Ordered Electric Double‐Layer Architectures via Anion‐Dominated Solvation for 4.5 V Sodium‐Metal Capacitors

ABSTRACT

Elevating the operating voltage of sodium metal capacitors (SMCs) to 4.5 V is crucial for achieving higher energy density, however, conventional carbonate‐based electrolytes suffer from cathode interfacial decomposition, disordering of the electric double‐layer (EDL) structure, and poor anode compatibility under high voltage. This study proposes an anion‐centered solvation reconstruction strategy. By introducing a low‐solvation molecular modulator that selectively coordinates with PF ₆ ⁻ anions, an anion‐dominated ordered EDL architecture is constructed on the cathode surface. This structure effectively suppresses EDL disordering and solvent oxidation under high voltage. Molecular energy‐level alignment enables sequential interfacial engineering: an ultra‐thin, high‐voltage‐adapted CEI‐EDL coupled interface on the cathode, and an F/B‐rich solid electrolyte interphase (SEI) on the anode for homogeneous sodium plating/stripping. With this designed all‐fluorinated electrolyte, the resulting SMCs achieve remarkably boosted performance within 2–4.5 V, delivering a high energy density of 185 at 300 W kg ⁻¹ , and an outstanding power density of 112.8 at 15 000 W kg ⁻¹ . This work not only demonstrates a viable high‐voltage SMCs system but, more importantly, establishes a distinctive anion‐centric solvation engineering paradigm, providing a novel approach for developing advanced storage devices with high‐energy/power density.