Lithium hexafluoroarsenate

The ecological risks based on possible degradation products [77-79] prevent its economic application. 

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Because of the special stabiHty of the hexafluoroarsenate ion, there are a number of appHcations of hexafluoroarsenates. For example, onium hexafluoroarsenates (33) have been described as photoinitiators in the hardening of epoxy resins (qv). Lithium hexafluoroarsenate [29935-35-1] has been used as an electrolyte in lithium batteries (qv). Hexafluoroarsenates, especially alkaH and alkaline-earth metal salts or substituted ammonium salts, have been reported (34) to be effective as herbicides (qv). Potassium hexafluoroarsenate [17029-22-0] has been reported (35) to be particularly effective against prickly pear. However, environmental and regulatory concerns have severely limited these appHcations. 

Lithium hexafluoroarsenate is thermally stable [54, 55] but shows environmental risks due to possible degradation products [56-58], even though it is itself not very toxic. Its LD 50 value is similar to that of lithium perchlorate [55]. Just like lithium hexafluorophosphate, it can initiate the polymerization of cyclic ethers. Polymerization may be inhibited by tertiary amines [59], or 2-methylfuran [60], yielding highly stable electrolytes. 

Lithium glasses, advantage of, 14 28-29 Lithium halides, 15 134, 138-140 Lithium hexafluoroarsenate, in lithium cells, 3 459... 

There are a few reports of poly(naphthalene) thin films. Yoshino and co-workers. used electrochemical polymerization to obtain poly(2,6-naphthalene) film from a solution of naphthalene and nitrobenzene with a composite electrolyte of copper(II) chloride and lithium hexafluoroarsenate. Zotti and co-workers prepared poly( 1,4-naphthalene) film by anionic coupling of naphthalene on. platinum or glassy carbon electrodes with tetrabutylammonium tetrafluoroborate as an electrolyte in anhydrous acetonitrile and 1,2-dichloroethane. Recently, Hara and Toshima prepared a purple-colored poly( 1,4-naphthalene) film by electrochemical polymerization of naphthalene using a mixed electrolyte of aluminum chloride and cuprous chloride. Although the film was contaminated with the electrolyte, the polymer had very high thermal stability (decomposition temperature of 546°C). The only catalyst-free poly(naphthalene) which utilized a unique chemistry, Bergman s cycloaromatization, was obtained by Tour and co-workers recently (vide infra). 

Lithium tetrafluoroborate, (LiBF4), lithium hexafluorophosphate, (LiPF6), lithium hexafluoroarsenate, (LiAsF ), lithium trifluoromethane sulfonate, (LiSOjCFj), are the electrolyte salts of the 21st Century. The performance of lithium ion cells, primary and secondary lithium cells depends on the purity of these compounds. Several hundred tons of these materials have been produced and many more tons — and perhaps thousands of tons — will be required in the near future. One of the largest automotive producers predicts that there may be a market for 10-15 million pounds of these salts. The demand for Lithium ion primary cells is also very huge in electronics, computers, communication systems and military applications. 

Electrolytic salts such as lithium perchlorate, lithium hexafluoroarsenate, and lithium tetrafluoroborate. 

V. R. Koch, J. Electrochem. Soc. 1979, 126, 181-187. Reactions of tetrahydrofuran and lithium hexafluoroarsenate with lithium. 

In 1994, Tadiran, an Israeli company, made the discovery described as follows This cell comprises as main components a negative electrode which is Lithium or Lithium alloy, a positive cathode which includes MnOa and an electrolyte which is 1,3-Dioxolane (148) with Lithium hexafluoroarsenate (LiAsFe) and a polymerization inhibitor [143]. 

Silver vanadium oxide is combined with a conductive carbon and a binder like PTFE to make the cathode. The usual electrolyte solution used is lithium hexafluoroarsenate (LiAsFs) in mixed organic solvents, like propylene carbonate and 1,2-dimethoxyethane. 

