Electrode and electrolyte materials for the development of high voltage lithium-ion batteries and secondary batteries based on alkali and alkaline-earth ions

The humankind is facing a global transition towards a decarbonized power sector, dominated by renewable energy sources such as solar and wind. In parallel, the market of electric vehicles is expanding in the automotive field, with a possible ban in Europe of selling new oil-fueled cars from 2030-2040. These two events have in common the necessity of relying on novel and better performing energy storage systems. Advancements in the Li-battery technology could be achieved designing novel electrolytes or high-voltage cathode materials. In addition, systems based on abundant metals, such as the multivalent magnesium, would offer secondary batteries characterized by a low-cost, a good energy density and a very high eco-friendliness. This Ph.D. work tried to give a solution in both the two fields. A brief summary of the main outcomes achieved in this project will be discussed. In particular, a solid polymer electrolyte was obtained by lithium functionalization of a poly(vinyl alcohol-co-vinyl acetate), forming lithium alkoxide functional groups [1]. In this material, the counter anion of Li+ is the overall polymer chain, giving rise to a single lithium ion conductivity. A second single lithium-ion conducting electrolyte was prepared by reacting glycerol with different quantities of lithium hydride. Here the lithium glycerolate component acts as a large and flexible macro-anion which is able to provide a room-temperature conductivity of 2.0∙10-4 S∙cm-1. In the last class of electrolytes, novel ionic liquid systems for Mg2+ conduction were studied. The proposed materials exhibit a magnesium conductivity value comprised between 10-4 and 10-3 S∙cm-1, an overpotential in the magnesium deposition < 50 mV vs. Mg/Mg2+, and a coulombic efficiency up to 99.94 % [2]. In the second part of this work, the improvement of the electrochemical features of various cathode materials was investigated. In the first case, the effect of the formation of CuO-rich regions and the addition of sacrificial graphite in olivine nanoparticles on the structural and electrochemical properties of this cathode material was studied. Secondly, improvements on the rate capability and specific energy of a high-voltage olivine cathode were gauged by V, Nb, or Ta insertion within the structure. A specific energy of 650 mWh∙g-1 was demonstrated. Finally, a cathode material for magnesium secondary battery which consists of a “chrysalis”-like graphene oxide surface functionalization of vanadium-based nanoparticles was proposed [3]. This functionalization allowed for the obtaining of a material able to: a) sustain extremely high current rates (1000 mA∙g-1, 1700 mW∙g-1 of specific power); and b) give specific capacity values up to 72 mAh∙g-1. [1] G. Pagot, F. Bertasi, K. Vezzù, G. Nawn, G. Pace, A. Nale and V. Di Noto, Solid State Ion., 2018, 320, 177-185. [2] G. Pagot, F. Bertasi, K. Vezzù, F. Sepehr, X. Luo, G. Nawn, E. Negro, S.J. Paddison and V. Di Noto, Electrochim. Acta, 2017, 246, 914-923. [3] G. Pagot, K. Vezzù, A. Nale, M. Fauri, A. Migliori, V. Morandi, E. Negro and V. Di Noto, J. Electrochem. Soc., 2020, 167, 070547.