The effect of organic expander materials on the performance, life, surface area and crystal structure of negative electrodes in valve regulated cells

Valve regulated cells containing lignosulfonates and synthetic organic additives in their negative plates have been evaluated to determine their effect on capacity and cycle life. The negative active material was examined throughout cycle life to determine the effect of the additives on surface area and crystal morphology. Capacity tests were conducted over a range of current densities at ambient temperature and −18°C on cells containing the additives at various levels. All of the materials increased the capacity but considerable differences were observed in the capacity/dosage level responses. All of the organic materials increase the surface area of the active material, and the surface area increases with concentration. The additives produce a morphology composed of small equiaxial grains with high porosity and surface area. During cycling a progressive reduction in surface area takes place which eventually produces a dense structure with low porosity. The capacity and cycle life data show that each additive has a different optimum concentration in the plate. There are also indications that considerably higher concentrations of organic additives can be used in valve regulated batteries than is customarily used in flooded systems.