Solid polymer electrolyte systems

Lithium secondary batteries can be classified into three types a liquid-type battery using liquid electrolytes, a gel-type battery using gel electrolytes mixed with polymer and liquid, and a solid-type battery using polymer electrolytes. The types of separators used in different types of secondary lithium batteries are shown in Table 20.1. The liquid Li-Ion cell uses microporous polyolefin separators while the gel polymer Li-Ion cells either use polyvinylidene difluoiide (PVdF) separator (e.g., PLION cells) or PVdF-coated microporous polyolefin separators. The PLION cells use PVdF loaded with silica and a plasticizer as the separator. The microporous structure is formed by removing the plasticizer and then filling with liquid electrolyte. They also are characterized as plasticized electrolyte. In solid polymer Li-Ion cells, the soM electrolyte acts as both electrolyte and separator. This chapter focuses only on the conventional liquid Li-Ion systems. 

Membrane-type fuel cells. The electrolyte is a polymeric ion-exchange membrane the working temperatures are 60 to 100°C. Such systems were first used in Gemini spaceships. These fuel cells subsequently saw a rather broad development and are known as (solid) polymer electrolyte or proton-exchange membrane fuel cells (PEMFCs). 

Paulus UA, Veziridis V, Schnyder B, Kuhnke M, Scherer GG, Wokaun A. 2003. Fundamental investigation of catalyst utilization at the electrode/solid polymer electrolyte interface. Part I. Development of a model system. J Electroanal Chem 541 77-91. 

The solid polymer electrolyte cells are viewed as being particularly appropriate for the treatment of high purity water systems, including the provision of ultra pure water for the pharmaceutical industry, cf. Ref. [205], The process is often coupled with UV radiation which serves to decompose unwanted, residual ozone [133],... 

A. LaConti, G. Smarz, F. Sribnik, "New Membrane-Catalyst for Solid Polymer Electrolyte Systems," Final Report prepared by Electro-Chem Products, Hamilton Standard for Los Alamos National Laboratory under Contract No. 9-X53-D6272-1, 1986. 

The results presented in Fig. 6.9 for a solid polymer electrolyte follow the same trend as that obtained for electrolytes based on low molecular weight liquid polymers. Fig. 6.10 (MacCallum, Tomlin and Vincent, 1986 Cameron, Ingram and Sorrie, 1987). The liquid polymer systems are very similar to conventional non-aqueous electrolytes which also show a... 

Solid polymer and gel polymer electrolytes could be viewed as the special variation of the solution-type electrolyte. In the former, the solvents are polar macromolecules that dissolve salts, while, in the latter, only a small portion of high polymer is employed as the mechanical matrix, which is either soaked with or swollen by essentially the same liquid electrolytes. One exception exists molten salt (ionic liquid) electrolytes where no solvent is present and the dissociation of opposite ions is solely achieved by the thermal disintegration of the salt lattice (melting). Polymer electrolyte will be reviewed in section 8 ( Novel Electrolyte Systems ), although lithium ion technology based on gel polymer electrolytes has in fact entered the market and accounted for 4% of lithium ion cells manufactured in 2000. On the other hand, ionic liquid electrolytes will be omitted, due to both the limited literature concerning this topic and the fact that the application of ionic liquid electrolytes in lithium ion devices remains dubious. Since most of the ionic liquid systems are still in a supercooled state at ambient temperature, it is unlikely that the metastable liquid state could be maintained in an actual electrochemical device, wherein electrode materials would serve as effective nucleation sites for crystallization. 

The solid polymer electrolyte approach provides enhanced safety, but the poor ambient temperature conductivity excludes their use for battery applications. which require good ambient temperature performance. In contrast, the liquid lithium-ion technology provides better performance over a wider temperature range, but electrolyte leakage remains a constant risk. Midway between the solid polymer electrolyte and the liquid electrolyte is the hybrid polymer electrolyte concept leading to the so-called gel polymer lithium-ion batteries. Gel electrolyte is a two-component system, viz., a polymer matrix... 

