Page 553 - Handbook of Battery Materials

17.2 Components of the Liquid Electrolyte 527

• empirical solvent parameters representing their acid-base properties and their
polarizability
and chemical categories referring to the functional group of the molecule (esters,
ethers, ketones, and so on), or molecular properties such as

• dipole moment µ (D),
• polarizability α,
• van der Waals volumes and radii or related size parameters,
• the electrostatic factor (EF = εµ).
Empirical solvent parameters are determined by thermodynamic or spectroscopic
experiments yielding parameters representing
• the ability of solvents to interact with acceptors such as protons, other cations,
or Lewis acids (e.g., BF 3 ,SbCl 5 ) as reflected by Gutmann’s donor number (DN)
[35–38] or Kamlet and Taft’s β-scale [39–42],
• the ability of solvents to interact with donors such as anions or Lewis bases,
as reflected by Dimroth and Reichart’s electron transfer (ET) (30)-scale [43, 44],
Mayer, Gutmann, and Gerger’s acceptor number (AN) [45], or Kamlet and Taft’s
α-scale [42, 46],
• the polarity of a solvent and the polarizability of solvent molecules expressed with
∗
the help of the solvatochromic parameter π of Kamlet et al. [39, 47–50].
Based on previous classifications and according to criteria discussed in Ref. [15]
we have extended the classification of solvents into eight classes:
1) amphiprotic hydroxylic solvents, typical examples being the alcohols,
2) amphiprotic protogenic solvents, for example, carboxylic acids,
3) protophilic h-bond donor solvents, for example, amines,
4) dipolar aprotic protophilic solvents, for example, pyridine,
5) dipolar aprotic protophobic solvents, for example, esters,
6) low-permittivity electron donor solvents, for example, ethers,
7) low-polarity solvents of high polarizability, for example, benzene,
8) inert solvents, for example, alkanes and perfluoroalkanes.

Because of the reactivity of pure or in-carbon-intercalated lithium, protic solvents
(classes 1–3) cannot be used in lithium batteries because hydrogen would be
formed according to the reaction:
+ − (17.1)
RH + Li → Li + R + 1/2H 2
A reported exception is n-butylamine [51], a solvent of class 3, because reaction
(17.1) does not take place. Hence, mainly solvents of the classes 5–8 are suited
for lithium batteries, but only under the condition that they are electrochemically
stable with lithium and cathode materials.
Table 17.1 shows a collection of solvents in alphabetical order used in lithium or
lithium-ion batteries. The table contains the names of the solvents, their acronyms,
◦
◦
the liquid range represented by melting (Θ m C) and boiling points (Θ C), and
◦
the physical properties at 25 C unless otherwise noted: dielectric permittivity ε,