Preparation Of Carbon Nanostructures With Large Interplanar Spacings For Energy Storage

Lithium-ion batteries?LIBs?have been widely applicated due to its good stability,long cycle life,low self-discharge,high specific capacity,no memory effect and friendly environment.However,the limited resources of lithium hindered its large-scale applications.Sodium-ion batteries?SIBs?possess identical physical and chemical properties to LIBs,and have abundant sodium resources in earth crust and ultimately the lower cost.These are considered the next generation secondary batteries.Graphite is extensively used anode material for commercial lithium-ion batteries.However,the small interplanar spacing?0.335 nm?of graphite materials limits the reversible deintercalation of ions,especially Na⁺with a large radius,which is not conducive to performance improvement.Therefore,the development of new high-performance anode materials has become a research hotspot.In this thesis,based on catalytic chemical vapor deposition?CCVD?technique,a novel carbon nanocapsule?CNC?was prepared by employing metal oxide of ZnO as a template.The morphological and structural features and Li⁺/Na⁺strorage properties of CNC were investigated.Furthermore,based on the concept of low cost and environmentally-friendly,the water-soluble Na₂CO₃ was selected as template to prepare ultra-thin carbon nanosheet?CNS?.The effect of reaction temperature on the growth of CNS was studied,and its Na⁺storage properties were analyzed.The CNC was prepared by catalytic electrochemical vapor deposition?CCVD?by employing ZnO nanoparticle as template and catalyst and acetylene as carbon source.The as-obtained CNC possesses three-dimensional?3D?hollow and opening capsule-like structure with with a wall thickness of 5-15 nm.The CNC also offers large specific surface area,rich active sites,and short ion diffusion distance.Meanwhile,the CNC has a large interplanar spacing of 0.42 nm in average,which is conducive to the reversible intercalation/deintercalation of ions.As anode materials for LIBs,the CNC deliveried an extremely high reversible capacity of 953 mAh/g?much higher than the theoretical capacity of graphite of 372 mAh/g?.As anode materials for SIBs,the CNC also exhibited an ultra-high reversible capacity of 468 mAh/g,and the average capacity loss was only 0.066 mAh/g per cycle when 1000 cycles were performed under large current density,reaching the advanced level of SIBs at present.At the same time,the study on ion storage mechanism found that the interplanar spacing of CNC can self-tune themselves during the charge/discharge process,and the average spacing increased from 0.42 nm to 0.44 nm,which demonstrated that CNC have the ability to self-tune their structure to accommodate the intercalation/deintercalation of ions.The higher spacing offers enhanced voids for ion storage and the open framework supports enhanced mass transport.Meanwhile,CNC maintained their overall morphology,composition and structure,illustrating the structural stability.Besides,the charge/discharge mechanism of the CNC is the intercalation/deintercalation of ions,which is also accompanied by a small amount of ion adsorption/desorption.Under a narrow voltage window,the electrolyte decomposition of the CNC-based battery systems was alleviated,so that the CNC performed a better cycling performance.Meanwhile,the extended application range of potential window indicates the application prospect in full batteries.On the basis of CCVD technology,a novel CNS was prepared by using low-cost and environmentally-friendly water-soluble Na₂CO₃ as the substrate.The as-prepared CNS has an ultra-thin flaky structure,and the CNS-600 has the largest interplanar spacing?average of 0.45 nm?and the best electrochemical performance.As an anode material of SIBs,CNS-600 delivered a discharge specific capacity up to 1451 mAh/g,while the long-cycle reversible capacity at high rate is up to 257 mAh/g.Compared to ZnO,The advantages of Na₂CO₃ substrate are large output,simpler preparation process and lower cost,which is more conducive to mass production.Overall,this work develops novel carbon nanomaterials with high interplanar spacing,combining with the design of the morphology structure,providing pathways for the development of carbon materials with high capacity,good stability,long life and good rate capability.