We report on single-phase Na_xV₂(PO₄)₃ compositions (1.5 ≤ x ≤ 2.5) of the Na super ionic conductor type, obtained from a straightforward synthesis route. Typically, chemically prepared c-Na₂V₂(PO₄)₃, obtained by annealing an equimolar mixture of Na₃V₂(PO₄)₃ and NaV₂(PO₄)₃, exhibits a specific sodium-ion distribution (occupancy of the Na(1) site of only 0.66(4)), whereas that of the electrochemically obtained e-Na₂V₂(PO₄)₃ (from Na₃V₂(PO₄)₃) is close to 1. Unlike conventional Na₃V₂(PO₄)₃, when used as positive electrode materials in Na-ion batteries, the Na_xV₂(PO₄)₃ compositions lead to unusual single-phase Na⁺ extraction/insertion mechanisms with continuous voltage changes upon Na⁺ extraction/insertion. We demonstrate that the average equilibrium operating voltage observed upon Na⁺ deintercalation from single-phase Na₂V₂(PO₄)₃ is increased up to an average value of ~3.70 V versus Na⁺/Na (thanks to the activation of the V⁴⁺/V⁵⁺ redox couple) compared to 3.37 V versus Na⁺/Na in conventional Na₃V₂(PO₄)₃, thus leading to an increase in the theoretical energy density from 396.3 Wh kg^–1 to 458.1 Wh kg^–1. Electrochemical and chemical Na⁺ deintercalation from c-Na₂V₂(PO₄)₃ enables complete Na-ion extraction, increasing energy density.