Inner Helmholtz Plane Reconstruction Enables High‑Voltage Sodium‑Ion Batteries

Parasitic reactions at the cathode–electrolyte interface are the primary cause of rapid capacity fading in sodium-ion batteries (SIBs) under high voltage. Conventional electrolyte regulation strategies primarily focus on the bulk solvation structure, while neglecting the pivotal role of the inner Helmholtz plane (IHP) in cathode–electrolyte interfacial stability. Herein, we propose a modulator-driven IHP reconstruction strategy to reshape the interfacial chemistry for high-voltage SIBs. We employ 4-amino-2-trifluoromethylbenzonitrile (ATMBN) as the molecular modulator, which possesses the dual functions of preferential adsorption within the IHP and induced enrichment of PF₆⁻. This synergistic effect enables compositional reconstruction of the IHP, thereby facilitating the formation of a NaF/Na₃N-rich cathode–electrolyte interphase (CEI). Consequently, the Na₃V₂O₂(PO₄)₂F (NVPOF) cathode exhibits an ultrahigh capacity retention of 90.03% after 1000 cycles when charged to 4.5 V. Moreover, a 1.8 Ah NaNi_0.33Fe_0.33Mn_0.33O₂ (NFM) || hard carbon (HC) pouch cell retains 80.33% of its initial capacity after 200 cycles within a voltage range of 1.5-4.2 V. This work establishes a new paradigm for high-voltage SIBs by harnessing the IHP to modulate cathode interfacial chemistry.