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Cathodes for lithium ion batteries: the benefits of using nanostructured materials

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      Abstract

      Commercially available lithium ion cells, which are the most advanced among rechargeable batteries available so far, employ microcrystalline transition metal oxides as cathodes, which function as Li insertion hosts. In search for better electrochemical performance the use of nanomaterials in place of these conventional ones has emerged as excellent alternative. In this review we present a brief introduction about the motivations to use nanostructured materials as cathodes in lithium ion batteries. To illustrate such advantages we present some examples of research directed toward preparations and electrochemical data of the most used cathodes in nanoscale, such as LiCoO2, LiMn2O4, LiMnO2, LiV2O5 e LiFePO4.

      Translated abstract

      As celas de íon lítio disponíveis comercialmente, as quais são as mais avançadas entre as baterias recarregáveis disponíveis até agora, empregam óxidos de metais de transição microcristalinos como catodos, os quais funcionam como matrizes de inserção de lítio. Em busca por uma melhor performance eletroquímica, o uso de nanomateriais no lugar dos materiais convencionais tem emergido como excelente alternativa. Nesta revisão nós apresentaremos uma breve introdução sobre as motivações de usar materiais nanoestruturados como catodos em baterias de íon-lítio. Para ilustrar tais vantagens apresentamos exemplos de pesquisas relacionadas com a preparação e dados eletroquímicos dos mais usados catodos em nanoescala, tais como LiCoO2, LiMn2O4, LiMnO2, LiV2O5 e LiFePO4.

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      Most cited references 185

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      Lithium Ion Solvation and Diffusion in Bulk Organic Electrolytes from First Principles and Classical Reactive Molecular Dynamics

       ,  ,   (2015)
      Lithium-ion battery performance is strongly influenced by the ionic conductivity of the electrolyte, which depends on the speed at which Li ions migrate across the cell and relates to their solvation structure. The choice of solvent can greatly impact both solvation and diffusivity of Li ions. We use first principles molecular dynamics to examine the solvation and diffusion of Li ions in the bulk organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and a mixture of EC/EMC. We find that Li ions are solvated by either carbonyl or ether oxygen atoms of the solvents and sometimes by the PF\(_6^-\) anion. Li\(^+\) prefers a tetrahedrally-coordinated first solvation shell regardless of which species are involved, with the specific preferred solvation structure dependent on the organic solvent. In addition, we calculate Li diffusion coefficients in each electrolyte, finding slightly larger diffusivities in the linear carbonate EMC compared to the cyclic carbonate EC. The magnitude of the diffusion coefficient correlates with the strength of Li\(^+\) solvation. Corresponding analysis for the PF\(_6^-\) anion shows greater diffusivity associated with a weakly-bound, poorly defined first solvation shell. These results may be used to aid in the design of new electrolytes to improve Li-ion battery performance.
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        Enzyme promiscuity in enolase superfamily. Theoretical study of o-succinylbenzoate synthase using QM/MM methods.

        The promiscuous activity of the enzyme o-succinylbenzoate synthase (OSBS) from the actinobacteria Amycolatopsis is investigated by means of QM/MM methods, using both density functional theory and semiempirical Hamiltonians. This enzyme catalyzes not only the dehydration of 2-succinyl-6R-hydroxy-2,4-cyclohexadiene-1R-carboxylate but also catalyzes racemization of different acylamino acids, with N-succinyl-R-phenylglycine being the best substrate. We investigated the molecular mechanisms for both reactions exploring the potential energy surface. Then, molecular dynamics simulations were performed to obtain the free energy profiles and the averaged interaction energies of enzymatic residues with the reacting system. Our results confirm the plausibility of the reaction mechanisms proposed in the literature, with a good agreement between theoretical and experimentally derived activation free energies. Our simulations unravel the role played by the different residues in each of the two possible reactions. The presence of flexible loops in the active site and the selection of structural modifications in the substrate seem to be key elements to promote the promiscuity of this enzyme.
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          General Allylic C–H Alkylation with Tertiary Nucleophiles

          A general method for intermolecular allylic C–H alkylation of terminal olefins with tertiary nucleophiles has been accomplished employing palladium(II)/bis(sulfoxide) catalysis. Allylic C–H alkylation furnishes products in good yields (avg. 64%) with excellent regio- and stereoselectivity (>20:1 linear:branched, >20:1 E:Z). For the first time, the olefin scope encompasses unactivated aliphatic olefins as well as activated aromatic/heteroaromatic olefins and 1,4-dienes. The ease of appending allyl moieties onto complex scaffolds is leveraged to enable this mild and selective allylic C–H alkylation to rapidly diversify phenolic natural products. The tertiary nucleophile scope is broad and includes latent functionality for further elaboration (e.g., aliphatic alcohols, α,β-unsaturated esters). The opportunities to effect synthetic streamlining with such general C–H reactivity are illustrated in an allylic C–H alkylation/Diels–Alder reaction cascade: a reactive diene is generated via intermolecular allylic C–H alkylation and approximated to a dienophile contained within the tertiary nucleophile to furnish a common tricyclic core found in the class I galbulimima alkaloids.
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            Author and article information

            Affiliations
            [1 ] Universidade de São Paulo Brazil
            Contributors
            Role: ND
            Role: ND
            Journal
            jbchs
            Journal of the Brazilian Chemical Society
            J. Braz. Chem. Soc.
            Sociedade Brasileira de Química (São Paulo )
            1678-4790
            August 2006
            : 17
            : 4
            : 627-642
            S0103-50532006000400002 10.1590/S0103-50532006000400002

            http://creativecommons.org/licenses/by/4.0/

            Product
            Product Information: SciELO Brazil
            Categories
            CHEMISTRY, MULTIDISCIPLINARY

            General chemistry

            nanoparticles, cathode, lithium-ion battery, nanotechnology

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