Polymer-electrolyte complexes conducting properties

Thermal and Conducting Properties of Polymer-LiC104 Mixtures. Plots of the conductivity, a, of homogeneous, transparent mixtures of LiCl04 PMMS-8 and PAGS-12 exhibit distinct maxima at ratios of ethylene oxide units to lithium (EO/Li of 20-25 (Figure 2). This behavior is typical for amorphous polymer electrolyte complexes (7, 8). An increase... 

Unique combinations of properties continue to be discovered in inorganic and organometallic macromolecules and serve to continue a high level of interest with regard to potential applications. Thus, Allcock describes his collaborative work with Shriver (p. 250) that led to ionically conducting polyphosphazene/salt complexes with the highest ambient temperature ionic conductivities known for polymer/salt electrolytes. Electronic conductivity is found via the partial oxidation of unusual phthalocyanine siloxanes (Marks, p. 224) which contain six-coordinate rather than the usual four-coordinate Si. 

These examples and the general subjects mentioned above illustrate that ion conduction and the electrochemical properties of solids are particularly relevant in solid state ionics. Hence, the scope of this area considerably overlaps with the field of solid state electrochemistry, and the themes treated, for example, in textbooks on solid state electrochemistry [27-31] and books or journals on solid state ionics [1, 32] are very similar indeed. Regrettably, for many years solid state electrochemistry/solid state ionics on the one hand, and liquid electrochemistry on the other, developed separately. Although developments in the area of polymer electrolytes or the use of experimental techniques such as impedance spectroscopy have provided links between the two fields, researchers in both solid and liquid electrochemistry are frequently not acquainted with the research activities of the sister discipline. Similarities and differences between (inorganic) solid state electrochemistry and liquid electrochemistry are therefore emphasized in this review. In Sec. 2, for example, several aspects (non-stoichiometry, mixed ionic and electronic conduction, internal interfaces) are discussed that lead to an extraordinary complexity of electrolytes in solid state electrochemistry. 

Solid polymer electrolytes (SPE) represent the newest and one of the most important (i.e. as far as potential applications are concerned) class of FIC solids. The area of polymer/salt complexes became extremely active following the work of Wright, who first reported that PEO is an excellent polymer host for a number of salts and that the resnlting polymer/salt complexes have significant electrical conductivities near room temperature. Armand extended the investigation of the electrical properties of the polymer/salt electrolytes and... 

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. 

The physical and electrochemical properties of a new class of hthium ion conducting polymer electrolytes formed by dispersing nanosized C CPO ) in the poly (vinyhdene fluoride-hexafluoro propylene) (PVDF-HFP) - LiClO complexes have been reported. The prepared membranes were subjected to XRD, SEM, TG-DTA, and FT-IR analysis. Ionic conductivity measurements have been made as a function of temperature and hthium salt concentrations. The polymeric film with a ratio of PVDF-HFP Ca3(PO )2 LiC10 75 15 10 offered maximum ionic conductivity. The interfacial property of Li/NCPE was also analyzed. The interaction that exists between the polymer and lithium salt species has been confirmed by FT-IR analysis. 

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... 

Measurement of Ionic Conductivity. The synthesis of solvent-free metal salt complexes of polyethylene oxides prompted detailed electrical measurements with the thought that these materials might prove to be useful electrolytes, in a hydrous environment, for high energy density batteries (13-15). Many fundamental properties of these polymer electrolytes have been examined and a large literature on the subject is available (16-17). We prepared a disk of one of our polyether complexes and measured its conductivity by impedance methods. 

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. 

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. 

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