Structure, charge transfer, and kinetic properties of NaVPO4F with Na+ extraction: a comprehensive first-principles study

Abstract

First-principles calculations combined with density functional theory were performed to illuminate the electrochemical properties of NaVPO₄F. During desodiation to VPO₄F, a ∼11% volume change was observed, which was ∼2% greater than that from LiVPO₄F to VPO₄F. An intermediate phase was observed while examining the structural stability during Na⁺ extraction from NaVPO₄F. The voltage profile showed a distinct charging plateau positioned at ∼4.0 V. Bader charge analysis elucidated the reduction of charge-oriented V cations during Na⁺ extraction. The achieved electron density profiles were examined to analyze the influence of Na⁺ extraction on V–F and V–O bonds during the desodiation process. The most facile diffusion pathway for Na⁺ was discerned, with a minimum energy barrier of 0.85 eV. On the basis of these results, NaVPO₄F was suggested as a promising cathode material for Na-ion batteries.