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| 铪基纳米线-碳复合材料的制备及其电化学性能研究
摘 要
随着世界经济的快速发展，化石能源的过度开采和消耗愈加严重，由此产生的环境问题也越来越引起人们的重视。科技的进步推动了新能源、新材料的发展。如今，由锂离子电池供能的电动汽车的使用正在逐渐普及，为化石能源的合理利用及环境保护起到了积极的促进作用。锂离子电池普遍存在能量密度较低、循环性能差的问题。相比锂离子电池，锂硫电池具有更高的能量密度（理论值为2600Wh·kg-1），但也存在着硫单质导电性差、充放电过程中活性物质体积膨胀大、多硫化物穿梭严重等问题，大大限制了锂硫电池的实际应用。为了解决上述问题，本文着眼于过渡金属氧化具有对多硫化物吸附作用的化学极性，以及一维HfC纳米线所构建的多导电通路的集流体，主要的实验内容为以下几个方面：
关键词：锂硫电池，氧化铪粉末，碳布，HfC纳米线，多硫化物
kg-1), but there are also poor conductivity of elemental sulfur,large volume expansion of active materials during charging and discharging, and serious polysulfide shuttles. Such problems greatly limit the practical application of lithium-sulfur batteries.In order to solve the above problems,this article focuses on the chemicalpolarity of transition metal oxidation that has the effect of adsorbing polysulfides, and the current collectors with multiple conductive paths constructed by one-dimensional HfC nanowires. The main experimental contents are as follows:
1.Explore the best sulfur-carrying capacity and the best conductive composite material using carbon cloth as the current collector. The positive electrode material is prepared by combining elemental sulfur with carbon nanotubes, and combining elemental sulfur with activated carbon,and setting four different concentration gradients of active material loading per unit area. The final test showed that the electrochemical performance of the cathode material compounded with carbon nanotubes as the conductive agent is better than that of activatedcarbon, and the unit sulfur loading of the carbon cloth as the current collector reaches the best electrochemical performance when the unit sulfur loading is 3~4cm2/g.
2.To improve the conversion efficiency of polysulfides and slow down the shuttle effect.The sol-gel method is used to prepare nano-hafnium oxide powder,and the low-pressure CVD method is used to grow HfC nanowires with electrospun fibers as the substrate and perform oxidation treatment; two types of hafnium-based compound materials, carbon nanotubes, and elemental sulfur are combined to prepare cathode materials. In this way, an efficient and stable "conduction-catalysis-adsorption" reaction interfaceis constructed to promote the conversion of polysulfides and improve battery performance. Among them, the superior conductivity of carbon nanotubes provides a strong guarantee for electron transmission,and polar materials such as hafnium oxide can inhibit the shuttle effect in the adsorption and catalysis of polysulfides. At a rate of 0.1C, the highest discharge capacity for the first time reached 1558 mAh/g,and even at a high current of 2C, it has a capacity of 550 mAh/g.
radients of active material loading per unit area.The final test showed that the electrochemical performance of the cathode material compounded with carbon nanotubes as the conductive agent is better than that of activatedcarbon, and the unit sulfur loading of the carbon cloth as the current collector reaches the best electrochemical performance when the unit sulfur loading is 3~4cm2/g.
2.To improve the conversion efficiency of polysulfides and slow down the shuttle effect.The sol-gel method is used to prepare nano-hafnium oxide powder,and the low-pressure CVD method is used to grow HfC nanowires with electrospun fibers as the substrate and perform oxidation treatment; two types of hafnium-based compound materials, carbon nanotubes, and elemental sulfur are combined to prepare cathode materials. In this way, an efficient and stable "conduction-catalysis-adsorption" reaction interfaceis constructed to promote the conversion of polysulfides and improve battery performance. Among them, the superior conductivity of carbon nanotubes provides a strong guarantee for electron transmission,and polar materials such as hafnium oxide can inhibit the shuttle effect in the adsorption and catalysis of polysulfides. At a rate of 0.1C, the highest discharge capacity for the first time reached 1558 mAh/g,and even at a high current of 2C, it has a capacity of 550 mAh/g.
3.Modifying the carbon cloth collector to further increase the electron transmission path and reduce the internal resistance of the battery. HfC nanowires are grown in situ on a carbon cloth substrate by a low-pressure CVD method, which is used as a self-supporting carrier for lithium-sulfur batteries, and then coated with HfO2/CNT@S to prepare battery cathode materials. The network structure formed by the interweaving of nanowires has ahigher specific surface area,which provides more active sites for the positive electrode material and speeds up the electron transport. Therefore, under high sulfur loading, the first discharge capacity at a rate of 0.1C reached 1656mAh/g, and the AC impedance test showed that the internal resistance of the current collector grown with HfC nanowires was 15.9 Ω.
Key Words: Lithium-sulfur battery,Hafnium oxide powder, carbon cloth, HfC nanowires, Polysulfide
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