MOFs衍生碳/CNTs/硫/金属氧化物复合材料的构筑及其在室温钠硫电池中的应用研究

With the widespread use of lithium-ion batteries, the distribution of limited lithium source is very uneven in the earth’s crust and lithium is becoming less and less; its price is getting more expensive. Therefore, it is inevitable to find a new alternative. Room temperature sodium-sulfur batteries (RT Na-S batteries) based on sodium and sulfur are being considered a low-cost option for large-scale energy storage applications, since Na-S batteries with high theoretical capacity and sodium and sulfur are abundant in the earth. However, RT Na-S batteries still face many technological obstacles. First, the poor conductivity of sulfur leads to low its electrochemical utilization. Second, high volumetric expansion is also serious issue during sodiation/desodiation process, causing the performance degradation of the cell during prolonged cycling. In addition, a critical challenge is the dissolution of polysulfides in the liquid electrolyte, which leads to the loss of active materials, poor cycling stability, as well as low Coulombic efficiency. MOFs derived carbon has the advantages of large specific surface area and outstanding adsorption performance, which could contribute to realize the fixation and loading of active sulfur. Carbon nanotubes can form three dimensional networks with MOFs by chemical process and improve the conductivity of the composites because of its high conductivity and unique tubular structure; Coating of metal oxides can form a strong chemical bond with the polysulfide to prevent the loss of sulfur from the matrix and inhibit the dissolution of the intermediate product. The MOFs derived carbon, carbon nanotubes and metal oxides have the different functions. Construction of MOFs derived carbon/CNTs/S/metal oxide hierarchical frameworks would jointly solve these important problems in HT Na-S batteries and improve the whole electrochemical performance. This study may provide theoretical guidance and technical support for the development of a comprehensive performance of HT Na-S batteries.

锂离子电池的广泛使用，使本来就分布不均、储量非常有限的锂资源日益匮乏，价格高昂。因此，寻找新的可替代品成为必然。室温钠硫电池由于理论容量高, 且电极所使用的钠和硫原料在地壳中储量极为丰富而被认为大有发展前景。但硫的电导率极低、充放电过程中体积膨胀和多硫化物溶解等问题导致其电化学性能不理想。本申请项目尝试利用具有大比表面积和高吸附性能的MOFs衍生碳来实现硫的有效固定与承载；利用具有高导电性和独特管状结构的碳纳米管提高材料的导电性和构筑三维网络通道；通过可与多硫化物形成强化学键的金属氧化物对负载硫的复合材料进一步包覆，抑制中间产物的溶解，防止硫溢出损失。将具有不同特点和功能的MOFs衍生碳、碳纳米管和金属氧化物三者有机结合，构筑出立体复合结构，多方位、多角度、协同解决钠硫电池所面临的问题，从而有效地提高钠硫电池的电化学性能，为开发综合性能优良的室温钠硫电池电极材料提供理论指导和技术支持。

室温钠硫电池低反应活性和快速容量衰减是阻碍其发展进程的两大问题。本项目以问题为导向，利用MOFs衍生碳、碳纳米管和金属氧化物三者所具有不同特性和功能，构筑出多层级立体复合结构，全方位、多角度、协同解决其核心问题，从而全面提高钠硫电池电化学性能。. 该项目主要做了五个方面研究内容：1)设计了由碳纳米管串联MOF衍生多面体碳载体材料, 将其应用在钠硫电池中，取得了优异的电化学性能。2)构建了一种MOFs衍生制备核壳结构的制备方法，合成系列MOFs衍生碳的核壳结构（如ZIF-67、ZIF-8、Cu-MOF等），并用于室温钠硫电池硫正极载体材料。3)合成碳纤维串联镍空心球载体材料，采用静电纺丝技术得到了金属及其化合物嵌入氮掺杂碳纤维复合结构，该结构能够有效容纳硫单质并在循环过程中缓解其体积膨胀，促进多硫化钠的转化过程。4)设计仿生枝叶状电极结构作为硫载体材料，构筑高效钴催化系统，深入探究室温钠硫电池中金属钴在充放电过程中的催化机理。5)重点设计合成了一系列金属硫族化合物, 该材料可以催化多硫化物的转化反应,并通过化学吸附抑制穿梭效应,从而获得良好的电化学性能，并将该方法推广到其它过渡金属二卤代物体系。通过该项目实施，设计合成出多种具有复合功能的室温钠硫电池正极载体材料，对钠硫电池导电性、多硫化物穿梭、容量和倍率性能的改善均有极大提升，并通过计算模拟了对多硫化钠的催化机理。. 项目执行期间获得了重庆市自然科学二等奖（排名第一）、川渝科技学术大会论文一等奖、第三届西部材料大会优秀论文一等奖、第十届重庆市科慧研究生创新创业大赛一等奖等荣誉；在Nat.Commun.、Adv. Mater., Adv.Energy Mater.、Adv.Funct.Mater.、Nano Energy、Adv. Sci.等期刊发表SCI论文30余篇；申请专利4项；所指导3位研究生获重庆市优秀学位论文；培养指导博士后2人、博士研究生3人，硕士生8人，目前在读硕士研究生13人；获得国家自然基金面上项目继续资1项、参加国际会议与学术交流20余次，承办会议3场，研究生参加相关学术会议13人次。