Molecular structure, interactions, and dynamics of novel Li-battery electrolytes

Lithium-ion batteries are one of the most promising candidates for energy storage in sustainable technologies such as electro-mobility or renewable energy systems. However, at present they are incapable to compete with the combustion engine to power vehicles in terms of capacity, price, and safety. The same shortcomings are also limiting the applicability in large-scale grid energy storage. A key component for improved performance is the electrolyte where a better understanding of the limiting mechanism at a molecular level is needed in order to achieve beyond state-of-the- art technology. This thesis focuses on understanding new types of electrolytes from structural and dynamical points of view. While the commonly used electrolytes consist of a mixture of organic solvents and moderate concentrations of lithium salts, recent studies suggest the use of super-concentrated electrolytes or the implementation of ionic liquids, as additives or as full replacement of the organic solvent, as promising development routes. A common feature of these new electrolytes is a complex structure with characteristic length scales exceeding those normally found in simple liquids. Due to their ionic nature and surfactant-like structure ionic liquids tend to display a mesoscopic ordering due to the competition between ionic and van der Waals interactions. Super-concentrated electrolytes on the other hand develop an ordering as a result of local coordination responsible for the solvation of the ions. This can also be expected to influence the dynamic behaviour and hence in the end the ion transport. In this thesis the structure and dynamics of these systems have been investigated using X-ray and neutron scattering techniques identifying common structural features between ionic liquids and super-concentrated electrolytes as well a multiple relaxation processes at different length scales. Moreover, the first solvation shells and molecular interactions were determined by Raman spectroscopy and the results linked to macroscopic properties, such as the phase behaviour and the ionic conductivity

Low dose X-ray speckle visibility spectroscopy reveals nanoscale dynamics in radiation sensitive ionic liquids

X-ray radiation damage provides a serious bottle neck for investigating {\mu}s to s dynamics on nanometer length scales employing X-ray photon correlation spectroscopy. This limitation hinders the investigation of real time dynamics in most soft matter and biological materials which can tolerate only X-ray doses of kGy and below. Here, we show that this bottleneck can be overcome by low dose X-ray speckle visibility spectroscopy. Employing X-ray doses of 22 kGy to 438 kGy and analyzing the sparse speckle pattern of count rates as low as 6.7x10-3 per pixel we follow the slow nanoscale dynamics of an ionic liquid (IL) at the glass transition. At the pre-peak of nanoscale order in the IL we observe complex dynamics upon approaching the glass transition temperature TG with a freezing in of the alpha relaxation and a multitude of milli-second local relaxations existing well below TG. We identify this fast relaxation as being responsible for the increasing development of nanoscale order observed in ILs at temperatures below TG.Comment: 7 pages, 5 figure

In-situ gelled electrolyte for lithium battery: Electrochemical and Raman characterization

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Arrested dynamics of the dipolar hard-sphere model

We report the combined results of molecular dynamics simulations and theoretical calculations concerning various dynamical arrest transitions in a model system representing a dipolar fluid, namely, N (softcore) rigid spheres interacting through a truncated dipole-dipole potential. By exploring different regimes of concentration and temperature, we find three distinct scenarios for the slowing down of the dynamics of the translational and orientational degrees of freedom: At low ({$\eta$} = 0.2) and intermediate (${\eta}$ = 0.4) volume fractions, both dynamics are strongly coupled and become simultaneously arrested upon cooling. At high concentrations ({$\eta$} $\lt$ 0.6), the translational dynamics shows the features of an ordinary glass transition, either by compressing or cooling down the system, but with the orientations remaining ergodic, thus indicating the existence of partially arrested states. In this density regime, but at lower temperatures, the relaxation of the orientational dynamics also freezes. The physical scenario provided by the simulations is discussed and compared against results obtained with the self-consistent generalized Langevin equation theory, and both provide a consistent description of the dynamical arrest transitions in the system. Our results are summarized in an arrested states diagram which qualitatively organizes the simulation data and provides a generic picture of the glass transitions of a dipolar fluid

Achieving enhanced ionic mobility in nanoporous silica by controlled surface interactions

