Improved fast-charging performances of phosphorus electrodes using the intrinsically flame-retardant LiFSI based electrolyte

Abstract

Red phosphorus (RP) has recently gained great attention for high-energy-density fast-charging lithium-ion batteries (LIBs) due to its high theoretical specific capacity (2596 mA h g−1) and safe lithiation voltage (ca. 0.7 V vs. Li+/Li). Here, we adopt a new electrolyte system, the thermally stable lithium bis(fluorosulfonyl)imide (LiFSI) in the mixed solvents of intrinsically flame-retardant triethyl phosphate (TEP) and fluoroethylene carbonate (FEC) as a solid electrolyte interface (SEI)-forming additive, resulting in an enhanced electrochemical performance for the application of P anode. LiFSI avoids the side effect of fluorination that is prone to occur at the surface of P particles in commonly used lithium hexafluorophosphate (LiPF6)-based electrolyte. As a result, combining the ternary synergy of LiFSI, TEP and FEC, a favorable and stable lithium fluoride (LiF) and non-LixPFy based SEI is constructed on the RP anode through the preferential reduction of the Li+ solvation structure, and subsequent reduction deposition of FSI− anion and FEC solvent. This stable SEI plays a critical role in alleviating the huge volumetric expansion of P, decreasing the reactivity of P anode within electrolyte during cycling process and thus enhancing the fast-charging performance of P anode.