Dynamic Fluorine Compensation Strategy Purifies Na ₃ V ₂ (PO ₄ ) ₂ F ₃ Phase Toward High‐Energy and Stable Sodium Storage

Abstract Na ₃ V ₂ (PO ₄ ) ₂ F ₃ (NVPF) is a promising sodium‐ion battery cathode due to its high voltage and structural stability, but suffers from fluorine loss, suboptimal capacity from limited Na⁺ extraction, and insufficient stability at deeper Na ⁺ (de)intercalation. Therefore, this study used in situ thermogravimetry‐infrared‐mass spectrometry for the first time to clarify the fluorine loss mechanism during the synthesis of NVPF. Based on this, a targeted dynamic fluorine compensation strategy is proposed, using NH ₄ F as a dual‐functional additive that combines the functions of fluorine source and pH buffer. The optimal NVPF‐ 12.5 NHF shows the characteristics of completely suppressing the impurity phase. In addition, by expanding the voltage window to 1.0–4.4 V to activate the redox reaction of V ²⁺ /V ³⁺ , the ultrahigh specific capacity of NVPF is achieved via the electrochemical insertion of additional Na ⁺ . The NVPF‐ 12.5 NHF cathode exhibits an astonishing specific capacity of 173.6 mAh g ⁻¹ at a rate of 0.3C (64 mA g ⁻¹ ), and maintains a specific capacity of 96.1 mAh g ⁻¹ at 33C. Furthermore, the capacity retention rate is more than 70% after 2000 cycles at 13C. These findings establish a scalable strategy for designing electrode materials with volatile components, offering significant potential to accelerate the practical deployment of sodium‐ion batteries.