We report a strategy to enhance the ionic mobility in an emerging class of gels, based on robust nanoporous silica micro-particles, by chemical functionalization of the silica surface. Two very different ionic liquids are used to fill the nano-pores of silica at varying pore filling factors, namely one aprotic imidazolium based (1-methyl-3-hexylimidazolium bis(trifluoromethanesulfonyl)imide, C6C1ImTFSI), and one protic ammonium based (diethylmethylammonium methanesulfonate, DEMAOMs) ionic liquid. Both these ionic liquids display higher ionic mobility when confined in functionalized silica as compared to untreated silica nano-pores, an improvement that is more pronounced at low pore filling factors (i.e. in the nano-sized pore domains) and observed in the whole temperature window investigated (i.e. from −10 to 140 °C). Solid-state NMR, diffusion NMR and dielectric spectroscopy concomitantly demonstrate this effect. The origin of this enhancement is explained in terms of weaker intermolecular interactions and a consequent flipped-ion effect at the silica interface strongly supported by 2D solid-state NMR experiments. The possibility to significantly enhance the ionic mobility by controlling the nature of surface interactions is extremely important in the field of materials science and highlights these structurally tunable gels as promising solid-like electrolytes for use in energy relevant devices. These include, but are not limited to, Li-ion batteries and proton exchange membrane (PEM) fuel cells

Glassy dynamics in asymmetric binary mixtures of hard-spheres

The binary hard-sphere mixture is one of the simplest representations of a many-body system with competing time and length scales. This model is relevant to fundamentally understand both the structural and dynamical properties of materials, such as metallic melts, colloids, polymers and bio-based composites. It also allows us to study how different scales influence the physical behavior of a multicomponent glass-forming liquid; a question that still awaits a unified description. In this contribution, we report on distinct dynamical arrest transitions in highly asymmetric binary colloidal mixtures, namely, a single glass of big particles, in which the small species remains ergodic, and a double glass with the simultaneous arrest of both components. When the mixture approaches any glass transition, the relaxation of the collective dynamics of both species becomes coupled. In the single glass domain, spatial modulations occur due to the structure of the large spheres, a feature not observed in the two-glass domain. The relaxation of the \emph{self} dynamics of small and large particles, in contrast, become decoupled at the boundaries of both transitions; the large species always displays dynamical arrest, whereas the small ones appear arrested only in the double glass. Thus, in order to obtain a complete picture of the distinct glassy states, one needs to take into account the dynamics of both species

Inner clocks of glass-forming fluids

Providing a physically sound explanation of aging phenomena in non-equilibrium amorphous materials is a challenging problem in modern statistical thermodynamics. The slow evolution of physical properties after quenches of control parameters is empirically well interpreted via the concept of material time (or internal clock) based on the Tool–Narayanaswamy–Moynihan model. Yet, the fundamental reasons of its striking success remain unclear. We propose a microscopic rationale behind the material time on the basis of the linear laws of irreversible thermodynamics and its extension that treats the corresponding kinetic coefficients as state functions of a slowly evolving material state. Our interpretation is based on the recognition that the same mathematical structure governs both the Tool model and the recently developed non-equilibrium extension of the self-consistent generalized Langevin equation theory, guided by the universal principles of Onsager’s theory of irreversible processes. This identification opens the way for a generalization of the material-time concept to aging systems where several relaxation modes with very different equilibration processes must be considered, and partially frozen glasses manifest the appearance of partial ergodicity breaking and, hence, materials with multiple very distinct inner clocks

Silver improves collagen structure and stability at demineralized dentin: a dynamic-mechanical and Raman analysis.

