Polymers electrolytes

Pol5Tner lithium-ion technology is also known commercially by the name LiPo. It has been commercialized more recently, particularly to serve the needs of model-making, and the need to have very varied formats of batteries, particularly in a flat pouch. LiPo technology is also to be found in electrically-assisted pedal cycles. More recently, it has been envisaged for electric vehicles or mobile devices. 

The basic principle of a jellified (or gelled) pol5mier electrolyte was put forward in the mid-1970s. It is based on the ability of a polymer film to combine two main properties  

Once the composition of the polymer matrix has been defined, the choice of liquid electrolyte needs to be carefully considered, because in particular it affects not only the mechanical strength of the membrane, but also the nature of the passivation layer which is formed on the surface of the lithium or of the graphite. 

Originally, it was the company Bellcore (Bell Communications Research, USA) which, in 1994, demonstrated the feasibility of operation of such a fluoride polymer-based separator. Today, the technology is commercialized by the South Korean company Dow Kokam which, like other companies (Sony, Toshiba, Panasonic, Samsung, SAFT, Valence, etc.) in 1994 purchased the license to exploit the patent filed by Bellcore. However, it seems that only Kokam has succeeded in solving the technical difficulties 

Using this type of electrolyte, it is possible to make flat and flexible batteries, without the risk of the electrolyte leaking if the external casing is broken. This casing is a pouch which is metalized on the outside and covered on the inside surface with a heat-sealable polymer. This type of battery is also lighter, because there is no solid metal casing. 

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Polymer electrolyte Polymer electrolytes Polymer emulsions Polymer flocculation Polymer gasoline... 

AFC = all line fuel ceU MCFC = molten carbonate fuel ceU PAFC = phosphoric acid fuel ceU PEFC = polymer electrolyte fuel ceU and SOFC = solid oxide fuel ceU. 

Polymer Electrolyte Fuel Cell. The electrolyte in a PEFC is an ion-exchange (qv) membrane, a fluorinated sulfonic acid polymer, which is a proton conductor (see Membrane technology). The only Hquid present in this fuel cell is the product water thus corrosion problems are minimal. Water management in the membrane is critical for efficient performance. The fuel cell must operate under conditions where the by-product water does not evaporate faster than it is produced because the membrane must be hydrated to maintain acceptable proton conductivity. Because of the limitation on the operating temperature, usually less than 120°C, H2-rich gas having Htde or no (

The successfiil synthesis of a transparent soHd polymer electrolyte (SPE) based on PEO and alkoxysilanes has been reported (41). The material possessed good mechanical properties and high electrical conductivity (around 1.8 x 10 S/cm at 25°C) dependent on the organic—inorganic ratio and PEO chain length. 

Three types of electrochemical water-spHtting processes have been employed (/) an aqueous alkaline system (2) a soHd polymer electrolyte (SPE) and (J) high (700—1000°C) temperature steam electrolysis. The first two systems are used commercially the last is under development. 

Solid Polymer E,kctroljte. The electrolyte in soHd polymer electrolyte (SPE) units is Nafion, a soHd polymer developed by Du Pont, which has sulfonic acid groups attached to the polymer backbone. Electrodes are deposited on each side of the polymer sheet. H" ions produced at the anode move across the polymer to the cathode, and produce hydrogen. The OH ions at the anode produce oxygen. These units have relatively low internal resistances and can operate at higher temperatures than conventional alkaline electrolysis units. SPE units are now offered commercially. 

Fig. 11. Solid polymer electrolyte (SPE) fuel cell (a) cell design and (b) power curve at 25°C.

As can be seen from Eigure 11b, the output voltage of a fuel cell decreases as the electrical load is increased. The theoretical polarization voltage of 1.23 V/cell (at no load) is not actually realized owing to various losses. Typically, soHd polymer electrolyte fuel cells operate at 0.75 V/cell under peak load conditions or at about a 60% efficiency. The efficiency of a fuel cell is a function of such variables as catalyst material, operating temperature, reactant pressure, and current density. At low current densities efficiencies as high as 75% are achievable. 

Refractive Index. The effect of mol wt (1400-4000) on the refractive index (RI) increment of PPG in ben2ene has been measured (167). The RI increments of polyglycols containing aUphatic ether moieties are negative drj/dc (mL/g) = —0.055. A plot of RI vs 1/Af is linear and approaches the value for PO itself (109). The RI, density, and viscosity of PPG—salt complexes, which maybe useful as polymer electrolytes in batteries and fuel cells have been measured (168). The variation of RI with temperature and salt concentration was measured for complexes formed with PPG and some sodium and lithium salts. Generally, the RI decreases with temperature, with the rate of change increasing as the concentration increases. 

