Phase Composition and Electronic Modulation of Na‐V‐PO ₄ Enabling a 3.8 V Higher‐Voltage Plateau for High‐Energy Sodium‐Ion Batteries

Abstract Two redox reactions, V ³⁺ /V ⁴⁺ and V ⁴⁺ /V ⁵⁺ , are accepted in Na ₃ V ₂ (PO ₄ ) ₃ (NVP) during the charge/discharge process. The discharge capacity at the higher‐voltage plateau ≈4.0 V varies with the heteroatom doping. To clarify this behavior, the V/PO ₄ ³⁻ ratio is tuned in this work. The results reveal that the composition of 3Na‐0.9V‐3PO ₄ is composed of the Na ₇ V ₄ (P ₂ O ₇ ) ₄ PO ₄ (NVPP) phase. Owing to the increased electron density around V donated by citrate ions, the apparent valence state approaches +3, resulting in a poor EPR signal. In the 3Na‐ x V‐3PO ₄ /C( x = 0.9–1.5) composites, the proportion of rod/tubular‐like NVPP regularly decreases, while the NVP phase becomes increasingly dominant with rising V content. This evolution is clearly reflected in the CV curves. NVPP/C phase delivers a discharge capacity of ≈40 mAh g ⁻¹ at 117 mA g ⁻¹ with a voltage plateau near 3.8 V. As the V content increases, this high‐voltage plateau becomes shorter, while that plateau associated with NVP/C extends, leading to the increase in discharge capacity. Crystal structure and the morphology of these composites remain stable, as well as the peak of V 2p _1/2 shifts during charging/discharging, while the electron signal at the V 2p _3/2 orbital nearly disappears. These finding offers a strategy to enhance high‐voltage plateaus in sodium‐ion batteries.