Investigation of the High-Rate Na ion Storage Property in Bulk Cu2-xSe plates

Abstract The traditional views hold the conversion and intercalation compounds without nanostructure used in ion batteries could not afford high-rate performance. This study demonstrated a bulk material of hexagonal plate-like Cu2−xSe with exposed (111) plane exhibits an ultrahigh rate performance without any assistance of high conducting graphene or carbon nanotube, et.al. The bulk Cu2−xSe plates, used as the anode of sodium ion battery, deliver a high capacity of 377.6 mA h g−1 at 0.1 A g−1 and maintain a capacity retention rate of 83.5% at 10 A g−1, as well as a long cycle life of 93.2% after 1000 cycles at 5 A g−1. Density functional theory analysis confirms that the (111) faceted Cu2−xSe plates with reduced migration energy for Na ion across the Cu2−xSe can enhance its electrochemical reaction kinetics. Moreover, the detailed Na ion insertion/extraction mechanism was demonstrated by combining the in situ and ex situ measurement technologies.