Insight into the sodium migration mechanism of langbeinite-type Na2CrTi (PO4)(3) by atomic simulation

YX Luo and TJ Sun and M Shui and J Shu, MATERIALS CHEMISTRY AND PHYSICS, 233, 339-345 (2019).

DOI: 10.1016/j.matchemphys.2019.05.079

In this work, atomistic simulation method based on pedone model is applied to observe the concerted motion of sodium ions in the pristine lattice of possible Na2CrTi(PO4)(3) anode material for sodium ion batteries. The simulation is carried out at a series of increasingly elevated temperature from 600 K to 1800 K in a super cell containing 27 unit cells. The superimposed Na+ trajectory at all time frames offers an intuitive, reliable image of the Na+ migration in crystal lattice. It reveals the migration mechanism for the first time. The sodium ion propagates in the crystal lattice three dimensionally and isotropically. This diffusion path determined directly by the environments of the large cage of metal ions framework is composed of alternating Na(1) and Na(2) ions. The direct hopping from Na(1) to Na(1) and Na(2) to Na(2) are not allowed. Na+ migration along the a axis owns a energy barrier of ca. 0.78 eV. The estimated diffusion coefficient at RT is 2.16.10(-16) cm(2) s(-1). Compared with those intensively investigated anode material for sodium ion battery or aqueous rechargeable sodium batteries, the mobility of sodium ion of this material is comparable. Therefore, we suppose that Na2CrTi(PO4)(3) is also a potential candidate for anode material of sodium ion batteries or aqueous rechargeable sodium ion batteries.

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