Phase-controlled synthesis of cobalt sulfides for lithium ion batteries.

The polyhedral CoS(2) with a narrow size distribution was synthesized by a facile solid-state assembly process in a sealed silica tube. The flux of potassium halide (KX; X = Cl, Br, I) plays a crucial role in the formation of polyhedrons and the size distribution. The S(2)(2-) groups in CoS(2) can be controllably withdrawn during heat treatment in air. The obtained phases and microstructures of CoS(2), Co(3)S(4), CoS, Co(9)S(8), and CoO depended on heating temperature and time. These cobalt materials, successfully used as the electrodes of lithium ion batteries, possessed good cycling stability in lithium ion batteries. The discharge capacities of 929.1 and 835.2 mAh g(-1) were obtained for CoS(2) and CoS respectively, and 76% and 71% of the capacities remained after 10 cycles. High capacities and good cycle performance make them promising candidates for lithium ion batteries. The approach combining solid-state assembly and heat treatment provides a simple and versatile way to prepare various metal chalcogeides for energy storage applications.