Studies On The Structure-properties Relationship Of Disordered Electrode Materials By Pair Distribution Function Technique

Disorder features in energy storage materials affect electrochemical performance deeply.However,due to the lack of tools for disorder characterization,there are few studies on structure-properties relationship of disordered electrode materials.Focusing on the aforementioned problems,in this thesis,we use total scattering and pair distribution function(PDF)analysis techniques to characterize the disordered features,guide the construction of the disordered structure model and explore the structure-properties relationship between structure disorder and electrochemical performances.The main results and conclusions are listed as follows:(1)Introducing Lorch function and distance cut off to optimize PDF data.PDF peaks of atoms with weak scattering ability would be easily affected by the noise induced by Fourier transformation,causing misleading results.Focusing on aforementioned problems,Lorch function and distance cut off are introduced to optimize PDF data,lowering effect of Fourier transformation noise on PDF patterns.(2)Using PDF to characterize the disordered features in disordered crystal of Prussian blue analogue(Ni HCF)and guide the construction of“liquid-like”disordered structure model,revealing the origin of excellent rate performance.In order to improve the rate performance of Ni HCF,we designed and synthesized samples with different degree of Na~+disorder and found that Ni HCF with high degree of disorder had better rate performance.At a current density of 50C,it still had capacity retention rate of about 75%.Reverse Monte Carlo modeling found local symmetry lowering and“liquid-like”features in Ni HCF.(3)Using PDF to characterize defect concentration of amorphous materials of ball milled graphite and guide graphite anodes design of high sodium storage capacity.Regarding to low capacity for sodium storage in graphite,we introduced defects through ball milling method and found as the milling time increases,the structure of ball milled graphite became more disordered and the sodium storage capacity rose.In this chapter,we used PDF to accurately characterize the defect content of ball milled graphite and explore the origin of sodium storage sites.(4)Using PDF to characterize the defect content in amorphous soft carbon materials,and further build up the structure model of amorphous soft carbon to guide the voltage profiles design for potassium storage.To regulate“slope-like”profiles,we manipulate degree of disorder inside mesophase pitch-based carbon microspheres-derived soft carbon to achieve voltage profiles adjustment.In order to understand the linkage between voltage profiles and internal structure,we used PDF to detect the disorder degree change and build up a structural model of disordered soft carbon,revealing the effect of disorder and defects on voltage profiles.Based on knowledge of disordered structure from PDF technique,this thesis helps understand structure-property relationship between structure disorder of energy storage materials and electrochemical performance,and provides significant insight into structure engineering for high-performance rechargeable batteries.