SnSb electrodes for Li-ion batteries: the electrochemical mechanism and capacity fading origins elucidated by using operando techniques

SnSb was synthesized by ultra-fast microwave solid-state synthesis. The lithiation/delithiation mechanism of SnSb was fully revisited through operando X-ray diffraction (XRD) and Sn-119 Mossbauer spectroscopy. While many studies have underlined the attractive electrochemical performance of SnSb as the electrode material for Li-ion batteries, only a few of them have focused on the complex electrochemical mechanism. In this work, the complementary results of operando XRD and Mossbauer spectroscopy were used to fully investigate this complex electrochemical system. The alloying mechanism with the reversible formation of Li3Sb and LiySn lithiated phases was confirmed and complemented with additional information on the nature of the LiySn phases, namely Li2Sn5, LiSn, Li5Sn2 and Li7Sn2. Moreover, we demonstrated that the improved performance of SnSb compared to a physical mixture of Sn and Sb lies in the nature of the interfaces between the lithiated phases at the end of discharge. The progressive decrease of the availability/accessibility of Sn for the regeneration of SnSb at the end of the charge was also identified as a major failure mechanism for the long-term cycling stability of SnSb electrodes.