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 °C), rate capability (519 mA h g−1 vs. 222 mA h g−1 at 3 C and 0 °C), and cycling stability (504 mA h g−1 vs. 253 mA h g−1 at 0.1 C after 100 cycles at −20 °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. © 2024 Elsevier B.V.