Constructing a Functional Fast‐Ion Conductor Interface for Vertically Aligned Titanium Boride Nanosheets to Achieve Superior Sodium‐Ion Storage Performances

Abstract Designing excellent anode materials to enhance the sluggish interfacial kinetics of Na ⁺ is a key challenge in improving the electrochemical performance of sodium‐ion batteries (SIBs). Herein, an ultra‐thin fast‐ionic conductor NaB ₅ C coating TiB ₂ nanoflowers with vertically aligned nanosheet arrays to form yolk–shell TiB ₂ @NaB ₅ C (TBNBC) nanospheres as an anode material for SIBs. The unique structure creates direct and short ion/electron transfer pathways and reserves enough space to prevent the uneven electrochemical reactions from TiB ₂ nanosheets aggregation and stacking, thus ensuring the long‐term cycling stability of SIBs. Additionally, the NaB ₅ C coating with fast‐ionic conductor functional interphase provides rapid Na ⁺ transport channels and effectively reduces the Na ⁺ de‐solvation barrier, accelerating Na ⁺ reaction kinetics. Furthermore, a homogeneous and robust solid electrolyte interphase (SEI) film including inorganic boron species and fluorine‐rich inner layer is constructed on the TBNBC electrode to delocalize stress and induce a uniform Na ⁺ flux, further promoting fast Na ⁺ interphase reaction kinetics. Consequently, the optimized composites achieve ultrastable cycling performances of 173 mAh g ⁻¹ over 5000 cycles at 10 A g ⁻¹ . More importantly, they also exhibit an outstanding capacity of 182.2 mAh g ⁻¹ at −20 °C. This work offers opportunities for the energy storage use of transition metal borides under extreme conditions.