Ultrahigh coulombic efficiency electrolyte enables Li||SPAN batteries with superior cycling performance

H Liu and J Holoubek and H Zhou and A Chen and N Chang and Z Wu and S Yu and Q Yan and X Xing and Y Li and TA Pascal and P Liu, MATERIALS TODAY, 42, 17-28 (2021).

DOI: 10.1016/j.mattod.2020.09.035

Raising the coulombic efficiency of lithium metal anode cycling is the deciding step in realizing longlife rechargeable lithium batteries. Here, we designed a highly concentrated salt/ether electrolyte diluted in a fluorinated ether: 1.8M LiFSI in DEE/BTFE (diethyl ether/bis(2,2,2-trifluoroethyl)ether), which realized an average coulombic efficiency of 99.37% at 0.5 mA cm(-2) and 1 mAh cm(-2) for more than 900 cycles. This electrolyte also maintained a record coulombic efficiency of 98.7% at 10 mA cm(-2), indicative of its ability to provide fast-charging with high cathode loadings. Morphological studies reveal dense, dendrite free Li depositions after prolonged cycling, while surface analyses confirmed the formation of a robust LiF- rich SEI layer on the cycled Li surface. Moreover, we discovered that this ether-based electrolyte is highly compatible with the low-cost, high-capacity SPAN (Sulfurized polyacrylonitrile) cathode, where the constructed Li parallel to SPAN cell exhibited reversible cathode capacity of 579 mAh g(-1) and no capacity decay after 1200 cycles. A cell where a high areal loading SPAN electrode (>3.5 mAh cm(-2)) is paired with only onefold excess Li was constructed and cycled at 1.75 mA cm(-2), maintaining a coulombic efficiency of 99.30% for the lithium metal. Computational simulations revealed that at saturation, the Li-FSI complex forms contact ion pairs, with a first solvation shell comprising DEE molecules, and a second solvation shell with a mix of DEE/BTFE. This study provides a path to enable high energy density Li parallel to SPAN batteries with stable cycling.Y

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