Multi-component nonaqueous electrolytes for rechargeable lithium cells

In this paper we examine the influence of various mixed-solvent electrolytes on the discharge capacity and charge-discharge cycle life of coin-type lithium (Li) metal/amorphous (a-) V2O5-P2O5 (95:5 in molar ratio) cells. The solvents used were ethylene carbonate (EC), propylene carbonate (PC), 2-methyl-tetrahydrofuran (2MeTHF), THF, 1,2-diethoxyethane and 4-methyl-1,3-dioxolane, LiAsF6 and LiCF3SO3 were used as the solute. The electrolyte solutions examined here contain binary, ternary and quaternary mixed solvent systems. The purpose of this work is to obtain an electrolyte solution which provides lithium cells with a higher rate capability than the previously studied EC/PC/2MeTHF ternary mixed system while suppressing the reduction in the cycle life. The stack pressure effect on the lithium cycling efficiency is minimized by the spacious internal electrode structure of the coin cell used in this work in order to investigate the influence of the electrolyte materials on the cell properties. Among the electrolyte systems examined here, the EC/PC/2MeTHF/THF (15:70:7.5:7.5 in volume) four-solvent mixed system provided the best cell performance. Its rate capability at 5 mA cm(-2) discharge was about twice that of EC/PC/2MeTHF ternary mixed solvent electrolyte with almost the same rechargeability. (C) 1997 Elsevier Science Ltd. All rights reserved.