Porous Nanostructured Efficient Bi-functional Catalyst And Their Electrochemical Performance

Rechargeable lithium-oxygen(Li-O2) batteries can provide a high theoretical energy density, and are expected to be potential to replace state-of-the-art lithium-ion batteries. However, the realistic application of Li-O2 batteries has been restricted by several serious challenges, including low energy efficiency, poor rate capacity and short cycle life. The development and design of catalyst on the air electrode is one of key ways to solve these challenges. In this paper, we developed two bi-functional catalysts for lithium-air batteries.We developed hierarchical mesoporous/macroporous La0.5Sr0.5CoO3-x nanotubes(HPN-LSC) as the bi-functional(ORR/OER) catalyst for Li-O2 batteries, which was prepared by a facile electrospining technique following calcination. The average outer diameter of the resulting HPN-LSC is around 118.2±1.2 nm. Furthermore, mesopores/macropores can be observed on the HPN-LSC surface. The sizes of macropores are 50-80 nm and the sizes of mesopores are 2-10 nm. The BET specific surface area of the HPN-LSC is found to be 17.18 m2/g. XRD patterns and HRTEM were used to elucidate the crystalline structure of the obtained HPN-LSC. The HPN-LSC/KB electrode displays excellent performance for Li-O2 batteries sustaining 50 cycles at a current density of 0.1 mA/cm2 with an upper-limit capacity of 500 mAh/g(KB: 13 cycles).Three-dimensional NiCo2O4 porous nanostructured arrays on the carbon nanofibers were prepared by electrospinning method and hydrothermal synthesis method. The thickness of the nanosheets are about 6-10 nm and the sizes of some holes on the nanosheets are between 10-20 nm. Three-dimensional NiCo2O4 porous nanostructured arrays on the carbon nanofibers have some advantages:(1) high specific surface area(BET specific surface area of 178.5 m2/g);(2) hierarchical mesoporous structure(5-10 nm and 20-40 nm);(3) NiCo2O4 nanosheets has good electrical conductivity and they grow directly on the carbon nanofibers. NiCo2O4/CNF/KB electrode was used for lithium-oxygen batteries, which enhances the energy efficiency, rate capacity and cycle life of resultant batteries. The NiCo2O4/CNF/KB electrode showed discharge specific capacity of the battery still maintain 6127 Amh/g at the current density of 500 Am/g and sustained 100 cycles at a current density of 250 mA/g with an upper-limit capacity of 500 mAh/g(KB: 27 cycles, CNF/KB: 42 cycles).In this paper, we explored the reaction mechanism of lithium-oxygen batteries by XPS and Raman. The discharge product of lithium peroxide was successfully detected by XPS and Raman. And we also prove that lithium peroxide can be reversible transformation in the process of charging and discharging.