Properties ionic resistance

The typical properties of some commercial microporous membranes are summarized in Table 4. Celgard 2730 and Celgard 2400 are single layer PE and PP separators, respectively, while Celgard 2320 and 2325 are trilayer separators of 20 and 25 fim thickness. Asahi and Tonen separators are single layer PE separators made by the wet process. Basic properties, such as thickness, gurley, porosity, melt temperature, and ionic resistivity are reported in Table 4. These properties are defined in section 6.1.3. 

Martino et al. have demonstrated the use of BN felt separators in engineering tests. They have high porosity ( 90%), and hence, low ionic resistance, in addition to excellent compatibility with other cell materials at the operating temperature of 470 °C. However, this separator is too expensive and has poor mechanical properties and so cannot prevent electrode shape change during cell operation. ... 

The chemical, physical, and thermal properties ana resistance to degradation of polysiloxanes is the result of the high energy (106 kcal/mol) and the relatively large amount of ionic character of the siloxane bond. The ionic character of the Si—O bond facilitates acid and base-catalyzed rearrangement and/or degradation reactions. Under inert conditions, highly purified polydiphenyl- and polydimethylsiloxanes are stable at 350 to 400 °C. 

In conclusion, microelectrodes possess unique electrochemical properties, namely, steady-state current response within short timescales, increased faradaic-to-capacitive ratio of the current intensity, independence of the ionic resistance from the distance between electrodes, and short time constants (fast response). 

Another class of interesting materials for separator is composed of nonwoven films, textile products processed directly from fibers that are bonded together. The fibrous structure of nonwoven materials offers a high porosity, which is necessary for high electrolyte absorbance and low ionic resistance, excellent thermal properties, combined with cost competitiveness. However, the excessively large pore size and broad pore size distribution of conventional nonwovens, which may provoke... 

Membrane-electrode assembly (MEA) is an anode-membrane-cathode composite structure in which each layer is made as thin as possible without losing the mechanical integrity of the composite structure or the electrochemical activity of the two electrodes. The functional advantages of such a structure include short diffusion paths of air and fuel gas to the electrochemical reaction sites, intimate contact of electrodes with the polymer electrolyte and low ionic resistance of the membrane. All these properties are needed to sustain high current and power densities [7]. 

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