Pinhole formation

Nonwoven materials such as cellulosic fibers have never been successfully used in lithium batteries. This lack of interest is related to the hygroscopic nature of cellulosic papers and films, their tendency to degrade in contact with lithium metal, and their susceptibility to pinhole formation at thickness of less than 100 fjim. For future applications, such as electric vehicles and load leveling systems at electric power plants, cellulosic separators may find a place because of their stability at higher temperatures when compared to polyolefins. They may be laminated with polyolefin separators to provide high-temperature melt integrity. 

Asahi Chemical Industry carried out an exploratory investigation to determine the requirements for cellulose based separators for lithium-ion batteries. In an attempt to obtain an acceptable balance of lithium-ion conductivity, mechanical strength, and resistance to pinhole formation, they fabricated a composite separator (39—85 /cellulosic fibers (diameter 0.5—5.0 /pore diameter 10—200 nm) film. The fibers can reduce the possibility of separator meltdown under exposure to heat generated by overcharging or internal short-circuiting. The resistance of these films was equal to or lower than the conventional polyolefin-based microporous separators. The long-term cycling performance was also very comparable. 

Various aspects of the use of PCHE and related materials as a dielectric layer in capacitor films has been described and patented by several workers [72,73]. The material properties that are important for this application are low moisture absorption (which allows for the formation of thin films with minimal pinhole formation), a high heat distortion temperature, and high breakdown voltage. 

Mechanical Properties. The mechanical properties of membranes for industrial applications are important, because of their influence on the membrane s resistance to wrinkling and pinhole formation. 

The technique of interspersing a layer with thin layers that eliminate pinhole formation can be applied to other systems as well. The method is, for example, successful in ST0/PrBa2Cu30y multilayers [14.70]. A layer-by-layer growth mode favors high quality multilayers with large critical thicknesses. The multilayer technique also opens possibilities to continuously vary the physical properties of the intermediate layers by combining two materials with different behaviors. 

For use in PV devices, the absorber layer must be uniform laterally on both the micrometer and centimeter length scales with respect to its composition, and vertically on the micrometer length scale with respect to its thickness. Lateral uniformity on the centimeter scale is a prerequisite for fabrication of larger area PV devices, and the vertical thickness needs to be uniform in order to avoid stress in subsequent deposited layers and to avoid pinhole formation. A final criterion to consider is that the absorber layer must adhere well to the substrate so that it can withstand subsequent thermal treatment. 

As a film preparation technique, this method has numerous advantages. The adsorption of the polymers is quasithermodynamic, with the chains adsorbing into a local minimum, which makes the films stable against many defects (dewetting, pinhole formation, etc.). Importantly, the technique is not limited to flat surfaces any geometry that can be immersed in solution (or have solution flowed through)... 

The indium, any uncoated substrate and uninsulated parts of the wires must be covered with epoxy resin (e.g., Resinlab EP1290 or HYSOL 9462). A sufficient thickness of epoxy should be used to minimize possibility of pinhole formation. 

Pinhole Flex Pinhole flex is the testing by which flex resistance of a specimen ean be determined. Pinhole formation is the criterion presented for measuring failure. 

FeaUxes Prevents microfoam and pinhole formation in coatings most often used in high solids and soh/.-free systems Properties Colorless to yel. liq. ref. index 1.412-1.416 0.9-1.1% NV Use Level 0.05-1.0%... 

There are various improvements that can be made to the presented model, some improvements could be accomphshed. Foremost among these possible future-work directions is the inclusion of nonisothermal effects. Such effects as ohmic heating could be very important, especially with resistive membranes or under low-humidity conditions. Also, as mentioned, a consensus needs to be reached as to how to model in detail Schroder s paradox and the mode transition region experiments are currently underway to examine this effect. Further detail is also required for understanding the membrane in relation to its properties and role in the catalyst layers. This includes water transport into and out of the membrane, as well as water production and electrochemical reaction. The membrane model can also be adapted to multiple dimensions for use in full 2-D and 3-D models. Finally, the membrane model can be altered to allow for the study of membrane degradation, such as pinhole formation and related failure mechanisms due to membrane mechanical effects, as well as chemical attack due to peroxide formation and gas crossover. 

Whereas uniform distribution of water within the membrane is desired, the permeability of the material to reactants (i.e., hydrogen or methanol and oxygen) has to be low to prevent direct chemical reaction between fuel and oxidant, which may lead to hotspots and, eventually, pinhole formation. Methanol permeability is a major challenge in the direct methanol fuel cell (DMFC), largely because methanol transport is strongly correlated with water transport, leading to significant penalties in fuel efficiency and poor cathode performance [189]. 

Short life because of pinhole formation and cracking ... 

It is important to consider a wide range of pressure drop to discover possible losses of selectivity, which can happen in more strict conditions (Bosko, Munera, Lombardo, Comaglia, 2010). In particular, in the case of Figure 4.11 (Bosko et al., 2010), the selectivity drop was connected with the pinhole formation in the dense phase. This formation, which can be caused by a long period of usage, induces the movement of other species, such as nitrogen, with a Knudsen and viscous mechanism. 

Dry-films, as introduced in 1970 and based on a patent of Celeste s, have largely replaced wet resist systems for the fabrication of printed circuits. Most pronounced advantages of dry-film photoresists over wet photoresists are the simplified handling and the diminished chance on pinhole formation. Furthermore, the availability of a range of well-defined thicknesses (25, 38 and 50 pm are mostly used) is especially important during electrolytic metal deposition. 

Fig. 17.14 Hours of lifetime at 120°C (before catastrophic failure of the PEM) versus fluoride ion release rates (by IC) for NSTF and Pt/C catalyst-based membrane electrode assemblies (MEAs) having the same type PEM and GDL. Cells of 100 cm2 were operated at 0.4 A/cm2, 120°C, 300 kPa, 61/84% inlet relative humidity (RH). Electrochemical surface area and crossover were measured daily at 75°C. Total lifetimes were -- CSOO h for the NSTF MEAs due to diagnostic testing at 75°C. End-of-life criteria were severe falloff of cell voltage and corresponding ramp-up of F-ion release indicative of membrane pinhole formation. From reference [5]...

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