Cycling performance and safety of rechargeable lithium cells with binary and ternary mixed solvent electrolytes

Abstract

The influence of electrolyte composition on the cycling performance and safety of AA rechargeable cells with a lithium metal anode, and an amorphous (a-) V2O5-P2O5 cathode was examined. The cells were cycled at a discharge current of 1000 mA and a charging current of 200 mA. The electrolytes were composed of ethylene carbonate (EC)/2-methyltetrahydrofuran (2MeTHF) binary and EC/propylene carbonate (PC)/2MeTHF ternary mixed solvents containing 40–70 vol% 2MeTHF to provide higher conductivity. The solute was 1.5mol dm−3 LiAsF6. The cycle life of the AA cells was evaluated by setting the end of cycle life at the cycle number where the discharge capacity fell to 50% of its maximum value. Cells with EC/2MeTHF (50:50) exhibited the longest cycle life among all the electrolytes examined here. Cells with EC/PC/2MeTHF (15:45:40) had the longest cycle life among the ternary mixed solvents systems. Fundamental abuse tests were also carried out on AA cells, which were cycled twice (fresh cells), cycled 100 times and cycled until the end of their cycle life. Neither the fresh nor the cycled cells with EC/PC/2MeTHF (15:45:40 ) smoked nor ignited in a 150 °C heating test or in an external short circuit test. However, the fresh cell with EC/2MeTHF (50:50) ignited in the 150 °C heating test. Summarizing the cycling and the abuse test results, the EC/PC/2MeTHF (15:45:40) ternary mixed systems exhibited the best performance. However, in terms of practical use, cell safety still requires further improvement.