Synthesis Of NiCo-based Spinel Compound Nanostructures And Their Performances As Applied In Lithium-air Batteries

The seeking of catalysts with high activities for oxygen reduction reaction?ORR?and/or oxygen evolution reaction?OER?and optimization of the air electrode structure are believed to be the two key factors for improving the performances of lithium-O₂ batteries.In this thesis,vaiours spinel structures based on NiCo-compounds with different morphologies and structures have been synthesized and studied as high efficient catalysts for li-air batteries,exploring the relations between the morphology of catalyst,the structure of the air electrode and the performance of lithium-O₂ batteries.First of all,two kinds of NiCo-spinel oxides with different morphology,urchin-like NiCo₂O₄ and rod-like NiCo₂O₄,have been prepared successfully via one pot hydrothermal method and employed as cathode catalyst at the air electrode in rechargeable non-aqueous lithium-O₂ batteries.The testing results show that the rod-like NiCo₂O₄ could deliver more discharge/charge specific capacity and exhibit better cycling performance than that of the urchin-like NiCo₂O₄,due to the higher specific surface area,larger pore diameter and pore volume of the rod-like structure.Hierarchical bowl-like NiCo₂O₄ electrocatalysts have also been synthesized on carbon fiber paper?current collector?directly via a controllable and facile electrochemical deposition method with the assistance of silica spheres as hard template and then applied as air electrodes without any conducting additive or binder for lithium-O₂ batteries.This novel cathode exhibites excellent electrochemical performance(the initial discharge capacity is9624 mAh g^-1 and the coulombic efficiency can reach up to 95.4%at the current density of100 mA g^-1).Based on the work of nickel cobalt oxide,ternary nickel cobalt sulfide?NiCo₂S₄?nanotubes array,which has higher electronic conductivity than metal oxide counterparts have been also synthesized on the carbon fiber papers?NiCo₂S₄ NTs@CFPs?successfully through a facile hydrothermal method and then applied as freestanding,binder-free air electrode directly in lithium-O₂ batteries.Compared with the NiCo₂O₄ NWs@CFPs,the NiCo₂S₄ NTs@CFPs air electrode shows higher discharge/charge capacity and superior cycling life,which can be lasted for 485 cycles at the current density of 300 mA g^-1 under the capacity limitation of 500 mAh g^-1,which can be ascribed to the intrinsic high catalytic activity,novel morphology and special air electrode structure of the NiCo₂S₄.