Probing Interfacial Processes of Lithium Ion Batteries

In the last decade, lithium ion batteries held a major role in the path towards personal electronics due to being lightweight and providing a high energy density. However, several problems have been identified with lithium ion batteries. Due to inherent instability, lithium ion batteries are known to have issues with safety and capacity loss. Our goal is to advance the understanding of the electrochemical processes, specifically the interfacial processes at the anode, to continue their advancement in our electronic age. At the interface of the electrolyte and anode, during the first several charging and discharging cycles, appears a protective layer by interaction of decomposed electrolyte at the electrode surface. This protective layer, termed the solid electrolyte interphase, is of particular importance as it increases the stability, impeding dendrite growth, and ultimately leading to improved capacity and safety. Our electrolyte is a lithium salt (LiClO4) with ethylene carbonate (EC) in a tetrahydrofuran (THF) solvent, leading, primarily, to one of the main SEI contributors, lithium ethylene dicarbonate (LiEDC). By spectroscopically probing the interface with sumfrequency generation and simultaneously scanning with cyclic voltammetry, we are able to see the SEI contribution formation in real time.Ope

On-demand nanoengineering of in-plane ferroelectric topologies.

Hierarchical assemblies of ferroelectric nanodomains, so-called super-domains, can exhibit exotic morphologies that lead to distinct behaviours. Controlling these super-domains reliably is critical for realizing states with desired functional properties. Here we reveal the super-switching mechanism by using a biased atomic force microscopy tip, that is, the switching of the in-plane super-domains, of a model ferroelectric Pb0.6Sr0.4TiO3. We demonstrate that the writing process is dominated by a super-domain nucleation and stabilization process. A complex scanning-probe trajectory enables on-demand formation of intricate centre-divergent, centre-convergent and flux-closure polar structures. Correlative piezoresponse force microscopy and optical spectroscopy confirm the topological nature and tunability of the emergent structures. The precise and versatile nanolithography in a ferroic material and the stability of the generated structures, also validated by phase-field modelling, suggests potential for reliable multi-state nanodevice architectures and, thereby, an alternative route for the creation of tunable topological structures for applications in neuromorphic circuits

Long-lived photoinduced polar states in metal halide perovskites

Ferroic polarization in hybrid perovskites is crucial for enhancing photovoltaic performance and developing potential electronic applications. Controlling ferroic polarization with an optical field enables probing of ferroic polarization without the unwanted interface ionic effects caused by electronic contacts. This study employs ultrafast near-infrared photoexcitation to control dynamic structural transitions in soft single crystalline hybrid Cu (II) halide perovskites, achieving a long-lived polar state (beyond 104 s) at room temperature. We probe reversible long-lived polar domains under near-infrared photoexcitation using in-situ second harmonic generation microscopy. Theoretical calculation informs the polar lattice microstrain likely induced by anisotropic structure deformation in octahedral copper halide under near-infrared photoexcitation. The reversible slow structure deformation is further confirmed by in-situ photo-induced X-ray diffraction measurement. This work provides a material platform for understanding, controlling, and probing polarization under photoexcitation. Our methodology enables the identification of previously undiscovered polar phases in ferroelectric halide perovskites

Hexafluoroisopropanol-Promoted Metal-Free Allylation of Silyl Enol Ethers with Allylic Alcohols

A metal-free protocol for the reaction of silyl enol ethers with allylic alcohols based on the use of 1,1,1,3,3,3-hexafluoroisopropanol as a promoter able to activate both reactants, is described. This simple and straightforward transformation proceeds smoothly under mild conditions, rendering the corresponding allylated products in generally good yields.Financial support from the University of Alicante (UAUSTI16-03, UAUSTI16-10, VIGROB-173) and the Spanish Ministerio de Economía, Industria y Competitividad (CTQ2015-66624-P) is acknowledged

Pinacol Rearrangement and Direct Nucleophilic Substitution of Allylic Alcohols Promoted by Graphene Oxide and Graphene Oxide CO2H

Graphene oxide (GO) and carboxylic acid functionalized GO (GO–CO2H) have been found to efficiently promote the heterogeneous and environmentally friendly pinacol rearrangement of 1,2-diols and the direct nucleophilic substitution of allylic alcohols. In general, high yields and regioselectivities are obtained in both reactions using 20 wt % of catalyst loading and mild reaction conditions.Financial support from the University of Alicante (UAUSTI16-03, VIGROB-173), and Spanish Ministerio de Economía y Competitividad (CTQ2015-66624-P) is acknowledged

Catalyse par un acide Brønsted assistée par les composés nitro : activation des liaisons C(sp3)–O and C(sp3)–F

