Polyacetylene cathode

Type I Polyacetylene Cathode In Conjunction with Lithium Anode (1) p-doped (CH)y cathode and LI anode. Cells were... 

Type II Polyacetylene Cathode in Conjunction with a Polyacetylene Anode (i) neutral (CH)V cathode + n-doped (CH)Y anode. Since both neutral and reduced (CH)X have good stability in an electrolyte of 1M L1C104 in tetrahydrofuran a voltaic cell can be constructed using (CH)x as the cathode and (CH- )x as the anode. During discharge the (CH y)x gives up an electron to the (CH)X producing the net overall reaction ... 

Reduction can be effected by doping with alkali metals, either in the vapour phase or in solution, e.g. with naphthalide salts in THE Electrochemical doping is very well possible, for instance with LiB(Me)4 or NaB(Ph)4 in solution with a polyacetylene cathode. The representation (CH)M is often used to denote a certain composition. 

Polyacetylene proved qnite incapable of working in a realistic battery context, and MacDiarmid did not mention this application in his Nobel lectnre of October, 8 2000. However, other materials have proven their worth, and prototype batteries made with polypyrrole and polyaniline as cathodes (positives), and metal or lithiated carbon materials as anodes (negatives), have been demonstrated in dne conrse by the Japanese and German indnstry, for instance. Novdk et al. (1997) have reviewed the field in detail. 

The concept of electrochemical intercalation/insertion of guest ions into the host material is further used in connection with redox processes in electronically conductive polymers (polyacetylene, polypyrrole, etc., see below). The product of the electrochemical insertion reaction should also be an electrical conductor. The latter condition is sometimes by-passed, in systems where the non-conducting host material (e.g. fluorographite) is finely mixed with a conductive binder. All the mentioned host materials (graphite, oxides, sulphides, polymers, fluorographite) are studied as prospective cathodic materials for Li batteries. 

Fig. 9.10 shows a typical CV of a (CH), film in a LiClO -propylene carbonate electrolyte. The voltammogram presents well-defined peaks both in the anodic (doping) and in the following cathodic (undoping) scans this confirms that the doping process of polyacetylene, as suggested by (9.10), can indeed be driven electrochemically and in a reversible way. 

Polyacetylene can be controllably oxidized or reduced by simple electrochemical procedures Cyclic voltammetry studies on free-standing films of cw-polyacetylene show that they can be reversibly oxidized at ca +3.6 V Li and reversibly reduced at ca +1.4 V vs Li. The reactions occurring at the cathode (equation 18a) and at the anode (equation 18b) are given below. 

A battery cell where both the electrodes consist of dopable polymer is shown in Figure 5.23. The electrolyte in this case consists of Li+ClO 4 dissolved in an inert organic solvent, usually tetrahydro-furan or propylene carbonate. When two sheets of polyacetylene or PPP are separated by an insulating film of polycarbonate saturated in an electrolyte (lithium perchlorate), and completely encapsulated in a plastic casing, a plastic battery can be made. The two sheets of polyacetylene or PPP act as both anode and cathode for the battery. A schematic is shown in Figure 5.24. Although doped polyacetylene and polyaniline electrodes have been developed, polypyrrole-salt films are the most promising for practical appKcation. 

Nigrey, P.J., et al. 1981. Lightweight rechargeable storage batteries using polyacetylene, (GH), as the cathode-active material. 7 Electrochem Soc 128 1651. 

The synthesis of coherent silvery films of polyacetylene through the cathodic initiation of polymerization has been reported by Huang et al. [386]. Once the applied current through a low-temperature solution saturated with acetylene gas exceeded a critical value, a red color appeared at the cathode-solution interface, which indicated the preliminary growth of polyacetylene film. The red color may be attributed to the transmission of light through cis-rich polyacetylene. Dimethyl formamide was determined to be the best solvent, and nickel or copper cathodes were found to be well suited for the rapid growth of thick polyacetylene films. 

Battery designs using electroactive polymers feature the EAP as the cathode, which is separated from an anode (such as Li, Na, Mg, and Zn) by an electrolyte. Normally, high specific energies of up to 3.5 V can be obtained (409). EAPs that have been used in rechargeable batteries include polyacetylene-, PANI-, PPy-, PT-, and PPP-based materials (410). The current drawback to full utilization of EAPs for rechargeable batteries is the rate limitations associated with low ionic mobilities of the polymers as well as the electrolytes (14). 

More recently, an all-polymer battery based on derivatized polythiophenes supported on graphite-coated supports was described (139). In this instance, polythiophene functioned more effectively in the n-doping region and provided an improved cell discharge voltage of 2.4 V and capacities of 9.5-1.5 mAh g. A recent approach is the development of a polymer/polsrmer battery based on polyaniline anode and poly-l-naphthol cathode (140). This device has been reported with an impressive cell voltage of 1.4 V, a specific capacity of 150 Ah g, and a loss of 15% of cell capacity after 100 cycles. Other attempts at fabricating battery systems have been made (141) with polyacetylene, polypyrrole, and polyanibne (142),... 

Polymers. Electronically conductive polymers may also be used as cathode materials in rechargeable lithium batteries. The most popular polymers are polyacetylene, polypyrrole, polyaniline, and polythiophene, which are made conductive by doping with suitable anions. The discharge-charge process is a redox reaction in the polymer. The low specific energy, high cost, and their instability, however, make these polymers less attractive. They have been used in small coin-type batteries with a lithium-aluminum alloy as the anode. 

Electrochemical synthesis of polyacetylene was carried out with platinum foil as cathode and nickel foil as anode with nickel bromide in acetonitrile as an electrolyte at room temperature to precipitate in the form of powder in the cell [101]. Chen and Shy [53] observed a thin layer of black material on a surface of the platinum cathode when a voltage of 4-40 V was applied for about 50 min. During this stage, no precipitation of polyacetylene was observed in the solution. The material has the same chemical structure as those produced by the standard Ziegler-Natta catalyst as examined by elemental analysis, infrared spectroscopy. X-ray diffraction, and differential scanning calorimetry. 

As an example, the polyacetylene cations HC H+ are considered. They are readily produced in a hot-cathode discharge source fed with a mixture of acetylene diluted with helium. Ion-molecule reactions lead to polymerization. When a particular species is selected according to the number of carbon atoms in the chain, with currents in the nA range, and codeposited with excess neon, the electronic absorption spectra can be measured. Figure 2 shows the characteristic strong transitions for the species... 

Figure 20. Cathodic current derived from a trans polyacetylene electrode in the dark and on illumination.

A number of other battery types have been published (54) by MacDiarmid, for example, a dual polyacetylene electrode battery has been described in which there is a pCCH) cathode and an n-(CH)x anode in 1 M LiClO with the solvent being propylene carbonate or sulfolane. 

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