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Controllable Sysnthesis And Sodium-ion Storage Properties Of The Heteroatom-containing Carbon Nanomaterials

Posted on:2023-10-19Degree:MasterType:Thesis
Country:ChinaCandidate:L L WangFull Text:PDF
GTID:2531306776965169Subject:Chemical engineering
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Recently,the energy crisis and environmental pollution have become increasingly serious with the rapid progress of the global economy and science and technology.Therefore,new renewable energy sources for example solar energy,tidal energy,and wind energy attract people’s close attention.However,these new energy sources have problems of instability and discontinuity.Therefore,it is very important to convert these renewable energy sources into non-polluting,clean,and green electrical energy by using energy conversion systems,and then use stable chemical energy storage systems to store this electrical energy.Among them,the rechargeable ion battery is an efficient energy conversion and storage system.At present,secondary batteries that have been widely used in various fields are LIBs,including various electronic products and electric vehicles.With the rapid expansion of market demand,the large-scale application of LIBs is limited by the uneven distribution of raw material reserves and high costs.Therefore,there is an urgent need to find alternatives to LIBs.SIBs are considered to be the best candidate due to their low price and abundant reserves of sodium resources,as well as their similar electrochemical performance to LIBs.However,the lack of suitable anode materials,which is a major factor,has limited the development of SIBs.However,progress has been made in the research and development of anode materials in recent years.Among the most reported anode materials for SIBs,carbon-based materials have attracted numerous attention due to their abundant resources,low price,high stability,and high safety.However,they still suffer from low specific capacity,low electrical conductivity,poor rate performance,poor long-cycle stability,and slow reaction kinetics.To solve these problems,this paper were carried out the strategy of microstructure design and heteroatom introduction to prepare the corresponding carbon-based anode materials for SIBs.The main research contents are as follows:Firstly,Uniform nanofiber membranes were fabricated by simple electrospinning and its surface MOF(ZIF-8)growth,which was followed by annealing in the N2atmosphere to prepare N/P co-doped hard carbon nanofibers(N/P-HCNFs)with uniform morphology.The results show that N/P-HCNFs have the larger specific surface area and pore volume,larger interlayer spacing,and abundant defects that provide additional active sites for Na+storage.Furthermore,their kinetics were investigated,and N/P-HCNF exhibited a higher Na+diffusion coefficient as well as a higher pseudocapacitive contribution at the same scan rate.Therefore,N/P-HCNF exhibits excellent rate capability and excellent long-term cycle life,and the reversible specific capacities of N/P-HCNF are 271 and 100 mAh g-1 at different current densities of 0.1 and 10.0 A g-1,respectively.And it had a 95%capacity retention after5000 cycles at 1.0 A g-1.In situ Raman findings reveal a"physicochemical-non-stoichiometric intercalation"sodium storage mechanism for N/P-HCNFs.The above results indicate that heteroatom doping can not only enhance the electron and charge transfer kinetics of carbon nanofibers,but also enlarge their interlayer spacing and introduce a large number of defects and reactive sites to adsorb more Na+.Secondly,Hierarchical porous carbon nanosheets(HPCNS)were successfully prepared by simple physical mixing followed by one-step annealing using oleic acid as the carbon source and zinc acetate as the template.The results show that HPCNS-800 has a large specific surface area and pore volume and an abundant micro-mesoporous structure,which shortens the Na+diffusion distance and provides more active sites for Na+storage.The HPCNS-800 has less oxygen content by FTIR,XPS,and EA results.In addition,its kinetics were studied and HPCNS-800 has a higher Na+diffusion coefficient.Therefore,HPCNS-800 provides reversible specific capacities of 323.6 and 138.5 mAh g-1 at different current densities of 0.05 and 20.0 A g-1,respectively,indicating its excellent rate capability.Meanwhile,HPCNS-800provides a capacity of 130.0 mAh g-1 with 96%capacity retention after 5700 cycles at a high current density of 10.0 A g-1,showing good long-cycle stability.The above results indicate that the introduction of the hierarchical pore structure and the modulation of oxygen content can enhance the electron and charge transfer kinetics of carbon materials,which can also provide additional reaction sites to facilitate the storage of Na+.Thirdly,when polyacrylonitrile was used as a carbon source sulfur-rich nitrogen-doped carbon(S-NC)was successfully prepared,uniformly mixed with sublimated sulfur powder,and then annealed in the N2 atmosphere.The results show that S-NCs have large interlayer spacing,better electrical conductivity,and meso/macroporous structure.The smaller specific surface area reduces irreversible reactions,which prompted higher first coulombic efficiencies.The XPS results show that the introduction of sulfur provides sulfur-containing covalent bonds C-S and S-S that can reversibly react with sodium.Therefore,the S-NCs exhibit excellent electrochemical performance,which provided high reversible specific capacities of464.7 and 203.6 mAh g-1 at 0.1 and 10.0 A g-1,respectively.Besides,the S-NCs exhibit an excellent long cycle life,with a specific capacity of 229.0 mAh g-1 after1800 cycles at a high current density of 5.0 A g-1,with a capacity retention rate of85%.The above results show that the introduction of sulfur can not only increase the interlayer spacing and conductivity of carbon materials,but also provide more reactive sites,so effectively promoted the storage capabilities of Na+.
Keywords/Search Tags:sodium-ion battery, carbon anode material, heteroatoms doping, kinetics analysis, sodium storage mechanisms
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