树状高分子改性尖晶石铁氧体@氮掺杂碳微纳纤维/Li2S6复合电极的制备及其电化学行为研究

The lithium sulfur batteries with a high sulfur loading have electrochemical instability. Based on our previous research results, this project proposes innovatively improving the high mass loading and stability of the sulfur electrode by PAMAM dendrimer modified spinel type ferrites@nitrogen doped carbon micro/nanofibers. The multifunctional synergy effects between PAMAM and MFe2O4@nitrogen doped carbon micro/nanofibers, which have adsorption polysulfides and catalytic lithium/sulfur redox reactions. The composite electrodes are prepared by electrospinning technology and PAMAM dendrimer-induced chemical cross-linking method, which are prepared by the three-dimensional networks structure of PAMAM/MFe2O4@nitrogen doped carbon micro/nanofibers and loaded Li2S6 catholyte. To improve the physicochemical properties of MFe2O4@nitrogen doped carbon micro/nanofibers surface and improve its electrochemical properties by regulating the surface polar functional group, coating layer and interface structure of PAMAM. With combination of the experimental results and theoretical computation, the exploration and cognition of functional polymer PAMAM and spinel-type ferrites influence on the electrochemical behaviors of composite electrodes. Improving the stability of sulfur electrode and the mechanism of the electrochemical behaviors with PAMAM/MFe2O4@nitrogen doped carbon miro-nanofibers will be explored. The modeling of kinetic in multi-phases of the composite electrode systems will be constructed. Based on the above investigations, the rational relation of organic-inorganic composite materials will be.constructed to interfaces structure, sulfur electrode stability and electrochemical behaviors. These fundamental studies are significant for the development of new electrodes system for lithium sulfur batteries.

针对锂硫电池高硫负载电极电化学稳定性不佳的问题，本项目基于前期研究基础，提出综合利用树状高分子聚酰胺-胺(PAMAM)吸附聚硫锂和尖晶石铁氧体(MFe2O4)@氮掺杂碳微纳纤维催化锂/硫氧化还原反应的协同效应，提升高硫电极稳定性。通过电纺丝和化学交联法制备三维网络结构PAMAM/MFe2O4@氮掺杂碳微纳纤维，负载Li2S6形成复合电极。调控PAMAM表面极性官能团、包覆层及表界面结构，改善MFe2O4@氮掺杂碳微纳纤维表面理化特性，提高其电化学性能；结合实验研究和理论计算，认知功能高分子PAMAM和不同晶体结构尖晶石铁氧体对电极电化学行为的影响规律；揭示PAMAM/MFe2O4@氮掺杂碳复合结构与聚硫锂的相互作用和提高电极电化学性能的微观机制，构筑有机-无机复合材料体系多相界面反应过程动力学模型，建立“界面结构-电极稳定性-电化学行为”之间的关系，为锂硫电池新型电极体系发展奠定科学基础。

高载硫电极构筑、高容量和稳定性是高比能锂硫电池的研究热门方向。本项目基于静电纺丝工艺，调控纺丝液类型实现了不同氮掺杂碳纤维（NCFs）。在纺丝液前驱体分别加入金属有机框架材料ZIF-8和ZIF-67，实现了高氮含量的NCFs和Co, N共掺杂NCFs复合膜。基于树枝状高分子PAMAM修改NCFs，制备PAMAM@NCFs有机/无机微纳纤维膜，采用Li2S6溶液为活性物质制备自支撑三维结构膜电极，实现了高载硫复合电极的电化学循环稳定性。基于上述优化工艺制备的NCFs, 通过电纺丝-水热相结合工艺制备系列自支撑三维网络结构硫化物MS2(M=Co, Sn)@NCFs及尖晶石MN2O4(M= Co, Ni, Zn； N=Fe, Co))@NCFs复合微纳纤维膜，以Li2S6溶液为活性物质制备膜电极，无需硫热熔融、粘结剂及相应的涂布工艺。自支撑复合膜微纳纤维呈连续网络结构，为离子和电子的传输提供有效路径；基于多级孔结构复合纤维可有效吸附多硫化物及纤维修饰材料（硫化物/尖晶石氧化物）催化锂/硫氧化还原反应的协同效应，有效抑制多硫化物溶出，提高活性物质利用率。基于电化学分析技术，相比于NCFs, MS2(M=Co, Sn)@NCFs和MN2O4(M= Co, Ni, Zn； N=Fe, Co)@NCFs复合微纳纤维膜可有效提升硫化锂沉积容量并改善高载硫电极电化学反应动力学。基于非原位扫描电镜技术，研究了上述复合膜电极“固硫”作用机制及多硫化物“穿梭效应”对金属锂负极的表面形态及组分的影响。