Electrochemical alloying/dealloying mechanism of ternary intermetallic Cu6- δZn2+δSb2 (δ = 0 and 1) as anode for Li-ion and Na-ion batteries

Abstract

Ternary intermetallics with nominal composition Cu6-δZn2+δSb2 (δ ​= ​0 and 1) are synthesized by high-temperature solid-state synthesis and characterized using powder X-ray diffraction. Electrochemical characterization of ternary intermetallic Cu6- δZn2+δSb2 (δ ​= ​0 and 1) as a potential anode in Li-ion and Na-ion batteries is studied. Cu6Zn2Sb2 as a material for Li-ion storage shows an initial lithiation capacity of 300 ​mAhg−1, which falls to 200 ​mAhg−1 for the next delithiation cycle corresponding to dealloying of ~3 Li-ions. The ex-situ powder XRD studies at different stages of charging and discharging revealed Li3Sb alloy as the final product with no Li–Zn alloying during Li-ion insertion. The Na-ion insertion follows a different mechanism in Cu6Zn2Sb2, forming Na–Zn (NaZn13) and Na3Sb in the first and subsequent cycles. The first cycle capacity for Na alloying is found to be ~320 ​mAhg−1. The reaction mechanism for Li-ion and Na-ion alloying with Cu5Zn3Sb2 results in Li–Zn and NaZn13 alloy formation. The capacity retentions of Cu6Zn2Sb2 and Cu5Zn3Sb2 during Li-ion reaction are found to be ~36 ​mAhg−1 and ~109 ​mAhg−1 after 20 cycles at a C-rate of C/20. Cu5Zn3Sb2 electrodes show three times as much capacity retention in comparison with Cu6Zn2Sb2 electrodes as the Zn alloying reaction is found to be a contributing factor for capacity retention. The effect of additives during charge-discharge cycling of the ternary intermetallic is characterized using 2% and 5% Fluoroethylene Carbonate (FEC). The initial capacities improved for both Cu6Zn2Sb2 and Cu5Zn3Sb2, but the capacity retention properties improved only for the Cu6Zn2Sb2 for Li-alloying reactions.