Competitive Anion Coordination Modulates Anode Interfacial Chemistry for Wide‐Temperature Sodium Batteries

Sodium‐ion batteries (SIBs) offer a promising, cost‐effective alternative for large‐scale energy storage due to the abundance of
sodium. However, their practical deployment is challenged by sluggish interfacial kinetics and unstable interphase formation,
which severely limit performance across wide temperature ranges. Here, we demonstrate that competitive coordination between
strongly (OTF$^−$) and weakly (PF$_6^−$) coordinating anions can be harnessed to fundamentally modulate the anode interphase and
solvation kinetics in hard carbon systems. Through integrated molecular dynamics simulations, spectroscopic analysis, and
density functional theory, we reveal how PF6− attenuates the excessive Na$^+$–OTF$^−$ binding, thereby optimizing the solvation
sheath for accelerated desolvation and promoting the formation of a uniform, fluorine‐rich solid–electrolyte interphase with
enhanced ionic transport and mechanical integrity. This tailored interface enables exceptional performance from −30°C to 60°C,
including a capacity of 78.4 mAh g$^{−1}$ at 5 A g$^{−1}$ (room temperature), 77% capacity retention after 2600 cycles at −30°C, and
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stable high‐rate operation at 60°C. Full cells and pouch cells assembled with hard carbon (HC) and commercial Na4Fe3(-
PO4)2(P2O7) (NFPP) were successfully charged and discharged at −20°C. This work unfolds competitive anion coordination as a
fundamental principle governing interfacial chemistry and solvation dynamics, providing a mechanistic foundation for the
rational design of wide‐temperature sodium batteries.