Objective: This study aimed to evaluate the effect of silver loaded nanoparticles (NPs) application on dentin remineralization. Methods: Polymethylmetacrylate-based NPs and silver loaded NPs (Ag-NPs) were applied on demineralized dentin surfaces. Dentin was characterized morphologically by scanning electron microscopy, mechanically probed by a nanoindenter to test nanohardness and Young modulus, and chemically analyzed by Raman spectroscopy after 24 h and 7 d of storage. Untreated surfaces were used as control. Data were submitted to ANOVA and Student-Newman-Keuls multiple comparisons tests (P<0.05). Results: After Raman analysis, dentin treated with Ag-NPs obtained the lowest mineralization and intensity of stoichiometric hydroxyapatite when compared with specimens treated with undoped-NPs. The lowest relative mineral concentration, expressed as the ratio phosphate or carbonate/phenyl group, and crystallinity was attained by dentin treated with with Ag-NPs, after 7 d. Ag-NPs application generated the highest values of collagen crosslinking (intensity at 1032 cm-1 band). The molecular conformation of the collagen’s polypeptide chains, amide-I and CH2 also attained the highest peaks in dentin treated with Ag-NPs. Staggered and demineralized collagen fibrils were observed covering the dentin surfaces treated with Ag-NPs, at both 24 h and 7 d. Samples treated with Ag-NPs attained the lowest values of nanohardness and Young’s modulus at 7 d of storage. Conclusions: Peritubular and intertubular dentin were remineralized when using undoped-NPs. After 7 d, collagen treated with NPs was remineralized but dentin treated with Ag-NPs attained an improved collagen matrix structure and stability but the lowest mineralization and crystallinity.This work was supported by the Ministry of Economy and Competitiveness (MINECO) and European Regional Development Fund (FEDER). Project MAT2017-85999-P MINECO/AEI/FEDER/UE

Nanoparticles antidegradation activity at bonded dentin

The objective was to assess doxycycline (Dox) and zinc (Zn) doped nanoparticles' (NPs) potential to protect the resin-dentin interface from cariogenic biofilm. Three groups ofpolymeric NPs were tested: unloaded, loaded with zinc and with doxycycline. NPs were appliedafter dentin etching. The disks were exposed to a cariogenic biofilm challenge in a Drip-FlowReactor during 72 h and 7 d. Half of the specimens were not subjected to biofilm formation butstored 72 h and 7 d. LIVE/DEAD® viability assay, nano-dynamic mechanicalassessment, Raman spectroscopy and field emission electron microscopy (FESEM) analysiswere performed. The measured bacterial death rates, at 7 d were 46% for the control group, 51%for the undoped-NPs, 32% for Dox-NPs, and 87% for Zn-NPs; being total detected bacteriareduced five times in the Dox-NPs group. Zn-NPs treated samples reached, in general, thehighest complex modulus values at the resin-dentin interface over time. Regarding the mineralcontent, Zn-NPs-treated dentin interfaces showed the highest mineralization degree associatedto the phosphate peak and the relative mineral concentration. FESEM images after Zn-NPsapplication permitted to observe remineralization of the etched and non-resin infiltratedcollagen layer, and bacteria were scarcely encountered. The combined antibacterial andremineralizing effects, when Zn-NPs were applied, reduced biofilm formation. Dox-NPs exertedan antibacterial role but did not remineralize the bonded interface. Undoped-NPs did notimprove the properties of the interfaces. Application of Zn-doped NPs during the bondingprocedure is encouraged

Use of multivariate NMR analysis in the content prediction of hemicellulose, cellulose and lignin in greenhouse crop residues

Se ha introducido el uso del análisis multivariado de RMN en el desarrollo de modelos de predicción precisos, que potencialmente surgen de una correlación entre los perfiles de metabolitos solubles y la composición de la pared celular, para la determinación de los contenidos de hemicelulosa, celulosa y lignina en 8 especies de residuos de cultivos de invernadero. El presente artículo demuestra que los cubos discriminantes provenientes de un modelo PLS-DA en combinación con modelos lineales proporcionan una herramienta útil y rápida para la determinación de la composición de la pared celular de estos desechos vegetales. También se han aplicado métodos de regresión lineal regularizados para evitar el sobreajuste, produciendo modelos mejorados específicamente para determinaciones de lignina y celulosa. Los modelos predictivos también se presentan en una aplicación de escritorio disponible en http://www2.ual.es/NMRMBC/solutions. Para verificar la racionalidad y confiabilidad de los modelos, se realizaron experimentos de control siguiendo protocolos generalmente aceptados y se compararon con nuestros valores predichos