Separators negative ribs

Negative ribs have been utilized recently to resolve another issue. In normal applications, the separators have not been the typical failure mode of the battery. As such, there has been an effort to reduce the mass of the separator. This is achieved by reducing the back-web thickness. Over the years the typical back-web has migrated from 300 pm to as low as 150 pm. Even at 150 pm for the back-web thickness, the... 

A mixture of powdered poly(vinyl chloride), cyclohexanone as solvent, silica, and water is extruded and rolled in a calender into a profiled separator material. The solvent is extracted by hot water, which is evaporated in an oven, and a semiflexible, microporous sheet of very high porosity ( 70 percent) is formed [19]. Further developments up to the 75 percent porosity have been reported [85,86], but these materials suffer increasingly from brittleness. The high porosity results in excellent values for acid displacement and electrical resistance. For profiles, the usual vertical or diagonal ribs on the positive side, and as an option low ribs on the negative side, are available [86],... 

In contrast to most conventional separators for flooded batteries, separators for gel batteries have ribs positioned not only towards the positive plate, but also towards the negative plate in order to facilitate the gel-fllling process. For batteries with pasted positive plates, the separator is usually laminated with a glass fleece, which protects the positive plate against shedding, especially in cycle applications. Although this surface fleece stabilizes the active material, the present design of gel batteries cannot prevent completely the expansion of the positive material and the occurrence of PCL-2. The most important characteristics of separators used in gel batteries are listed in Table 7.2 (adapted from Ref. 12). 

In a flooded lead-acid battery, the sulfuric acid serves as both the electrolyte for conductance of the ions and it also promotes the electrochemical reaction. To achieve optimum performance from a battery, the amount of sulfuric acid should be stoichio-metrically balanced around the other reactants, namely, the positive and negative active material. The amount of electrolyte between electrodes is fixed by the 3D structure of the flooded lead-acid separator. Normally facing the positive electrode, there are ribs protruding off the planar surface of the substrate that serve to fix the distance between the electrodes and thus the volume available for the electrolyte [27]. Figures 4.9 and 4.10 illustrate some typical profiles. 

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