Transition metal disulfide/graphene nanocomposites for Na-ion batteries: design and electronic interactions

该提案解决了过渡金属二硫化物（TMD）和石墨烯异质结构中的电子相互作用。二维层状结构，层间相互作用弱，表面体积比大，为钠离子电池的高级负极材料提供了巨大的潜力，钠离子电池因其低成本和丰富的钠含量而成为锂离子电池的一个有前途的替代品。通过在复合材料中添加纳米碳相，可以克服纯TMD电极的导电性差和高团聚风险。近年来，越来越多的科学出版物证明了TMD和石墨烯纳米杂化材料在锂离子电池和钠离子电池中具有优异的电化学性能，其中大多数都报道了容量和可循环性方面的有效电化学参数。本课题旨在研究钠离子嵌入TMD/石墨烯复合材料的物理过程，并详细了解复合材料的（微观）结构-性能-电化学性能之间的关系。我们重点研究了三种过渡金属——钼、钨和钒的二硫化物及其与石墨烯的复合材料。该项目包括(i)详细阐述这些复合材料的合成程序，（ii）表征其形态、结构和电子特性，以及（iii）研究Na嵌入的影响。实验和理论方法的结合，包括高分辨率显微镜，光谱学，使用实验室和同步加速器源的x射线光电子和吸收光谱学，以及理论量子化学方法将应用于本项目。此外，为了提高Na离子的扩散迁移率和活性位点的可及性，我们将在TMD复合材料中引入空位和杂原子缺陷，并研究这种修饰对TMD复合材料结构、电子和导电性能的影响。最后，TMD/石墨烯材料将在可变电化学循环条件下作为钠离子电池电极进行测试。电极的化学稳定性将通过暴露在空气中来评估。利用固体核磁共振技术研究了放电后复合电极的反应产物及钠嵌入效应。结果将分析电导率特征的电化学阻抗测量。预计该项目在调整TMD/石墨烯复合材料（微观）结构和电子性能的基础上设计的TMD/石墨烯复合材料将有助于开发具有高容量和稳定循环的先进钠离子电池电极材料。

The proposal addresses electronic interactions in heterostructures of transition metal disulfides (TMD) and graphene. Two-dimensional layer-structures, weak interlayer interactions and large surface-to-volume ratio of TMDs offer a great potential to act as advanced anode materials for sodium ion batteries, which are a promising alternative to lithium ion batteries due to the low cost and abundance of sodium. The poor electrical conductivity and high agglomerate risk of pure TMD electrodes can be overcome by interspersing nanocarbon phases within the composite material. The synergetic interactions of TMD and graphene nanohybrid materials for superior electrochemical performance in lithium and sodium ion batteries have been demonstrated in a quickly increasing number of scientific publications in recent years, most of which report on efficient electrochemical parameters in terms of capacity and cyclability. This proposal aims on the study of the physical processes occurring upon sodium ion intercalation in TMD/graphene composites and detailed understanding of the relationship between (micro-) structure - properties - electrochemical performance of these composite materials. We focus on disulfides of three transition metals - molybdenum, tungsten and vanadium - and their composites with graphene. The project comprises (i) elaborating synthesis procedures of these composites, (ii) characterisation of their morphology, structure and electronic properties, and (iii) studies of the effects of Na intercalation. A combination of experimental and theoretical approaches including high-resolution microscopy, optical spectroscopy, x-ray photoelectron and absorption spectroscopy using laboratory and synchrotron sources, and a theoretical quantum chemistry approach will be applied in this project. Furthermore, to improve the Na ion diffusion mobility and accessibility of active sites, we will introduce vacancy and heteroatom defects into TMD composites, and investigate the effects of this modifications on the structural, electronic and conducting properties. Finally, the TMD/graphene materials will be tested as electrodes for Na ion batteries at variable electrochemical cycling conditions. Chemical stability of electrodes will be evaluated by exposure to air. The reaction products of discharged composite-containing electrodes and effects of Na intercalation will be studied by solid-state NMR. The results will be analysed towards electrical conductivity characterized by electrochemical impedance measurement. It is anticipated that design of TMD/graphene composites elaborated in the project based on tuning their (micro-)structure and electronic properties will contribute to development of advanced electrode materials for Na ion batteries with high capacilty and stable cycling.