Batteries, polymer

The lithium-ion-polymer battery, which uses a cathode that contains lithium instead of cobalt, is likely to eventually replace lithium-ion. Lithium-ion-polymer batteries boast a longer life expectancy (over 500 charge-and-discharge cycles as opposed to around 400), much more versatility (they are flat and flexible and can be cut to fit almost any shape), and better safety (far less likely to vent flames while recharging). 

The knowledge that conducting polymers can be charged, i.e. oxidized and reduced, raised early on the question of possible applications, such as the construction of a polymer battery. But basic research was long unable to explain the charge storage mechanism. 

The enormous efforts put into the basic research and development of conducting polymers are naturally related to hopes of feasible technical apphcations The starting point of this development was the discovery that PA can fimction as an active electrode in a rechargeable polymer battery. Since then, the prospects of technical application have grown considerably Apart from the battery electrode, conducting polymers are discussed as potential electrochromic displays... 

The development of a rechargeable polymer battery is being pursued worldwide. Its attraction lies in the specific weight of polymers, which is considerably lower than that of ordinary inorganic materials, as well as potential environmental benefits. In principle there are three different types of battery. The active polymer electrode can be used either as cathode (cell types 1, 2), or as anode (cell type 3), or as both cathode and anode (cell type 4) (Fig. 14). As the most common polymer materials are usually only oxidizable, recent research has concentrated on developing cells with a polymer cathode and a metal anode. 

Fig. 14. Cell types for a polymer battery with active polymer anode, cathode or both respectively...

A promising candidate for a polymer battery that does not possess the typical disadvantages of PA is PPy 126-178.256-259) jjg cjj-cuit voltage lies near 3.5 V vs Li /Li. Charge capacity is about 70 to 85 A h kgand the effective energy density... 

The field of modified electrodes spans a wide area of novel and promising research. The work dted in this article covers fundamental experimental aspects of electrochemistry such as the rate of electron transfer reactions and charge propagation within threedimensional arrays of redox centers and the distances over which electrons can be transferred in outer sphere redox reactions. Questions of polymer chemistry such as the study of permeability of membranes and the diffusion of ions and neutrals in solvent swollen polymers are accessible by new experimental techniques. There is hope of new solutions of macroscopic as well as microscopic electrochemical phenomena the selective and kinetically facile production of substances at square meters of modified electrodes and the detection of trace levels of substances in wastes or in biological material. Technical applications of electronic devices based on molecular chemistry, even those that mimic biological systems of impulse transmission appear feasible and the construction of organic polymer batteries and color displays is close to industrial use. 

In battery applications, new hthium ion batteries called lithium ion polymer batteries (or more simply but misleadingly, lithium polymer batteries) work with a full matrix of ionically conducting polymer, this polymer being present inside the porous electrodes and as a separator between the electrodes. They are offered in attractive flat shapes for mobile applications (mobile phones, notebooks). 

Polymer Batteries The discovery that doping of polyacetylene produced a highly conducting material was followed swiftly by the realization that this material was a rechargeable battery material which, optimistically, might lead to lightweight... 

As to anodes, in most of the research work a generously dimensioned sheet of lithium metal has been used. Such an electrode is rather irreversible, but this is not noticed when a large excess of lithium is employed. Li-Al alloys and carbon materials inserting lithium cathodically during recharging can be used as anodes in nonaqueous solutions. Zinc has been used in polymer batteries with aqueous electrolyte (on the basis of polyaniline). 

E—Lithium Lithium anode Iodine, sulfur dioxide, thionyl chloride, and iron disulfide Secondary Lithium-iron disulfide batteries, lithium-ion batteries, and lithium polymer batteries... 

The starting point for applications was the discovery that PA can function as an active electrode [2] in a rechargeable polymer battery. Since then, the prospects of... 

However, some of the basic problems of polypyrrole and of the other heterocyclic polymers act to limit the performance of the lithium/polymer battery, and thus its wide applicability. These are essentially slow kinetics, self-discharge and low energy content. 

Although the diffusion of the counterion is faster in polypyrrole than in polyacetylene, its value is still low enough to influence the rate of the electrochemical charge and discharge processes of lithium/polymer batteries. Indeed the current output of these batteries is generally confined to a few mA cm . Possibly, improvements in the electrode kinetics, and thus in the battery rates, may be obtained by the replacement of standard ... 

Another problem still to be solved in polymer batteries is the self-discharge of the polymer electrode in common electrolyte media. Effectively, the majority of the polymer electrodes show a poor charge retention in organic electrolytes. In situ spectroscopic measurements (Scrosati et al., 1987) have clearly demonstrated the occurrence of spontaneous undoping processes. A typical example is illustrated in Fig. 9.17 which is related to the change of the absorbance of doped polypyrrole upon contact with the electrolyte. 

The majority of polymer electrodes cannot be doped to very high levels. For instance, polypyrrole may reach doping levels of the order of 33%. This inherent limitation combined with the fact that the operation of the lithium/polymer battery requires an excess of electrolyte (to ensure... 

More recently, solid state batteries with lithium conducting polymer electrolytes have been extensively studied. The development has focused on secondary batteries for an electric vehicle, because lithium polymer batteries have a theoretical energy density that approaches 800 W h kg ... 

Fig. 11.15 Loss of capacity with cycle life for polymer batteries (Kapfer et al, 1990).

The potential use of polymeric ion-exchange membranes in the next generation single-ion secondary lithium polymer batteries was shown by Sachan et al 84,85 Conductivities exceeding 10 S/cm with transference numbers of unity were achieved for Nafion converted to the Li+ salt form. 

Lithium polymer electrolytes formed by dissolving a lithium salt LiX (where X is preferably a large soft anion) in poly(ethylene oxide) PEO can find useful application as separators in lithium rechargeable polymer batteries.Thin films must be used due to the relatively high ionic resistivity of these polymers. For example, the lithium-ion conductivity of PEO—Li salt complexes at 100 °C is still only about Viooth the conductivity of a typical aqueous solution. 

Figure 14. Scanning electron micrographs of Celgard PVdF coated separators used in lithium gel polymer batteries (a) surface SEM, (b) cross-section SEM of coated trilayer, and (c) cross section of PVdF coating.

Hiroshi, T. In Advanced Technologies for Polymer Battery, Oyama, N., Ed. CMC Tokyo, 200X p 165 (in Japanese). 

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