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Energy storage materials. Chemical synthesis, crystal structure, theoretical models

Michele Catti

Inorganic materials of interest for ionic conductivity in lithium batteries and for hydrogen storage (also in collaboration with Pirelli) are presently studied. The focus is on relationships between structural properties, chemical composition, ionic mobility and reactivity with hydrogen, in the frame of a more general study of phase transformations in the solid state. Both experimental and computational methods are employed.


Chemical synthesis is performed by a variety of techniques, including high-temperature treatments in controlled atmosphere. A thorough crystallographic characterization is then carried out by X-ray powder diffractometry.  For the purpose of fully determining the crystal structure of the phases obtained, neutron diffraction data are often collected in several European  centres (e.g., the ISIS facility at the neutron spallation source of the Rutherford Appleton Laboratory, U.K.). The reactions of hydrogen absorption and desorption are studied by a PCI (Pressure-Composition-Temperature) apparatus from the thermodynamic and the kinetic point of view. Measurements of electrical (complex impedance spectroscopy) and electrochemical properties are performed in the laboratory of Prof. C.M. Mari within a collaboration.


The theoretical investigations are based on quantum-mechanical periodic DFT methods, with the aim of modelling the relative stability, the structural properties and the ionic transport of crystalline phases.



Recently studied materials are the fast lithium ion conductors of the LLTO family (Li0.3La0.567TiO3) with perovskite structure. Neutron diffraction data,  electrical measurements and ab initio simulations allowed us to  clarify the mechanism of Li+ ion diffusion in this material. A complex series of phase transformations, also dependent on the thermal history, was revealed by Rietveld refinements from neutron data. The Li+ ion disorder explains the two-dimensional high ionic mobility in the (001) plane. By DFT calculations, it was possible to interpret the long-range structural results on the basis of local models of the Li+ ion environment. The least-energy ion mobility pathways are also under investigation, with the aim of calculating the activation energy for the lithium transport process.  The study of other classes of lithium ion conductors has been now undertaken.

Mg-based alloys and borohydrides are being presently investigated for their hydrogen storage properties, in collaboration with CORIMAV-Pirelli. The materials, synthesized by the ball milling technique, show promising H-absorption behaviour for particular compositions and crystal structures.