Programme

P.74 -- Poster, VCTP-44

Date: Thursday, 1 August 2019

Time: 08:30 - 10:00

First-principles study of Na$_2$Fe$_3$(SO$_4$)$_4$: A new material of potential cathodes for the sodium-ion rechargeable batteries

Thien Lan Tran (1,2), Nhu Thao Dinh (1) and Van An Dinh (2,3)

(1) Hue University of Education, 34 Le Loi Str., Hue, Vietnam. (2) Nanotechnology Program, VNU Vietnam Japan University, Luu Huu Phuoc Str., My Dinh I, Hanoi, Vietnam. (3) Center for Atomic and Molecular Technology, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871, Japan.

Recently, there are many sulfate-based polyanion materials suitable for the fabrication of cathode of Na-ion rechargeable batteries (NIBs), such as Na$_{2+2x}$M$_{2-x}$(SO$_4$)$_3$ (M = Fe and Mn ) [1,2]. Na$_2$Mn$_3$(SO$_4$)$_4$ was successfully synthesized in 2016 and demonstrated as a promising cathode material for NIBs [3]. Furthermore, Iron is a non-polluting and abundant material in the Earth's crust, leading to the idea of replacement of Mn by Fe to form Na$_2$Fe$_3$(SO$_4$)$_4$ as a new potential material for NIBs. In this work, we propose a new cathode material by using Density Functional Theory method. A systematic study of spatial structure, electronic structure, potential and diffusion mechanisms of ions Na in the material Na$_2$Fe$_3$(SO$_4$)$_4$ using the generalized gradient method with an effective U correction factor (GGA + U) is presented. Applying the simultaneous motion model of vacancy and accompanying polaron proposed by V.A. Dinh et al. [4], we reveal the diffusion mechanism through the exploration of element diffusion processes (EDPs). The diffusion pathways of Na ions along the [100], [010] and [001] directions are demonstrated by combination of EDPs. This material exhibits a wide band gap semiconductor behavior with a band gap of 3.612 eV. The calculated open-circuit voltage is 4.01 V corresponding to the redox pair Fe$^{+3}$/Fe$^{+2}$. Na-ions diffusion along the [100] and [001] directions costs an activation energy of 881 meV for both pathways. In the [010] direction, a pathway with a lower activation energy of 808 meV was also found. 1. D. Dwibedi et al., J. Mat. Chem. A 3 (36), 18564-18571 (2015). 2. P. Barpanda et al., Nat. Commun.5, 4358 (2014). 3. J. Gao et al, J. Mat. Chem. A 4 (30), 11870-11877 (2016). 4. V. A. Dinh et al., App. Phys. Express 5 (4), 045801 (2012).

Presenter: Tran Thien Lan