Dielectric Confinement Chemistry Realizes Ester‐Electrolyte‐Compatible Sodium Metal Batteries Over a 100°C Range

ABSTRACT Sodium metal batteries (SMBs) have attracted intensive attention due to the high theoretical capacity and abundance of sodium (Na). However, severe parasitic reactions between electrolyte and Na at elevated temperatures and sluggish Na + desolvation process at cryogenic conditions significantly restrict the SMBs applicability, especially with ester‐based electrolytes. Here, a high‐voltage, carbonate ester‐compatible SMB capable of stable operation across a 100°C temperature range has been realized for the first time through dielectric confinement chemistry. Specifically, Lewis acidic dielectric nanoparticles were incorporated into a typical ester electrolyte, thereby inducing dielectric confinement regions for capturing anions and solvents. This configuration greatly decreases the proportion of free ester solvents, which reduces the undesired electrode/electrolyte contact and resultant parasitic reactions. Meanwhile, the weakened interactions between cations and solvents/anions facilitate the desolvation process and elevate ionic conductivity. Consequently, when pairing Na metal with a high voltage Na 3 V 2 (PO 4 ) 2 F 3 cathode, the fabricated SMBs retain 80% capacity retention for 3300 and 480 cycles at 25°C and 60°C, featuring 3‐fold improvements relative to those with the baseline electrolyte. Stable operation even at −40°C has also been achieved. This work provides a facile electrolyte design strategy for developing carbonate ester‐compatible SMBs over wide temperature ranges.