In-situ Synchrotron X-ray Powder Diffraction Characterisation of Cu6Sn5 Lithium-ion Battery Anodes

Abstract

Sn-based anodes have been widely studied for applications in lithium-ion batteries due to their superior storage capacities. However, the large volume changes during lithiation and delithiation often result in poor cyclic performances. Intermetallic compounds (IMCs) combining Sn with an element that does not react with lithium are commonly used to reduce the stresses in these anodes. One such example, the IMC Cu6Sn5, has been proven to improve the cyclic performance of Sn as an anode. Sn-based anodes also have lithiation voltages around 0.4 V vs. Li/Li+, making them less prone to lithium dendrite growth and therefore intrinsically safer. This work investigates the lithiation and delithiation mechanisms of a Cu6Sn5 anode fabricated via direct growth of the Cu6Sn5 IMCs on the Cu current collector by melt-solid contact. In-situ synchrotron X-ray powder diffraction revealed the “real-time” crystallographic changes of the anode during the lithiation and delithiation processes, which are confirmed by high-voltage transmission electron microscopy. The study shows a reversible two-step reaction during cycling, and highlights the differences in the reaction mechanisms at higher lithiation/delithiation rates than those reported in the published literature. Figure 1