Lithium fluoride layer formed by thermal evaporation for stable lithium metal anode in rechargeable batteries

Abstract

In this study, lithium fluoride (LiF) was deposited on lithium (Li) metal by thermal evaporation in order to reduce degradation of Li metal batteries caused by growth of Li dendrites. Li | Li symmetric cells were used to measure impedance changes, overvoltage after cycling at 1 mA/cm2 and 1 mAh/cm2, and surface images after 100 cycles. In addition, the residual capacity and Coulombic efficiency after 0.5C charge/discharge cycling were confirmed using LiCoO2|Li cells. Based on electrochemical impedance spectroscopy measurements, Li | Li symmetric cells made of LiF-coated Li showed no impedance changes, even 12 h after fabrication. During the overvoltage test with Li | Li symmetric cells, the cell with a 300 nm thick LiF layer showed highest stability under repeated cycling. The surface of the 300 nm LiF-coated Li was relatively smooth and almost no abnormal growth of Li was observed. In the LiCoO2|Li cells, 200 nm and 300 nm LiF-coated cells showed the best performance in terms of residual capacity. The 300 nm LiF-coated Li cell exhibited close to 100% Coulombic efficiency and remained more stable than the bare Li cell.