Improvement of charge-discharge cycling efficiency of Li by low-temperature precycling of Li

Under low-temperature conditions (at -10 or 0 degrees 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 ar Li trifluoromethanesulfonate was higher than that observed in the corresponding electrolyte systems at 25 degrees C. When the charge-discharge cycling of Li in the low-temperature electrolytes was followed by cycling al 25 degrees C, the charge-discharge at 25 degrees 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 degrees C.