Desenvolvimento de aditivos a partir de grafite esfoliado e funcionalizado para aplicações em baterias chumbo-ácido

Abstract

Lead-acid batteries are one of the main devices among existing energy storage devices. These batteries, which have their main application in automobiles, have characteristics such as low production cost, high recycling and low self-discharge. However, for advanced systems, such as in hybrid electric vehicles (HEV), these batteries need improvement due to premature failures caused by the accumulation of lead sulfate crystals on the negative plates when applied at a high rate of partial state of charge (HRPSoC). One of the ways to avoid this is the addition of small amounts of carbonic materials as additives in the composition of the negative plates. However, many of these carbon-based materials, such as graphene, are difficult to apply due to high-cost production routes. Therefore, this work aims to perform the synthesis of graphite oxide (GrO), microwave exfoliated graphene oxide (MEGO) and microwave exfoliated functionalized graphene oxide (α-MEGO) using alternative routes of exfoliation and oxidation of graphite and evaluate the performance of these materials as additives in the composition of the negative actives mass (NAM). The characterization carried out on GrO, synthesized from the modified Hummers method, showed efficient oxidation and formation of defects in the carbon chain, leading to a 21 % increase in the active area and an improvement in the stability of its dispersion in water compared to the graphite. In the case of MEGO, synthesized from microwave reduction, an efficient synthesis was also identified, obtaining a partially reduced material with oxygenated groups in its structure, leading to an increase 544 % of the active area compared to the GrO. About α-MEGO, a process of thermal reduction of the sample was identified, obtaining a material with morphological characteristics and organization of the carbon chain similar to reduced graphene oxides (rGO), leading to a 17 % increase in active area of the material compared to MEGO. Negative plates produced conventionally and containing graphite, GrO, MEGO and α-MEGO additives showed similar morphological and compositional characteristics. In terms of macroporosity, negative plates containing MEGO and α-MEGO additives showed superior results compared to conventional plates and plates containing graphite and GrO. From electrical tests carried out in P|N|P cells, it was observed that the carbonic additives did not directly influence the results of capacity and capacity reserve. In durability tests, cells containing α-MEGO showed a 39 % improvement compared to conventional cells. This proves the benefits brought by carbon additives in the composition of negative plates under a high rate of partial state of charge and the potential of the synthesized additive when applied in lead-acid batteries for advanced systems.