The Preparation,Structure And Electrochemical Properties Of Carbon-Based Core-shell Composites

The development of new portable electronic equipment and artificial intelligence equipment has put forward higher requirements for the technology of lithium battery with high energy storage density,and the electrode material,as an important.part of the lithium battery system with high energy storage density,determines the capacity and cycle stability of the battery.Ti-niobium oxide with high theoretical specific capacity has little change in lattice parameters and cell volume in the process of delamination of lithium ions and high reversibility.Moreover,the charge/discharge potential is around 1.6 V,and it is difficult to produce solid electrolyte membrane and lithium dendrite during the cycle.Compared with lithium titanate with the same potential,it has higher specific capacity.However,the low electronic conductivity of ti-niobium oxide limits the improvement of its electrochemical performance.In order to solve the problem of low conductivity,carbon materials with advantages of low cost,corrosion resistance and high conductivity are used as the main active materials of lithium batteries.Nanoparticles with one dimensional carbon nanotubes composite materials,high volume ratio of 3D surface can be obtained heterostructure nano materials,especially the direct growth on the conductive carbon substrate has a larger surface area and electronic ion transport way 3D core/shell nanofibers,preparation of high performance lithium ion battery electrode materials is an effective strategy design.The microspheres of Ti2Nb10O29 and TiNb2O7 were prepared by solvent heat method.Ti2Nb10O29 and TiNb2O7 electrodes have capacity of 179 mA h g-1 and 146 mA h g-1 for over 1000 cycles at charging and discharging rate of 10 C.Ti2Nb10O29 and TiNb2O7 particles were encapsulated in a porous and flexible nitrogen-doped carbon nanofiber array(CNF@ThNb10O29,CNF@TiNb2O7)by solvent thermal method and electrospinning method to study their electrochemical lithium storage characteristics.At charge and discharge rate of 10 C,CNF@Ti2Nb10O29 has a reserved capacity of 189 mA h g-1 after 1000 cycles.Under the charge and discharge current density of 16 C,CNF@TiNb2O7 composite electrode material has a holding capacity of 210 mA h g-1,with holding capacity of 67.3%.The porous carbon nanofiber array is conducive to electrolyte penetration into the composite material,and the synergistic effect of the carbon nanofiber array framework with the doped niobium titanate nanoparticles improved the contact area of CNF@Ti2Nb10O29 and CNF@TiNb2O7 electrode to electrolyte,Li ion flux,electrode conductivity and the electrochemical performance of the composite material.Ti2Nb10O29 and TiNb2O7 particles were grown on carbon nanofibers(Ti2Nb10O29/CNF,TiNb2O7/CNF)by means of electrostatic spinning and solvent heating.At the current density of 10 C,after 5000 ultra-long cycles,the TiNb2O7/CNF 3D composite electrode material still has the retention capacity of 153.6 mA h g-1,and the energy retention rate is up to 85%.In situ Raman spectroscopy was used to analyze the working state of the electrode during the charge-discharge cycle.The TiNb2O7/CNF 3D composite electrode has good electrochemical reaction stability.Material studio software was used for simulation calculation to establish the complete carbon core structure and the carbon core structure model with C-N bond.It was found that the N defect with vacancy introduced had lower diffusion potential and energy barrier than the complete carbon core structure,and C-N bond in the carbon core structure enabled a stronger adsorption force in the diffusion reaction of composite lithium ions.TiNb2O7/CNF 3D composite with excellent cycling performance,a large number of nano/micro holes in the 3D composite electrode material can not only serve as an electrolyte reservoir,but also ensure full contact between the electrolyte and TiNb2O7,leading to the high rate of cycling stability and capacity retention of the composite electrode,TiNb2O7/CNF composite electrode is able to meet the higher rate and the stability lithium ion batteries required.The sulphur load of SnO2 prepared by hydrothermal method/carbon micro ball(SnO2/CAs@S)and sulphur load of carbon micro ball(CAs@S)as the electrode material of lithium battery,the results show that the SnO2/CAs@S composite electrode compared with CAs@S core-shell structure has more excellent electrochemical performance,in the process of electrochemical reaction,package volume increasing sulfur effectively,to spread beyond polysulfide were suppressed,inhibition of volume change during the process of circulation at the same time.The structure of the SnO2/CAs@S electrode microspheres remained good after the cycle,and the surface SnO2 nano-shell structure enhanced the structural stability of SnO2/CAs@S.In the lithium sulfur battery system,the capacity of microsphere-loaded sulfur electrodes is about 700 mA h g-1,which is more than twice the capacity of the titanium niobate composite electrode.The titanium niobate composite electrode can meet the demand of lithium ion battery with higher charge and discharge rate and stable charge and discharge.