Carbon solvents

Figure 28. Activated carbon solvent recovery plant.

In contrast to DEC/LiC104 solutions, where typical reaction products of carbonate solvents including alkyl carbonates, alkoxides, and Li2C03 are formed at the lithium surface, DEC/LiPF6 solutions yield LiF and Li20 only [168]. 

The decomposition reactions of the preferred organic carbonate solvents are [152,192] ... 

Usually, an addition of a diluent (solvent), increases the conductivity, but also influences the stability window. It has been found, that among the most popular organic solvents, 2 M solutions in acetonitrile showed the highest conductivity level (EMImN(Tf)2 47 mS/cm and EMImPFe 60 mS/cm) and a broader stability window (ca. 4 V) [12]. Carbonate solvents decrease the cathodic limit by ca. 0.2-0.4 V, depending on the carbonate structure. It is worth noting that different authors give different stability windows for the same ionic liquid [10] this is partially due to different electrode materials. 

There is no question that the development and commercialization of lithium ion batteries in recent years is one of the most important successes of modem electrochemistiy. Recent commercial systems for power sources show high energy density, improved rate capabilities and extended cycle life. The major components in most of the commercial Li-ion batteries are graphite electrodes, LiCo02 cathodes and electrolyte solutions based on mixtures of alkyl carbonate solvents, and LiPF6 as the salt.1 The electrodes for these batteries always have a composite structure that includes a metallic current collector (usually copper or aluminum foil/grid for the anode and cathode, respectively), the active mass comprises micrometric size particles and a polymeric binder. 

Glassy carbon solvent, methanol supporting electrolyte, 0.5 M NaC104... 

The radical-like products readily abstract halide ligands from halo-carbon solvents ... 

Aurbach and co-workers performed a series of ex situ as well as in situ spectroscopic analyses on the surface of the working electrode upon which the cyclic voltammetry of electrolytes was carried out. On the basis of the functionalities detected in FT-IR, X-ray microanalysis, and nuclear magnetic resonance (NMR) studies, they were able to investigate the mechanisms involved in the reduction process of carbonate solvents and proposed that, upon reduction, these solvents mainly form lithium alkyl carbonates (RCOsLi), which are sensitive to various contaminants in the electrolyte system. For example, the presence of CO2 or trace moisture would cause the formation of Li2COs. This peculiar reduction product has been observed on all occasions when cyclic carbonates are present, and it seems to be independent of the nature of the working electrodes. A single electron mechanism has been shown for PC reduction in Scheme 1, while those of EC and linear carbonates are shown in Scheme 7. ... 

When the graphite anode was cycled in the electrolytes based on these carbonate solvents, it was found... 

This corrosion of the SEI by linear carbonate solvents would undoubtedly produce adverse effects on the performance of lithium ion cells. During longterm cycling, the damaged SEI has to be repaired constantly by the same electrochemical reactions that occurred in the initial formation process, which consumes the limited lithium ion source in the cell and increases the impedance at the electrode/ electrolyte interface. 

Safety and Hazards. The linear carbonate solvents are highly flammable with flash points usually below 30 °C. When the lithium ion cell is subject to various abuses, thermal runaway occurs and causes safety hazards. Although electrode materials and their state-of-charge play a more important role in deciding the consequences of the hazard, the flammable electrolyte solvents are most certainly responsible for the fire when a lithium ion cell vents. The seriousness of the hazard is proportional to the size of the cell, so flame-retarded or nonflammable lithium ion electrolytes are of special interest for vehicle traction batteries. 

Among these new borates, particular attention should be paid to a salt based on oxalato ligands, which has aroused intense interest recently in the lithium ion research and development community. This salt was invented by Lischka et al. and independently synthesized and investigated by Xu and Angell, who also gave it the popular name LiBOB. Following these extensive physical characterizations, a rather comprehensive electrochemical evaluation was conducted on this salt by Xu et 155,324,488,489 found that the solutions of LiBOB in mixed carbonate solvents met the complete set of stringent requirements for electrolyte solute intended for lithium ion cell applications (1) it is anodically stable on the surface of composite cathode materials up to 4.3 V, (2) it can form a protective SEI on the... 

Behr A, Bahke P, Klinger B, Becker M (2007) Application of carbonate solvents in the telomerisation of butadiene with carbon dioxide. J Mol Catal A Chem 267 149-156... 

The Fluor Solvent Process removes CO2 from natural gas and various industrial gas streams by dissolving the CO2 in a propylene carbonate solvent. The process is based on the principle that CO2 is much more soluble in low-temperature propylene carbonate than other common gases. It should be noted that the process cannot be used when H2S is present1. 

In reviewing the intrinsic electrochemical behavior of nonaqueous systems, it is important to describe reactions of the most common and unavoidable contaminants. Some contaminants may be introduced by the salts (e.g., HF in solutions of the MFX salts M = P, B, As, etc.). Other possible examples are alcohols, which can contaminate esters, ethers, or alkyl carbonates. We examined the possible effect of alcoholic contaminants such as CH3OH in MF and 1,2-propylenegly-col at concentrations of hundreds of ppm in PC solutions. It appears that the commonly used ester or alkyl carbonate solvents are sufficiently reactive (as described above), and so their intrinsic reactivity dominates the surface chemistry if the concentration of the alcoholic contaminant is at the ppm level. We have no similar comprehensive data for ethereal solutions. However, the most important contaminants that should be dealt with in this section, and which are common to all of these solutions, are the atmospheric ones that include 02, H20, and C02. The reduction of these species depends on the electrode material, the solvent used, and their concentration, although the cation plays the most important role. When the electrolyte is a tetraalkyl ammonium salt, the reduction products of H20, 02 or C02 are soluble. As expected, reduction of water produces OH and... 

Schemes 1 and 2 provide the most probable reduction patterns of alkyl carbonate solvents on Li surfaces (with references included). Table 3 provides a summary of the various surface species formed on lithium in the commonly used Li battery electrolyte solutions (with references included). Scaling the rela-...

---