Prepararion And Electrochemical Performance Of Carbon Nanotubes Supported Cobalt Based Compounds As Anode Materials

At present,Lithium ion battery has been applied in the field of daily electronic devices,new energy vehicles and industry energy store.However,the limited lithium resources and expensive lithium prices seriously restrict the large-scale application of Lithium ion battery.Because sodium and lithium belong to the alkali metal elements,they share similar physical and chemical properties.Considering the abundance of sodium resources,sodium ion battery is expected to become a new generation of energy and power battery.Reviewing the commercialization of lithium ion batteries,it is vital to develop the electrode materials with excellent comprehensive performance in commercialization of sodium ion battery.Among the anode materials in sodium ion battery,cobalt oxide/sulfide and other transition metal oxide/sulfide have potential application value,because of their high theoretical capacity.However,cobalt oxide/sulfide have the problems of poor conductivity and volume expansion in electrochemical reaction.These problems reduce the electrochemical properties of cobalt oxide/sulfide,and limit their practical applications as anode materials in sodium ion batteries.To improve the cycling performance and rate capability of cobalt oxide/sulfide,in this paper,cobalt oxide/sulfide were combined with carbon nanotubes with good conductivity and stable structure.Co₃O₄/CNTs and Co₉S₈/CNTs nanocomposite materials were prepared,while bare Co₃O₄ and Co₉S₈ were used as comparative experiments.The composition,morphology and microstructure of the samples were observed by means of XRD,Raman spectrum,TG,SEM,TEM and so on.Then,the electrochemical properties of the anode electrode materials of sodium ion battery were tested by CV,EIS and the charging and discharging tests.The main contents of the work are as follows:?1?Bare Co₃O₄ and Co₃O₄/CNTs composites were successfully prepared by hydrothermal method,and these obtained materials were used as anode materials in sodium ion battery.The effect of adding to CNTs on the morphology and electrochemical properties of the materials were discussed.The results showed that bare Co₃O₄ formed microspherical structure.When the carbon nanotubes were introduced,the Co₃O₄ microsphere structure was changed into the nanocubes structure.The nanocubes could be uniformly loaded on the surface of the carbon nanotubes,forming Co₃O₄-NC/CNTs composite material.In the voltage range of 0.01-3.00V,at the current density of 100mA g^-1,Co₃O₄-NC/CNTs composite materials delivered a reversible capacity of 441mA h g^-1 after 100 cycles,while in the same condition discharge capacity of bare Co₃O₄ electrode only was 70mA h g^-1,far less than the capacity of composites.The rate capacity of 258mA h g^-1 was obtained in Co₃O₄-NC/CNTs composite at the current density of 1600mA g^-1,but the rate capacity of bare Co₃O₄ was 110 mA h g^-1 at the same density.The results reflected that the cycle performance and rate capablity of Co₃O₄-NC/CNTs composite electrode were better than that of bare Co₃O₄ electrode.?2?By controlling the hydrothermal conditions,Co₉S₈-NP/CNTs and Co₉S₈-F/CNTs composites were successfully prepared.Co₉S₈-NP/CNTs represent the structure of CNTs loaded on Co₉S₈ nanoparticles.Co₉S₈-F/CNTs represent the coaxial tubular structure of Co₉S₈ with CNTs.Compared with bare Co₉S₈,the electrochemical performance of the three kinds of materials were investigated by electrochemical testing.The results showed that in the voltage range of 0.01-3.00V,at the current density of 100mA g^-1,bare Co₉S₈electrode after 100 cycles the discharge capacity was only 107mA h g^-1.In the two composites,the reversible discharge specific capacity of Co₉S₈-F/CNTs was matained 440mA h g^-1 after 100 cycles.At the same voltage range and current density,Co₉S₈-NP/CNTs composites delivered a discharge specific capacity of 480mA h g^-1.Compared with bare Co₉S₈ electrode under the same conditons,the reversible capacity of two kinds of composites was more than 4times the capacity of bare Co₉S₈.When the current density was increased to1600mA g^-1,the rate capacity of two kind of composites could still reach above 200mA h g^-1,but the rate capacity of Co₉S₈ was quite low,which was only 76mA h g^-1.The impedance test and fitting results and also shows that the impedance and conductivity of Co₉S₈-NP/CNTs charge transfer are better than that of Co₉S₈-F/CNTs,the final Co₉S₈-NP/CNTs composite ion diffusion distance is shorter,faster diffusion rate,higher electrochemical reaction activity,showed better charge-discharge performance and higher rate capacity than Co₉S₈-F/CNTs.