Control of lithium metal anode cycleability by electrolyte temperature

Precycling of lithium (Li) metal on a nickel substrate at low temperatures (0 and - 20 degrees C) in propylene carbonate (PC) mixed with dimethyl carbonate (DMC) and Li hexafluorophosphate (LiPF6) (LiPF6-PC/DMC) was found to enhance Li cycleability in the subsequent cycles at a room temperature (25 degrees C). In contrast when the precycling at the low temperatures was performed in PC mixed with 2-methyltetrahydrofuran (2MeTHF) and LiPF6 (LiPF6-PC/2MeTHF), no improvement in the Li cycling efficiency was observed in the subsequent cycles at 25 degrees C. These results suggest that the low-temperature precycling effect on the Li cycleability depends on a co-solvent used in the PC-based electrolytes. Ac impedance analysis revealed that the precycling in the low-temperature LiPF6-PC/DMC electrolyte provided a compact Li interface with a low resistance. In marked constant to this, a Li anode interface formed by the precycling in the LiPF6-PC/2MeTHF system was irregular and resistive to Li-ion diffusion. The origins of the low-temperature precycling effect dependent on the co-solvents were discussed. (C) 1999 Elsevier Science S.A. All rights reserved.