Li-battery technology is today mainly developed as small energy delivery systems for portable devices.¹However, in recent years the growing interest in renewable energy and in electric vehicles exploiting electric power requires the development of new, high capacity and long life batteries.¹ In this context Li-S battery technology became of great interest due to the high theoretical energy density of 3500 Wh kg^-1, estimated to lead to 3-5 times increase in practical energy density compared to commercial Li-ion battery today available.²

Even though the Li/S battery system has been widely investigated, several issues related to the lithium-sulfur electrochemical reaction still hinder the practical realization of this technology. Indeed, the electrochemical reaction mechanism involves a series of steps with formation of soluble polysulfide species. ³ This dissolution leads to the loss of active material from the solid electrode and to the “shuttle effect” of the polysulfide with consequent capacity reduction and limited cycling-life of the battery. Furthermore, sulfur has a very low electronic conductivity thus requiring the addition of a conducting matrix. In this contribution we present the role of the carbon-matrix on the performance of Li-S cells based on liquid and solid electrodes. Various carbon and carbon-sulfur compounds have been taken into account and investigated. We demonstrated how the surface area, the pore structure and the free volume in the electrode are the significant driving forces to improve the Li-S electrochemical reaction.

References

(1) B. Scrosati, J. Garche, J. Power Sources. 195 (2010) 2419-3046.

(2) Y. Yang, G. Zheng, Y. Cui, Energy Environ. Sci.6 (2013) 1552-1558.

(3) X. Ji, L.F. Nazar, J. Mater. Chem. 20 (2010) 9821−9826.