Nitrogen-Doped Graphene-Wrapped Cu2S as a Superior Anode in Sodium-ion Batteries

Abstract Sodium-ion batteries (SIBs) have been attracting an ever-growing research interest, mainly ascribed to their cost-effectiveness. However, SIBs have been significantly hindered by lack of a suitable anode. Herein, an exceptional Cu2S-based composite anode is developed via a facile ball-milling method, in which Cu2S particles are wrapped by nitrogen-doped graphene sheets (Cu2S@NG). This Cu2S@NG composite anode enables extremely long cycling life, ultra-stable cyclability with high capacity, and excellent rate capability. The superior performance of the Cu2S@NG composite is owing to its intriguing core-shell structure and the exceptional properties of both the Cu2S and NG. In this study, it is found that the NG shell yields multiple merits in improving the performance of Cu2S: (i) mitigating the loss of active materials, (ii) constituting a stable interface, (iii) providing improved electrical conductivity and good ionic transfer, and (iv) enhancing mechanical integrity. Additionally, the vital effects of different voltage windows and a surface coating via atomic layer deposition on further enhancing performance are clarified. Significantly, the electrochemical mechanism of Cu2S during sodiation/desodiation is unveiled using advanced synchrotron-based in-situ X-ray diffraction and X-ray adsorption spectroscopy. This work represents a great advance in seeking high-performance anodes in SIBs.