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

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 NaB5C coating TiB2 nanoflowers with vertically aligned nanosheet arrays to form yolk–shell TiB2@NaB5C (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 TiB2 nanosheets aggregation and stacking, thus ensuring the long‐term cycling stability of SIBs. Additionally, the NaB5C 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.