超级电容器复合材料NixCo3-xS4/石墨烯的合成及储能机理研究

Recently, binary metal sulfides NixCo3-xS4 have attracted great interest due to their potential applications for higher energy density and power density pseudocapacitors. However, the understanding of the charge storage mechanism is still preliminary because of the low degree of crystallinity and uncontrolled performance. It is proposed to study the evolution of surface chemistry of NixCo3-xS4 pseudocapacitors during the process of charge storage with in-operando Raman spectroscopy and Materials Studio calculations. Based on the chemical information inferred by spectroscopic features and calculations, the mechanism of the charge storage is expected to be unraveled. Moreover, a facile strategy involving in-situ precipitation process and low temperature solution-based ion exchange reaction will be developed for preparing NixCo3-xS4/graphene material. Specifically, nickel cobalt hydroxides are obtained by in-situ precipitation of Ni2+ and Co2+ on the surface of graphene due to the increasing pH of the solution caused by the reduction of graphene oxide using hydrazine. Then low temperature solution-based ion exchange reaction is applied to fabricate NixCo3-xS4 directly from nickel cobalt hydroxides. This facile method enables us to accurately control the preparation of NixCo3-xS4/graphene materials. Finally, the relationship between the synthetic condition, structure and performance of materials is elucidated，and the synergy effect in the NixCo3-xS4/graphene composite is revealed. Based on the aforementioned study, NixCo3-xS4/graphene composites with excellent performances are expected.

近期发现的二元过渡金属硫化物NixCo3-xS4赝电容材料具有高能量、高功率密度的潜在优势，受到学术界的极大关注，但因材料结晶度低且性能不可控导致对其电荷储存机理研究尚不深入。本项目设计采用in-operando拉曼光谱分析与Material Studio材料计算相结合的方法，开展电荷储存机理研究，以期阐明NixCo3-xS4充放电过程的结构变化机理，揭示结构对粒子传输特性及物质转换的作用规律。提出“原位沉淀-低温离子交换”新方法合成NixCo3-xS4/石墨烯复合材料，利用水合肼还原氧化石墨烯后体系碱度上升实现镍钴元素原位沉淀，通过离子交换实现氧化物向硫化物转型，以此解决材料合成不可控的难题，阐明合成条件-材料结构-材料性能三者的内在关系，揭示复合材料的协同作用机制，从而获得电化学性能优异的NixCo3-xS4/石墨烯复合材料。

针对二元过渡金属硫化物赝电容材料诸多亟待解决的问题，本项目设计合成了一系列镍钴基金属硫化物电极材料并对其进行改性。同时，对项目相关研究进行拓展，设计合成了镍钴氢氧化物和单金属硫化物并研究其电化学性能和改性策略。主要研究结论如下：.通过电沉积法制备了NiCo2S4薄膜电极材料，探究了Ni/Co比例和电沉积参数对材料形貌、结构和电化学性能的影响。结果表明，材料中的Ni/Co摩尔比并不随反应物中Ni/Co配比呈线性变化，当反应物中Ni/Co摩尔比为4:5时，制备的材料是NiCo2S4。材料的比电容随镍元素含量的升高而升高，循环稳定性随着钴元素含量的提高而提高。在沉积电位-1.0V(vs.Ag/AgCl)，沉积温度55℃，沉积时间通过控制电荷量为0.75C∙cm-2，反应物Ni/Co配比4:5时获得的材料性能达到最佳。在1A∙g-1下比电容可达1168F∙g-1，在5A∙g-1电流密度下循环2000次容量不衰减。.通过水热-离子交换法制备了NixCoyS4和NixCoyS4/rGO超级电容器电极材料。NixCoyS4/rGO复合材料中Co2+在晶体的径向生长中起着至关重要的作用，而Ni2+对比电容的贡献更高。Ni1.64Co2.40S4/rGO丰富的孔结构有利于缓解电极反应过程中的体积效应，而石墨烯良好的机械性能有利于提高材料的结构稳定性，抑制结构坍塌。当氧化石墨烯添加量为0.25g∙L-1时制备的材料性能最佳，在2A∙g-1和20A∙g-1下的比电容分别为260.9F∙g-1和140.0F∙g-1，在10A∙g-1下经过5000次循环后容量保持率可达90.4%。与活性炭组装的非对称超级电容器Ni1.64Co2.40S4/rGO//AC在10A∙g-1下经过10000次循环后保持率高达92.6%；Ni1.64Co2.40S4/rGO复合材料在1A∙g-1下的能量密度可达47.2Wh∙kg-1；在10000W∙kg-1的大功率密度下，对应的能量密度依然高达30Wh∙kg-1。通过硫源、硫离子浓度和硫化深度的调控，实现了对材料和器件电化学性能的调控。本研究对镍钴基超级电容器电极材料的制备和改性进行了广泛和深入的研究，对后续科研工作具有重要的借鉴意义。