Fluorinated solvent coupled anions-derived hybrid interphase enabled highly reversible and cryogenic silicon anode

Silicon (Si) has emerged as a prominent candidate for high-energy batteries due to its exceptionally high theoretical capacity and favorable lithiation potential. However, its electrochemical performance at subzero temperatures is significantly hampered by slow ion transport and sluggish ion diffusion processes. Here, we present a weakly solvating electrolyte formulated with 1 M lithium bis(fluorosulfonyl)imide (LiFSI) in a mixture of fluoroethylene carbonate (FEC) / methyl trifluoroacetate (MTFA). This electrolyte is elaborated to enhance the ion desolvation process and facilitate the formation of an anion-coupled fluorinated solvent-derived hybrid solid electrolyte interphase (SEI) on Si anodes, thereby significantly improving the electrochemical performance. Comprehensive characterizations paired with molecular dynamics (MD) calculations reveal that the hybrid SEI consists of an organic outer layer and a lithium fluoride (LiF) and sulfurized species-rich inner layer, which maintain the structural integrity of the electrode while promoting rapid Li⁺ diffusion even at cryogenic temperatures. As anticipated, the Si electrode demonstrates exceptional delivery capacities of approximately 3100-2600 mAh g^-1 at subzero temperatures ranging from 0 °C to -20 °C and a reversible specific capacity of around 2100 mAh g^-1 even at -30 °C.