Electrospinning Preparation Of Anode Material For Carbonaceous And Phosphorus-based In Sodium Ion Batteries

Renewable clean energy has received extensive attention without the need to consume fossil fuels and increase environmental pollution.In order to combine sustainable energy with the power grid,large-scale energy storage systems are important in peak conversion operations.Among different energy storage technologies,electrochemical secondary batteries are a promising method because of their high energy conversion efficiency,flexibility,and ease of maintenance.Lithium ion batteries have high energy density,long cycle life and environmental friendliness and are successfully used in energy storage devices such as electric vehicles,portable devices and mobile phones.However,due to the uneven distribution of lithium in the earth's crust,the lack of reserves,and the increasing demand,the price of lithium resources and the cost of lithium ion batteries are constantly rising.Moreover,sodium metal is located below the lithium in the periodic table,and thus sodium has physicochemical properties similar to lithium in many aspects.In addition,sodium is abundant and low-cost,so sodium ion batteries are regarded as a new focus in clean energy solutions.At present,research topics on sodium ion batteries are basically aimed at electrode materials.In this dissertation,the doped carbon materials and phosphorus-based composites were obtained by electrospinning and chemical synthesis methods.The application of these materials in the anode electrode of sodium ion batteries was studied.The first chapter describes the research background and development significance of sodium ion batteries,and summarizes the research status of the current anode and cathode materials and electrolytes of sodium ion batteries.In the second chapter,the basic device and working principle of electrospinning technology are introduced in detail,and the instruments and methods used to characterize the physical and electrochemical properties of the electrode materials used in the experiments are briefly described.In the third chapter,we used electrospinning method,polyacrylonitrile as carbon source and nitrogen dopant,and polystyrene as pore-forming agent to prepare multichannel carbon nanofiber,and sublimed sulfur was used as sulfur dopant to prepare a flexible sulfur-rich nitrogenous multichannel carbon nanofiber material.By adjusting the content of sulfur,a sulfur-rich flexible nitrogen-doped carbon material with good sodium storage properties was obtained.The reversible capacity was 336.2 mA h g-1 after 100 cycles at the current density of 50 mA g-1;the specific capacity was maintained at 187 mA h g-1 after 2000 cycles under 2 A g-1 conditions.This performance is mainly attributed to the large number of defects generated by S,N doping and active reaction sites,the extended layer spacing and the synergistic effect of the three-dimensional crosslinking multichannel structure.The density functional theory calculations demonstrate that nitrogenous carbon nanofibers doping with sulfur could not only promote the adsorption of sodium but also favor electrons transfer.In the fourth chapter,we first synthesized a flexible multichannel carbon nanofiber material,followed by a KOH chemical activation method to generate a large specific surface area and rich pore structure.On this basis,a porous multichannel carbon nanofiber loaded red phosphorus flexible composite material was prepared by vaporization-condensation-conversion process.The core-shell structure design can effectively alleviate the large volume expansion of red phosphorus in the reaction process.The porous cross-linked structure not only helps to improve the overall conductivity of the material but also favors to increase the loading capacity of red phosphorus.Therefore,the red phosphorus-based composite electrode has excellent sodium storage performance:the capacity was 1455 mA h g 1 after 70 cycles at the current density of 100 mA g-1;and the capacity was 500 mA h g-1 at the high rate of 10 A g-1;and the specific capacity was maintained at 700 mA h g-1 after 920 cycles at 2 A g-1.In the fifth chapter,we point out the innovations and the areas that need to be improved in this thesis,and look forward to the future research work.