High-Performance NaVO₃ with Mixed Cationic and Anionic Redox Reactions for Na-Ion Battery Applications

Sodium-ion batteries (NIBs) are a potential low-cost alternative to lithium-ion batteries for large-scale energy storage, but many high-capacity NIB cathode materials undergo irreversible structural changes during charge and discharge, leading to fast capacity fading. Herein, monoclinic NaVO₃ exhibits good cycle performance with high capacity as a cathode material for NIBs. In situ synchrotron X-ray diffraction studies show that the material structure is virtually invariant during Na⁺ (de- )intercalation, with the a and b lattice parameters changing only by 0.13 and 0.19%, respectively. The material undergoes an oxygen redox reaction during initial charge while delivering a remarkable specific capacity of 245 mAh g^-1 (1.2-4.7 V) with contributions from cationic (V⁴⁺/V⁵⁺) and anionic (O^2-/O^-) redox couples during discharge. The stable VO₄ tetrahedral framework also enables the material to give superior rate and cycle capabilities, with a capacity of 164 mAh g^-1 (67% utilization) at a current of 1000 mA g^-1 (about 5C) and a capacity retention of 90% after 50 cycles. Density functional theory calculations further verify the stability of the material and the charge-discharge mechanism. This work can broaden the horizon for designing high-energy cathode materials with enhanced structural stability for sodium-ion batteries.