A covalently bonded, LiF-rich solid electrolyte interphase for Li metal batteries with superior low-temperature performance

Abstract

The solid electrolyte interphase (SEI) layer plays a critical role in determining the performance of lithium metal batteries (LMBs). Here, we show that treating Li foils with 4,4,5,5,5-pentafluoropentanol (PFPO) results in the formation of a novel LiF-rich organic/inorganic SEI layer (designated as LiF-PO) that enhances the performance of LMBs. Compared to the native SEI layer that is electrochemically formed in LMBs, the LiF-PO SEI layer is mechanically robust, adopts a compact structure, and exhibits high Li+ conductivity. These features enable Li//Li symmetric cells to exhibit superior performance metrics, even at low temperatures, including inhibited Li dendrite growth, reduced polarization voltage, and elongated cycling lifetime. Moreover, compared to lithium-sulfur cells prepared using bare Li foils, the cells prepared using PFPO-treated Li foils also exhibit markedly improved performance at low temperatures in terms of specific capacity (796 mA h g(-1) vs. 559 mA h g(-1) at 0.1 C and -20 degrees C), rate capability (519 mA h g(-1) vs. 222 mA h g(-1) at 3 C and 0 degrees C), and cycling stability (504 mA h g(-1) vs. 253 mA h g(-1) at 0.1 C after 100 cycles at -20 degrees C). The lessons learned from our study establish new principles for designing high-performance SEI layers and may be extended to other types of metal batteries.