Cosolvency criterion

Due to the core importance of the SEI formation on carbonaceous anodes, the majority of the research activities on additives thus far aim at controlling the chemistry of the anode/electrolyte interface, although the number of publications related to this topic is rather limited as compared with the actual scale of interest by the industry. Table 9 summarizes the additives that have been described in the open literature. In most cases, the concentration of these interface-targeted additives is expected to be kept at a minimum so that the bulk properties of the electrolytes such as ion conduction and liquid ranges would not be discernibly affected. In other words, for an ideal anode additive, its trace presence should be sufficient to decouple the interfacial from bulk properties. Since there is no official standard available concerning the upper limit on the additive concentration, the current review will use an arbitrary criterion of 10% by weight or volume, above which the added component will be treated as a cosolvent instead of an additive. 

Choquette et al. investigated the possibilities of using a series of substituted sulfamides as possible electrolyte solvents (Table 12). These compounds are polar but viscous liquids at ambient temperature, with viscosities and dielectric constants ranging between 3 and 5 mPa s and 30 and 60, respectively, depending on the alkyl substituents on amide nitrogens. The ion conductivities that could be achieved from the neat solutions of Lilm in these sulfamides are similar to that for BEG, that is, in the vicinity of 10 S cm Like BEG, it should be suitable as a polar cosolvent used in a mixed solvent system, though the less-than-satisfactory anodic stability of the sulfamide family might become a drawback that prevents their application as electrolyte solvents, because usually the polar components in an electrolyte system are responsible for the stabilization of the cathode material surface. As measured on a GC electrode, the oxidative decomposition of these compounds occurs around 4.3—4.6 V when 100 fik cm was used as the cutoff criterion, far below that for cyclic carbonate-based solvents. 

Crystallization is often used as a method of product isolation. Crystallization of the reaction product may be induced if, to the reaction medium, in which it is well soluble, a cosolvent is added in which the product is insoluble. Because for the latter purification method the solubility should be high at high temperatures but much lower at low temperatures, the temperature coefficient of the solubility becomes an important criterion for the employment of a solvent. A further guide is the fact that substances tend to dissolve in solvents with similar polarities, so that a solvent and cosolvent for the recrystallization of a given product can be selected according to the polarities. 

Eq. (8) is a rigorous thermodynamic equation at infinite protein dilution it allows one to derive a simple criterion for salting-itr or salting-out at low cosolvent concentrations. Indeed, at low cosolvent concentrations (C3 0) it becomes... 

Tables 2 and 3 also demonstrate that /21 constitutes a criterion for the cosolvent behavior. For cosolvents belonging to the first group (urea, guanidine hydrochloride, etc. see Introduction), J21 > 0 and J23 < 0 (because J23 = lim((9 In y2)l X3))x2 = —/21). In contrast for cosolvents belonging to the second group (inorganic salts, glucose, glycerol, etc.) /21 0 and J23 > 0.

Based on the previous considerations, some authors proposed thermodynamic-based approaches to SAS. De la Fuente Badilla et al attempted to develop a thermodynamic-based criterion for optimum batch antisolvent precipitation (GAS) using a definition of the volume expansion that takes into account the molar volume of the system studied. They analyzed various binary and ternary systems and concluded that the pressure corresponding to a minimum value of the liquid-phase volume expansion coincides with the pressure at which the solute precipitates. In a subsequent work, Shariati and Peters further highlighted the role of SC-CO2 in GAS. It acts as a co-solvent (cosolvency effect) at lower concentrations, whereas at higher concentrations it acts as an antisolvent. 

The expression provides a criterion to predict whether or not the mixed solvent is expected to be a cosolvent of the polymer. When T, is a UCST (as is the case in these phase separation studies), -dx /dT > 0 and (dTc/dx)o has the same sign as the numerator of the equation. Choosing solvent 1 such that T 2 < T, then (dTc/dx)o < 0 guarantees that the system will be a cosolvent one. Since %23 - Zi3 > 0, at T i, the numerator in the equation [5.4.1] is negative (cosolvent system) if the unfavorable interaction between the two liquids is large enough to compensate for their different affinity towards the polymer. The equation proposed gives a more detailed criterion for cosolvency than the simple criterion of G > 0. The information needed to predict (dTydx)o from equation [5.4.1] includes the binary interaction parameters of the polymer in each one of the two solvents as a function of temperature, and Xi2(G ) for the mixed solvent too. Table 5.4.1 summarizes results reported by Horta et al. for some cosolvents of polymethylmethacrylate (PMMA). ... 

Equation 10.50 allows one to derive a criterion for salting-in or salting-out for small cosolvent concentrations. Using the Gibbs-Duhem equation for a binary mixture, one can conclude that... 

As far as the three adjustable coefficients equations are concerned, i.e., Auslander s and polynomial, it should be noted that the treatment of our ED/cosolvent binary data doesn t represent a sufficiently severe test to select the more suitable expression for the best fit of the experimental values. In fact, at present, it is hard to appoint a selective criterion for comparing purposes like Equation 6, which is applicable to three-fitting parameters relations, too. Furthermore, the reproducibility of the experimental points is about the same obtained by applying the two adjustable coefficient equations. This evidence could suggest the choice of the simplest function containing a reduced number of fitting parameters with respect to the other, being ascertained that these coefficients are related to the specific solvent-cosolvent interactions. 

The expression provides a criterion to predict whether or not the mixed solvent is expected to be a cosolvent of the polymer. When T, is a UCST (as is the case in these phase separation studies), -d /dT > 0 and (dTc/dx)o has the same sign as the numerator of the equation. Choosing solvent 1 such that Tc2 Tci, then (dT, /dx)o < 0 guarantees that the system will be a cosolvent one. Since %23 Xis the numerator in the equation [5.4.1] is... 

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