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 similar to 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. (C) 2012 Elsevier Ltd. All rights reserved.