Sulfolane as Solvent for Lithium Battery Electrolytes

Abstract

The properties and applications in lithium batteries of solutions containing lithium perchlorate dissolved in sulfolane have been studied. Due to the high cryoscopic constant of sulfolane (85 K/mole), the freezing point can be considerably decreased. Also the viscosity can be decreased in a way similar to the idea of mixed carbonate solvents. Viscosity and conductivity obey the mified Walden rule. The addition of sulfolane to carbonate solvents increases their flash point fairly considerably.The capacity of experimental cells containing a LiCoO2 cathode and a carbon anode was ca. 33.33 mAh/g (related to anode material). The internal resistance of the cell increased, and an irreversible charge was observed on discharge curves and described. To some extent, the battery had the capability of a rechargeable one.
 The use of sulfolane (SL) as a highly polar solvent for electrochemical purposes has been the subject of previous studies [1] – [6]. Its advantages are high permittivity, excedent thermal stability and resistance to strong oxidation potentials. However, there are some disadvantages such as rather high viscosity and correspondingly also low conductivity of salt solutions in this solvent, and a rather high freezing point (+ 28.4 °C).
 A similar problem arises in ethylene carbonate which exhibits excellent electrochemical properties if solvents with a sufficiently low freezing point and viscosity are added. It is commonly known that the loss of conductivity is not so detrimental , and the freezing point depression can make such mixed solvents useful. Therefore the blends of ethylene carbonate (abbreviated as EC) with other solvents (mostly dimethyl carbonate DMC) are used as solvents for preparation of electrolytes for lithium batteries.
 The main objective of the present paper is to attempt to suppress the weaknesses of sulfolane by adding a solvent with a sufficiently low freezing point and viscosity in order to facilitate the use of sulfolane for various electrochemical applications in electrochemical science and technology.