Nonaqueous Batteries with LiClO[sub 4]-Ethylene Carbonate as Electrolyte

Abstract

An evaluation of the use of ethylene carbonate as a solvent for high-energy nonaqueous batteries has been performed. The results are compared with those obtained for propy]ene carbonate. A 1.0M LiC104-EC solution has higher conductivity, lower viscosity, and lower influence on the polarization of Li, CuF2, and NiS electrodes than an analogous LiCIO4-PC solutionJ Discharge curves at 1.0 and 2.4 mA/cm 2, obtained under the same conditions in 1.0M LiC104-EC and PC solutions for Li-CuF2 and Li-NiS cells, gave better results when EC was used. A test cell Li/1.0M LiC104-EC/CuF2, capable of providing about 200 Whr/kg (outside casing excluded) when discharged at 1.0 mA/cm 2 at 30~ has been fabricated. Research on the development of high-energy non-aqueous batteries has been focused mostly on propyl-ene carbonate (PC) electrolytic solutions. In 1964, Elliott et al. (1) pointed out that addition of ethylene carbonate (EC) to such solutions improved the system by increasing the dielectric constant, decreasing the viscosity, and increasing the conductivity of the solutions. No further investigation on the use of this solvent in nonaqueous batteries has been reported since, however. Pistoia, De Rossi, and Scrosati (2) have recently shown in a preliminary note some of the advantages of using EC solutions in electrochemical cells, for instance the higher specific conductivity with respect to the PC solutions. EC is solid at room temperature (mp 36.2~ but the high molal lowering of the freezing point (5.5~ can give liquid solutions at room temperature. Furthermore, the addition of only 9% PC is sufficient to obtain another 5~ decrease in the freezing point. On the other hand, the use of EC solutions of low salt concentration, which are solid at room temperature , would significantly reduce the solubility shown by many substances used as cathodes (e.g., CuC1, CuF2, NiF2, and others) and the resulting self-discharge processes. Batteries containing the above-mentioned solid EC solutions could be thermally activated and should need a very low activation energy because of the small temperature increase necessary to melt the solutions. Electrolytic solutions in aprotic solvents must possess certain basic properties in order to be used in a battery ; they must: (a) be inactive toward the electrodes and, particularly , have low solubility effects toward the cathodic materials (b) have sufficiently high conductivity to minimize the IR losses in voltage (c) not appreciably influence the electrode polarization and allow high utilization coefficients, especially of the positive electrode