capacity performance, but a bit low power output. Positive plates prepared with 3BS pastes, which are then converted into 4BS ones during plate curing at 90 °C, have high initial capacity and power performance, but shorter cycle life. Batteries with plates produced with 4BS pastes and then cured at 90 °C for less than 4 h have both satisfactory power output and cycle life. The obtained results indicate that the conditions of positive plate curing exert a strong influence on the performance of batteries with PbSnCa grids.