Improvement of Charge-Discharge Cycling Efficiency of Li by Low- Temperature Precycling of Li.

Under low-temperature conditions (at -10 or 0°C) the charge-discharge cycling efficiency of lithium (Li) metal on a nickel (Ni) substrate in mixed electrolytes, ethylene carbonate and dimethyl carbonate, containing Li hexafluorophosphate or Li trifluoromethanesulfonate was higher than that observed in the corresponding electrolyte systems at 25°C. When the charge-discharge cycling of Li in the low-temperature electrolytes was followed by cycling at 25°C, the charge-discharge at 25°C maintained the high cycleability observed at the low temperatures. This suggests that precycling under the low-temperature conditions improved the efficiency in the following cycles at room temperature. AC impedance analysis revealed that the precycling in the low-temperature electrolytes provided a low-resistance Li interface which remained on the Li metal even after a rise in temperature to 25°C.