MacMullin number

Permeability. The separators should not limit the electrical performance of the battery under normal conditions. Typically the presence of separator increases the effective resistivity of the electrolyte by a factor of 6—7. The ratio of the resistivity of the separator filled with electrolyte divided by the resistivity of the electrolyte alone is called MacMullin number. MacMullin numbers are as high as 10—12 have been used in consumer cells. 

Image analysis has been used to characterize the pore structure of synthetic membrane materials. The Celgard films have also been characterized by scanning tunneling microscopy, atomic force microscopy, and field emission scanning electron microscopy. The pore size of the Celgard membranes can also be calculated from eq 5, once the MacMullin number and gurley values are known. 

S.3. Diaphragm Resistance. The calculation of the resistance across a separator, such as an asbestos or a polymeric diaphragm, is identical to the method employed to determine the resistance of an electrolyte between two parallel plates. However, the distance between the two faces of a separator is not equal to its thickness, as the liquid path in the separator is tortuous and the area is restricted by the finite porosity. Therefore, the 1/A term in the parallel plate configuration should be modified to read as [tortuosity x length]/[porosity x area] or as the ratio of tortuosity to porosity, which is called the MacMullin number. The MacMullin number, characterizing a... 

The separator suppliers often provide their products with Gurley numbers which characterize air permeability (Chap 1 Table 1.10) of the films. The battery industry, however, is interested in the electric resistance of the separators wetted with the electrolyte solutions as discussed earlier. The electric resistance can be expressed in the units of specific area resistance (in 2 cm ), or via MacMullin number which is the ratio of the resistance of the separator filled with electrolyte divided by the resistance of the electrolyte alone. Although, generally, the thinner... 

Patel et al. [71] carried out numerical simulations to calculate MacMuUin numbers for packing of ellipsoids as well as experimental measurements. For commercial separators commonly used in lithium batteries they found a range of MacMullin numbers from 8.5 to 16.1. 

Ferebee and Spotnitz [72] reported MacMullin numbers for various Celgard separators in the range of 5.8-8.7. 

Thorat et al. [73] measured a MacMullin number of Celgard 2400 of 14.9, in good agreement with the value obtained by Patel et al. 

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