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-di scharge cycling efficiency of lithium (Li) metal on a nickel (Ni) subs trate in mixed electrolytes, ethylene carbonate and dimethyl carbonate , containing Li hexafluorophosphate ar Li trifluoromethanesulfonate wa s higher than that observed in the corresponding electrolyte systems a t 25 degrees C. When the charge-discharge cycling of Li in the low-tem perature electrolytes was followed by cycling al 25 degrees C, the cha rge-discharge at 25 degrees C maintained the high cycleability observe d at the low temperatures. This suggests that precycling under the low -temperature conditions improved the efficiency in the following cycle s at room temperature. AC impedance analysis revealed that the precycl ing in the low-temperature electrolytes provided a low-resistance Li i nterface which remained on the Li metal even after a rise in temperatu re to 25 degrees C.