Isotropic Sodiation Behaviors of Ultrafast-Chargeable Tin Crystals

High-rate performance and mechanical stability of anode materials are the two important characteristics that are necessary to develop fast-charging batteries with longevity. In the present study, we demonstrate that both high rate performance and mechanical stability of the anode can be achieved with the Na–Sn battery system. Experiments show that the sodiation rate in crystalline Sn (c-Sn) is 2–3 orders of magnitude faster than that reported for the Li–Si system. Furthermore, this extraordinary rate is nearly the same regardless of the orientation of c-Sn, which can improve the cycle life by retarding the pulverization of c-Sn. Two main microstructural features responsible for the observed characteristics are identified: (1) a transformation from crystalline to amorphous phase occurring at thin layers of c-Sn near the interfacial front and (2) pipe diffusion of Na through sodiation-induced dislocations. In this study, the observed behaviors are explained by elucidating the diffusion kinetics, whereas the associated mechanistic origins are analyzed by resolving the diffusion process of Na+ near the Na/Sn interface using atomic simulations