PE microporous membrane

Teijin has announced an R D product that seems similar to that of Sumitomo Chemical. The lithium-ion battery separator developed by Teijin consists of three layers a PE microporous membrane sandwiched between porous layers of meta-aramid polymer. This membrane can maintain physical integrity at 250 °C. A spot-heating test indicates that the membrane does not rupture even at temperatures as high as 400 °C. Teijin has announced plans to build a hne capable of producing 25 million m /year in 2011. 

Combining earlier work in which they had prepared microfiltration membranes from melt-extruded polyethylene (PE) with pore sizes in the region of 0.045 jtim, Elyashevich et al. [1041] deposited P(ANi) onto these PE microporous membranes, used as supports or hosts. They found that the combined PE-P(ANi) membranes had conductivities of 0.2 S/cm, and showed promise as gas separation membranes which were sturdier and more durable than free-standing P(ANi) membranes. 

The copolymer PAMS (AN-MMA-St) prepared by emulsion polymerization can be dissolved in organic electrolyte by heating and then coated on both sides of a PE microporous membrane. After cooling and solidification by cross-linking, the gel polymer electrolyte that is obtained shows an ionic... 

In another example, PEO is mixed with PEG-dimethyl acrylate in a certain ratio, and then the mixture is coated on a PE microporous membrane, solidified by heating, and dried. After absorbing organic electrolytes, a gel polymer electrolyte supported by the PE membrane is obtained. The crystallinity of the PE microporous membrane remains the same, while that of the PEO decreases, which is beneficial for the adsorption of the organic electrolyte and increases the channels for ion conduction. The surface morphology of the membrane depends on the polymer ratio. The porosity increases with increasing content of the cross-linked component. The ionic conductivity of the gel polymer electrolyte is 1.0 x 10 S/cm, and the electrochemical window is 4.5 V. The coulombic efficiency of the assembled battery is 100% at 1.0 C but needs improvement at high current rates. 

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. 

The separators used in major lithium primary systems are listed in Table 8. The majority of the lithium primary systems shown in Table 8 use microporous membranes (single layer PP or PE) as separators. Some of the systems are discussed below. 

Microporous polymeric membrane separators are characterized by pore sizes in the micrometer scale. Microporous polymeric membrane separators are mainly made of polyethylene (PE), polypropylene (PP), and the combinations of them (PE/PP and PP/PE/PP) because of their high chemical and mechanical stabilities. According to the number of layers, they can be classified into monolayer and multilayer polymeric microporous membranes. 

Most of the available commercial microporous membranes such as PSf, PES, polyamide, cellulose, polyethylene, polypropylene, and PVDF are prepared by phase inversion (phase separation) processes. The concept of phase separation in... 

The typical properties of some commercial microporous membranes are summarized in Table 6.4. Celgard 2730 and Celgard 2400 are single-layer PE and PP separators, respectively, while Celgard 2320 and 2325 are Trilayer separators of... 

In particular, MD is a thermally driven membrane operation in which a temperature gradient is applied between the two sides of a microporous membrane. This temperature difference results in a vapour pressure difference, leading to the transfer of water in vapour form through the membrane to the condensation surface. Hydrophobic membranes made in polyvi-nylidenefluoride (PVDF), polypropylene (PP), polyethylene (PE) and poly-tetrafluoroethylene (PTFE) with pore sizes of 0.2-1.0 pm are typically used. 

Membrane surfaces can also be modified by heat treatment. The PES HFMs were prepared by dry-wet spinning method and heated in an oven at 120,150, and 180°C. The membrane shrank by heating. It was noticed that pore size decreased from 8.16 nm for untreated hollow fiber to 3.8 nm with 1 minute heating and then increased to about 6 nm with 5 min heating at 150°C. With an increase in heating temperature, the pore size of the membrane decreases [77,78]. Charkoudian et al. reported increased levels of protein adsorbed in thermally treated poly-acrylamide-modified PVDF microporous membranes in comparison to thermally untreated polyacrylate-modified membranes [79]. 

Cycle life In 20 AH LiMn204/graphite cells, the were able to show 1450 cycles at 74% capacity retention, compared to 1000 cycles with 46% retention for a PE/PP microporous membrane. 

A trilayer stmcture of PP/PE/PP Celgard microporous membranes provides exceptional puncture strength [19]. In addition, the low-melting PE layer (135 °C) can act as a thermal fuse, while the higher-melting PP (165 °C) layers provide... 

Due to the fact that the affinity of PE and PP membrane with electrolyte is poor, a lot of researchers are focused on it. Cheng and Sun [57] coat PP membrane (Celgard 2400 single-layer membrane) with PE mixed with nanometer silicon dioxide to improve the wettability of the membrane. Miao et al. [58] coat a three-layer composite microporous membrane (PP/PE/PP) with polyvinylidene fluoride (PVDF) surface processing (Figure 12.18). This technology reduces the membrane thickness and battery volume. 

FIGURE 12.18 Microporous membrane of three layered structure (PP/PE/PP) with PVDF. (FromMiao, R. et al Power Sources, 184,420, 2008.)... 

Errede LA, Jefson GB, Langager BA, Olson PE, Ree BR, Reichert ME, Sinclair RA, Stofko JJ (1988) Reactive microporous composite membranes. In Leyden DE, Collins WT (eds), Chemically modified surfaces in science and industry, vol 2 Proceedings of the chemically modified surfaces symposium, Fort Collins, Colorado, June 17-19 1987. Gordon and Breach Science Publishers, New York, p 91... 

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