The non-aqueous lithium-oxygen battery has been attracting increasing attention over the past years primarily due to its high capacity and energy density. However, to make the technology viable, many issues, such as high discharge-charge potential gap, low round-trip efficiency, and short cycle life, in this complex system need to be urgently addressed. One of the major reasons leading to those issues is the sluggish reaction kinetics of the oxygen reduction and oxygen evolution reactions (ORR/OER) at the cathode of the battery. Although many cathode catalytic materials have been proposed and synthesized to accelerate the ORR/OER process, cathode electrodes still surfer from the problems of poor chemical/electrochemical stability and low catalytic activity. The primary objectiv...[ Read more ]

The non-aqueous lithium-oxygen battery has been attracting increasing attention over the past years primarily due to its high capacity and energy density. However, to make the technology viable, many issues, such as high discharge-charge potential gap, low round-trip efficiency, and short cycle life, in this complex system need to be urgently addressed. One of the major reasons leading to those issues is the sluggish reaction kinetics of the oxygen reduction and oxygen evolution reactions (ORR/OER) at the cathode of the battery. Although many cathode catalytic materials have been proposed and synthesized to accelerate the ORR/OER process, cathode electrodes still surfer from the problems of poor chemical/electrochemical stability and low catalytic activity. The primary objective of this thesis is to prepare and characterize the cathode electrode with high capacity, good chemical/electrochemical stability and enhanced catalytic activity. Based on state-of-the-art non-aqueous electrolyte, this thesis focuses on developing stable cathode electrodes with high discharge-charge capacity and low charge voltage.

To address the low capacity and instability issues, two non-carbon cathode electrodes are prepared, including perovskite metal oxide cathode and manganese oxide cathode. The perovskite metal oxide cathode composed of Co₃O₄/LaNiO₃ composite is prepared by a simple and controllable impregnation method. With the excellent catalytic activity of LaNiO₃ and Co₃O₄, the as-prepared Co₃O₄/LaNiO₃ cathode delivers a reversible specific capacity of 436.3 mAh g^-1 and shows no degradation during 30 cycles. The manganese oxide cathode composed of MnO₂-stainless steel (SS) felt is prepared for the first time as a binder-free cathode and delivers a reversible specific capacity of 1,781 mAh g^-1. To further increase the specific capacity of manganese oxide, a binder-free MnO_2-x nanosheet-SS electrode is prepared and investigated, in which the specific capacity increases to 7,300 mAh g^-1 with high content of Mn(III) and oxygen vacancy and the discharge/charge cycle test shows no degradation for 120 cycles, leading to an excellent performance.

To reduce the charge voltage, two electrodes made of RuO₂/Co₃O₄ nanoflake and carbon paper supported Cr₂O₃ are prepared. In the RuO₂/Co₃O₄ nanoflake cathode, RuO₂ is uniformly decorated on the surface of Co₃O₄ nanoflake, providing more reaction sites and promoting the uniform distribution of discharge products. It is experimentally shown that the RuO₂/Co₃O₄ cathode delivers an increased discharge capacity of 3,420 mAh g^-1 and a decreased charge voltage of 4.1 V. With the carbon paper supported Cr₂O₃ cathode, it is found that the uniformly distributed Cr₂O₃ leads to a sheet-like discharge product morphology and a charge voltage of lower than 4.0 V, which is the lowest terminal charge voltage among all the non-precious materials reported in the literature.

To address the issue of decreased practical specific capacity as a result of forming conventional electrodes using catalyst materials and inert substrate/current collector, we propose and fabricate an integrated porous electrode made of perovskite LaNiO₃. It is demonstrated that this novel electrode with a well-designed structure and excellent catalytic activities of LaNiO₃ can deliver a high practical capacity of 1.064 mAh cm^-2 and good cycle stability with no degradation after 25 cycles.

Keywords: lithium-oxygen batteries; non-aqueous; cathode electrode; transition metal oxide; integrated electrode.