Liquid electrolytes organic electrolyte salts

It should be emphasized that ionic liquids are simply organic salts that happen to have the characteristic of a low melting point. Many ionic liquids have been widely investigated with regard to applications other than as liquid materials as electrolytes, phase-transfer reagents [12], surfactants [13], and fungicides and biocides [14, 15], for example. 

The electrolytic cells in use in extractive metallurgy mostly operate with liquid electrolytes which may be either aqueous or nonaqueous. In some cases it is possible to use only non-aqueous electrolytes, while in others it is possible to use either aqueous or nonaqueous electrolytes. A nonaqueous electrolyte may be of the organic or of the molten salt varieties. 

The preferred electrolytes if the solvent is water are KC1 and NaN03. If the solvent is a non-aqueous organic liquid, then we prefer salts of tetra-alkyl ammonium, such as tetra-n-butylammonium tetrafluoroborate, "BrnN+BF. ... 

Electrolytes are ubiquitous and indispensable in all electrochemical devices, and their basic function is independent of the much diversified chemistries and applications of these devices. In this sense, the role of electrolytes in electrolytic cells, capacitors, fuel cells, or batteries would remain the same to serve as the medium for the transfer of charges, which are in the form of ions, between a pair of electrodes. The vast majority of the electrolytes are electrolytic solution-types that consist of salts (also called electrolyte solutes ) dissolved in solvents, either water (aqueous) or organic molecules (nonaqueous), and are in a liquid state in the service-temperature range. [Although nonaqueous has been used overwhelmingly in the literature, aprotic would be a more precise term. Either anhydrous ammonia or ethanol qualifies as a nonaqueous solvent but is unstable with lithium because of the active protons. Nevertheless, this review will conform to the convention and use nonaqueous in place of aprotic .]... 

As a result, the acid strength of the proton is approximately equivalent to that of sulfuric acid in nonaqueous media. In view of the excellent miscibility of this anion with organic nonpolar materials, Armand et al. proposed using its lithium salt (later nicknamed lithium imide , or Lilm) in solid polymer electrolytes, based mainly on oligomeric or macro-molecular ethers. In no time, researchers adopted its use in liquid electrolytes as well, and initial results with the carbonaceous anode materials seemed promising. The commercialization of this new salt by 3M Corporation in the early 1990s sparked considerable hope that it might replace the poorly... 

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 ... 

Ue M, Ida K, Mori S. Electrochemical properties of organic liquid electrolytes based on quaternary onium salts for electrical double-layer capacitors. Journal of the Electrochemical Society 1994 141(ll) 2989-2995. 

A unique approach in nonaqueous electrochemistry which may be applicable to several fields, especially for batteries, was recently presented by Koch et al. (private communication). They showed that it is possible to use solid matrices based on lithium salts contaminated with organic solvents as electrolyte systems. These systems demonstrate several advantages over liquid systems based on the same solvents and salts as solutions. Their electrochemical windows are larger, especially in the anodic direction (oxidation reactions), and it appears that their reactivity toward active electrodes (e.g., Li, Li—C) is much lower than that of the liquid electrolyte systems. 

Room-temperature ionic liquids are the promising electrolytes for the electrodeposition of various metals because they have the merits of both organic electrolytes and high-temperature molten salts. Ionic liquids can be used in a wide temperature range, so temperatures can be elevated to accelerate such phenomena as nucleation, surface diffusion and crystallization associated with the electrodeposition of metals. In addition the process can be safely constracted because ionic liquids are neither flammable nor volatile if they are kept below the thermal decomposition temperature of the organic cations. 

One-dimensional ion conduction is achieved for columnar liquid crystalline ionic liquids 10a,b [29]. In the macroscopically ordered states of these columnar materials, ionic conductivities parallel to the columnar axis (ay) is higher than those perpendicular to the axis (ox)- For example, compound 10b shows the conductivities of 3.1 X 10 S cm (ay), 7.5 x 10 S cm (cJx), and anisotropy (ay/ Qx) of 41 at 100°C. These materials function as self-organized electrolytes. They dissolve a variety of ionic species such as lithium salts. Compound 10b containing LiBp4 (molar ratio of LiBp4 to 10b 0.25) exhibits the conductivities of... 

One can quote exceptions to these generalizations. The tetraalkylammonium salts as a class are liquid at temperatures below 300 K. There are liquid electrolytes— produced from dissolving AICI3 into some complex organics—which are liquid at room temperature (Tables 5.3 and 5.4). Above the normal range of 300-1300 K is another set of molten electrolytes, the molten silicates, borates, and phosphates, for which the characteristic temperature range is 1300-2300 K (Tables 5.5 and 5.6). 

It has long been known that liquid electrolyte systems that melted in the low hundreds of degrees were available in systems of metal chlorides and AICI3, and that some tetraalkylammonium salts melted at < 373 K. Hurley and Wier in 1951 showed that a 2 1 mixture of some complex organic chlorides with AICI3 gave liquid electrolytes at room temperatures. The discovery remained undeveloped for more than 25... 

Water is one of the most widely used solvents because of its availability, low cost, nontoxicity, and safety as well as its ability to dissolve a wide variety of substances. Sometimes when the solubility or any other property of water does not allow it to be used, a polar or a nonpolar organic solvent can be used. In certain applications, neat organic solvents fall short of the mark as far as their dissolving power or other properties are concerned. It is then necessary to use solvent mixtures. These mixtures can be binary (two components), tertiary (three components), or a multicomponent mixture. Many times, one of the components may be a solid. One very common example of this can be found in liquid chromatography where an electrolyte solution (buffer + salt) is used in many applications as a mobile phase. 

Room temperature ionic liquids (RTILs) are molten salts whose melting points are below room temperature. RTILs are formed when the constituent ions are sterically mismatched, thereby hindering crystal formation [17]. As polar solvents, RTILs have unique applications as tunable and environmentally benign solvents with very low volatility, high fire resistance, excellent chemical and thermal stability and wide liquid temperature range and electrochemical windows [17-19]. Solvent applications of RTILs include, for example, organic synthesis [17,20, 21], separations [22, 23], storage and transportation of hazardous chemicals [24], polymeric electrolytes [25, 26], dissolution of natural products [27] and synthesis of hollow metal oxide microspheres [28]. 

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