Enhanced Cyclability in Rechargeable Li-O₂ Batteries Based on Mn₃O₄ Hollow Nanocage/Ketjenblack Catalytic Air Cathode

Mn₃O₄ hollow nanocages (MOHNs) of mean diameter 250 nm and composed of a number of Mn₃O₄ nanoparticles of mean diameter 25 nm are synthesized via a facile template method using C spheres as the hard template and MnCl₂ as the Mn source. The C sphere templates are prepared by a hydrothermal method using glucose as the C source. The hydrophilic nature of the surface of the C sphere templates allows the adsorption of Mn²⁺ ions, resulting in the MOHNs upon thermal annealing of the Mn-adsorbed C sphere templates in air. The MOHNs possess a crystalline phase and a hollow-cage porous nanostructure with a high specific surface area of 90.65 m²/g and a linear paramagnetic behavior at room temperature. These MOHNs, when combined with ketjenblack (KB) C blacks to form MOHN/KB catalytic air cathodes in nonaqueous Li-O₂ batteries (LOBs), exhibit a high and stable reversible restrained specific capacity of 600 mAh/g in excess of 50 discharge-charge cycles at a specific current of 400 mA/g. The pure KB air cathode-based LOBs can only sustain ∼ 15 cycles at the same conditions.