Crystal Structure of Na2V2(PO4)(3), an Intriguing Phase Spotted in the Na3V2(PO4)(3)-Na1V2(PO4)(3) System

Sunkyu Park (1, 2) , Ziliang Wang (3) , Zeyu Deng (3) , Iona Moog (4) , Pieremanuele Canepa (5) , Francois Fauth (6) , Dany Carlier (2, 7, 8) , Laurence Croguennec (2, 7, 8) , Christian Masquelier (1) , Jean-Noel Chotard (1, 8)

1 LRCS - Laboratoire réactivité et chimie des solides - UMR CNRS 7314
2 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
3 Department of Materials Science and Engineering
4 TIAMAT
5 Deparment of Chemical and Biomolecular Engineering
6 ALBA Synchrotron light source [Barcelone]
7 ALISTORE-ERI - Advanced Lithium Energy Storage Systems - ALISTORE-ERI
8 RS2E - Réseau sur le stockage électrochimique de l'énergie

The Na superionic conductor (NASICON) Na3V2(PO4)(3) is an important positive electrode material for Na-ion batteries. Here, we investigate the mechanisms of phase transition in NaxV2(PO4)(3) (1 <= x <= 4) upon nonequilibrium battery cycling. Unlike the widely believed two-phase reaction in a Na3V2(PO4)(3)-Na1V2(PO4)(3) system, we determine, for the first time, the structure of a recently reported intermediate Na2V2(PO4)(3) phase using operando synchrotron X-ray diffraction. Density functional theory calculations further support the existence of the Na2V2(PO4)(3) phase. We propose two possible crystal structures of Na2V2(PO4)(3) analyzed by Rietveld refinement. The two structure models with the space groups P2(1)/c or P2/c for the new intermediate Na2V2(PO4)(3) phase show similar unit cell parameters but different atomic arrangements, including vanadium charge ordering. As the appearance of the intermediate Na2V2(PO4)(3) phase is accompanied by symmetry reduction, Na(1) and Na(2) sites split into several positions in Na2V2(PO4)(3), in which one of the splitting Na(2) position is found to be a vacancy, whereas the Na(1) positions are almost fully filled. The intermediate Na2V2(PO4)(3) phase reduces the lattice mismatch between Na3V2(PO4)(3) and Na1V2(PO4)(3) phases, facilitating a fast phase transition. This work paves the way for a better understanding of great rate capabilities of Na3V2(PO4)(3).

Domaines: Chimie inorganique; Cristallographie

Sunkyu Park, Ziliang Wang, Zeyu Deng, Iona Moog, Pieremanuele Canepa, et al.. Crystal Structure of Na2V2(PO4)(3), an Intriguing Phase Spotted in the Na3V2(PO4)(3)-Na1V2(PO4)(3) System. Chemistry of Materials, 2022, 34 (1), pp.451-462. ⟨10.1021/acs.chemmater.1c04033⟩. ⟨hal-03634263⟩