Preparation Of Low-dimensional Carbon-based Nanomaterials Based On Doping Modification And Research On Advanced Energy Storage Applications

In the background of the rapid technological and economic development of today’s society,the consumption of non-renewable resources such as fossil fuels is leading to a serious energy crisis,while its carbon dioxide emissions are increasing year by year,triggering the greenhouse effect.The development and use of clean energy is the key to address these issues,but most renewable clean energy sources face intermittent difficulties and require energy storage systems to improve their efficiency.Therefore,the development of electrochemical energy storage systems with lower cost,higher energy density and longer cycle life has become a key issue.Lithium-ion and sodium-ion batteries（LIBs/SIBs）,as mature and efficient energy storage devices,share similar energy storage mechanisms,and the structural properties of their anode materials have a critical impact on the overall battery performance.Carbon material has become a common anode material for LIBs/SIBs due to its low cost.However,the shortcomings of low theoretical capacity,poor rate performance and cycling performance have seriously restricted its rapid development.To address the above key scientific issues,this paper takes the expansion of energy storage sites of low-dimensional carbon materials（carbon nanofibers and carbon nanosheets）and optimization of carbon matrix conductivity as the starting point,and modifies the carbon-based carriers by loading metal and doping non-metallic heteroatoms（N,S）strategies,while effectively alleviating the volume expansion of alloy-based electrode materials during charging and discharging,and improving the carbon matrix by microstructure design to improve the conductivity and kinetic performance through morphological design.In this paper,the structural characteristics and energy storage mechanism of the modified low-dimensional materials are explored,revealing the synergistic effects between the active components and the potential mechanism of electrochemical performance improvement.The potential of heterogeneous component-tuned low-dimensional carbon materials for practical applications is demonstrated through full-cell assembly and testing.The main work can be summarized as follows:（1）Composite electrodes with longitudinal cavities of N and S co-doped carbon nanofibers loaded with Sb（Sb@N,S-CNFs）were designed by a four-functional template-assisted strategy combined with electrospinning technique and calcination process.The thermolysis of the Sb₂S₃ template and the volatilization of partial Sb led to the formation of longitudinal cavities in the pore channels of the N-doped carbon nanofibers,while the derived Sb nanorods and Sb nanodots were uniformly distributed in the carbon fiber matrix,in addition to which S doping in the carbon fiber matrix also occurred.This well-designed multi-layered structure not only effectively alleviates the problem of large volume changes of Sb components during charging and discharging,but also improves the ionic conductivity and electronic conductivity of the carbon fiber matrix.Based on the above advantages,the Sb@N,S-CNFs electrode（Sb@N,S-CNFs-1h）calcined for 1 h has good stability in the half-cell test and full-cell cycling test and high capacity retention in the rate test.The half cell still has a high capacity retention of85.1%after 1000 cycles at a current density of 2 A g^-1,and the full cell maintains a high specific capacity of approximately 95 m Ah g^-1 after 100 cycles at a current density of240 m A g^-1.（2）Based on the conclusion obtained in work 1 that the content of Sb in the longitudinal pores and the amount of Sb embedded in the carbon matrix changed regularly with calcination time,a longitudinal pore carbon nanofiber composite（N/S,Sb-CNFs）with N and S co-doped and inlaid with Sb nanodots was successfully prepared by means of increasing the calcination temperature and extending the calcination time.N/S,Sb-CNFs can be directly used as the negative electrode of sodium ion batteries,avoiding the use of conductive and binder and showing high capacity and good cycling stability.The design of this work is centered on the effective use of low-dimensional metal sulfide templates in electrospinning and the assembly and testing of flexible full cells.The introduction of N,S,and Sb in N/S,Sb-CNFs significantly increases the active storage sites for sodium ions and greatly enhances the capacity and conductivity of carbon fibers through a series of characterization analyses.The reversible capacity of N/S,Sb-CNFs at 0.1 A g^-1 is 307.5 m Ah g^-1.Specifically,the flexible sodium ion full cell assembled with N/S,Sb-CNFs demonstrates the ability to sustain electrical energy output under different bending conditions.This synthetic strategy is universal and enables the design of self-supporting membrane electrodes and shows its potential for better applications in wearable devices.（3）Based on the principle of Schiff base reaction,two-dimensional carbon-based composite nanomaterials were constructed by the integration of amino and carbonyl condensation reactions in the presence of transition metal ions.With the occurrence of the condensation reaction,the transition metal ions coordinately chelate with the remaining thiocarbonyl groups and the formed C=N bond,and finally form N,S doubly doped two-dimensional metal sulfide quantum dots embedded in two-dimensional metal sulfide quantum dots.A two-dimensional graphene-like carbon material doped with N and S dual elements and enriched with a concave pore structure on the surface was further obtained by a simple etching step.Compared with traditional graphene,this two-dimensional carbon material is easy to control in size,thickness,distribution of concave pores and electronic density of states,which can effectively improve the specific surface area and tap density of the material,and has the advantages of low cost and high yield.It reflects its application value as active material and conductive additive.This two-dimensional material has excellent electrochemical performance as the anode of lithium-ion batteries:at 5 A g^-1,the capacity can reach 2.3 times that of graphite electrodes,and it still maintains a specific capacity of more than 400 m Ah g^-1 after 5000 cycles.