Design and Synthesis of Nanostructured Carbon-based Air Electrodes for Lithium-Oxygen Battery Application

Abstract

Lithium-oxygen (Li-O2) batteries, with their exceptionally high theoretical energy density, are promising for the next-generation energy storage systems. However, their practical realization is hindered by several challenges, including sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), poor cycle life, and low round-trip efficiency. Developing advanced carbon-based air electrodes is crucial for addressing these limitations. These electrodes must possess optimal porosity, conductivity, and stability to facilitate efficient mass transport and charge transfer. Additionally, incorporating suitable catalysts can significantly improve the kinetics of the ORR and OER. This research investigated the impact of carbon-based electrode porosity and Pt and Ru oxide catalysts on the performance of Li-O2 batteries by conducting two main studies.
First, to study the effect of the textural properties of the carbon air electrode on the battery performance, conventional zeolite-templated carbon (ZTC) and house-of-card ZTC (HZTC), were synthesized, characterized, and tested in the battery. Zeolite-templated carbon is a unique class of carbon materials that is derived from zeolite templates through a controlled carbonization process. It exhibits a distinct curved, non-stacked graphene framework that possesses a high specific surface area and a uniform micropore size. These features make it a promising material for battery applications. In the second study, ruthenium dioxide (RuO2) and platinum (Pt) were supported, separately, on ZTC to investigate the composites’ potential as an electrocatalyst for OER and ORR in Li-O2 battery. Ruthenium dioxide and platinum, with their excellent catalytic activity, are promising candidates for enhancing the performance of Li-O2 battery. The catalysts were loaded in two methods, namely mixing and incipient wetness impregnation (IWI), in different amounts and the effect of the different combinations on the composite’s catalytic activity in the battery was investigated. In both studies, the battery performance was evaluated by measuring the full specific capacity, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and battery cycling. Also, an in-depth EIS study using a three-electrode cell was conducted at different states of charge. This was particularly important for understanding the dynamic behavior of the cell during operation.
The results demonstrated the potential of zeolite-templated carbon as a promising air electrode material for Li-O2 batteries. Both ZTC and HZTC exhibited significant specific capacities of 4,012 mA-h g -1 and 3,954 mA-h g -1 , respectively, at a current density of 100 mA g -1 . A notable improvement was observed in the charging overpotential for HZTC, which exhibited a value of 0.51 V compared to 0.86 V for ZTC. The enhanced performance of HZTC can be attributed to the presence of larger mesopores within its structure. These mesopores facilitated the formation of smaller and less crystalline discharge products, resulting in lower charge transfer resistance. This, in turn, led to easier decomposition of the discharge products during the charging process, thereby reducing the overpotential.
Catalyst incorporation into ZTC electrodes significantly enhanced rechargeability, cyclability, and OER kinetics, though a trade-off with specific capacity was observed due to partial blockage of the carbon support’s effective surface area. Optimal formulations, i.e. Pt-ZTC_IWI 10% and RuO2-ZTC_IE 25.9%, exhibited the best overall performance, benefiting from high Pt dispersion and the amorphous, defect-rich structure of RuO2, respectively. Structural analysis confirmed that the IWI method promoted Pt and RuO2 crystallinity in both Pt-ZTC and RuO2-ZTC samples. Also, the IWI method contributed to the enhanced dispersion of Pt in the Pt-ZTC samples. In terms of battery performance, the Pt-ZTC_IWI 10% electrode achieved the lowest charge overpotential (0.59 V at 500 mA-h g⁻¹), while the RuO2-ZTC_IE 25.9% electrode delivered the highest specific capacity (1,905 mA-h g⁻¹ at 100 mA g⁻¹). EIS also highlighted the importance of maintaining charging voltages below 4.5 V to reduce degradation and maximize energy efficiency in the studied cells.
Overall, this work demonstrates that engineering the carbon framework, optimizing catalyst structure and distribution, and employing advanced diagnostic tools like three-electrode EIS are all essential for improving the performance of Li–O2 batteries.

Date of Award	2025
Original language	American English
Supervisor	Maryam Khaleel (Supervisor)