Gurley value

The Gurley number is used to characterize membranes because the measurement is accurate and easy to make, and deviations from specified values are a good indication of problems. A higher Gurley value than specified can indicate the membrane has surface damage a lower value than specified can indicate pinholes. 

Gurley (Air Permeability). Air permeability is proportional to electrical resistivity, for a given separator morphology. It can be used in place of electrical resistance (ER) measurements once the relationship between gurley and ER is established. The separator should have low gurley values for good electrical performance. 

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. 

In Table 12.7 representative properties of four traditional separators are presented [2]. It is obvious that the membranes produced by the dry process distinguish themselves with a high orientation-dependent tensile strength and a low Gurley value. The low Gurley value indicates less tortuous pore... 

The data were cited directly from the product brochiffes. Gurley value was expressed as the time in seconds required to pass 100 mL of air through 6.45 cm (1 in. ) of membrane under a pressure of 31.0 cm (112 in.) of water... 

The typical value of DM permeability varies from 1 to 10 Darcy (1 Darcy = 10-8 cm2) from Gurley measurement. 

The design to decrease R is straightforward in that the electronic or ion conductivity of the components has a direct influence on the value of For instance, separators with different porosity and pore tortuosity lead to different values of apparent electrolyte resistance, since these two factors play a critical role in the polarization inside the separator. (In fact, air permeability and the Gurley number are more frequently used in industry to evaluate the degree of penetrability of active species through the separator than the terminologies such as porosity, tortuosity, and polarization [9].) The separators with more porous and less tortuous pore structure result in smaller Ro (or polarization). 

The ER is a more comprehensive measure of permeability than the Gurley number (air permeability) in that the measurement can be carried out in the actual electrolyte solution. Thus, the measurement reflects the compatibility of the separator with the electrolyte (e.g., the value of the ER will reflect pores that are nonwetting). The magnitude of the ER can be used to estimate ohmic losses in a cell. Unfortunately, ER is significantly more difficult to measure than air permeability. Battery makers may find evaluating the electrical performance of a spirally wound cell made with dummy electrodes and a particular separator an efficient means of measuring ER [60]. 

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