A Disordered Rock Salt Anode for Long-Lived All-Vanadium Sodium-Ion Battery

Rechargeable batteries wherein both the cathode and the anode are vanadium-based phases are promising grid-energy storage candidates, offering long cycle life and easy recycling. However, their system-level energy density must be improved to lower their footprint and operating costs. In this work, an all-vanadium sodium-ion battery that uses a new disordered rock salt (DRS) anode, Na3V2O5 (DRS-NVO), is proposed. For DRS-NVO, {$\approx$}2 Na+ ions can be reversibly cycled at {$\approx$}0.7 V versus Na/Na+. Structural characterization by X-ray diffraction and pair distribution function (PDF) analysis reveal increased local distortions during Na+ insertion but the overall DRS structure is maintained. The material shows exceptional stability and rate capability, achieving 10 000 cycles in half-cell tests at rates of up to 20 C. Molecular dynamics simulations produce voltage profiles and ion diffusivities in good agreement with experimental results. Pairing the DRS-NVO anode with a Na3V2(PO4)3 (NVP) cathode yields a cell (NVO\textbar NVP) voltage of 2.7 V, with symmetric voltage profiles and an energy efficiency {$>$}93\%. This all-vanadium sodium-ion battery exhibits excellent cycling stability, retaining 80\% of its capacity after 3 000 cycles. Levelized cost-of-storage (LCOS) evaluations based on a cell design model confirm the cost-effectiveness, positioning NVO\textbar NVP as a competitive grid-scale energy storage solution.