Carbonos mesoporosos incorporados com enxofre para baterias Li-S: síntese, caracterização e estudo de viabilidade técnica e econômica preliminar

Abstract

This work reports the use of mesoporous carbons (CMs) derived from tannin biomass obtained through the solvent-free method and therefore incorporated with sulfur for applications in Li-S batteries. Sulfur incorporation was performed using the melt diffusion method, which presents a series of variables explored in the literature, including the type of reactor used, the amount of sulfur incorporated, the use of an additional heating step and the textural properties of the support material used. Thus, this work sought to understand how each of these variables impacts the electrochemical performance of the material. CM and CMa, the latter derived from the physical activation of CM with CO2, presented volume of 0.56 and 0.85 cm3 g-1 and specific surface area of 668 and 1180 m2 g-1, respectively, with high surface area and pore volume, which makes them promising for applications in Li-S batteries, being able to accommodate the element and retain polysulfides in the pores. The type of reactor used, divided between pressurized and unpressurized, showed that the pressure of the system impacts on the result, with materials obtained in pressurized systems presenting initial capacities between 783 and 907 mAhgS-1, while that obtained in the unpressurized system presented initial capacity of 501 mAhgS-1. The amount of sulfur, which ranged between 25% and 66% by mass of sulfur, shows that the amount of S of 50% is the best proportion as it combines the amount of active material with electrochemical performance, resulting in the initial capacity of 783 mAhgS-1. The use of the activated material CMa, compared to CM, showed a decrease in specific capacity, decreasing from 783 mAhgS-1 to 504 mAhgS-1. This can be attributed to the confinement of the species in the micropores, channels where there is space to accommodate the volume changes during the reaction. The additional step of heating to 300°C is mainly used to remove surface sulfur, which in fact occurs. However, compared to the material without the additional heating step, the material has a lower capacity, corresponding to 765 mAhgS-1. The preliminary technical feasibility study indicates that technically, the technology is feasible. From an economic point of view, preliminarily, the material has costs close to those of commercially available analogues. Thus, through this work it is possible to understand the influence on the electrochemical performance of each of the sulfur incorporation variables in the CMs obtained. In addition, the preliminary feasibility study indicates that the scaling of the process is feasible, and it is possible to obtain larger quantities of material per batch.