Tracking the phase transformation and microstructural evolution of Sn anode using operando synchrotron X-ray energy-dispersive diffraction and X-ray tomography

Abstract

Tin (Sn) holds great promise as an anode material for next-generation lithium (Li) ion batteries but suffers from massive volume change and poor cycling performance. To clarify the dynamic chemical and microstructural evolution of Sn anode during lithiation and delithiation, synchrotron X-ray energy-dispersive diffraction and X-ray tomography are simultaneously employed during Li/Sn cell operation. The intermediate Li-Sn alloy phases during de/lithiation are identified, and their dynamic phase transformation is unraveled which is further correlated with the volume variation of the Sn at particle- and electrode-level. Moreover, we find that the Sn particle expansion/shrinkage induced particle displacement is anisotropic: the displacement perpendicular to the electrode surface (z-axis) is more pronounced compared to the directions (x- and y-axis) along the electrode surface. This anisotropic particle displacement leads to an anisotropic volume variation at the electrode level and eventually generates a net electrode expansion towards the separator after cycling, which could be one of the root causes of mechanical detachment and delamination of electrodes during long-term operation. The unraveled chemical evolution of Li-Sn and deep insights into the microstructural evolution of Sn anode provided here could guide future design and engineering of Sn and other alloy anodes for high energy density Li- and Na-ion batteries.