Coordination Chemistry Enabled Multifunctional Electrolytes for High‐Rate and Long‐Cycle Sodium‐Metal Batteries

ABSTRACT Sodium‐metal batteries (SMBs) are gradually emerging as a powerful supplement to lithium‐ion batteries (LIBs) due to their prominent advantages in resources, cost, performance, and other aspects. However, their practical implementation is hindered by the unstable solid electrolyte interphase (SEI). This interfacial issue triggers dendrite growth and electrolyte consumption, resulting in shortened cycle life and low coulombic efficiency of the batteries. This study proposes a highly efficient strategy: incorporating a solvent‐coordinating additive‐tetramethoxygermane (Ge(OCH 3 ) 4 ) into the conventional electrolyte. This additive weakens the coordination ability between sodium ions (Na + ) and solvents, thereby accelerating Na + transport kinetics. Simultaneously, it enables the in situ formation of a germanium/germanium oxide (Ge/GeO 2 )‐containing SEI layer on the sodium (Na) metal surface, which in turn reduces the nucleation energy barrier of Na metal. This dual functionality facilitates the uniform nucleation and deposition of Na + . As a result, the Na||Na symmetric cell cycles stably over 3500 cycles at a high current density of 10 mA cm −2 . Furthermore, the Na 3 V 2 (PO 4 ) 3 (NVP)||Na full cell achieves ultra‐high‐rate performance up to 100 C and demonstrated stable cycling for 4400 cycles at 20 C, with a capacity retention of 93.3%. This work provides an effective approach for the design of advanced SMB electrolyte systems.