Fiber-in-Tube Design of Co9S8-Carbon/Co9S8: Enabling Efficient Sodium Storage

The sodium-ion battery is a promising battery technology owing to its low price and high abundance of sodium. However, the sluggish kinetics of sodium ion makes it hard to achieve high-rate performance, therefore impairing the power density. In this work, a fiber-in-tube Co9S8-carbon(C)/Co9S8 is designed with fast sodiation kinetics. The experimental and simulation analysis show that the dominating capacitance mechanism for the high Na-ion storage performance is due to abundant grain boundaries, three exposed layer interfaces, and carbon wiring in the design. As a result, the fiber-in-tube hybrid anode shows a high specific capacity of 616mAhg(-1) after 150 cycles at 0.5Ag(-1). At 1Ag(-1), a capacity of ca. 451mAhg(-1) can be achieved after 500 cycles. More importantly, a high energy density of 779Whkg(-1) and power density of 7793Wkg(-1) can be obtained simultaneously.