Enhanced Electrochemical Performance of Sb and Sb2O3 Composite By Electrodeposition for Na-Ion Batteries
Authors: Hong Kyung-Sik , Nam Do-Hwan , Lim Sung-Jin , Kwon HyukSang 
Published: February 2020

Introduction

As lithium reserves in natural resource cannot keep up with Li-ion battery market, concerns about a continuous supply of lithium and increasing of lithium price are emerging. Na-ion batteries are considered as an alternative to Li-ion batteries for large-scale applications due to the low-cost and abundance of sodium resources. While a variety of cathodes materials for Na-ion batteries have been reported [1], the availability of anode materials is much rarer. Among the candidates, Sb is very attractive anode materials for Na-ion battery due to high theoretical capacity (660 mAh/g).[2]

Currently, sodium storage materials through conversion reaction mechanism have been reported, such as Sb2O4
[3], Sn-SnS-C[4], rGO/Sb2S3
[5], etc. These materials can give higher capacity because of the lower weight of the non-metal elements, as well as improvement of mechanical stability due to buffer matrix. Therefore, in this study, metallic antimony (Sb) and antimony trioxide (Sb2O3) composite were prepared by the electrodeposition from potassium antimony tartrate bath and electrochemical properties of Sb/Sb2O3 composite for Na-ion batteries are investigated. Additionally, the phase transition processes in sodium insertion/deinsertion of Sb/Sb2O3composite is investigated by ex-situ analysis.

Experimental

Sb/Sb2O3electrodes were prepared by the electrodeposition at a constant current density in a potassium antimony tartrate bath. The electrodeposition was conducted using a standard three-electrode cell; Cu foil was used as a cathode, pure Pt sheet was used as an anode, and a saturated calomel electrode (SCE) was used as a reference electrode. The solution was stirred magnetically at 240 rpm and the electrodeposition was performed at room temperature.
The electrochemical properties of the Sb/Sb2O3 electrodes were investigated using two-electrode cell with electrode area of 1 cm2 assembled in an Ar-filled glove box. The cell consists of the Sb/Sb2O3 electrodes as a working electrode, a pure Na as a counter electrode and 1 M NaClO4 dissolved in a mixture of propylene carbonate (PC) and 0.5 vol. % of fluoroethylene carbonate (FEC) as an electrolyte. The electrochemical test was conducted by constant current with a current density of 60 mA/g in the potential range of 0.01 ~ 2.5 V vs. Na/Na+ at 25 oC. The phase transition with cycling was examined by ex-situ X-ray diffraction (XRD), and Raman spectroscopy.

Results and discussion

Figure 1.(a) shows the surface morphology of Sb/Sb2O3 composite prepared by the electrodeposition. Sb/Sb2O3 composite exhibits granular texture and deposited uniformly along the Cu substrate. Energy dispersive spectroscopy (EDS) analysis shows that the electrodeposits are composed of antimony and oxygen. Formation of crystalline Sb2O3 (cubic) as well as metallic Sb (rhombohedral) was confirmed by XRD analysis. Other impurity phases are not detected. (Figure 1. (b))
The Sb/Sb2O3 electrode shows improved cycling stability rather than pure Sb electrode. The Sb/Sb2O3 electrode maintains a capacity of 613.2 mAh g-1 after 50 cycles that corresponds to 98.78 % of its initial charge capacity (620.8 mAh g-1) with a high coulombic efficiency above 95 %. In order to determine the reaction reversibility of Sb2O3 with Na+ ion, ex-situ XRD and Raman spectroscopy analysis with cycling were performed. It is confirmed that Sb2O3 reacts with Na+ ion reversibly by ex-situ analysis and reversible formation of Na2O by conversion reaction was expected. Accordingly, superior cycle stability of Sb/Sb2O3 composite results from Na2O which acts as buffer matrix and prevents agglomerating Sb particles.

Figure 1
. (a) SEM images and (b) XRD patterns of Sb/Sb2O3composite

References

[1] M. D. Slater, D. Kim, E. Lee, C. S. Johnson, Advanced Functional Materials 2013, 23, 947.
[2] J. Qian, Y. Chen, L. Wu, Y. Cao, X. Ai, H. Yang, Chemical Communications 2012, 48, 7070.
[3] Q. Sun, Q. Q. Ren, H. Li, Z. W. Fu, Electrochemistry Communications 2011, 13, 1462.
[4] L. Wu, X. Hu, J. Qian, F. Pei, F. Wu, R. Mao, X. Ai, H. Yang, Y. Cao, Journal of Materials Chemistry A 2013, 1, 7181.
[5] D. Y. W. Yu, P. V. Prikhodchenko, C. W. Mason, S. K. Batabyal, J. Gun, S. Sladkevich, A. G. Medvedev, O. Lev, Nat Commun 2013, 4.