Stanislav Levchenko

Lithium‐oxygen (Li‐O₂) battery is considered a high‐energy alternative to Li‐ion one due its characteristic electrochemical conversion process, with the additional advantage of lower cost and environmental impact. However, this emerging battery still requires an enhancement of stability and lifespan to allow its use as a practical energy storage system. In this work we investigate an electrode material benefitting of multiwalled carbon nanotubes (MWCNTs), few layer graphene (FLG), and gold nano‐powder catalyst to improve the Li‐O₂ battery performances in terms of energy efficiency, cycle life and stability. Morphological, structural, and electrochemical tests indicate that the composite electrode can actually boost the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and enhance the Li‐O₂ process reversibility, with a capacity of 1000 mAh g⁻¹ over 70 cycles. On the other hand, the tests reveal the role of the gold in decreasing the polarization and increasing the cell life. Therefore, the results suggest the combination of carbons with various morphologies as a suitable architecture for hosting the Li‐O₂ reaction products and allowing their reversible reaction. On the other hand, the results highlight the necessity for a better tuning the noble metal characteristics to further enhance the cell performances.

Lithium-oxygen (Li-O₂) batteries are nowadays among the most appealing next-generation energy storage systems in view of a high theoretical capacity and the use of transition-metal-free cathodes. Nevertheless, the practical application of these batteries is still hindered by limited understanding of the relationships between cell components and performances. In this work, we investigate a Li-O₂ battery by originally screening different gas diffusion layers (GDLs) characterized by low specific surface area (2 g^-1) with relatively large pores (absence of micropores), graphitic character, and the presence of a fraction of the hydrophobic PTFE polymer on their surface (2 cells using bare GDLs as the support indicates that the oxygen reduction reaction (ORR) occurs at potentials below 2.8 V vs Li⁺/Li, while the oxygen evolution reaction (OER) takes place at potentials higher than 3.6 V vs Li⁺/Li. Furthermore, the relatively high impedance of the Li-O₂ cells at the pristine state remarkably decreases upon electrochemical activation achieved by voltammetry. The Li-O₂ cells deliver high reversible capacities, ranging from ∼6 to ∼8 mA h cm^-2 (referred to the geometric area of the GDLs). The Li-O₂ battery performances are rationalized by the investigation of a practical Li⁺ diffusion coefficient (D) within the cell configuration adopted herein. The study reveals that D is higher during ORR than during OER, with values depending on the characteristics of the GDL and on the cell state of charge. Overall, D values range from ∼10^-10 to ∼10^-8 cm² s^-1 during the ORR and ∼10^-17 to ∼10^-11 cm² s^-1 during the OER. The most performing GDL is used as the support for the deposition of a substrate formed by few-layer graphene and multiwalled carbon nanotubes to improve the reaction in a Li-O₂ cell operating with a maximum specific capacity of 1250 mA h g^-1 (1 mA h cm^-2) at a current density of 0.33 mA cm^-2. XPS on the electrode tested in our Li-O₂ cell setup suggests the formation of a stable solid electrolyte interphase at the surface which extends the cycle life.