Enhanced Electrochemical Performance of Sb and Sb2O3 Composite By Electrodeposition for Na-Ion Batteries

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.