The feasibility of sodium-ion batteries as an alternative to lithium-ion batteries in large-scale storage systems largely depends on the availability of advanced electrode materials leading to enhanced energy density and operational sustainability. Herein, we present a novel βpolymorph of sodium vanadium pyrophosphate NaVP 2 O 7 with the KAlP 2 O 7 -type structure obtained via hydrothermal synthesis and further thermal dehydration of a hydrophosphate intermediate. β-NaVP 2 O 7 demonstrates attractive electrochemical behavior as a Na-ion positive electrode (cathode) material with practically achieved a reversible capacity of 104 mAh/g at C/10 current density, an average operating voltage of 3.9 V vs Na/Na + , and only 0.5% volume change between the charged and the discharged states. Electrode material exhibits excellent C-rate capability and cycling stability, providing a capacity of 90 mAh/g at 20C discharge rate and <1% capacity loss after 100 charge−discharge cycles. In the low-voltage region (≈1.5 V vs Na/Na + ), β-NaVP 2 O 7 reversibly intercalates additional sodium cations, leading to extraordinary overall Na-ion storage ability exceeding 200 mAh/g within the 1.5−4.4 V vs Na/Na + voltage region. This material is one of only a few materials that exhibit reversible sodium-ion storage over such a large potential window.

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New sodium vanadium(III) hydrogenphosphate hydrate NaV(HPO4)2(H2O)0.5 and sodium vanadium(III) hydrogenphosphate β‐NaV(HPO4)2 were prepared in mild hydrothermal conditions. The crystal structures of NaV(HPO4)2(H2O)0.5 [space group Cc, Z = 4, a = 8.46174(19) Å, b = 9.52583(19) Å, c = 8.69376(15) Å, β = 110.9553(11) °, V = 654.41(2) Å3] and β‐NaV(HPO4)2 [space group C2/c, Z = 4, a = 7.8681(3) Å, b = 9.8451(3) Å, c = 8.5180(2) Å, β = 107.626(2) °, V = 628.85(3) Å3] were solved and refined from X‐ray powder diffraction data. Both compounds were used as precursors in a new route for the preparation of attractive cathode material β‐NaVP2O7. The formation of the structure motive providing fast sodium ion diffusion at the first synthesis stage and its further conservation upon stepwise dehydration was revealed. The oversized Na+‐embedding channels are stabilized by site‐coordinated water in NaV(HPO4)2(H2O)0.5 structure. The topology resemblance and difference in known sodium vanadium(III) complex phosphates are discussed.