Facile Growth of Metal-Rich Cu1.75S and Cu1.8S Microspheres Assembled with Mesoporous Nanosheets and Their Application in Na-Ion Batteries

Abstract

Heterogeneous structured-metal sulfides are widely used in various applications due to their excellent electrochemical activity. We report a facile synthesis of Cu1.75S/Cu1.8S microspheres assembled with mesoporous nanosheets and their application in sodium-ion batteries. This unique structure is obtained by a simple reaction of Cu2O octahedra and Na2S in an optimized molar ratio of 1-2.5 in an aqueous solution at room temperature without any other capping agents and chemicals. It is revealed that roxbyite CuiisS has preferential growth along the c direction leading to nanosheets with highly exposed (008) facets. The Cu1.75S is transformed into a digenite Cu1.8S phase without a significant morphological change by a thermal treatment. The Cu1.75S and Cu1.8S microspheres with thin sheets have particle sizes of similar to 2 mu m, surface areas of 5.9 and 3.3 m(2) g(-1), and mesopores mainly in a range of 2-50 nm. Remarkable sodium storage properties were achieved, including charge capacities of 324 and 327 mAh g(-1) at 0.1 C, stable cyclabilities of 93% and 96% over 500 cycles at 3 C, and high-rate capabilities of 285 (88%) and 290 mAh g(-1) (90%) at 3 C in a voltage range of 0.3-2.1 V versus Na/Na+.