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Desenvolvimento de materiais de cátodo à base de polímeros condutores para baterias de ião sódio
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As baterias de ião sódio surgem como uma alternativa às baterias de ião lítio convencionais, mais baratas e mais abundante em termos de recurso. No entanto, o atraso na comercialização das mesmas está relacionado com o desenvolvimento de materiais catódicos com capacidade e potencial semelhante aos existentes nas baterias de ião lítio. Assim, este trabalho dedica-se ao desenvolvimento de novos materiais de cátodo à base de polímeros eletronicamente condutores capazes de incorporar ião sódio durante a descarga e sua expulsão durante a carga. Os fluxos mássicos que ocorrem nos filmes poliméricos de polietilenodioxiotiofeno dopados com poliestirenosulfonato são investigados por técnicas eletroquímicas, microgravimétricas e por efeito miragem. A sua morfologia e constantes dielétricas são analisadas, respetivamente, por microscopia de força atómica e por elipsometria ex-situ. Estes filmes foram sintetizados potenciodinamicamente em meio aquoso com diferente número de ciclos e a duas velocidades de varrimento, e potenciostaticamente durante dois períodos de tempo. A caracterização dos filmes foi realizada em meio orgânico numa ampla janela de potencial. A informação combinada das técnicas microgravimétricas e do efeito miragem permitiu a distinção entre fluxos de solvente e iónicos, sendo estes últimos avaliados quantitativamente através da ferramenta matemática de convolução temporal. Foi identificada a participação dominante do ião sódio (95%) nos fluxos iónicos. Os polímeros resistiram a 1000 ciclos de carga/descarga rápida, registando perda de massa inferior a 60%. Estes dados suportam a existência de dopagem pseudo catiónica quasi-ideal, uma vez que a participação do catião sódio é completamente dominante durante o processo de conversão redox para filmes finos de PEDOT:PSS. Este facto, conjuntamente com um valor de capacidade específica superior a 60 mAh.g-1, torna este material bastante competitivo comparativamente aos cátodos convencionais como é o caso da perovskite.
Sodium ion batteries appear as an alternative less expensive and more abudant than the conventional lithium ion batteries. However, the delay in their commercialization is related to the development of cathode materials with capacity and potential similar to those found in lithium ion batteries. Thus, this work is devoted to the development of new cathode materials based on electronically conductive polymers capable of incorporating sodium ion during discharge and their expulsion during charge. The mass fluxes occurring in the polyethylenedioxothiophene polymer films doped with polystyrenesulfonate are investigated by electrochemical, microgravimetric and by mirage effect techniques. Their morphology and dielectric constants are analyzed, respectively, by atomic force microscopy and ex-situ ellipsometry. These films were synthesized potentiodynamically in aqueous medium with different number of cycles and at two scanning rates, and potentiostatically for two time periods. The characterization of the films was carried out in organic medium in a wide window of potential. The combined information of microgravimetric techniques and the mirage effect allowed the distinction between solvent and ionic fluxes, the latter being evaluated quantitatively through the mathematical tool of temporal convolution. The dominant participation of sodium ion (95%) in the ionic fluxes was identified. The polymers resisted at 1000 load / discharge cycles, with a mass loss of less than 60%. These data support the existence of quasi-ideal pseudo-cation doping, since the participation of the sodium cation is completely dominant during the redox conversion process for PEDOT: PSS thin films. This, together with a specific energy value greater than 60mAh.g-1, makes this material very competitive compared to conventional cathodes such as perovskite.
Sodium ion batteries appear as an alternative less expensive and more abudant than the conventional lithium ion batteries. However, the delay in their commercialization is related to the development of cathode materials with capacity and potential similar to those found in lithium ion batteries. Thus, this work is devoted to the development of new cathode materials based on electronically conductive polymers capable of incorporating sodium ion during discharge and their expulsion during charge. The mass fluxes occurring in the polyethylenedioxothiophene polymer films doped with polystyrenesulfonate are investigated by electrochemical, microgravimetric and by mirage effect techniques. Their morphology and dielectric constants are analyzed, respectively, by atomic force microscopy and ex-situ ellipsometry. These films were synthesized potentiodynamically in aqueous medium with different number of cycles and at two scanning rates, and potentiostatically for two time periods. The characterization of the films was carried out in organic medium in a wide window of potential. The combined information of microgravimetric techniques and the mirage effect allowed the distinction between solvent and ionic fluxes, the latter being evaluated quantitatively through the mathematical tool of temporal convolution. The dominant participation of sodium ion (95%) in the ionic fluxes was identified. The polymers resisted at 1000 load / discharge cycles, with a mass loss of less than 60%. These data support the existence of quasi-ideal pseudo-cation doping, since the participation of the sodium cation is completely dominant during the redox conversion process for PEDOT: PSS thin films. This, together with a specific energy value greater than 60mAh.g-1, makes this material very competitive compared to conventional cathodes such as perovskite.
Descrição
Tese de mestrado integrado, Engenharia da Energia e do Ambiente, Universidade de Lisboa, Faculdade de Ciências, 2018
Palavras-chave
Bateria de Ião Sódio EDOT:PSS Dopagem Pseudo Catiónica Efeito miragem Teses de mestrado - 2018