Preparation Of Cobalt-based Oxygen (sulfur) Compound/nitrogen Doped Carbon Composite Material And Study On Its Lithium Storage Performance

Cobalt-based oxides（sulfides）are considered to be a very promising anodematerial for lithium-ion batteries due to their advantages of high theoretical specific capacity and stable chemical properties,compared with traditional graphite-based anode materials for lithium-ion batteries.As anode materials,nevertheless,cobalt-based oxides（sulfides）face the problem of low rate capacity and poor cycle stability.At present,the construction of cobalt-based oxides（sulfides）composite with carbon-based materials is an effective strategy to improve electrochemical performance.Therefore,a series of hierarchical structure cobalt-based oxides（sulfides）/N-doped carbon composites were successfully synthesized using a simple hydrothermal method combined with a calcined process.Their phases,morphologies,microstructure characterization and electrochemical performance were tested,and the main results are as follows:（1）The Co-based coordination polymer precursor with ultra-fine 1D nanowire structure was successfully synthesized under hydrothermal conditions by using imidazole-4,5-dicarboxylic acid（H₃IDC）and Co（Ac）₂.The mesoporous ultra-fine Co₃O₄/N-doped carbon（Co₃O₄/NC）nanowires were prepared by morphology conserved transformations of the precursor through calcined process.These mesoporous ultra-fine Co₃O₄/NC nanowires are all less than 20 nm in diameter,which are constructed by Co₃O₄nanocrystals with several nanometers.The Co₃O₄/NC nanowires electrode displays excellent electrochemical performance:a reversible capacity of 1294 m A·h·g^-1after 500 cycles at 0.1 A·g^-1.Especially,a reversible capacity of 896.8 m A·h·g^-1after 1000 cycles at 1 A·g^-1.（2）The ultra-fine cobalt-based coordination polymer nanowires were used as a matrix,and it was coated by polymerized of dopamine at room temperature to obtain a polydopamine-cobalt-based coordination polymer nanowires.Combined with low-temperature calcination,polydopamine derived nitrogen-doped carbon uniformly coated hierarchical structure Co₃O₄/NC composite was obtained.The composite shows more excellent lithium storage performance.The initial coulomb efficiency of hierarchical structure Co₃O₄/NC composite electrode is 76%.And the reversible capacity of hierarchical structure Co₃O₄/NC composite electrode is 1439 m A·h·g^-1after 500 cycles at 0.2 A·g^-1,and 929 m A·h·g^-1after 1500 cycles at 1.0 A·g^-1.（3）The ultra-fine polydopamine-cobalt-based coordination polymer nanowires were used as a matrix,which it was sulfurized with sulfur powder.By changing the amount of sulfur powder,three kinds of nitrogen-doped carbon uniformly coated cobalt-based sulfide composites were obtained including Co₉S₈/NC,Co S/NC and Co S₂/NC.Among them,the hierarchical structure Co₉S₈/NC composite electrode shows the best electrochemical performance:a reversible capacity of 874 m A·h·g^-1after 200 cycles at 0.1 A·g^-1,the initial coulomb efficiency is 83%and 677 m A·h·g^-1after 1200 cycles at 1.0 A·g^-1.