Predelithiation-driven ultrastable Na-ion battery performance using Si,P-rich ternary M-Si-P anodes

The sluggish reaction kinetics of Si with Na restricts its efficient use as an anode in Na-ion batteries (NIBs). In this study, a general predelithiation approach was implemented for the first time to fully exploit the advantages of ternary Si,P-simultaneously-rich M-Si-P anodes for an ultrastable NIB performance. Two CoSi₃P₃ and FeSi₄P₄ intermetallics in hybrids with carbon nanotubes were predelithiated and subsequently employed as NIB anodes with an optimized electrolyte, delivering a high initial capacity and Coulombic efficiency (581 mAh g⁻¹ and ⁓80% at 50 mA g⁻¹, respectively), exceptional cyclic stability (>300 cycles at 200 mA g⁻¹), and improved rate capability. The predelithiation generated a thin F-rich inorganic solid-electrolyte interphase (SEI) film, and the optimized NIB electrolyte formed additional stable organic/inorganic SEI compounds on the outermost section of the active materials, causing reversible Na_xSi/Na₃P formation/decomposition reactions, reconstructing CoSi₃P₃/FeSi₄P₄ nanocrystals during charging, preventing the aggregation and coarsening of transition metals, and tolerating severe volume changes. This study demonstrated predelithiation as a promising strategy for the application of Si-rich anodes in NIBs.