The development of energy storage devices that can efficiently operate at temperatures below 0 ^°C is necessary for both terrestrial and space-based applications. NASA has previously carried out pioneering work that has enabled Li-ion batteries to operate at temperatures down to -30 ^°C through the development of new carbonate electrolyte formulations. [1-2] However, secondary batteries that utilize lithium metal anodes instead of conventional graphite anodes could significantly boost energy density and specific energy, but the behavior of lithium electrodes at low temperatures are largely unknown. In this work, we investigate the effect of sub-zero temperatures on electrochemical behavior, morphological evolution, and solid-electrolyte interphase (SEI) formation of Li metal anodes in carbonate and ether solvents. Electrolytes made with solvents such as ethylene carbonate and ethyl methyl carbonate with ester co-solvents (e.g., ethyl propionate) exhibit sufficient conductivity and show effective Li deposition/stripping down to -30 ^°C, but with relatively low average Coulombic efficiencies (CEs) of ~70 % (similar to the room-temperature CE of ~73 %). The introduction of SEI-stabilizing additives such as fluoroethylene carbonate (FEC) boosts the average Coulombic efficiency across a range of temperatures (CE = ~94 %). Ether-based electrolytes, on the other hand, enable Li deposition/stripping down to -70 ^°C with high CEs (~95 %). Interestingly, investigation of the Li morphology after cycling revealed that distinct Li morphologies form at different temperatures, which may be related to differences in SEI chemistry and structure. These results provide important new information for engineering Li metal anodes for efficient operation under a variety of conditions.

References

[1] Smart, M. C., B. V. Ratnakumar, L. D. Whitcanack, K. B. Chin, S. Surampudi, H. Croft, D. Tice, and R. Staniewicz. "Improved low-temperature performance of lithium-ion cells with quaternary carbonate-based electrolytes." Journal of power sources 119 (2003): 349-358.

[2] Smart, M. C., B. V. Ratnakumar, Larry D. Whitcanack, Kiah A. Smith, Stuart Santee, Robert Gitzendanner, and Vince Yevoli. "Li-Ion Electrolytes Containing Ester Co-Solvents for Wide Operating Temperature Range." ECS Transactions 11 (2008): 99-108.