Dottorato in SCIENZE CHIMICHE

Titolo della tesi: Synthesis and characterization of electrolytic and electrodic materials for high voltage lithium batteries

In the energetic transition from fossil fuels to renewable energies, energy storage systems play a fundamental role. Renewable energies are sustainable sources but intermittent, thus requiring a storage system to collect energy and supply it homogeneously. Lithium ion batteries (LIBs) have been developed after the discovery that inorganic structures can intercalate guests within their structures, thus lithium is a perfect candidate for intercalation reactions. LIBs electrodic and electrolytic components depend on the electrochemical properties and final application of the cell, from high energy density to high power density. Nickel substituted manganese spinel LiNi0.5Mn1.5O4 (LNMO) is a cathodic active material void of cobalt with a high operating potential of 4.7 V vs Li+/Li and thus high energy capability. High voltage is a critical regime where a high value of Gibbs free energy is available for bad chemical reactions damaging irreversibly the electrochemical performances of the cell. In this context, the PhD project focused on the development of suitable electrolyte systems withstanding such high oxidating potentials and on improving stability of LNMO cathode active material. Liquid and polymeric electrolyte systems have been developed and characterized to enhance safety and stability of the electrochemical cell in the beginning of the project. Successively, transition metal and lithium metal doping strategy of LNMO spinel structure demonstrated improved features. Finally, a deep investigation of the electrode-electrolyte solid interface (SEI), a solid conductive layer that grows on the electrode surface during electrochemical operation, has been accomplished with highly resolved operando x-ray techniques using synchrotron radiation, for the complete comprehension of the electrochemical reactions occurring at the interface.