Although the literature on electrodeposited electroactive and passivating polymers is vast, surprisingly few studies exist on the solid-state electrical properties of such films, with a focus on systems derived from phenolic monomers, - and apparently none exist on the use of such films as solid polymer electrolytes. To characterize the nature of ultrathin electrodeposited polymers as dielectrics and electrolytes, solid-state electrical measurements are made by electrodeposition of pofy(phenylene oxide) and related polymers onto planar ITO or Au substrates and then using a two-electrode configuration with a soft ohmic contact as the top electrode (see Figure 27). Both dc and ac measurements are taken to determine the electrical and ionic conductivities and the breakdown voltage of the film. 

Liq./solid/liq. systems offer best prospects, if solid electrolytes can be made thin, tough, and chemically resistant as well as conductive. Turnaround efficiency can be high, in both the Na/3-Al203/S and the H2/solid-polymer-electrolyte/Cl2 systems, as class examples. 

PEO and Related Systems. High ionic conductivities have been characteristically associated with polymer-alkali metal complexes, which are receiving great deal of research attention as electrolytes for solid state batteries. LiC104 dispersed homogeneously in cross-linked (P-cyanoethyl methylsiloxane) polyO-cyano-ethyl methylsiloxane-co-dimethylsiloxane) shows a network film conducting in the order of 10 s ohm-1 cm-1 at room temperature [106]. 

Inaba et al. [29] have introduced a different cell to work with gaseous compounds (Fig. 4). A metal-plated solid polymer electrolyte (SPE) composite electrode faces the gas to be reduced. On the other side, the SPE is in contact with 0.1 M NaOH in which a Pt wire and an Ag/AgCl reference electrode are immersed. This system permits the electroreduction of insoluble reactants in water without employing organic solvents. For example, 2-chloro-l,l,l,2-tetrafluoroethane (HCFC 124) is transformed into 1,1,1,2-tetrafluoroethane (HFC 134a). The cathodic reaction can be written as follows ... 

Ionically conducting polymers and their relevance to lithium batteries were mentioned in a previous section. However, there are several developments which contain both ionically conducting materials and other supporting agents which improve both the bulk conductivity of these materials and the properties of the anode (Li)/electrolyte interface in terms of resistivity, passivity, reversibility, and corrosion protection. A typical example is a composite electrolyte system comprised of polyethylene oxide, lithium salt, and A1203 particles dispersed in the polymeric matrices, as demonstrated by Peled et al. [182], By adding alumina particles, a new conduction mechanism is available, which involved surface conductivity of ions on and among the particles. This enhances considerably the overall conductivity of the composite electrolyte system. There are also a number of other reports that demonstrate the potential of these solid electrolyte systems [183],... 

Figure 30 Schematic of the UHV/antechamber/transfer chamber system for electrochemical measurements involving solid polymer electrolytes. Insert A provides an exploded view of the HOPG(bp) sample holder and Li[C/R]/PE0(LiC104) stainless steel holder (SSH) arrangement attached to both magnetically coupled manipulators. Insert B shows in detail the assembled H0PG(bp)/PE0(LiC104) cell in the UHV chamber. MCM = magnetically coupled manipulator GV = gate valve N = nipple CN = ceramic nipple SSH = stainless steel holder TMP = turbomolecular pump. (From Ref. 6.)...

Ion conducting polymers may be preferable in these devices electrolytes because of their flexibility, moldability, easy fabrication and chemical stability (for the same reasons that they have been applied to lithium secondary batteries [19,48,49]). The gel electrolyte systems, which consist of a polymeric matrix, organic solvent (plasticizer) and supporting electrolyte, show high ionic conductivity about 10 5 S cnr1 at ambient temperature and have sufficient mechanical strength [5,7,50,51], Therefore, the gel electrolyte systems are superior to solid polymer electrolytes and organic solvent-based electrolytes as batteries and capacitor materials for ambient temperature operation. 

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