A second class of important electrolytes for rechargeable lithium batteries are soHd electrolytes. Of particular importance is the class known as soHd polymer electrolytes (SPEs). SPEs are polymers capable of forming complexes with lithium salts to yield ionic conductivity. The best known of the SPEs are the lithium salt complexes of poly(ethylene oxide) [25322-68-3] (PEO), —(CH2CH20) —, and poly(propylene oxide) [25322-69-4] (PPO) (11—13). Whereas a number of experimental battery systems have been constmcted using PEO and PPO electrolytes, these systems have not exhibited suitable conductivities at or near room temperature. Advances in the 1980s included a new class of SPE based on polyphosphazene complexes suggesting that room temperature SPE batteries may be achievable (14,15). 

The general configuration of one system that has reached an advanced stage of development (22) is shown in Figure 1. The negative electrode consists of thin lithium foil. The composite cathode is composed of vanadium oxide [12037-42-2] 6 13 with polymer electrolyte. Demonstration... 

Fig. 1. Configuration for a soHd polymer electrolyte rechargeable lithium cell where the total thickness is 100 pm.

Monovalent cations are good deflocculants for clay—water sHps and produce deflocculation by a cation exchange process, eg, Na" for Ca ". Low molecular weight polymer electrolytes and polyelectrolytes such as ammonium salts (see Ammonium compounds) are also good deflocculants for polar Hquids. Acids and bases can be used to control pH, surface charge, and the interparticle forces in most oxide ceramic—water suspensions. 

Polymer electrolyte fuel cells can be obtained from several developers. These fuel cells deliver about 5 kW of power and measure 30 by 30 by 70 cm (12 X 12 X 28 in.). For the large produc tion volume anticipated if the automotive industry were to adopt the PEFC, a system cost of less than 100/kW may be reached eventually. 

Ishikawa, M., Morita, M., lhara, M. and Matsuda, Y., Electric double layer capacitor composed of activated carbon fiber cloth electrodes and solid polymer electrolytes containing alkylammonium salt, J. Electrochem. Soc., 1994, 141(7), 1730 1734. 

A possible solution to this problem is to use an electrolyte, such as a solid polymer electrolyte, which is less reactive with lithium metal [3]. Another simple solution is the lithium-ion cell. 

Figure 11.9. Conductivity vs temperature plot for two ionically conducting crystals and for a polymer electrolyte, LiTf-aPtO40, which is based on amorphous poly(ethylene) oxide (after Ratner...

Ratner, M.A. (2000), Polymer Electrolytes Ionic Transport Mechanisms and Relaxation Coupling, MRS Bull. 25(3), 31. 

The first use of ionic liquids in free radical addition polymerization was as an extension to the doping of polymers with simple electrolytes for the preparation of ion-conducting polymers. Several groups have prepared polymers suitable for doping with ambient-temperature ionic liquids, with the aim of producing polymer electrolytes of high ionic conductance. Many of the prepared polymers are related to the ionic liquids employed for example, poly(l-butyl-4-vinylpyridinium bromide) and poly(l-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide [38 1]. 

Noda and Watanabe [42] reported a simple synthetic procedure for the free radical polymerization of vinyl monomers to give conducting polymer electrolyte films. Direct polymerization in the ionic liquid gives transparent, mechanically strong and highly conductive polymer electrolyte films. This was the first time that ambient-temperature ionic liquids had been used as a medium for free radical polymerization of vinyl monomers. The ionic liquids [EMIM][BF4] and [BP][Bp4] (BP is N-butylpyridinium) were used with equimolar amounts of suitable monomers, and polymerization was initiated by prolonged heating (12 hours at 80 °C) with benzoyl... 

The most promising fuel cell for transportation purposes was initially developed in the 1960s and is called the proton-exchange membrane fuel cell (PEMFC). Compared with the PAFC, it has much greater power density state-of-the-art PEMFC stacks can produce in excess of 1 kWA. It is also potentially less expensive and, because it uses a thin solid polymer electrolyte sheet, it has relatively few sealing and corrosion issues and no problems associated tvith electrolyte dilution by the product water. 

Gottesfeld, S., and Zawodzinski, T. A. (1998). Polymer Electrolyte Fuel Cells, Advances m Electrochemical Science and Engineering, ed. R. Alkire et al. NewYork Wiley. 

Ren, X. Springer, T. E. and Gottesfeld, S. (1998). Direct Methanol Fuel Cell Transport Properties of the Polymer Electrolyte Membrane and Cell Performance. Vol. 98-27. Proc. 2nd International Symposium on Proton Conducting Membrane Euel Cells. Pennington, NJ Electrochemical Society. 

The aim of this chapter is to give a state-of-the-art report on the plastic solar cells based on conjugated polymers. Results from other organic solar cells like pristine fullerene cells [7, 8], dye-sensitized liquid electrolyte [9], or solid state polymer electrolyte cells [10], pure dye cells [11, 12], or small molecule cells [13], mostly based on heterojunctions between phthaocyanines and perylenes [14], will not be discussed. Extensive literature exists on the fabrication of solar cells based on small molecular dyes with donor-acceptor systems (see for example [2, 3] and references therein). 

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