Controllable Synthesis And Performance Research Of Transition Metal-based Micro/Nano-structured Composites For Electrode Materials

Constructing a transition metal oxide anode into a micro/nano structure or compounding with other materials is an effective way to improve the performance of lithium-ion batteries.Synthesis of a material with excellent performances in a controllable approach,is a prerequisite for achieving the modification of electrodes and large-scale manufacturing.In this thesis,we have prepared micro/nano-structured,Fe-based and Mn-based composite electrodes in the dealloying process by tuning the composition of the precursor alloys,adding surfactants,regulating the concentration of the etching solutions or etching routes,incorporating strong oxidants ingredients in the dealloying process.XRD,SEM,EDS,XPS and other characterization methods were used to analyze the structures,and the electrochemical performances were tested by galvanostatic charge-discharge cycles,cyclic voltammetry and electrochemical impedance spectrometry.The results have shown that the material structures and electrochemical performances can be controlled and modified by altering these dealloying conditions.1.Select the binary or ternary Fe-based and Mn-based alloys with different compositions for dealloying.The results have shown their products with AB2O4 spinel-type structures.Among them,the higher Mn contents are more likely to perform a series of octahedral morphologies,while the Fe,Cu,and the Ni ones tend to perform sheet-shaped products.In the electrochemical tests,the results have shown in the AB2O4structure,the B component contributes the Li-ion storage capacity,and the A component mainly dominate their electrochemical activities.In addition,the micro/nano structure of the composites and its synergistic effects also have a significant impact on electrochemical performance.Therefore,the amount of different doping elements in the Mn-based and Fe-based alloy precursors can effective influence the microstructure,morphology,and electrochemical performance of the dealloyed products.2.The nonionic,anionic and cationic surfactants were participated into the dealloying process of Fe-based and Mn-based alloys,and then compare the envolution of the structures.It is found that the action mechanism of different types of surfactants on product morphology and products is different.For the nonionic surfactant PVP,it is shown that they have slow down the reaction rate of Al and NaOH,thus resulted in the variety of the morphologies of the dealloyed products and their crystallinity deterioration.While the anionic surfactant does not changed the chemical composition,crystal structure or even the product,but they directly affected by crystallinity and had some effect on the morphology.Moreover,the cationic surfactant CTAB acts as a structure-directing agent in the dealloying reaction,which significantly improves the crystallinity and micro-morphology of the product.The addition of these three surfactants affected the lithium storage properties and electrochemical stability of the product in different ways.The results showed that the type of surfactant,the amount of addition,the critical micelle concentration,the degree of polymerization,and the radical have different influence on the dealloyed products.Viewing the controlling method is facile,efficient,and adjustable,it has prospective practical applications.3.Firstly,the effects of different concentrations of NaOH etching solution on the structure and electrochemical properties of the product were compared.The results have shown that the appropriate concentration can improve the stability of the product Mn₃O₄/CuMn₂O₄ during charge and discharge.Especially the 5M product is optimal,showing a good cyclic performance(596 mAh g^-1 after 600 cycles of 200 mA g^-1charging/discharging)and rate performance(114 mAh g^-1 even at the current density of2000 mA g^-1)and satisfying current charge and discharge stability.Afterward,we further prepared Mn₃O₄/CuMn₂O₄ anodes by acid-alkaline two-steps etching,then compared the crystallinity and microstructure with the previous product.However,it is necessary to control the actual content of the oxide to avoid adverse effects on the electrochemical reaction caused by the small amount of the active material.Finally,by adding a strong oxidant of H2O2 into the dealloying system,we have compared the difference of the product with the pristine ones.The have results shown that the addition of H₂O₂ modifies the structure of Fe₃O_4/NiFe₂O₄ by significantly reducing the grain size homoginazing the morphology of the product.Also,the Li-ion storage performance and the stability have been improved at the same time.It can be seen that the above experiments can achieve controllable preparation of product structure and performance in the actual dealloying production and application process,and have reference value and practical significance.