Topochemical and phase transformation induced Co 9 S 8 /NC nanosheets for high-performance sodium-ion batteries.

In this paper, a cobalt-based sulfide nanosheet structure (Co 9 S 8 /NC) was successfully synthesized by topochemical and phase transformation processes from a dodecahedral cobalt-based imidazole skeleton (ZIF-67) as a self-template. The 2D sheet structure facilitates full contact of electrode materials with the electrolyte and shortens the diffusion distance for electrons and ions. In addition, the nitrogen-doped carbon framework derived from ZIF-67 promotes electron transfer and provides a reliable skeleton to buffer volume expansion during discharging and charging. Finally, Co 9 S 8 /NC exhibits excellent rate capability and stable cycling performance for the anode of a sodium ion battery, delivering a specific capacity remaining at 530 mA h g -1 after 130 cycles at a current density of 1 A g -1 .