Structural Design And Electrochemical Performance Of 1D Phase Change Self-standing Materials

With the development of the portable electronic product and electric vehicle market,the performance of lithium-ion battery(the key energy storage equipment),needs to be further improved.Furthermore,high specific capacity,excellent cycle stability of positive and negative electrode materials are essential for developing lithium-ion battery.One-dimensional nanomaterials have high specific surface area,which can provide more active sites for electrochemical reactions.The pore structure of the material can effectively shorten the ion diffusion path.Therefore,One-dimensional nanomaterials have been widely concerned by researchers.In this paper,we chose two kinds of promising electrode materials:lithium titanate(Li4TisO12)and lithium iron manganese phosphate(LiFeo.4Mno.6PO4).By electrospinning technique,we designed and synthesized one-dimensional self-supporting electrode materials which can promote ion/electron transport.In order to solve the problems of low electronic and low specific capacity of Li4Ti5O2,we prepared oxygen-vacancy Li4Ti5O12/CNT composite,which featured as 1D self-supporting carbon nanofibers.Firstly,one-dimensional Li4Ti5O12 nanofibers were successfully prepared by electrospinning.After high-temperature sintering in anoxic atmosphere(vacuum),a large number of oxygen vacancy defects are generated in the material,which greatly increase the interface charge storage capacity of the electrode material.The discharge specific capacity of the first cycle at 0.1C is 348 mAh g-1.At the same time,the polymer nanofibers transform into amorphous carbon nanofibers in the carbonization process,and cross-link each other to form a three-dimensional conductive network as a self-supporting electrode substrate.In order to further improve the performance of self-supporting Li4Ti5O12 electrode materials,we added carbon nanotubes(CNTs)into the electrospun precursor solution,and formed Li4Ti5O12/CNT composites nanofibers,which significantly improved the electric conductivity of Li4Ti5O12 self-supporting electrode materials.Then,1D porous LiFeo.4Mno.6PO4/carbon nanofiber was synthesized by ionic liquid[BMIm]H2PO4 assisted electrospinning technology.During the process,the H2PO4'anion is used as the source of PO43-,and the cation is carbonized to form an N-doped carbon layer coated on the surface of LiFeo.4Mn0.6PO4 nanoparticles.At the same time,the carbonized of cation would left some macropores.The N-doped carbon layer coating can improve the conductivity of LiFeo.4Mn0.6PO4,and the pore structure are beneficial for the penetration of the electrolyte.Meanwhile,ionic liquid as a soft template can assist nanofibers to form a mesoporous structure with uniform pore size,which effectively shortens the ion diffusion path.The high specific surface area of one-dimensional nanomaterials(287.4m2g-1)also provides more active sites for electrochemical reactions.This work provides a simple and versatile method for designing one-dimensional porous self-supporting electrode structures.The results of these thesis researches provide a new sight for the porous self-supporting electrode designing,and also have important significance for the interface charge storage development.