Synchronous sulfurization and carbonization using sulfur-rich metal-organic frameworks for fast-charge sodium-ion batteries

Metal sulfides are one of the most promising anode materials for sodium-ion batteries (SIBs) due to their high theoretical capacity and appropriate electrode potential. However, these materials are still suffering from the low conductivity, large volume change during the charge-discharge process, sluggish reaction kinetics and poor cycle stability. Herein, we report a new strategy to synthesize CoSx-carbon composite (CoSx@C) from a sulfur-rich metal-organic framework for SIBs. The synchronous sulfurization and carbonization facilitated the formation of homogenous composites and the small amount of carbon in the composites significantly enhanced the intrinsic conductivity. As a result, the obtained CoSx@C electrodes showed a high specific capacity of 664 mAh g−1 after 400 cycles at 0.5 A g−1. When the current density increased from 0.2 to 5 A g−1, the capacity only decreased slightly from 653 to 601 mAh g−1, with retention as high as 90%. The capacity and the rate performance outperformed most of the reported cobalt sulfide anodes for SIBs.