Preparation And Electrochemical Properties Of Three Dimensional Self-standing Oxide Cathode For Lithium-air Battery

Li-O2 battery is considered as a promising battery system because of its high theory specific capacity and theory specific energy. Li-O2 battery also has wonderful cyclying performance and enviormental friendly. At present, the researches on the Li-O2 battery is still in the primary stage, the cycle performance and energy conversion efficiency of the battery need to be promoted. And the research and development of high efficiency cathode catalyst is considered as a key role to improve the performance of the lithium air battery.3D graphene, 3D graphene-Co₃O₄ and 3D graphene-Co₃O₄-PPy electrodes were prepared by CVD method, hydrothermal method and electrochemical polymerization method respectively. SEM, XRD, energy spectrum and other test results show that high quality 3D graphene, graphene with unstable-combined weblike structure Co₃O₄ nano array, 3D graphene-Co₃O₄-PPy are successfully prepared. 3D graphene, 3D graphene-Co₃O₄ and 3D graphene-Co₃O₄-PPy electrode are assembled into the lithium-O2 batteries, respectively. Their first discharge specific capacities were 731.3 mAh g-1, 2384.5 mAh g-1 and 498 mAh g-1. Lithium-O2 battery with the 3D graphene-Co₃O₄ electrode can stable cycle over 30 times when the capacity limited to 500 mAh g-1.Novel vertically self-standing Ni@Co₃O₄ web-like nanofiber arrays（Ni@ Co₃O₄-WNFs） were synthesized via a facile hydrothermal method. The Co₃O₄ nanofibers were grown on a macroporous nickel foam skeleton and intertwined together as a special web structure containing both micropores and mesopores. This self-standing and carbon binder free bifunctional electrocatalyst was directly used as a cathode for rechargeable Li-O2 batteries. These Li-O2 batteries containing Ni@Co₃O₄-WNFs cathode exhibit enormously enhanced performance in that a rare high specific capacity of 17118 mAh g-1 at a current of 0.1 mA cm-2 was demonstrated. Furthermore this was shown over 128 and 61 stable cycles with the capacity limited to 500 and 1000 mAh g-1.Ni@Co₃O₄ nanowire array electrode（Ni@Co₃O₄-NWs） was prepared by a hydrothermal method, and Ni@Co₃O₄-WNFs-PPy composite electrode was prepared by electrochemical polymerization PPy on the surface of Ni@Co₃O₄-WNFs electrode. Ni@Co₃O₄-NWs electrode shows the uniform distribution of nanowire array, which gather together like grasses. PPy fills the pores of the Ni@Co₃O₄-WNFs material and has covered the Co₃O₄ catalyst. After assembled as Li-O2 batteries, the battery with Ni@Co₃O₄-NWs electrode and the battery with Ni@Co₃O₄-WNFs-PPy composite electrode exhibit a fisrt discharge capacity of 2396.4 and 1057 mAh g-1 respectively. And when the capacity limited to 500 mAh g-1, they can stable cyclying 13 and 14 circles respectively.Special Fe₃O₄ nano sheet arrays electrode（Ni@Fe₃O₄-WNPs） was prepared by hydrothermal method. A large number of mesoporous pores are formed between the sheets and sheets, which are composed of a grid structure stably.The Li-O2 battery Ni@Fe₃O₄-WNPs electrode shows a first discharge capacity of 1955 mAh g-1, the battery can over 21 stable circles with the capacity limited to 500 mAh g-1.