Cobalt Based Metal Origanic Framework Derived Composite As Lithium-air Battery Cathode Catalyst

Lithium-Air battery has attracted great consideriation due to it's theoretical energy density up to 11.8 kWh/kg.However,the practical electrochemical performance of the battery shows high charge and discharge overpotential,low energy efficiency and short cycle life.The choice of catalyst and rational design of the positive electrode structure are important for improving the performance of the battery.Metal origanic frameworks are porous coordination polymers which offers fast mass transfer channel and a large number of catalytic active sites.It is an ideal catalyst for lithium air batteries.In this dissertation,the cathode catalysts?Co@NCNT/P?were prepared by heating treatment of ZnCo-Zeolitic Imidazolate Frameworks?ZIFs?.The strcture and composition characterization of catalyst demonstrated it was N-doped carbon nanotube polyhedron composite.When Co@NCNT/P was used for lithium-air battery cathode catalyst,the battery delivered a specific capacity over 17000 mAh/g at 0.1 A/g and terminal discharge voltage of 2 V.The discharge and charge overpotentials were only 0.15 V and 1.05 V respectively when the specific capacity was limited to 1000 mAh/g at a current density of 0.1 A/g.The battery cycled over 350 times when the specific capacity was limited to 1000 mAh/g at a higher current density of 1 A/g.The N-doped carbon nanotube and uniform distribution of catalyst active sites endow catalyst with high catalytic activity,thus getting higher rate ability and longer cycle life.In order to get fully use of catalyst and accelerate the mass transport,the wood was used to prepare a biomimetic three-dimensional pore structure substrate?Wood-D?by carbonization method.Wood-D/Co₃O₄/C was obtained by Pyrolysis of Co-ZIF growing on Wood-D.The characterization of structure and composition about Wood-D/Co₃O₄/C shows the porous Co₃O₄/C are uniformly distributed on the surface of Wood-D/Co₃O₄/C.The battery of Wood-D/Co₃O₄/C deliver discharge specific capacity more than 6mAh/cm² at a current density of 0.1 mA/cm².At a current density of 1 mA/cm² and a limited specific capacity of 1 mAh/cm²,380 cycles can be achieved without discharge voltage reduce or charge voltage ascension,the discharge and charge voltage are aways higher than 2.6 V and lower than 4.3 V during cycling.When the specific capacity was restricted to 1 mAh/cm²,the discharge voltage platform are 2.87 V and 2.63 V respected to the current density of 0.1 mA/cm² and 1 mA/cm²,and the charging voltages are all lower than 4.25 V.The surface of electrode capillary adsorbs a thin layer of electrolyte constructing a lithium-ion diffusion channels,and hollow channels is used for forms a gas diffusion mass transfer channel.The phase-sepration mass transfer channel can rapidly transport oxygen and lithium ions which fully make use of the ability of electrode at high rates and long cycling process.