基于三维石墨烯/介孔金属有机框架纳米复合材料的高性能锂硫电池研究

Lithium-sulfur batteries hold great promise for nex-generation high-energy-density batteries due to its very high theoretical energy density and low cost and are of significance to the development of mobile electronics and electric vehicles, etc. However, the poor electrical conductivity and huge volume expanse of sulfur cathode as well as the fatal shuttle effect of polysulfide severely impede the commercialization of lithium-sulfur batteries. In the present project, we will develop a series of three-dimensional graphene (3DG)/mesoporous metal-organic frameworks (MOFs) composite aerogels and their derived 3DG/prous metal oxide/phosphide/sulfide and 3DG/nitrogen-doped porous carbon composite aerogels as the sulfur host for lithium-sulfur battery cathode. We will adjust the porous structure of the 3DG/MOF and 3DG/MOF derivatiives and their interations with polysulfide to increase the sulfur loading and restrain the solubility of polysulfide. Meanwhile, we will modify the network of 3DG by introducing the heteroatoms or creating nanoholes in the basal plane of graphene to increase the additional polysulfide adsorption and the flux of electron and ions. By rationally combining them together, we aim to develop frees-standing high-performance lithium-sulfur battery cathode with high sulfur loading and long cylcing life and obtain a deep understanding of the component-structure-property relationship of the synthesized 3DG/MOF and 3DG/MOF derivatiives, which will pay the way to the development of efficient electrochemical energy storage products based on graphene and MOFs as well as their derivatives.

锂硫电池由于很高的能量密度和很低的成本是目前最有前景的高比能量电池，其开发对于便携式电子设备、电动车等移动用电设备的发展至关重要。然而硫正极很差的导电性和巨大的体积膨胀，以及多硫化物的“穿梭效应”严重降低了其实用性。本项目拟开发一系列三维石墨烯(3DG)/介孔金属有机框架(MOF)纳米复合气凝胶和其热转化产生的3DG/多孔金属氧/磷/氮化物和3DG/氮掺杂多孔碳气凝胶，并将其作为硫载体用于锂硫电池正极材料。通过调控介孔MOF及其多孔衍生物的孔结构和与多硫化物的强相互作用来增加硫的负载量和抑制多硫化物的溶解，再加上3DG多孔导电网络的进一步修饰和协同作用最终获得既具有很高硫负载量和又具有长期循环稳定性的自支撑高性能锂硫电池正极材料，并深入研究3DG/介孔MOF和3DG/介孔MOF衍生物的组分-结构-电化学性能关系，为石墨烯和MOF及其衍射物在高效电化学储能产品的开发做好铺垫。

三维石墨烯是由二维石墨烯在宏观尺度上构成的一种新型碳纳米材料，它可以在保持石墨烯超大比表面积、超高导电率等优异特性的同时，克服石墨烯片层间的π-π作用力，有效阻隔石墨烯片层的自我无序堆叠进而实现其宏观结构的稳定性。三维石墨烯独特的结构特点使其在电化学储能、催化、吸附等领域的应用中表现出独特的优势。本项目在执行期间提出了界面工程策略、将金属有机骨架（MOF）纳米晶体封装于三维石墨烯网络，实现了石墨烯-介孔MOF复合材料的可控制备，通过原位限域合成、快速微波等策略，将FeS2、Fe2O3、空心Fe2O3、BiOCl等超小纳米颗粒均匀分散并原位嵌入到石墨烯，制备出了一系列三维石墨烯/金属氧/磷/硫化物复合材料，通过控制反应条件，利用XRD、SEM、TEM等表征手段，探讨了无机纳米粒子在三维石墨烯载体上的生长机理采用电化学测试技术，如循环伏安、交流阻抗等技术，研究了复合电极材料的充放电特性、倍率性能、循环稳定性、以及电极材料的脱嵌锂/钾过程及电子/电荷转移过程等；探讨了三维石墨烯载体和MOF等纳米粒子之间的协同作用机制，揭示了复合电极材料的组分、结构、与电化学性能之间的内在联系，成功了制备出了一系列兼具高功率密度和高能量密度且长稳定的高效锂/钠/钾离子电池负极材料和锂硫电池正极材料。上述研究为高效锂/钠/钾离子电池和锂硫电池的实际应用提供了新的思路。