Design And Performance Study Of Carbon-based Anode Materials For Sodium-ion Battery

In the past few decades,in order to alleviate the climate anomalies caused by a large number of carbon emissions,traditional fossil fuels are gradually being replaced by new energy-saving and environmental protection equipment.At present,lithiumion battery is the most widely used in all kinds of energy storage equipment,but the limited abundance of lithium resources and its special geographical distribution make the terminal price of lithium battery keep rising.Therefore,the search for alternative energy storage technology has become a top priority in the modern society.Sodium ion batteries have great potential in the field of rechargeable energy storage due to their large reserves of metal sodium in the crust,uniform global distribution and the same working principle as lithium-ion batteries.But,the ionic radius of Na+（1.02 （?））is much larger than that of Li+（0.76 （?））.When the electrode material has a large volume change during the insertion/extraction out of Na+,causing the structural collapse of the main material,resulting in slow reaction kinetics and unsatisfactory cycle stability.Moreover,Na+ has a larger energy barrier that can be inserted into many electrode materials,which may bring the problems of limited capacity and poor rate capability.Therefore,finding the appropriate electrode material for Na+ storage still remains a great challenge.Therefore,for the sake of solving the problems of large volume changes,poor conductivity,and uns Tab.solid electrolyte interface for the cycle of sodium ion batteries,researchers generally believe that carbon materials have a variety of controllable structures,which is not only conducive to regulating their electrochemical performance,but also plays an significant role in the design of matrix structure and the synthesis of s Tab.composite materials.In addition,carbon based materials have more attractive properties such as long cycle stability,small electrochemical reaction volume changes,high electronic conductivity,low cost,and resource economy.Therefore,this article focuses on the above issues and conducts a series of research on negative electrode materials for sodium ion batteries.The research results are as follows:In this dissertation,Co-MOF-74 precursor was first synthesized by simple hydrothermal synthesis,and then porous Co/C hybrid materials were synthesized by vapor deposition method as anode materials for sodium ion batteries.The rod-shaped Co-MOF-74 precursor,which has the advantages of large specific surface area and rich unsaturated metal active sites,exhibits high sodium storage performance.Nanostructure design has the advantages of shorter electron transport paths,larger electrode electrolyte contact areas,and better adaptation to the strain caused by sodium ion insertion/extraction.In addition,the pyrolysis synthesis of porous Co/C hybrid materials enhances the conductivity of the anode,which is administer to the rapid charging and discharging of the battery.The results showed that porous Co/C hybrid materials exhibited excellent electrochemical performance in sodium ion batteries,reaching a high capability of 205.8 m Ah·g^-1 at 0.1 A·g^-1,with a capability retention rate of 99.35% after 300 cycles.We propose a simple and convenient synthesis method to construct a novel carbon based anode material for sodium ion batteries.（1）In this dissertation,a rod-shaped porous S doped cobalt selenide carbon nanomaterial(CoSe_（1-x）S_x/C,S≤0.05%)has been successfully developed as a prefect property anode material.The unique mesoporous structure on the surface of CoSe_（1-x）S_x/C anode material can reduce the collapse of electrode material structure caused by volume expansion,and maintain structural stability during electrochemical redox reactions.Porosity provides a way for the rapid passage of electrolyte,thereby ensuring the rapid diffusion of ions.In addition,the vacancies caused by S doping increase the number of active sites,promote redox reactions,and thereby improve electrochemical performance.Carbon matrix can improve electrical conductivity,further improving charge transfer efficiency and Na+ diffusion kinetics.Therefore,at a current density of 1 A·g^-1,the specific discharge capacity of the first coil of Co Se（1-x）Sx/C electrode is as high as 782.1 m Ah·g^-1,which the first coulomb efficiency reaches 96.24%.After 100 cycles,the specific capacity is still 358.8 m Ah·g^-1.In addition,Co Se（1-x）Sx/C exhibits excellent magnification performance,maintaining excellent electrochemical performance after cycling at different current densities.This work provides a new insight into the rational design of rod shaped structures with controllable high conductivity,and boosts the progress of anode materials for sodium ion batteries.（2）In this dissertation,Bi Sb/CNT alloy material was prepared using carboxylic carbon nanotubes as a carbon substrate by a simple and rapid solvent-free microwave synthesis method,and used as the anode material for sodium ion batteries.The advantages of microwave pyrolysis are solvent-free,simple preparation,short time,and high yield.The experimental results show that Bi Sb/CNT exhibits excellent electrochemical performance,reaching 282.71 m Ah·g^-1 after 200 cycles at a current density of 0.1 A·g^-1,and cycle stability.It is worth noting that under the action of microwave radiation,metal ions will rapidly reduce to nanoparticles and have a strong interaction with the carbon nanotube matrix,which can buffer the volume change of the Bi Sb/CNT alloy electrode during the cycling process,preventing the anode material from falling off the current collector and causing a short circuit in the battery.In addition,Bi Sb alloy has a high theoretical specific capacity and a low sodium potential,greatly improving the electrochemical performance of sodium ion batteries.The microwave synthesis process used in this article has the advantages of rapid and controllable synthesis of a large number of samples at one time,providing a new idea for large-scale preparation of anode materials for sodium ion batteries.In short,this dissertation presents the reasonable structural design of the anode of the sodium ion battery from the different dimensions of the material,which provides a novel route for the configuration design of the carbon-based anode of the sodium ion battery.