Among the high capacity anodes, antimony (Sb) shows a high theoretical capacity of 660 mAh/g by forming Na₃Sb, safer working potential and less volume expansion compared to graphite anodes for Na-ion batteries(NIBs) [1]. Sb-based intermetallic systems can actively take part in sodiation /de-sodiation reaction. The relatively small volume change during charge-discharge reactions makes them promising anodes for Na-ion batteries. Cu₂Sb has extensively been studied as intermetallic Sb-based anode for Na-ion storage. The anodes are capable of transferring three electrons in the redox reaction giving rise to a capacity of 250 mAh/g which is closely 77% of its theoretical capacity [2]. In this study, a ternary intermetallic Sb-based alloy Cu₃ZnSb has been investigated to attain better electrochemical performance.

Ternary Cu₃ZnSb crystallises in tetragonal space group P4/nmm (129) with lattice parameters a = 4.2171 (3) Å and c = 8.6925 (11) Å [3]. The structure is built up with [Cu₃Sb] slabs that correspond to the unit cells of Cu₂Sb and planer 4⁴ nets of Zn atoms. The planar nets of Zn atoms are interspersed between two adjacent [Cu₃Sb] slabs. The structure of Cu₃ZnSb can be viewed as stacking of Cu₂Sb-unit cells interleaved with CsCl type b’-brass (CuZn) layers along c-direction (Figure 1a).

Ternary Cu₃ZnSb anodes exhibit an initial discharge capacity of 323 mAh/g when cycled at a rate of 0.05C in the voltage range of 0.005 – 2 V (Figure 1b). The average voltage can be calculated as 0.4 V with respect to Na/Na⁺. Although, the discharge capacity fades in the initial cycles, from the 6^th cycle onwards a reversible capacity of 56 mAh/g has been observed for the pristine material.

References

1. Darwiche , C. Marino , M. T. Sougrati , B. Fraisse , L. Stievano and L. Monconduit, J. Am. Chem. Soc., 2012,134, 20805 – 20811.
2. Baggetto , E. Allcorn , R. R. Unocic , A. Manthiram and G. M. Veith, J. Mater. Chem. A,2013, 1, 11163 - 11169.
3. Misra, B. Koley, S. Chatterjee, S. Mallick, and P. P. Jana Inorg. Chemi. 2018,57 (19), 11970-11977.