Polymer-electrolyte complexes mechanical properties

The mechanical properties of X depend partly on the length of the oli-goethyleneoxy groups. The polymers are solid for x=l, highly viscous gums for x=3 and elastomers for x=7.2. The maximum conductivity of these complexes at 30 °C are reported in Table 16. Gel electrolytes have also been obtained by adding propylene carbonate (PC) (10-50 wt%) to these polynorbornene de-... 

Another approach extensively apphed in recerrt years to improve the ion conductivity ((, lithiirm ion transference number (C), mechanical properties, and the electrode-electrolyte interfacial stability of a polymer electrolyte is the addition of inorganic or ceramic fillers into the polymer-salt complexes (Capiglia et al., 1999 Kim et al., 2003 Chen-Yang et al., 2008 Croce et al., 2001 Rahman et al., 2009 Shen et al., 2009 Zhang et al., 2011 Munichandratah et al., 1995 Wiec-zorek, 1992). Micro and nano-sized inorganic filler such as silicone oxide (SiO ), alumina (AI2O3), ceria (CeO ), and so on are incorporated into PEO-salt complex in an effort to improve the mechanical, thermal stabihty, and ion conductivity of PEO-based polymer electrolytes. The effect of nano-fillers on the thermal properties of the PEO-based polymer complex varies with the type of nano-particles as well as the polymer-salt complex host matrix. 

PEO can coordinate alkali metal ions strongly and is used as a solid polymer electrolyte [20-22]. However, conventional PEO-Li salt complexes show conductivities of the order of 10 S/cm, which is not sufficient for battery, capacitor and fuel-cell applications. A high crystalline phase concentration limits the conductivity of PEO-based electrolytes. Apart from high crystallinity, PEO-based electrolytes suffer from low cation transport number (t ), ion-pair formation and inferior mechanical properties. Peter and co-workers [23] reported the modification of PEO with phenolic resin for improvement in mechanical properties and conductivity. 

Poly (ethylene oxide) (PEO) - LiX complexes appear to be the most suitable electrolytes for lithium polymer batteries, however, the local relaxation and segmental motion of the polymer chains remain a problem area (Armand et al., 1997). Therefore, the PEO-based electrolytes show an appreciable ionic conductivity only above 100°C (Gorecki et al., 1986). This is, of course, a drawback for applications in the consumer electronic market. On the other hand, the gel polymer electrolytes although offer high ionic conductivity and appreciable lithiiun transport properties it suffers from poor mechanical strength and interfacial properties (Croce et al., 1998 Gray et al., 1986 Kelly et al., 1985 Weston et al., 1982). Recent studies reveal that the nanocomposite polymer electrolytes alone can offer safe and reliable lithium batteries (Appetecchi... 

Simple network structure can further form interpenetrating networks (IPNs). An IPN is a kind of alloy formed by two or more kinds of polymers. In the preparation process, at least one polymer is made during the formation of another kind of polymer. IPNs have a continuous structure with two phases and combines the merits of different polymer materials. This method has been widely used in the preparation of pol uner electrolytes since 1987. For example, epoxy resin (EPO) can be used as a supporting skeleton to provide good mechanical properties. Complexes of linear PEO with alkali metal salt are enclosed in the network during the preparation process of the EPO and are used as channels for ion conduction. At a ratio of EPO to PEO-LiX (11%) of 30 70, the IPN polymer electrolyte has the highest ionic conductivity of about 10 S/cm at 25°C. 

Metal complexes with, e.g., phenantroline derivatives, could be (electro-) polymerized to form electroactive films [203, 632-637], Polymeric complexes of nickel allowed a switching of the mechanical properties of the film according to the redox state and the presence of barium ions [638], Dissolution of sacrificial metal electrodes into electrolytes containing chelating polymer provided the desired electroactive films [639, 640]. Even mixed metal polymers (containing, e.g., Pd and Cu) have been constructed, which are very useful for catalytic purposes [194]. 

Investigation of ionic conductivity in crystalline soft solids has followed two paths crystalline polymer salt complexes and plastic crystals. Although the latter are not strictly polymer electrolytes they have similar mechanical properties and help to provide a more complete view of ion transport in non-amorphous soft solids. 

The requirements for application of polymer electrolytes in PECs is, of course, that they can complex desired redox species, that their conductance is high enough (due to high conductivity and/or small thickness), and that their mechanical and electronic properties are such that interfaces with desired electronic properties can be formed between the electrolyte and the semiconductor. We also require the optical absorption to be sufficiently low within the polymer film, so that negligible conversion losses are introduced in this manner. They should furthermore be stable over considerable periods of time, and should not allow deleterious reactions at the interface between the polymer film and the semiconductor. 

Phases that are in a non-equilibrium thermodyrmmic state may be present in polymer electrolytes. Because the ionic transport mechanisms and crystallisation kinetics can be very slow (especially at low temperatures), the system may be far from equilibrium. An electrolyte formed at a precise composition corresponding to an identified crystalline complex normally contains crystalline and amorphous material at that composition and at all temperatures below the melting temperature of the complex. In this case, there may be a divergence between the result expected for a certain property based on the phase diagram and that which is actually obtained in practice. 

Conductivity within conducting electroactive polymers (CEPs) is a complex issue. A polymer that can exhibit conductivity across a range of some 15 orders of magnitude most likely utilizes different mechanisms under different conditions. In addition to the electronic conductivity exhibited by CEPs, they possess ionic conductivity because of the solvent or electrolyte incorporated during synthesis. The experimental parameters encountered during synthesis (as listed and discussed in Chapter 2) have an effect on the polymer conductivity. In particular, the electrochemical conditions, the solvent, the counterion, and monomers used during synthesis influence the electronic properties of the resulting polymer. 

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