Synthesis Of Co Based Metal Composite Oxides As Electrocatalyst For Rechargeable Lithium-air Batteries

Rechargeable lithium-oxygen(Li-O2) batteries have received much research attention recently due to its much higher theoretical energy density(11,000 Wh kg-1) compared to current state-of-the-art lithium-ion batteries and have been considered to be one of the most promising systems as high-energy storage in the electric vehicle field. However, before their practical applications, there are many obstacles to overcome such as low round-trip efficiency, low rate capability, and poor cycling stability. Recently, great efforts have been made to improve the electrochemical performance of Li-oxygen batteries by employing bifunctional catalyst in oxygen electrode.Therefore, in this paper, our research attention was concentrated to the preparation of cheaper and efficient catalyst for lithium oxygen batteries.The major research results are presented as follows:(1) We reported for the first time the preparation of one-dimensional porous La0.5Sr0.5CoO2.91 nanotubes through a simple and efficient electrospinning technique combined with post-annealing route, as highly active bifunctional catalysts for lithium oxygen battery.When the La0.5Sr0.5CoO2.91 nanotubes were employed as Li-O2 batteries cathode, these materials displayed an initial discharge capacity of 7205 mAh g-1 with a plateau at around 2.66 V at a current density of 100 mA g-1. It was found that the La0.5Sr0.5CoO2.91 nanotubes promoted both oxygen reduction and oxygen evolution reactions in alkaline media and a nonaqueous electrolyte, thereby improving the energy and coulombic efficiency of the Li-O2 batteries. The cyclability was maintained for 85 cycles without any sharp decay under a limited discharge depth of 1000 mAh g-1, suggesting that such a bifunctional electrocatalyst is a promising candidate for the oxygen electrode in Li-O2 batteries.(2) We reported the preparation of three-dimensional ordered mesoporous(3DOM) CuCo2O4 materials through a hard template technique, as highly active bifunctional catalysts for lithium oxygen battery. Characterization of the catalyst by X-ray diffractometry(XRD) and transmission electronmicroscopy(TEM) confirms the formation of a single-phase, 3-dimensional, ordered mesoporous CuCo2O4 structure. The as-prepared CuCo2O4 nanoparticles possess a high specific surface area of 97.1 m2 g-1. Cyclic voltammetry demonstrates that mesoporous CuCo2O4 catalyst enhances the kinetics for either oxygen reduction reaction(ORR) or oxygen evolution reaction(OER). The Li-O2 battery utilizing 3DOM CuCo2O4 shows a higher specific capacity of 7456 mAh g-1 than that with pure Ketjen black(KB). Moreover, the CuCo2O4-based electrode enables much enhanced cyclability with a 610 mV smaller discharge-recharge voltage gap than that of the carbon-only cathode at a current rate of 100 m A g-1. Such excellent catalytic performance of CuCo2O4 could be associated with its larger surface area and 3D ordered mesoporous structure.(3) We have synthesized the three-dimensional ordered mesoporous(3DOM) ZnCo2O4 materials via a hard template and used as bifunctional electrocatalysts for rechargeable Li-O2 batteries. The as-prepared Zn Co2O4 nanoparticles possess a high specific surface area of 127.2 m2 g-1 and a spinel crystalline structure characterized by Brunauer-Emmett-Teller(BET) surface area and X-ray diffractometry(XRD). The Li-O2 battery utilizing 3DOM ZnCo2O4 shows a higher specific capacity of 6024 mAh g-1 than that with pure Ketjen black(KB). Moreover, the ZnCo2O4-based electrode enables much enhanced cyclability with a 220 mV smaller discharge-recharge voltage gap than that of the carbon-only cathode at a current rate of 100 mA g-1. Such excellent catalytic performance of ZnCo2O4 could be associated with its larger surface area and 3D ordered mesoporous structure.