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Separators are used between the positive and negative plates of a lead acid battery to prevent short circuit through physical contact, Dendrites (treeing) most and shredded active material. Separators cause some obstructions for the flow of ions i.e. electricity between the electrodes. Separators therefore must have the following characteristics:

  • They must be porous—high porosity gives a high rate of flow of ions.
  • Pore size must be small enough to restrict the flow of colloid particles but not restrict the ions.
  • They must be as thin as possible.
  • Electrical resistance must be very high.
  • They are a little larger than the plates to prevent material shorting the plates.

To balance these criteria, the choice of separator shifted from wood to rubber to glass mat to cellulose based separators to sintered PVC separator to micro porous PVC/polyethylene separator. An effective separator must meet a number of mechanical properties. Permeability, porosity, pore size distribution, specific surface area, mechanical design and strength, Electrical resistance, ionic conductivity, and chemical compatibility with the electrolyte. In service the separator must have good resistance to acid and oxidation.

In the battery service condition the following reaction can be shown:

·          PbO2 + 2H+ + SO4-2 = PbSO4 + H2O + ½ O2

·          PbO2 + (oxidizable separator material) + H2SO4 = PbSO4 + (oxidized material)

Moreover, the battery service temperature can be as high as 70 to 80 degrees Celsius. The separator must be capable of resisting thermal degradation as far as possible.



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Last Updated: Saturday, December 22, 2007 - 5:49 PM Eastern Time.