Sulfur vacancies in Co9S8-x/N-doped graphene enhancing the electrochemical kinetics for high-performance lithium-sulfur batteries

A sufficient areal capacity is necessary for achieving high-energy lithium-sulfur batteries, which require sufficiently high sulfur loading in the cathode materials. Therefore, the kinetically fast catalytic conversion of polysulfide intermediates is especially important for the full utilization of sulfur. Herein, Co9S8-x/N-doped graphene (Co9S8-x/N-G) is used as a sulfur host material and electrocatalyst in a high-sulfur-loading cathode, in which sulfur vacancies are generated via the hydrogen reduction of stoichiometric Co9S8. The produced sulfur vacancies in Co9S8-x/N-G effectively improve the adsorption ability for polysulfide anions, and theoretical calculations indicate that Co9S8-x has lower adsorption energy for polysulfides than Co9S8. Furthermore, electrochemical experiments reveal that the electrode process kinetics for the catalytic conversion of polysulfides are enhanced by sulfur vacancies. As a result, the S/Co9S8-x/N-G cathode with a high sulfur loading of 14.6 mg cm(-2) delivers a high areal capacity of 12.9 mA h cm(-2), and long-term cycling stability with a slow decay rate of 0.035% per cycle during 1000 cycles at 1C. Additionally, the pouch cell shows foldable flexibility and a stable areal capacity of 5.9 mA h cm(-2) at a sulfur loading of 7.1 mg cm(-2). The results show that enhancing the polysulfide conversion process kinetics using sulfur vacancies could be an effective approach for obtaining high-performance lithium-sulfur batteries.

Automated summary

This study demonstrates that enhancing the adsorption ability for polysulfide anions by introducing sulfur vacancies in a high-sulfur-loading cathode can improve the kinetics of the polysulfide conversion process, leading to high-performance lithium-sulfur batteries. The sulfur vacancies in Co9S8-x/N-G effectively improve the electrode process kinetics for the catalytic conversion of polysulfides, resulting in a high areal capacity and long-term cycling stability. These results suggest that utilizing sulfur vacancies could be an effective approach for achieving high-energy lithium-sulfur batteries.