Dinâmica molecular de líquidos iônicos para sistemas de armazenamento de energia
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Data
2019
Autores
Sampaio, Abner Massari [UNIFESP]
Orientadores
Siqueira, Leonardo José Amaral de [UNIFESP]
Tipo
Dissertação de mestrado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Líquidos Iônicos (LI’s) são sais fundidos à baixas temperaturas e têm sido amplamente
estudados como eletrólitos para baterias e supercapacitores, em função de suas estabilidades
eletroquímicas, viscosidades relativamente baixas e condutividades iônicas intrínsecas. Neste
trabalho, um conjunto de parâmetros de campo de força foi proposto para o líquido iônico
bis(trifluorometano-sulfonil)imideto de 2-metóxi-etil-metil-sulfônio ([S12G1][NTf2]) puro e em
solução 1,5 M e 3,0 M com acetonitrila. Os parâmetros demonstraram ser capazes de descrever
satisfatoriamente propriedades de transporte deste líquido iônico (viscosidade e condutividade
iônica), bem como a sua densidade em diferentes temperaturas. Análises da estrutura do líquido
iônico puro e em solução com acetonitrila foram realizadas e demonstram que os ânions estão
preferencialmente arranjados na região do átomo de enxofre do cátion e evitam a região da
função éter devido à repulsão gerada da interação com o átomo de oxigênio. Já os cátions, estão
arranjados na região dos átomos de oxigênio e enxofre do ânion e evitam a região dos átomos
de flúor. As análises estruturais também elucidam qual o impacto da presença de acetronitrila
no arranjo entre cátions e ânions. Simulações do líquido iônico confinado entre eletrodos de
carbono poroso também foram realizadas. Os resultados obtidos apontam que a organização
estrutural do líquido iônico [S12G1][NTf2] é bastante distinta da estrutura obtida utilizando-se o
líquido iônico bis(trifluorometano-sulfonil)imideto de 2-(metóxi)-etil-trietil-fosfônio
([P222,2O1][NTf2]), também estudado em nosso grupo de pesquisa, e promovem uma melhor
performance do líquido iônico contendo o cátion sulfônico em termos de energia armazenada
pelo supercapacitor.
Ionic liquids are molten salts at low temperatures and have been widely studied as electrolytes for batteries and supercapacitors due to their electrochemical stability, relatively low viscosity, and intrinsic ionic conductivity. In this work, a set of force field parameters was proposed for the pure ionic liquid 2-methoxy-ethyl-methylsulfonium bis(trifluoromethanesulfonyl)imide ([S12G1][NTf2]) and its 1,5 M and 3,0 M solutions with acetonitrile. The parameters are able to describe transport properties (viscosity and ionic conductivity) of this ionic liquid as well as its density at different temperatures. Structure analysis of the pure ionic liquid and its mixtures with acetonitrile were performed and demonstrated that the anions are preferably arranged in the region of the sulfur atom of the cation and avoid the ether function region due to the repulsion generated from the interaction with the oxygen atom. The cations are arranged around the oxygen and sulfur atoms of the anion and avoid the fluorine atoms region. The structural analyzes also elucidate the impact of the presence of acetonitrile in the arrangement between cations and anions. Simulations of the confined ionic liquid between porous carbon electrodes were also performed. The results show that the structural organization of the sulfonium based ionic liquid [S12G1][NTf2] is slightly different from the structure obtained using the 2-methoxy-ethyl-triethylsulfonium bis(trifluoromethane-sulfonyl)imide ([P222,2O1][NTf2]) - also studied in our research group – and promote a better performance in terms of energy stored by the supercapacitor, in spite of lower electrochemical window
Ionic liquids are molten salts at low temperatures and have been widely studied as electrolytes for batteries and supercapacitors due to their electrochemical stability, relatively low viscosity, and intrinsic ionic conductivity. In this work, a set of force field parameters was proposed for the pure ionic liquid 2-methoxy-ethyl-methylsulfonium bis(trifluoromethanesulfonyl)imide ([S12G1][NTf2]) and its 1,5 M and 3,0 M solutions with acetonitrile. The parameters are able to describe transport properties (viscosity and ionic conductivity) of this ionic liquid as well as its density at different temperatures. Structure analysis of the pure ionic liquid and its mixtures with acetonitrile were performed and demonstrated that the anions are preferably arranged in the region of the sulfur atom of the cation and avoid the ether function region due to the repulsion generated from the interaction with the oxygen atom. The cations are arranged around the oxygen and sulfur atoms of the anion and avoid the fluorine atoms region. The structural analyzes also elucidate the impact of the presence of acetonitrile in the arrangement between cations and anions. Simulations of the confined ionic liquid between porous carbon electrodes were also performed. The results show that the structural organization of the sulfonium based ionic liquid [S12G1][NTf2] is slightly different from the structure obtained using the 2-methoxy-ethyl-triethylsulfonium bis(trifluoromethane-sulfonyl)imide ([P222,2O1][NTf2]) - also studied in our research group – and promote a better performance in terms of energy stored by the supercapacitor, in spite of lower electrochemical window