The
unstable electrode–electrolyte interface and the narrow
electrochemical window of normal electrolytes hinder the potential
application of high-voltage sodium metal batteries. These problems
are actually related to the solvation structure of the electrolyte,
which is determined by the competition between cations coordinated
with anions or solvent molecules. Herein, we design an electrolyte
incorporating ethyl (2,2,2-trifluoroethyl) carbonate and fluoroethylene
carbonate, which facilitates a pronounced level of cation–anion
coordination within the solvation sheath by enthalpy changes to reduce
the overall coordination of cation–solvents and increase sensitivity
to salt concentration. Such an electrolyte regulated by competitive
coordination leads to highly reversible sodium plating/stripping with
extended cycle life and a high Coulombic efficiency of 98.0%, which
is the highest reported so far in Na||Cu cells with ester-based electrolytes.
Moreover, 4.5 V high-voltage Na||Na3V2(PO4)2F3 cells exhibit a high rate capability
up to 20 C and an impressive cycling stability with an 87.1% capacity
retention after 250 cycles with limited Na. The proposed strategy
of solvation structure modification by regulating the competitive
coordination of the cation provides a new direction to achieve stable
sodium metal batteries with high energy density and can be further
extended to other battery systems by controlling enthalpy changes
of the solvation structure.