Electrolytes aprotic organic

Throwaway Cells with Electrolyte Solutions Prepared from Aprotic Organic Solvents... 

The corrosion resistance of lithium electrodes in contact with aprotic organic solvents is due to a particular protective film forming on the electrode surface when it first comes in contact witfi tfie solvent, preventing further interaction of the metal with the solvent. This film thus leads to a certain passivation of lithium, which, however, has the special feature of being efiective only while no current passes through the external circuit. The passive film does not prevent any of the current flow associated with the basic current-generating electrode reaction. The film contains insoluble lithium compounds (oxide, chloride) and products of solvent degradation. Its detailed chemical composition and physicochemical properties depend on the composition of the electrolyte solution and on the various impurity levels in this solution. 

The available choice of lithium salts for electrolyte application is rather limited when compared to the wide spectrum of aprotic organic compounds that could make possible electrolyte solvents. This difference could be more clearly reflected in a comprehensive report summarizing nonaqueous electrolytes developed for rechargeable lithium cells, in which Dahn and co-workers described over 150 electrolyte solvent compositions that were formulated based on 27 basic solvents but only 5 lithium salts. ... 

Electrolyte solutions of various aprotic organic solvents are used in primary lithium batteries. Among the organic solvents are alkyl carbonates [PC (er = 64.4-), ethylene carbonate (EC, 89.640°c)> dimethyl carbonate (DMC, 3.1), diethyl carbonate (DEC, 2.8)], ethers [DME (7.2), tetrahydrofuran (THF, 7.4), 2-Me-THF (6.2),... 

The most commonly used electrolytes for lithium batteries are liquid solutions of lithium salts in aprotic organic solvents. As already discussed in Chapter 4, the main parameters which govern the choice of the electrolyte are ... 

Reference electrodes in organic solvents ordinarily are not as stable with time as those with aqueous electrolytes. Most aprotic organic solvents undergo slow chemical change from reactions of impurities, hydrolysis of the solvent by traces of water, or reaction with a component of the half-cell reaction. The stability of reference electrodes should be checked frequently by comparison with fresh reference electrodes prepared with recently purified solvents and electrolytes. 

There are several ways in which the solvent-supporting electrolyte system can influence mass transfer, the electrode reaction (electron transfer), and the chemical reactions that are coupled to the electron transfer. The diffusion of an electroactive species will be affected not only by the viscosity of the medium but also by the strength of the solute-solvent interactions that determine the size of the solvation sphere. The solvent also plays a crucial role in proton mobility water and other protic solvents produce a much higher proton mobility because of fast solvent proton exchange, a phenomenon that does not exist in aprotic organic solvents. 

For the electrolytic deposition of aluminum there are various types of aprotic organic electrolytes which can be distinguished by their aluminum source ... 

The key to this process [63, 64] was the addition of a quaternary ammonium salt (tetraethy-lammonium p-toluenesulfonate or tetraethylammonium ethylsulphate) to the reaction medium, which increased the solubility of acrylonitrile in the aqueous electrolyte and generated an aprotic organic layer on the cathode surface that inhibited the synthesis of propionitrile by-products (formed by the simple reduction of acrylonitrile). 

Association constants of electrolytes in organic solvents obtained from Raman and IR measurements are known, e.g. for Nal and KI in AN AgNOj in AN LiSCN in polar solvents and ethers NaCo(CO)4 in polar aprotic... 

The main problem arose with respect to the negative electrode. Complications typical for galvanic practice appear under its charge, that is, under cathodic deposition of lithium. As pointed out in Chapter 11, the surface of lithium in aprotic electrolytes is covered by a passive film (SEI) because of the chemical interaction with the components of electrolyte the organic solvent and anions. This film has the properties of solid electrolyte with conductivity by lithium ions. The film is sufficiently thin (its thickness does not exceed several nanometers) and it protects lithium safely from... 

We have seen that the idea of an electrode film system is useful for electrochemistry of molten salts including low-temperature ionic liquids. It is not restricted, however, to this field only. As an example, the protective layer on lithium metal in aprotic organic electrolytes could be mentioned. This layer, so-called solid electrolyte interphase (SEl), exhibits properties of a polyfunctional conductor with high ionic conductivity (Li ions are the carriers) and low electronic conductivity of semiconductive nature. Some peculiarities of film systems with semiconductive character of electronic conductivity are considered below. 

PVPA is a water-soluble white powder, insoluble in aprotic organic solvents. PVPA shows a similar structure to poly(aciylic acid) (PAA) and poly(vinyl-sulfonic acid) (PVSA). Whereas PAA is a weak electrolyte and PVSA is a strong electrolyte, PVPA is intermediate. It shows in reality only one step in neutralization, although should theoretically exhibit two distinctly different steps, like the VPA monomer. Hence, PVPA behaves as a monobasic acid, because the second proton of the monomer unit cannot be ionized in aqueous media. It is assumed that the charge density of the fully ionized PVPA is very high and that the second ionization step does not occur. 

Liquid electrolyte lithium-ion technology uses mixtures of aprotic organic solvents (which are not likely to donate a proton) because the graphite-lithium electrode is very unstable in the presence of compounds with labile hydrogen.22 The solvents used are alkyl earbonates (carbonates of ethylene, propylene, dimethyl, etc.) ethers, in which a lithium salt that... 

A wide variety of solvents has been used for polymerization. In most cases polypyrrole is prepared from electrolyte solutions employing aprotic organic solvents, but since the initial work of Diaz etal. [4] much work has been done on polymerization reaction in aqueous solutions [50,111-12], achieving films with properties similar to those produced from organic solutions. For example, high-quality polypyrrole films (conductivities higher than 500 S cm ) in aqueous solution ofp-toluensulphonate have been obtained [116]. 

A variety of materials have been investigated for the positive electrode (the cathode during discharge), such as intercalation solid compounds, soluble inorganic cathodes, and polymeric materials. Liquid aprotic organic and inorganic electrolytes are used in many cells. Solid polymer electrolytes are also popular as they may provide a safer design because of their lower reactivity with lithium. These materials are identified in Fig. 34.1. 

---