Armoring SiOx with a conformal LiF layer to boost lithium storage

Abstract

The LiF-rich solid electrolyte interphase (SEI) is an emerging research hotspot to improve battery performance. Its high Li-ion conductivity and high interfacial energy result in fast lithiation/de-lithiation in electrode materials while at the same time protect materials from pulverization. Currently, the developed LiF-rich SEI fabrication methods are based on electrolyte decomposition upon cycling, but so far have only been applied to Li metal or Si anodes. Furthermore, the influences of LiF on the electrochemical behavior of the electrolyte are not fully understood. Here, a new pre-coating approach is proposed to fabricate a conformal LiF layer on both anode and cathode materials (silicon suboxide (SiO_x) and LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) as examples). LiF assisted the increase in the specific capacity of a SiO_x electrode from 301 to 1034 mA h g⁻¹ after 100 cycles at 500 mA g⁻¹. In addition, a full cell assembled with a prepared anode (SiOG@LiF3) and cathode (NCM811@LiF3) showed outstanding cycling stability. Combining density functional theory (DFT) calculation with SEM and XPS characterization revealed for the first time that the pre-coating LiF layer had a strong preferential adsorption of LiPF₆ molecules on the surface, leading to the formation of inorganic-rich SEI during cycling; thereby enabling a fast Li-ion uptake/removal process and improving the electrode integrity.