Blue films of poly pyridazine with conductivities up to 10 S cm" can be grown from a 0.4 M solution of pyridazine (Fig. 8) dissolved in benzonitrile into which 0.2 M lithium perchlorate has been added as a supporting electrolyte [196]. Applying a potential of approximately 4 V between a conducting glass (ITO) anode and a nickel cathode produced a typical current density of about 1.5 mA/cm. This electrolyte composition appears to produce the highest quality films. Other solvents such as acetonitrile, poropylene carbonate, and nitrobenzene as well as other salts including lithium tetrafluoroborate, lithium hexafluoroarsenate, or tetrabutylam-monium perchlorate produce films, but of lower quality. 

Polyselenophene (Fig. 16c) has been prepared. However, due to the difficulty in obtaining the monomer, the polymer has not been extensively investigated. Polymers of selenophene prepared electrochemically under appropriate conditions yield films with maximum conductivities of 10"- S cm [330,331]. Samples of p-doped selenophene produced chemically have conductivities on the same order of magnitude [332]. Applying 3-10 V between two electrodes in an electrolyte of 0.1 to 1 M lithium tetrafluoroborate or lithium perchlorate dissolved in benzonitrile or propylene carbonate gives polyselenophene films, as does the combination of tetrabutylammonium tetrafluoroborate in benzonitrile. However, other salts such as lithium hexafluoroarsenate, lithium hexafluorophosphate, tetrabutylammonium perchlorate, or silver perchlorate in combination with solvents such as acetonitrile or nitrobenzene were reported to produce either powders or no products at all [330,331,333]. 

When the synthetic conditions of the experiment are altered, the conductivity of the resulting film is substantially lowered [27]. For example, substitution of lithium tetrafluroborate for lithium hexafluoroarsenate caused the conductivity of the film to drop to 40 S cm". Furthermore, substitution of acetonitrile for nitrobenzene lowered the conductivity of the film even more to 1.0 S cm". ... 

Conducting polynaphthalene films can be prepared by the electrochemical polymerization of napthalene (Fig. 22). Satoh et al. [362,372] reported a synthetic scheme which is directly analogous to that for the preparation of polyparaphenylene outlined in the previous section. A nitrobenzene mixture containing 0.1 M copper(ll) chloride, 0,1 M lithium hexafluoroarsenate, and 0.1 M naphthalene a conducting... 

Anthracene (Fig. 23) has also been polymerized using a method similar to that for the preparation of polyparaphenylene and polynaphthalene. A composite electrolyte of copper(II) chloride and lithium hexafluoroarsenate produced polyanthracene with a conductivity of 10" S cm" [362,372]. An electrolyte of lithium hexafluoroarsenate and NiCl2[P(allyl)2Ph]2, which has successfully produced polyparaphenylene, gives polyanthracene with a conductivity of 1.2 x 10" S cm" [369]. Elemental analysis, nuclear magnetic resonance, and infrared results are consistent with polyanthracene. 

The electrolyte solution consists of a lithium salt in an organic solvent. Commonly used salts include lithium hexafluorophosphate, lithium perchlorate, lithium tetra-fluoroborate, lithium hexafluoroarsenate, lithium hexafluorosilicate, and lithium tetraphen)dborate. Organic solvents used in the electrolyte solution are ethylene carbonate, dieth)d carbonate, dimethyl carbonate, methyl ethyl carbonate, and propylene carbonate, to name the most important ones. When a lithium ion battery is charged, the positive lithium ions move from the positive electrode to the negative one. The process to insert the lithium ions into the graphite electrode is called intercalation. When the cell is discharging, the reverse occurs. 

Lithium perchlorate LiC104 Lithium Lithium hexafluoroarsenate tetralluoroborate LiAsFg LiBp4 Lithium fluoroaUcyphosphates LiFAP Lithium bis(oxalato) borate LiBOB... 

Conductive salts for the electrolyte mixture are to be chosen with preferably low lattice energy. So solvation is easy and a high percentage of the solute might be dissociated in the solution. For most systems salts of lithium are chosen which are combined with big complex anions such as, e.g. lithium perchlorate LiC104, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate LiAsFg, lithium hexafluoropho-... 

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