A Li+-conductive microporous carbon–sulfur composite for Li-S batteries

In this paper, we propose a new strategy to develop high performance sulfur electrode by impregnating sulfur into the micropores of a Li+-insertable carbon matrix with the simultaneous use of a carbonate electrolyte, which does not dissolve polysulfides, to restrain the solution of the reaction intermediates of sulfur. To proof this concept, we prepared a Li+-insertable microporous carbon–sulfur composite by vaporizing sulfur into the micropores of the nanofiber-wired carbon microspheres. The experimental results demonstrate that, in the carbonate electrolyte of 1 M LiPF6/PC-EC-DEC, such S/C composite electrode exhibits not only stable cycling performance with a reversible capacity of 720 mAh g−1 after 100 cycles, but also superior high coulombic efficiency of ∼100% upon extended cycling (except the first three cycles). The structural and electrochemical analysis indicates that the improved electrochemical behaviors of the S/C composite arise from a new reaction mechanism, in which Li+ ions and electrons transport through the carbon matrix into the interior of the cathode and then react with the embedded sulfur in the S/C solid–solid interfaces, avoiding the solution of the intermediates into the bulk electrolyte. More significantly, the structural design and working mechanism of such a sulfur cathode could be extended to a variety of poorly conductive and easily soluble redox-active materials for battery applications.

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► A carbon–sulfur composite was prepared by vaporizing sulfur into the nanopores of Li+-conductive carbon microspheres.
► The redox reaction of S8 molecules embedded in the nanopores of carbon microspheres proceeds through a solid–solid mechanism at the S/C interfaces.
► The carbon–sulfur composite exhibits a stable cycling performance and a superior high coulombic efficiency of 100%.