CuSe₂ Nanocubes Enabling Efficient Sodium Storage

As the most promising candidate for lithium-ion batteries (LIBs), the electrochemical performance of sodium-ion batteries (SIBs) is highly dependent on the electrode materials. Copper selenides have established themselves as potential anode materials for SIBs due to their high theoretical capacity and good conductivity. However, the poor rate performance and fast capacity fading are the major challenges to their practical application in SIBs. Herein, single-crystalline CuSe₂ nanocubes (CuSe₂ NCs) are successfully synthesized via a solvothermal method. As an anode of SIBs, the CuSe₂ NCs render an almost 100% initial Coulombic efficiency, an outstanding long cycle life, e.g., 380 mA h g^-1 after 1700 cycles at 10 A g^-1, and an unprecedented rate performance of 344 mA h g^-1 at 50 A g^-1. Ex situ X-ray diffraction (XRD) patterns reveal the crystalline transformation of energy-storage materials, and the density functional theory (DFT) conclusion suggests that fast and stable ion diffusion kinetics enhances their electrochemical performance upon sodiation/desodiaton. The investigation into the mechanism provides a theoretical basis for subsequent practical applications.