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.