NaNbV(PO₄)₃: Multielectron NASICON-Type Anode Material for Na-Ion Batteries with Excellent Rate Capability

NASICON-type NaNbV(PO₄)₃ electrode material synthesized by the Pechini sol-gel technique undergoes a reversible three-electron reaction in a Na-ion cell which corresponds to the Nb⁵⁺/Nb⁴⁺, Nb⁴⁺/Nb³⁺, and V³⁺/V²⁺ redox processes and provides a reversible capacity of 180 mAh·g⁻¹. The sodium insertion/extraction takes place in a narrow potential range at an average potential of 1.55 V versus Na⁺/Na. Structural characterization by operando and ex situ X-ray diffraction disclosed the reversible evolution of the NaNbV(PO₄)₃ polyhedron framework during cycling, while XANES measurements in the operando regime confirmed the multielectron transfer upon sodium intercalation/extraction into NaNbV(PO₄)₃. This electrode material demonstrates extended cycling stability and excellent rate capability maintaining the capacity value of 144 mAh·g⁻¹ at 10 C current rates. It can be regarded as a superior anode material suitable for application in high-power and long-life sodium-ion batteries.