Abstract
Antimony selenide (Sb2Se3) is a promising alternative to commonly used NIB anodes, storing 12 Na+ per formula unit, to achieve a capacity of 670 mAh g-1. The (de)sodiation mechanism is very complex: the material progresses through multiple phases when interacting with Na+, including intercalation, con-version, and alloying reactions. These multiple chemical transformations may kinetically limit the material at high rates, however, Sb2Se3 can deliver almost 150 mAh g-1 at 5000 mA g-1. Understanding this unusual behavior is important not only to rationalize the electrochemical performance, but also for the design of other materials capable of working at high (dis)charge rates. Meanwhile, subtle phase transitions or transformations of active battery materials can be traced in operando X-ray diffraction (XRD), which enables the extraction of real-time information about potentially hidden mechanistic pathways, including the discovery of new materials. In this study, operando XRD and X-ray absorption spectroscopy (XAS) were employed to unravel the mysteries of the (de)sodiation mechanism of Sb2Se3 anodes. Complete elucidation of the reaction pathway was further enabled by solid-state NMR, ex situ work, and ab initio simulations.