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

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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.