The Construction And Study Of Metal Based Energy Storage Anodes

Due to its high theoretical capacity,low working voltage,stable and simple fabrication process,metal-based material has become a potential anode for energy storage devices.However,the poor electrochemical stability caused by the serious volume change in the cycles hinders the realization of its objective of market-oriented commercialization.This paper is devoted to the construction of the metal-based anodes with the stable electrochemical performances for the second batteries,the study of their nucleation and growth mechanisms by the basic characterization methods,the analysis of the influences of reaction conditions to their composition,structure and morphology,and the research of the influence of the composition,structure and morphology changes to the metal-based anodes electrochemical performances of as well as their energy storage mechanism,thereby,to obtain an effective way for preparing a metal-based anodes with excellent electrochemical properties.The metal-based anodes studied in this paper can be divided into two parts:for lithium ion battery and for sodium ion battery.1.Metal-based anodes for lithium ion battery: manganese-based,iron-based and ferromanganese-based materials.?1?On the basis of transition metal manganese,the effects of material composition and morphology on their properties were studied.Spinel Mn₃O₄ was prepared by hydrothermal method with the manganese salt and ammonia as the main reactants,and the materials are nanorods accompanying with some overgrowths.The bad contact and wetting between materials and electrolyte,poor transfer/diffusion of ion/electron and serious volume change in the cycles caused by the large size dimensions and low conductivity leaded to its unstable electrochemical performances.To solve this problem,reduced graphene oxide were introduced as the supporting materials,which can improve the stability ofanodes structure and conductivity.Mn₃O₄/reduced graphene oxide with excellent cycling stability and rate performances was obtain,while analyzing the influence of reduced graphene oxide to composite morphology and size and studying the nucleation and growth mechanisms,energy storage mechanisms and energy storage improvement mechanism of composite.The initial discharge specific capacity is 897.2 mAh g^-1,and reversible specific capacity can maintain at ca.450 mAh g^-1 after 100 cycles,which is as four times as that of the materials without reduced graphene oxide.In this work,the introduction of reduced graphene oxide can improve the cycling stability of Mn₃O₄/reduced graphene oxide,however,the poor coulombic efficiency in the initial cycle resulted to the low reversible capacity of composite.So,to redesign the structure of materials,a polypyrrole film is coated on the surface of composite to reduce the capacity loss caused by the formation of solid electrolyte interface?SEI?film in the initial cycle,and the coulombic efficiency in the initial cycle almost doubled.Meanwhile,EIS was employed to analyze and grasp the working mechanism of the polypyrrole film.?2?On the basis of transition metal iron,the effect of structure change on their properties was studied.The theoretical capacity of Fe₂O₃ is obviously higher than that of Fe₃O₄,but it showed lower actual test capacity.The similar hydrothermal methods were employed to prepare Fe₂O₃ and Fe₃O₄.Comparing the similarities and differences between two materials,the difference in the structure was found to be the main factor which leaded to this phenomenon.Fe₃O₄ with cubic phase had bigger lattice volume and higher voidage than Fe₂O₃ with tetragonal phase,which was more suitable for the insertion and desertion of lithium ions without serious volume changes.Therefore,Fe₃O₄ can get a reversible specific capacity of 921.1 mAh g^-1 at the current density of 50 mA g^-1after 15 cycles,while the reversible specific capacity of Fe₂O₃ was only 328.3mAh g^-1.?3?In addition to the composition,morphology and structure,the factors affecting the properties of materials with similar characters are studied by taking ferromanganese-based materials as example.Fe₃O₄ and MnFe₂O₄ with same inverse spinel structure were prepared through the same hydrothermal method,and it was found that there were big differences between in electrochemical performances between them.Analyzing the energy storage mechanisms of them,it was found that the energy storage mechanism of Fe₃O₄ is reversible,but for MnFe₂O₄,it will decompose into Fe₃O₄ and MnO with smaller scale in the cycles.The difference in energy storage mechanism leaded to a more stable cycling performance of Fe₃O₄,while the reversible specific capacity of MnFe₂O₄ was only half of Fe₃O₄ after 55 cycles,which was resulted from the structural collapse caused by the decomposition of the material.2.For the metal-based anodes for sodium ion batteries,tin-based materials were taken as the main object.?1?Taking SnS₂ as example to explore the preparation methods of SnS₂ sheets which have potential sodium storage.By the regularity study of raw material proportioning and reaction time,which can influent their growth,the nucleation and growth mechanisms and the effects of reaction condition on their composition,structure and morphology were analyzed.?2?Composing the SnS₂ sheets with suitable carbon materials,the influencing regularities of the kinds and the amounts of carbon materials on the properties of composites were studied.Meanwhile,to obtain the tin-based composite anode with excellent sodium storage performances,the ways of carbon materials to impact energy storage mechanisms and performance improvement mechanisms of composites were analyzed.