Mechanical properties, lithium polymer

To overcome the poor mechanical properties of polymer and gel polymer type electrolytes, microporous membranes impregnated with gel polymer electrolytes, such as PVdF. PVdF—HFP. and other gelling agents, have been developed as an electrolyte material for lithium batteries.Gel coated and/ or gel-filled separators have some characteristics that may be harder to achieve in the separator-free gel electrolytes. For example, they can offer much better protection against internal shorts when compared to gel electrolytes and can therefore help in reducing the overall thickness of the electrolyte layer. In addition the ability of some separators to shutdown... 

The most simple and efficient approach is based on gelation which is a simple method that allow a good compromise between the retention of the IL and its fluidity inside the polymeric network. These so called ion gels are simpler than solid polymer electrolytes and exhibit improved conductivities. In fact ion gels hold both the processability and mechanical properties of polymers, but with added physico-chemical properties and were primary developed as replacements for current solid-state polyelectrolytes in energy devices, such as dye-sensitized solar cells, supercapacitors, lithium ion batteries, and fuel cells. (Fernicola et al., 2006 Galinski et al., 2006 Le Bideau et al., 2011 Lu et al., 2002 Mazille et al., 2005 Stephan, 2006)... 

Lithium-Ion Cel Polymer Battery The Hthium-ion gel polymer batteries offer better performance than that of solid polymer electrolyte batteries. The gel electrolyte is a polymer matrix swollen with a liquid electrolyte, and the batteries that employ gel electrolyte are known as gel polymer batteries. The detailed information on this type of battery can be found in other chapters of this book and in a review [33]. Most of the gel electrolytes have been made employing PEO, poly(acrylonitrile) (PAN) [34], poly(methyl methacrylate) (PMMA) [35, 36], and PVdF [37, 38]. The poor mechanical properties of polymer and gel polymer electrolytes have led to an alternative approach where microporous membranes are impregnated with gel polymer electrolytes [39-42]. The process builds upon the work of Abraham et al. who saturated commercial polyolefin separators with a solution of lithium salt in a photopolymerizable monomer and a nonvolatile... 

The liquid electrolytes used in lithium batteries can be gelled by addition of a polymer [25] or fumed silica [26], or by cross linking of a dissolved monomer [271. Depending on the mechanical properties, gelled electrolytes can be used as separators, or supported by a conventional [27]... 

A polymer electrolyte with acceptable conductivity, mechanical properties and electrochemical stability has yet to be developed and commercialized on a large scale. The main issues which are still to be resolved for a completely successful operation of these materials are the reactivity of their interface with the lithium metal electrode and the decay of their conductivity at temperatures below 70 °C. Croce et al. found an effective approach for reaching both of these goals by dispersing low particle size ceramic powders in the polymer electrolyte bulk. They claimed that this new nanocomposite polymer electrolytes had a very stable lithium electrode interface and an enhanced ionic conductivity at low temperature. combined with good mechanical properties. Fan et al. has also developed a new type of composite electrolyte by dispersing fumed silica into low to moderate molecular weight PEO. 

Most structural PMCs consist of a relatively soft matrix, such as a thermosetting plastic of polyester, phenolic, or epoxy, sometimes referred to as resin-matrix composites. Some typical polymers used as matrices in PMCs are listed in Table 1.28. The list of metals used in MMCs is much shorter. Aluminum, magnesium, titanium, and iron- and nickel-based alloys are the most common (see Table 1.29). These metals are typically utilized due to their combination of low density and good mechanical properties. Matrix materials for CMCs generally fall into fonr categories glass ceramics like lithium aluminosilicate oxide ceramics like aluminnm oxide (alnmina) and mullite nitride ceramics such as silicon nitride and carbide ceramics such as silicon carbide. 

Tristar polybutadienes prepared by the intermediacy of lithium acetal initiators were also converted to three dimensional networks in a liquid rubber formulation using a diisocyanate curing agent. Table IV shows normal stress-strain properties for liquid rubber networks at various star branch Hn s. It can be seen that as the branch Mn increases to 2920, there is a general increase in the quality of the network. Interestingly, the star polymer network with a star branch Mn of 2920 (Mc=5840) exhibits mechanical properties in the range of a conventional sulfur vulcani-zate with a Me of about 6000-8000. 

The commerical polybutadiene (a highly 1,4 polymer with about equal amounts of cis and trans content) produced by anionic polymerization of 1,3-butadiene (lithium or organolithium initiation in a hydrocarbon solvent) offers some advantages compared to those manufactured by other polymerization methods (e.g., it is free from metal impurities). In addition, molecular weight distributions and microstructure can easily be modifed by applying appropriate experimental conditions. In contrast with polyisoprene, where high cis content is necessary for suitable mechanical properties, these nonstereoselective but dominantly 1,4-polybutadienes are suitable for practical applications.184,482... 

The addition of lithium salts can alter the melting, flow behavior, and mechanical properties of aliphatic polyamides (1-4). These effects have been attributed to the formation of a labile network resulting from the salt interacting with the amide group of the polymer. Subsequent work using polycaprolactam lithium chloride demonstrated a direct binding of the lithium ions to the carbonyl oxygen (5). 

Ji, J., Keen, J., Zhong, W.-H., 2011. Simultaneous improvement in ionic conductivity and mechanical properties of multi-functional block-copolymer modified solid polymer electrolytes for lithium ion... 

Kureha KF polymer is a PVdF product developed by Kureha Corporation, Tokyo Japan. KF polymer has a high chemical resistance and desirable mechanical properties. One of its most remarkable characteristics is that the irregular bonding of its molecular chain is lower than that of any of the other PVdFs, an attribute that leads to a perfectly crystallized polymer. These valuable properties allow lithium-ion secondary batteries to combine long-term, stable performance with a minimum amount of swelling by the organic electrolyte. 

Unfortunately, none of the hyperbranched polymers smdied to date has demonstrated good mechanical properties. A hyperbranched PC is also expected to be a brittle material, but such a stmcture may prove interesting as a highly functionalized prepolymer for composites, coatings, and other applications. Hyperbranched PCs were synthesized and characterized by Bolton and Wooley. ° The products were prepared by the polymerization of an A2B monomer derived from l,Ll- nT(4 -hydroxyphenyl)-ethane. Silylation of the phenol terminated material with rert-butyldimethylsilyl chloride, followed by degradation of the carbonate hnkages by reaction with lithium aluminum hydride and analysis of the products by HPLC... 

The ceramic fillers (e.g., AI2O3, SiOa, TiOa) can greatly influence the characteristics and properties of polymer electrolyte by enhancing the mechanical stability and the conductivity [135, 175-178]. Prosini et al. [179] in a PVdF-HFP polymer matrix used y-LiAlOa, AI2O3, and MgO as fillers to form self-standing, intrinsically porous separators for lithium-ion batteries. The MgO-based separators showed the best anode and cathode compatibilities. 

Zhonghai and co-workers [154] studied the mechanical properties of carbon fibre reinforced films of this polymer as a function of the degree of crosslinking with triethylenetetramine. In general, an improvement in mechanical properties resulted in little or no effect on the electrical properties of this polymer, which is a strong candidate for the fabrication of lithium battery electrodes. 

---