碳包覆镍钴硫化物/石墨烯复合材料的制备及电化学性能研究

Due to their fascinating advantages such as high theoretically specific capacitance, strong redox activity and significant electrochemical stability, make NiCo2S4 and composite materials based on NiCo2S4 to be good supercapacitor electrode materials and attracte increasing attention. Although numerous efforts have been devoted to improve the performance of NiCo2S4-based materials and remarkable progress has been made in recent years, it is believed that there are several shortcomings, such as low specific capacitance in reality, poor electrical conductivity and insufficient service life stability should be overcomed to promote the supercapacitors into applications. Consequently, for the first time, we creatively design a new core-shell structured rGO/NiCo2S4 composite material, in which the reduced graphene oxide (rGO) acts as the “core” and NiCo2S4 nanosheets as the “shell”, in which the NiCo2S4 nanosheets grow criss-crossing perpendicular to the graphene surface. Moreover, the rGO/NiCo2S4 materials were further modified by carbon layer to form porous conductive network and denoted as rGO/NiCo2S4/C. Based on the new design, we will study the correlative mechanism and synthesis methods deeply to achieve the composite materials with enhanced electrochemical performance such as quick charge-discharge efficiency property, big surface area, abundent active site, core-shell and network coexist structure. Firstly, we will prepare the precursor nanosheets materials grow criss-crossing perpendicular to the graphene surface with excellent morphologic characteristics through in-situ growth mechanism. Secondly, we develop a sulfofication process to enable the precursor materials being transform into sulfide to from a core-shell structured rGO/NiCo2S4 composite material. Thirdly, uniform carbon shell on the particles and continuous carbon film network connecting adjacent particles, which has high specific surface and some pore structure were designed. Subsequently, by adjusting the reaction parameters to regulate the microstructure of rGO/NiCo2S4/C composite nano-material, we will explore the effect laws of microstructure on their electrochemical properties to achieve high specific capacity, good rate capability and long cycle life. Especially, this project will present a simple and effective strategy for the synthesis of a high-performance rGO/NiCo2S4/C composite and provide a valuable theory and design reference for the preparation of relative special nano-structured materials.

镍钴硫化物及其复合材料具有理论比容量高、氧化还原活性优异、化学稳定性好等优点，可用作超级电容器正极材料并引起了广泛关注。但这类材料现存在实际比容量低、导电性差、循环稳定性差等缺点。为此，本项目首次构建了以石墨烯为核、镍钴硫化物纳米片垂直于石墨烯表面交错生长形成核壳结构复合材料，并用多孔碳层修饰该复合材料形成完整的导电网络。通过系统开展前驱体纳米片材料在石墨烯表面的原位生长机理及可控合成、前驱体硫化作用转化为镍钴硫化物、纳米颗粒表面及颗粒之间多孔碳层修饰路线设计与工艺、石墨烯/镍钴硫化物/碳活性材料的电化学性能调控方法等创新研究，以获得具有电子“快速通道”、巨大比表面积和优异电化学活性、兼具核壳结构与碳导电网络特殊结构的超级电容器正极材料，可有效提升超级电容器的比容量、倍率性能、稳定性和循环寿命，并形成相应的特殊纳米结构材料制备理论体系和工艺方案，能为开展其他纳米材料的制备提供有价值的借鉴。

单一石墨烯材料片层容易堆叠和团聚，制约了其实际应用。通过表面造孔和复合等手段制备石墨烯复合物可以提升材料综合性能。镍钴基化合物具有理论比容量高、氧化还原活性优异、化学稳定性好等优点，可用作超级电容器正极材料。但这类材料存在实际比容量低、导电性差、循环稳定性差等问题。为此，本项目首次构建以多孔石墨烯为骨架，制备多孔石墨烯与镍钴氧化物的复合物材料：rGO/NiCo2S4/C。复合材料中垂直于多孔石墨烯表面贯穿于石墨烯部分孔洞，生长NiCo2S4/C结构单元。部分闲置的孔洞与NiCo2S4/C单元在石墨烯上呈毗邻分布。NiCo2S4/C结构单元中，NiCo2S4纳米片在石墨烯表面整齐均匀排布。复合材料异质结构各组分间存在很强的相互作用，这一特殊结构促进了电解液的扩散，利于电化学活性的发挥。结构上结合了片层多孔、片间孔道及片与颗粒的复合等特点，性质上兼具了高电子离子传输效率、多电化学活性位点、高电化学反应活性等优势，可有效提升材料的比容量、倍率性能、稳定性和循环寿命。通过对该复合材料的设计、制备、电化学特性的综合调控与研究，得到电极材料比容量大于2500F/g，电流密度20A/g比容量保持80%以上，循环寿命3000次比容量保持90%以上。