Lead-acid batteries separators

Reprinted from W. Bohnstedt, Automotive lead/acid battery separators a global overview, J. Power Sources, 1996, 59, 45-50, with kind permission from Elsevier Science S.A., Lausanne. 

Electric road vehicles have been reduced to insignificance, as mentioned already by, vehicles with combustion engines. Another electric vehicle — the electrically driven submarine — presented a continuous challenge to lead-acid battery separator development since the 1930s and 1940s. The wood veneers originally used in electric vehicles proved too difficult to handle, especially if tall cells had to be manufactured. Therefore much intense effort took place to develop the first plastic separators. In this respect the microporous hard rubber separator, still available today in a more advanced version, and a micro-porous PVC separator (Porvic I) merit special mention 28]. For the latter a molten blend of PVC, plasticizer and starch was rolled into a flat product. In a lengthy pro-... 

Chain guides, star wheels, feed screws Truckbeds, hopper bunker liners Suction box covers, rollers, foil blades Knee, shoulder and hip implants Food preparation surfaces Lead acid battery separators Ballistic cloth, fishing lines and nets Snow ski soles, snowmobile boogie wheels... 

With regard to flooded lead-acid battery separators, the normal materials of construction are relatively noncompressible and they fix the electrode distance, providing a degree of compression on the electrodes, at least where the ribs contact the plate surface. In flooded designs, separators with a laminate layer are regularly utilized to provide more support of the active material that is likely to shed during deep discharge. Because the laminate thickness is normally a small portion, say, 10% to 20%, of the total structure thickness, the amount of compression or resiliency is minimized. 

Fig. 2. Cutaway view of a tubular positive lead—acid battery, (1) Positive tubular plate (2) iiegatwe plate (3) separator (4) connecting strap (5) ceU cover (6)...

The lead—acid battery is comprised of three primary components the element, the container, and the electrolyte. The element consists of positive and negative plates connected in parallel and electrically insulating separators between them. The container is the package which holds the electrochemically active ingredients and houses the external connections or terminals of the battery. The electrolyte, which is the Hquid active material and ionic conductor, is an aqueous solution of sulfuric acid. 

A lead-acid battery consists of electrolytic cells, each containing an anode of porous lead, a cathode of primarily lead peroxide (PbO,), and electrodes of metallic lead. The anode and cathode are separated by nonsulfuric acid and water. 

From this — albeit rather rough — overview, the proportions become clear around 45 percent of all battery sales worldwide and thus also separator sales worldwide are in lead-acid batteries and... 

The historical development of the separator and of the lead-acid storage battery are inseparably tied together. When referring to lead-acid batteries today one primarily thinks of starter batteries or forklift traction batteries, but the original applications were quite different. 

The very first functioning lead-acid battery was presented by Gaston Plante in 1860 spirally would lead sheets served as electrodes, separated by a layer of felt — the first separator of a lead-acid battery [12], This assembly in a cylindrical vessel in 10% sulfuric acid had only a low capacity, which prompted Plante to undertake a variety of experiments resulting in many improvements that are still connected with... 

Finally, one development results from returning to a basic idea from the dawn of the lead-acid battery, wherein the functions of support for the positive active material and of the separator are combined into one component the gauntlet separator [84] consisting of a coarsely porous, flexible support structure coated with micropo-rous polyethylene material for separation. The future has to show whether this approach will be able to meet all demands. 

Polyethylene separators offer the best balanced property spectrum excellent mechanical and chemical stability as well as good values for acid availability and electrical resistance have established their breakthrough to be the leading traction battery separator. Rubber separators, phenolic resin-resorcinol separators, and mi-croporous PVC separators are more difficult to handle than polyethylene separators their lack of flexibility does not allow folding into sleeves or use in a meandering assembly in addition they are more expensive. 

Separators for Valve Regulated Lead-Acid Batteries... 

Table 13. Separators for valve-regulated lead -acid batteries (liquid electrolyte)...

One version of the microporous, filled polyethylene separator ( PowerSep ) [113], which is so successful in the lead-acid battery, is also being tested in nickel-cadmium batteries. This separator is manu-... 

They are fabricated from a variety of inorganic, organic, and naturally occurring materials and generally contain pores that are greater than 50—100 A in diameter. Materials such as nonwoven fibers (e.g. nylon, cotton, polyesters, glass), polymer films (e.g. polyethylene (PE), polypropylene (PP), poly(tetrafluo-roethylene) (PTFE), poly (vinyl chloride) (PVC)), and naturally occurring substances (e.g. rubber, asbestos, wood) have been used for microporous separators in batteries that operate at ambient and low temperatures (<100 °C). The microporous polyolefins (PP, PE, or laminates of PP and PE) are widely used in lithium based nonaqueous batteries (section 6.1), and filled polyethylene separators in lead-acid batteries (section 7.3), respectively. 

Lead-acid batteries can be classified into three major types or categories, namely, automotive (SLI), stationary, and motive power (industrial). In addition, there are many special batteries that cannot be easily categorized as either of the above types. As these types of batteries are constructed with different materials and design to meet the requirements of their intended end uses, each requires a particular separator with specific material composition, mechanical design, and physical, chemical, and electrochemical properties that are tailored for the battery and its relevant specific uses. These batteries are generally available in flooded electrolyte or valve regulated (sealed) versions. In this section the types... 

Table 9. Typical Separators Used in Lead-Acid Battery Systems...

The battery separator currently used by most flooded cell type lead-acid battery manufacturers are of the microporous PE type. It was invented in the late 1960s by W. R. Grace Co. The term... 

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