Desenvolvimento e otimização de baterias de lítio-enxofre baseadas em compósitos de enxofre com materiais de carbono porosos

Abstract

Lithium-sulfur batteries are promising energy storage devices for various commercial applications, especially in the automotive sector, given their high theoretical energy density and capacity. However, crucial problems such as the shuttle effect, which promote the irreversible loss of active material and anode passivation, still prevent large-scale production of this type of battery. Therefore, in this work, materials for cathodes based on a solvent-free synthesis were proposed, that sought to mitigate the adversities related to the durability of Li-S devices and were environmentally friendly. A systematic study of the configurations of this type of system was also carried out to determine the one that would provide the construction of Li-S cells with the best electrochemical performance. Finally, a gel polymer electrolyte was produced for application in these batteries. The results obtained for the synthesized materials demonstrated the impact of the degree of sulfur incorporation on the electrochemical performance. The material incorporated in a 1:1 sulfur/carbon mass ratio exhibited capacities of 797 and 309 mAh g-1 under rates of 0.1C and 2C, respectively. The material incorporated in a 2:1 mass ratio presented capacities of 541 and 114 mAh g-1 under the same current densities. This shows that saturating the carbon host with sulfur is not the ideal strategy to achieve high values. Regarding the battery optimization process, it was found that the production of cathodes by spreading, the use of coin cells and the use of a carbon-coated current collector were decisive in achieving satisfactory electrochemical performance. The gel polymer electrolyte studied in this work was produced from a poly (ionic liquid), ionic liquid and lithium salt. Electrochemical impedance spectroscopy tests under different temperatures showed ionic conductivities of 8.6 mS cm-1 at 105 ºC and 2.2 mS cm-1 at 35 ºC. The electrochemical stability window of the electrolyte evaluated by linear sweep voltammetry was 2.35 V, wide enough for application in lithium-sulfur batteries.