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

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 Cu1.75S 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 ∼2 μm, surface areas of 5.9 and 3.3 m2 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+.