Hybrid functional study of the NASICON-type Na₃V₂(PO₄)₃: crystal and electronic structures, and polaron–Na vacancy complex diffusion

Abstract

The crystal and electronic structures, electrochemical properties and diffusion mechanism of NASICON-type Na3V2(PO4)3 have been investigated based on the hybrid density functional Heyd-Scuseria-Ernzerhof (HSE06). A polaron-Na vacancy complex model for revealing the diffusion mechanism is proposed for the first time in the field of Na-ion batteries. The bound polaron is found to favorably form at the first nearest V site to the Na vacancy. Consequently, the movement of the Na vacancy will be accompanied by the polaron. Three preferable diffusion pathways are revealed; these are two intra-layer diffusion pathways and one inter-layer pathway. The activation barriers for the intra-layer and inter-layer pathways are 353 meV and 513 meV, respectively. For further comparison, the generalized gradient approximation with an onsite Coulomb Hubbard U (GGA+U) is also employed.

Boron Substituted Na3V2(P1−xBxO4)3 Cathode Materials with Enhanced Performance for Sodium‐Ion Batteries

“…The spin up density of states (DOS) of Na 3 V 2 (PO 4 ) 3 and the projected DOS of atoms as labeled in Figure 3c are displayed in Figure S5 in the Supporting Information. It clearly shows that Na 3 V 2 (PO 4 ) 3 is a semiconductor with a large band gap of 2.57 eV and the high energy occupied regions in valence band are mainly ascribed to the V‐3d states with little contribution of O‐2p states, while the low energy occupied regions in conduction band are mainly ascribed to the O‐2p states with little contribution of V‐3d states, which are in agreement with the other theoretical calculation result using HSE06 hybrid function 39. All the V‐3d states and O‐2p states are nearly the same.…”

A Promising High‐Voltage Cathode Material Based on Mesoporous Na3V2(PO4)3/C for Rechargeable Magnesium Batteries

“…After the desodiation process, the remaining peaks for the ED‐NVP electrode were consistent with an NaV 2 (PO 4 ) 3 phase ( a =8.417(5) Å, c =21.535(6) Å, and volume=1321.4(5) Å 3 ), indicating a two‐phase reaction between Na 3 V 2 (PO 4 ) 3 and NaV 2 (PO 4 ) 3 during the desodiation process . The decrease in the unit cell volume results from the shrinkage of the V−O bonds, whereas the P−O bond lengths remain unchanged, which contributes to the structural stability of NVP . Upon discharging, reflections from the NaV 2 (PO 4 ) 3 phase become weaker, while those from an intermediate phase corresponding to Mg x V 2 (PO 4 ) 3 (in this case, x <0.85) are enhanced with increasing amount of inserted Mg 2+ ions.…”

Na 3 V 2 (PO 4 ) 3 @NC composite derived from polyaniline as cathode material for high‐rate and ultralong‐life sodium‐ion batteries

“…During this period, with the reduction reaction of 36 it is proved that the precursor began to form NVP material gradually in this temperature range and tended to be stable at about 800 C, which is consistent with the previous literature reports. [37][38][39] In addition, the quality continues to be lost after 550 C because the PAN undergoes a cracking reaction at high temperatures to form NVP@NC.…”