Propriedades físicas de materiais avançados utilizados em eletrodos de baterias recarregáveis

Abstract

In this work we present a study of the structural, vibrational and mechanical properties of two novel materials with promising applications in the energy storage field. The first study refers to potential compounds to be used as cathodes in sodium batteries, as they provide good energy density, low toxicity and high availability of its raw material, thus being a natural substitute for the already widespread lithium-ion batteries. Carbonophosphates of lamellar structure containing different first series transition metals as Na3MCO3PO4 (M = Mn, Fe, Co and Ni) are assessed in a wide range of pressure and temperature conditions, revealing several structural parameters. Bulk modulus, thermal expansion coefficients, Grüneisen parameters and their components were determined from the experimental data. We noticed that a change in the transition metal inside the octahedron [MO6]−2 following the sequence Mn ! Fe ! Co ! Ni causes a structural rearrangement of the entire unit cell to a more compact form, making the structure less susceptible to pressure and temperature, leading to a greater influence of phonon-phonon interactions on its lattice parameters. In the second study of this thesis, we observed that supported samples of nanographite immersed in a fluid, an excellent material for constructing rechargeable battery anodes, can be detached from their substrate by applying hydrostatic pressure. This process is based on waves formation on the surface caused by the difference in the compressibility of the substrate and graphene sheets, and on the adsorption of the transmitting medium on the surface of the latter. The detachment ends with the total delamination of the sample or with the solidification of the medium, following a universal behavior independent of the number of graphene layers. These results are extremely useful in practical use of high pressure experiments in systems governed by Van der Waals forces.