WS nanosheets@ZIF-67-derived N-doped carbon composite as sodium ion battery anode with superior rate capability.

Devising novel composite electrodes with particular structural/electrochemical characteristics becomes an efficient strategy to advance the performance of rechargeable battery. Herein, considering the homogeneous transition metal sulfide with N-doped carbon derived from zeolitic imidazolate framework-67 (ZIF-67) and WS with large interlayer spacing, a laurel-leaf-like CoS/WS@N-doped carbon bimetallic sulfide (CoS/WS@NC) is engineered and prepared via a step-by-step method. As an electrode material for sodium ion batteries (SIBs), CoS/WS@NC composite delivers high capacities of 480 and 405 mA h g at 0.1 and 1.0 A g, respectively. As the current density increases from 0.1 to 5.0 A g, it provides specific capacity of 359 mA h g with a capacity retention rate of 78.0%, which is higher than that of CoS@NC (63.5%) and WS (58.6%). The CoS/WS@NC composite anode maintains a stable specific capacity (354 mA h g at 2.0 A g). It also exhibits a high capacitive contribution ratio of 90.8% at 1.0 mV s. This study provides a new and reliable insight for designing bimetallic sulfide with two-dimensional nanostructure for energy storage.