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Development of ionic liquid inspired materials for energy storage
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O desenvolvimento de soluções de armazenamento de energia seguras e eficientes é es- sencial para a transição de tecnologias à base de combustiveis fósseis para alternativas mais sustentáveis. Esta dissertação teve como objetivo conceber eletrólitos em gel (EGP) à base de celulose capazes de desempenho comparável com eletrólitos comerciais à base de carbonatos orgânico, aumentando a segurança. A formulação de novos eletrólitos baseou- se na racionalização do transporte de iões de lítio (Li+) e da dinâmica iônica subjacente. A hidroxipropilcelulose (HPC) foi usada para investigar as interações entre celulose e líquidos iônicos (LIs) derivados de imidazólio, utilizando ressonância magnética nuclear (RMN), rheo-RMN e reologia. Revelando o papel dos aniões e catiões na dissolução da celulose. Um solvente ternário para celulose, composto por um LI, [C4C1Im]Cl, e um solvente orgânico, dimetilsulfóxido (DMSO), foi explorado para estudar como a presença de água influencia a solubilidade do polímero e o emparelhamento iônico do LI. Este trabalho representa um passo em direcção um sistema mais complexo, aproximando-se da com- posição desejada para as formulações dos EGPs. Celulose foi modificada para produzir eletrólitos poliméricos (LIPs) denominados CellPILs, dos quais EGPs foram sintetizados, com o EGP derivado de metilimidazólio demonstrando o menor impedimento à difusão de Li+.
EGPs foram produzidos a partir de celulose micro (MCC) e nanocristalina (NCC), com diferentes substituintes, para avaliar o impacto da cristalinidade do polímero e dos grupos introduzidos. A produção de EGPs também foi estudada com derivados não iônicos de celulose, como a metilcelulose (MC), produzindo géis termorreversíveis em DMSO e LIs ou LIPs. Após a dopagem com LiTFSI, a mobilidade de Li+ foi analisada, a presença que um LIP aniónico aumentou significativamente a mobilidade desses iões, aproximando- se do desempenho dos eletrólitos líquidos convencionais. EGPs baseados em MC foram avaliados para aplicação em supercapacitores e dispositivos eletrocrômicos, revelando resultados promissores. Técnicas de espectroscopia RMN foram utilizadas para investigar as interações entre celulose, LIs e misturas de LIs/solventes orgânicos, sendo depois também usadas para estudar o processo de gelificação e a dinâmica iônica dos EGPs.
The development of high-performance and safe energy storage solutions is needed to transition out of fossil fuel-dependent technologies into greener alternative solutions. This Ph.D. aimed to develop gel-based electrolytes using cellulose, seeking to produce gel polymer electrolytes (GPEs) capable of performing at the level of commercial organic carbonate-based electrolytes while increasing safety. The formulation of new electrolytes depends on the rationalization of Li+ transport and ion dynamics. Hydroxypropyl cellulose (HPC) was used to study cellulose interactions with imidazolium ionic liquids (ILs) by nuclear magnetic resonance (NMR), rheology nuclear magnetic resonance (rheo-NMR) and rheology. The importance of the anion as well as the cation in cellulose dissolution was disclosed. Afterward, a ternary solvent system for cellulose was investigated, comprising an IL, [C4C1Im]Cl, and an organic solvent, dimethyl sulfoxide (DMSO), revealing how the presence of water modulates the solubility of the polymer and the ion-pairing of the IL. This work represents a step towards a more complex system, closely resembling the desired formulation of GPEs. Cellulose was modified to produce cellulose polymeric ionic liquids (PILs), CellPILs, from which GPEs were prepared. The 5 wt. % GPE prepared with the methyl-imidazolium-derived PIL exhibited the lower energy barrier regarding Li+ diffusion. GPEs were prepared from microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC) and different substituents to evaluate polymer crystallinity and the influence of the grafting groups. Non-ionic cellulose derivatives were also studied for GPE preparation. A commercial cellulose derivative, methyl cellulose (MC) was used to produce thermoreversible gels in DMSO and ILs or PILs. After doping with LiTFSI, the Li+ mobility was studied. Having an anionic PIL backbone enhanced Li+ mobility, being able to achieve a Li+ transport number similar to liquid electrolytes. MC-based GPEs were evaluated for application in supercapacitors and electrochromic devices revealing promising results in both. NMR spectroscopy techniques were used in the evaluation of the interaction of cellulose and ILs and ILs/organic solvent mixtures. Afterward, NMR was also the main technique to study the gelation process and ion dynamics in the GPEs.
The development of high-performance and safe energy storage solutions is needed to transition out of fossil fuel-dependent technologies into greener alternative solutions. This Ph.D. aimed to develop gel-based electrolytes using cellulose, seeking to produce gel polymer electrolytes (GPEs) capable of performing at the level of commercial organic carbonate-based electrolytes while increasing safety. The formulation of new electrolytes depends on the rationalization of Li+ transport and ion dynamics. Hydroxypropyl cellulose (HPC) was used to study cellulose interactions with imidazolium ionic liquids (ILs) by nuclear magnetic resonance (NMR), rheology nuclear magnetic resonance (rheo-NMR) and rheology. The importance of the anion as well as the cation in cellulose dissolution was disclosed. Afterward, a ternary solvent system for cellulose was investigated, comprising an IL, [C4C1Im]Cl, and an organic solvent, dimethyl sulfoxide (DMSO), revealing how the presence of water modulates the solubility of the polymer and the ion-pairing of the IL. This work represents a step towards a more complex system, closely resembling the desired formulation of GPEs. Cellulose was modified to produce cellulose polymeric ionic liquids (PILs), CellPILs, from which GPEs were prepared. The 5 wt. % GPE prepared with the methyl-imidazolium-derived PIL exhibited the lower energy barrier regarding Li+ diffusion. GPEs were prepared from microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC) and different substituents to evaluate polymer crystallinity and the influence of the grafting groups. Non-ionic cellulose derivatives were also studied for GPE preparation. A commercial cellulose derivative, methyl cellulose (MC) was used to produce thermoreversible gels in DMSO and ILs or PILs. After doping with LiTFSI, the Li+ mobility was studied. Having an anionic PIL backbone enhanced Li+ mobility, being able to achieve a Li+ transport number similar to liquid electrolytes. MC-based GPEs were evaluated for application in supercapacitors and electrochromic devices revealing promising results in both. NMR spectroscopy techniques were used in the evaluation of the interaction of cellulose and ILs and ILs/organic solvent mixtures. Afterward, NMR was also the main technique to study the gelation process and ion dynamics in the GPEs.
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Palavras-chave
Cellulose Ionic liquids Polymeric ionic liquids Gel polymer electrolytes Nuclear magnetic resonance