Polymer electrolytes cross-linked polymers

The process described is referred to as ion-exclusion as discussed by Asher and Simpson 9. The resins used are normal and the non-ionic molecules are assumed to be small enough to enter the pores. When large non-ionic molecules are involved, an alternative process called ion-retardation may be used, as discussed by Hatch et al. W]. This requires a special resin of an amphoteric type known as a snake cage poly electrolyte. The polyelectrolyte consists of a cross-linked polymer physically entrapping a tangle of linear polymers. For example, an anion exchange resin which is soaked in acrylic acid becomes entrapped when the acrylic acid is polymerised. The intricacy of the interweaving is such that counter-ions cannot be easily displaced by other counter-ions. On the other hand, ionic mobility within the resin maintains the electro-neutrality. The ionic molecule as a... 

Concentration of both polymer and cross-linking electrolyte play a major role in deciding the properties of intended hydrogel beads. Concentration of both polymer and electrolyte is calculated based on the ratio of number of cross-linking units present. Drug encapsulation efficiency of the prepared hydrogel beads depends mainly on type and concentration of electrolytes used in the process. 

Generally the polymer electrolyte of the polymer battery is classified into two kinds of the electrolyte One is a dry-type electrolyte composed of a polymer matrix and the electrolyte salt the other is a gel-type electrolyte in which polar solvent is added as a plasticizer to appropriate polymer matrix. In addition, the gel-type electrolyte is classified into thermoplastic gel and cross-linked gel. The research flow of SPE is shown in Fig. 21.1. 

Hydrogel electrolytes which include water-absorbable cross-linked polymers can show high electrical conductivity like liquid electrolytes. Thus they are clearly promising materials for all-solid-state rechargeable alkaline batteries. The rechargeable alkaline batteries have a peculiar safety mechanism in overcharging and overdischarging. For example, in Ni-MH batteries. 

Chapter 8 describes a strategy to improve the membrane properties by blending polymer electrolytes with other polymers. Different types of interactions are involved when cross-linking between polymers is formed. 

Valence Technology are now advancing toward commercializing a lithium rechargeable battery based on the Bellcore technology, although other efforts have focused on a new gelled system [125-127]. This electrolyte is a radiation-cross-linked polymer formed from a mixture of Hquid prepolymer compounds, typically PEO-based acrylates, which have crossHnkable unsaturated centers, a... 

Several other cross-linked polymer electrolytes are electronically conductive but cannot be used practically in lithium-ion batteries and are not discussed here. 

Figure 1. Temperature variation of the conductivity for a cross-section of polymer electrolytes. PESc, poly (ethylene succinate) PEO, polyethylene oxide) PPO, polypropylene oxide) PEI, poly(ethyleneimine) MEEP, poly(methoxyethoxy-ethoxyphosphazene) aPEO, amorphous methoxy-linked PEO PAN, polyacrylonitrile PC, propylene carbonate EC, ethylene carbonate.

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]... 

In the previously described electrophoretic methods, the capillary was filled with electrolytes only. Another mode of operation in capillary electrophoresis involves filling the capillary with gel or viscous polymer solutions. If desired, a column can be packed with particles and equipped with a frit.68 This mode of analysis has been favorably used for the size determination of biologically important polymers, such as DNA, proteins, and polysaccharides. The most frequently used polymers in capillary gel electrophoresis are cross-linked or linear polyacrylamide,69 cellulose derivatives,70-75 agarose,76 78 and polyethylene glycols. 

Buchi, F. N., Gupta, B., Haas, O. and Scherer, G. G. 1995. Performance of differently cross-linked, partially fluorinated proton-exchange membranes in polymer electrolyte fuel cells. Journal of the Electrochemical Society 142 3044—3048. 

To date there have been few reliable measurements of Hittorf transference numbers in solid polymer electrolytes because of experimental difficulties in applying the technique. Leveque, Le Nest, Gandini and Cheradame (1983) have, however, applied it to highly cross-linked networks where cells could be formed using a series of non-adherent thin... 

Polyphosphazene-based PEMs are potentially attractive materials for both hydrogen/air and direct methanol fuel cells because of their reported chemical and thermal stability and due to the ease of chemically attaching various side chains for ion exchange sites and polymer cross-linking onto the — P=N— polymer backbone. Polyphosphazenes were explored originally for use as elastomers and later as solvent-free solid polymer electrolytes in lithium batteries, and subsequently for proton exchange membranes. 

---