3D Ni-Ru porous air-cathodes for Li-air battery applications

Abstract

Lithium-ion batteries (LIBs) have been widely used in modern day technology such as electric cars, laptops, and phones. However, modern LIBs are reaching their theoretical energy density limit, resulting in research diverting attention towards alternate forms of lithium batteries such as lithium-air batteries (LABs). Theoretically utilising oxygen from ambient air as active material for the battery opens a pathway to achieving immensely high specific energies. Although LAB’s have the highest theoretical energy density, there is a significant discrepancy compared to the actual energy density due to factors such as sluggish reaction kinetics, revolving around oxygen redox reactions at the cathode. Recently, bimetallic catalysts have received the spotlight due to their enhanced oxygen reductive reaction (ORR) and oxygen evolution reaction (OER) properties as well as catalyst stability in comparison to monometallic catalysts. By incorporating a core-shell design of two metals, a synergistic effect of the two metal catalysts can be actualised. Herein we fabricate a freestanding 3D Ru-Ni air cathode by utilizing a versatile technique for 3D porous nanostructure fabrication: Proximity-field nano-Patterning (PnP), in order to fabricate polymeric 3D nanostructures followed by conformal coatings of Ni and Ru decoration via electrodeposition. The fabricated 3D Ni/Ru cathode was used in LAB Swagelok-type cell and exhibited high cell efficiency of ~80% was achieved, with a high discharge capacity of 1.63 mAh cm-2 at a current density of 0.025 mA cm-2. The 3D Ni/Ru also demonstrated superior ORR activity compared to 3D Ni, 3D Ni/Pd, and Ni/Ru foam electrodes.