Computational study of electron-transfers and singlet oxygen in aprotic metal-O2 batteries

Aprotic metal-oxygen batteries (MOBs), based on the electroreduction of molecular oxygen at a porous cathode, have attracted a vast interest in research, owing to their potential upgrade in terms of energy density and costs over present lithium-ion batteries. Despite their highly promising features, aprotic MOBs based on alkali and alkaline-earth metals still suffer severe limitations in their practical applicability. One of the main unresolved issues, especially with Li-O2 batteries, is represented by the high degree of parasitic reactivity. Singlet oxygen (1O2) is today held responsible for a major contribution to such reactivity, and the disproportionation of the superoxide anion is considered as one of the most likely source of 1O2 in the cell environment. Experimental evidences for electrolyte degradation and evolution of 1O2 have been reported, but the fundamental chemical mechanisms underlying these phenomena are still poorly understood. A valid strategy for contrasting the arise of side-reactions and materials degradation is to use redox mediators (RMs), which allow to recharge the battery with greatly reduced overpotentials. Understanding the con- nection of RM-assisted charging with the production 1O2 is likely to play a key role in the design of fully reversible and efficient practical MOBs in the future. In this thesis, quantum chemical computational methods were used to investigate reactive processes of electron-transfer involving reduced oxygen species in aprotic MOBs. The possibility of reactive pathways leading to the release of 1O2 was addressed in particular. The aim of the thesis was to apply theoretical methods to the modeling of reactive systems, in order to unravel part of the mechanisms which underpin the parasitic chemistry of MOBs. Despite their apparent simplicity, the reaction governing the chemistry of the cells involve a complex interplay of radical species and electronic excited states. For this reason, our approach was to use mainly ab-initio correlated multiconfigurational methods for a high-level description of potential energy surfaces and reaction energies. Owing to the computational costs of the methods, such an approach necessarily entails the resort to simplified models, including the exclusive use of implicit solvent and the neglect of solid phases and interfacial effects

A Computational Study on Halogen/Halide Redox Mediators and Their Role in 1O2 Release in Aprotic Li–O2 Batteries

We present a computational study on the redox reactions of small clusters of Li superoxide and peroxide in the presence of halogen/halide redox mediators. The study is based on DFT calculations with a double hybrid functional and an implicit solvent model. It shows that iodine is less effective than bromine in the oxidation of Li2O2 to oxygen. On the basis of our thermodynamic data, in solvents with a low dielectric constant, iodine does not spontaneously promote either the oxidation of Li2O2 or the release of singlet oxygen, while bromine could spontaneously trigger both events. When a solvent with a large dielectric constant is used, both halogens appear to be able, at least on the basis of thermodynamics, to react spontaneously with the oxides, and the ensuing reaction sequence turned out to be strongly exoergic, thereby providing a route for the release of significant amounts of singlet oxygen. The role of spin–orbit coupling in providing a mechanism for singlet–triplet intersystem crossing has also been assessed

Understanding the Role of Imide‐Based Salts and Borate‐Based Additives for Safe and High‐Performance Glyoxal‐Based Electrolytes in Ni‐Rich NMC811_{811} Cathodes for Li‐Ion Batteries

Herein, the design of novel and safe electrolyte formulations for high- voltage Ni-rich cathodes is reported. The solvent mixture comprising 1,1,2,2-tetraethoxyethane and propylene carbonate not only displays good transport properties, but also greatly enhances the overall safety of the cell thanks to its low flammability. The influence of the conducting salts, that is, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), and of the additives lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFOB) is examined. Molecular dynamics simulations are carried out to gain insights into the local structure of the different electrolytes and the lithium-ion coordination. Furthermore, special emphasis is placed on the film-forming abilities of the salts to suppress the anodic dissolution of the aluminum current collector and to create a stable cathode electrolyte interphase (CEI). In this regard, the borate-based additives significantly alleviate the intrinsic challenges associated with the use of LiTFSI and LiFSI salts. It is worth remarking that a superior cathode performance is achieved by using the LiFSI/LiDFOB electrolyte, displaying a high specific capacity of 164 mAh g−1 at 6 C and ca. 95% capacity retention after 100 cycles at 1 C. This is attributed to the rich chemistry of the generated CEI layer, as confirmed by ex situ X-ray photoelectron spectroscopy

Contributi per una flora vascolare di toscana. IX (507-605)

Contributions for a vascular flora of Tuscany. IX (507-605). New localities and/or confirmations concerning 98 specific and subspecific plant taxa of Tuscan vascular flora, belonging to 81 genera and 42 families are presented: Alisma, Baldellia (Alismataceae), Chenopodium (Amaranthaceae), Sternbergia (Amaryllidaceae), Bupleurum (Apiaceae), Vinca (Apocynaceae), Muscari, Polygonatum (Asparagaceae), Carlina, Centaurea, Chondrilla, Filago, Pallenis, Tagetes, Tr a - gopogon, Tyrimnus (Asteraceae), Impatiens (Balsaminaceae), Campsis (Bignoniaceae), Cardamine, Iberis, Isatis, Lepidium, Rorippa (Brassicaceae), Humulus (Cannabaceae), Centranthus (Caprifoliaceae), Atocion, Paronychia, Sabulina, Scleranthus (Caryophyllaceae), Euonymus (Celastraceae), Fumana (Cistaceae), Phedimus, Sedum (Crassulaceae), Juniperus (Cupressacesae), Carex, Cyperus, Schoenus (Cyperaceae), Erica (Ericaceae), Euphorbia (Euphorbiaceae), Astragalus, Cytisus, Gleditsia, Lotus, Trifolium, Vicia (Fabaceae), Geranium (Geraniaceae), Philadelphus (Hydrangeaceae), Phacelia (Hydrophyllaceae), Hermodactylus, Iris, Romulea (Iridaceae), Salvia, Ziziphora (Lamiaceae), Gagea, Lilium (Liliaceae), Lindernia (Linderniaceae), Mirabilis (Nyctaginaceae), Nymphaea (Nymphaeaceae), Ligustrum (Oleaceae), Oenothera (Onagraceae), Oxalis (Oxalidaceae), Plantago, Veronica (Plantaginaceae), Armeria (Plumbaginaceae), Eleusine, Festuca, Phleum, Setaria, Stipa, Tragu s (Poaceae), Stuckenia (Potamogetonaceae), Anemonoides, Ranunculus (Ranunculaceae), Reseda (Resedaceae), Aphanes, Cotoneaster, Eriobotrya, Malus, Rosa (Rosaceae), Galium (Rubiaceae), Nicotiana, (Solanaceae). In the end, the conservation status of the units and possible protection of the cited biotopes are discussed

Notulae to the Italian alien vascular flora: 1

In this contribution, new data concerning the Italian distribution of alien vascular flora are presented. It includes new records, exclusions, and confirmations for Italy or for Italian administrative regions for taxa in the genera Agave, Arctotheca, Berberis, Bidens, Cardamine, Catalpa, Cordyline, Cotoneaster, Dichondra, Elaeagnus, Eragrostis, Impatiens, Iris, Koelreuteria, Lamiastrum, Lantana, Ligustrum, Limnophila, Lonicera, Lycianthes, Maclura, Mazus, Paspalum, Pelargonium, Phyllanthus, Pyracantha, Ruellia, Sorghum, Symphyotrichum, Triticum, Tulbaghia and Youngia

Measurement of t(t)over-bar normalised multi-differential cross sections in pp collisions at root s=13 TeV, and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

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