Nitrogen functionalities in mesoporous carbons and their impact on the sulfur infiltration efficiency and in the electrochemical performance of Li-S cells

The cyclability of Li-S batteries depends strongly on electrochemical cell stability, which is affected by the dilution of lithium polysulfides in the electrolyte. One of the proposed solutions is the use of porous carbonaceous materials in the cathode that trap lithium polysulfide species and prevent them from reaching the electrolyte. This is possible by using dopant heteroatoms in the carbon framework such as nitrogen to generate anchoring sites reducing the shuttle effect. To understand how the sulfur infiltration process in carbonaceous materials is affected by the inclusion of nitrogen in the carbon structure and its effect on the electrochemical performance of Li-S batteries, in this study N-doped mesoporous carbons were prepared by varying the carbonization temperature, focusing on the structural and compositional variations. At the highest carbonization temperature (850 degrees C), a carbonaceous material with the lowest nitrogen content was obtained mainly prevailing the N quaternary functionality over N-pyrrolic and N-pyridinic. The sulfur infiltration into the pores of the material was improved due to the moderate polarity obtained under the carbonization temperature used (850 degrees C). Given the distribution of nitrogen functionalities, it was possible to obtain a material with a high degree of graphitization reflected in the electrochemical performance where after 100 cycles a discharge capacity of 422.3 mA h g-1 was reached with a Coulombic efficiency of 99%.