Alcohols are attractive electrophilic partners for nucleophilic substitution reactions as water is the only by-product in a reaction with protic nucleophiles. Despite being a highly desirable reaction, the scope of useful catalytic transformations remains limited to specific alcohol-nucleophile pairs and a general set of catalytic conditions remains elusive. This thesis describes the development of a general and mild catalyst system for the activation of a broad range of π-activated and aliphatic alcohols to address key limitations in the field. B(C6F6)3•H2O, a strong Brønsted acid, when combined with nitromethane has been found as a widely useful catalyst system for chemoselective alcohol substitution in the presence of acid sensitive functionalities and protecting groups without the typical compromises in reaction rates, substrate/nucleophile scope and catalyst loading. In particular, a co-catalytic effect of nitro compounds is described for the B(C6F6)3•H2O catalyzed azidation of tertiary aliphatic alcohols, enabling catalyst turnover for the first time. On the basis of kinetic, electronic, and spectroscopic investigations, higher order hydrogen-bonded aggregates of nitro compounds and acids are proposed as kinetically competent Brønsted acid catalysts at the origin of the enhanced reactivity. The utility of the new catalytic conditions has been extended beyond alcohol activation and applied to the cleavage of strong C–F bonds in defluorinative Friedel-Crafts reactions of tertiary aliphatic fluorides.Les alcools sont des partenaires électrophiles attractifs pour des réactions de substitution nucléophile puisque l'eau est le seul sous-produit de la réaction en présence de nucléophiles protiques. Malgré le fait que la réaction soit fortement intéressante, la portée des transformations catalytique reste limitée à une combinaison spécifique alcool/nucléophile, ce qui rend l’emploi d’un ensemble général de conditions catalytiques fortement élusif. Cette thèse décrit le développement d'un système général de catalyse doux pour l'activation d'une large gamme d’alcools π-activés ainsi que d’alcools aliphatiques abordant ainsi les limitations clés dans le domaine. B(C6F6)3•H2O, un acide de Brønsted fort quand il est combiné avec le nitrométhane, a été découvert comme étant un système catalytique idéal pour la substitution chimiosélective d'alcools en présence de fonctionnalités et de groupements protecteurs sensibles aux conditions acides sans le compromis typique entre vitesse de réaction, réactivité substrat/nucléophile et quantité de catalyseur. Plus particulièrement, un effet co-catalytique de composés nitro est décrit pour la réaction d’azidation des alcools aliphatiques tertiaires en employant B(C6F6)3•H2O, permettant, pour la première fois, un turnover catalytique. Sur la base des investigations cinétiques, électroniques et spectroscopiques qui ont été menées, des agrégats de composés nitro et d’acides liés par des intéractions hydrogènes sont proposé comme étant l’espèce catalytiques responsables de la cinétique de la catalyse observée. L'utilité des nouvelles conditions catalytiques a été étendue au-delà de l'activation d'alcool et appliquée au clivage des liaisons fortes C-F dans les réactions de Friedel-Crafts défluorinatives de fluorures aliphatiques tertiaires

Developing Spin and Polarization Order in 2D Hybrid Perovskites

Metal-halide perovskite (MHP) semiconductor materials have demonstrated a booming rise in optoelectronic performance, spanning IR to the ionizing radiation regimes. MHP crystals are largely enabled by avenues of multifunctionality, such as strong light absorption/emission, charge carrier conduction, and multiferroic properties, which are cooperatively engineered to break theoretical conversion efficiency limits. Without doubt, curiosity accumulates around the fundamental material physics of their broadly tunable optical, electronic, and magnetic properties. This work aims to impact the fundamental understanding of polarization and spin order in MHPs, while developing material solutions towards sensing and imaging from the IR to high energy (X-ray, gamma-ray) radiation. Bulk single crystals and single-crystalline like films of 2D-phase MHP are prepared with crystal chemistries that host multiferroic properties (ferroelectric-ferroelastic-ferromagnetic), exhibit strong light absorption/emission, and support carrier conduction. The broken inversion symmetry and strong orbital polarization of 2D-phase MHPs promote spatial ordering of excitonic states and spin-dependent Rashba band splitting, leading to excited state polarization and spin order. Several MHPs are developed as platforms to investigate the fundamental mechanisms involved in photo-ferroelectric and photo-ferromagnetic coupling. Ultra-fast spectroscopic measurements, such as transient absorption and time-resolved photoluminescence with temperature and light polarization dependence, reveals tunable coupling of photoexcited excitons. Further in-situ optical characterization uncovers extraordinary excited state dynamics in ferroelectric 2D-phase MHPs. Active control of the spin degree of freedom in ferroelectrics is shown using circularly polarized photoexcitation into the Rashba bands, where the resulting spin-polarized states are found to be spin-operability through varying interfacial spin. This optical-magnetic coupling behavior is further investigated through the magnetic and chemical depth sensitive polarized neutron reflectometry technique. Collectively, this work explores the microscopic structure-property behaviors of MHP to develop optical control and coupling with multifunctional properties toward breaking technical boundaries in optoelectronic devices