Research On Energy Storage Performance Of Crystal/Amorphous Transition Metal Composite Materials

In the past 20 years,lithium-ion batteries(LIBs)have been widely used in portable electronic devices,such as mobile phones,tablets,e-books,etc.,with the advantages of high energy density,small size,good cycle performance,light weight,and environmental friendliness.At the same time,large-scale applications have begun on large-scale equipment such as electric vehicles.Sodium and lithium belong to the same main group,have similar physical and chemical properties,and have relatively high reserves and distribution in the earths crust.This makes the research on sodium ion batteries(SIB s)more and more attentionAs an important part of lithium/sodium ion batteries,anode materials are one of the key factors affecting battery performance.The research direction of anode materials is mainly crystalline materials,and there is less research on amorphous materials.This work starts with the most common oxide amorphous glass and glass-ceramics to study its preparation,chemical composition,structure and lithium storage mechanism.At the same time,the preparation,structure,morphology and chemical composition of the cobalt-based transition metal sulfide were also explored,and the electrochemical performance and mechanism of the cobalt-based transition metal sulfide were analyzed.The specific content includes the following parts:1.MoO3-TeO2(MT)glass was synthesized by fusion quenching method,and the influence of different proportions of MoO3 and TeO2 on the electrochemical performance was explored.The structure and properties of the material were analyzed by X-ray diffraction,differential scanning calorimetry,Raman spectroscopy and X-ray photoelectron spectroscopy.It shows good cycle stability and rate performance in the test as an anode electrode material for LIBs.Through ex-situ X-ray diffraction,the phase transition process of the material in the charge and discharge process was explored,and it was found that the MT glass was accompanied by the formation of nanocrystals during the discharge/charge process.The precipitated nanocrystals are uniformly dispersed in the MT glass matrix to form an ordered/disordered structure We finally confirmed that Li2MoO4 nanocrystals were formed in the glass matrix,and the morphology of the glass after crystallizing and the distribution of nanocrystals in the glass matrix were observed by SEM and TEM2.On the basis of the first work,Al2O3-MoO3-TeO2(AlMoTe)glass was prepared by melting method,focusing on the effect of Al2O3 doping on the lithium storage performance of MT glass.Through Raman and X-ray photoelectron spectroscopy,the changes in the glass network structure caused by Al2O3 were analyzed.The test found that Al2O3 doping will significantly affect the activity of Mo involved in the redox reaction,thereby increasing the Li+ion diffusion rate and electronic conductivity.At the same time,the influence of different doping amounts of Al2O3 on the electrochemical performance of LIBs was explored,and it was found that when 7 mol%Al2O3 was doped in MT glass,the product obtained the best lithium storage performance.After 500 cycles at a current density of 1 A g-1,the capacity can be maintained at 253.9 mAh g-1.The capacity of MT glass is only 112.5 mAh g-1.Through the study of pseudocapacitance characteristics,the lithium storage mechanism of AlMoTe glass is determined.3.On the basis of the first two works,we further explored the application of Fe2O3-TeO2-MoO3 glass-ceramics in LIB s.The experimental idea is to pre-crystallize during the glass preparation process to obtain glass-ceramics and explore its lithium storage performance.We explored the relationship between the amount of Fe2O3 added and the size of crystallization,the type of crystallization and its electrochemical performance.It was found that when Fe2O3 and Fe2TeO6 are precipitated in the glass at the same time,the glass material exhibits high specific capacity and stable cycle performance.After 800 cycles at a current density of 1 A g-1,it exhibits a ratio of 463.2 mAh g-1.The reason for the increase in capacity is that Fe2O3 crystals exist in glass-ceramics,which provide more active sites for the insertion of Li+.Secondly,Fe2O3 nanocrystals embedded in the glass matrix to improve the electronic conductivity of the material.We also found that the lithium storage mechanism of Fe2O3-TeO2-MoO3 glass-ceramics is mainly controlled by the Faraday process and has a certain pseudocapacitance performance,but its contribution is only about 15%.4.The hollow honeycomb-shaped Co3S4/MoS2 composite material is prepared by using the zeolite imidazolate skeleton-67(ZIF-67)as the precursor and undergoing two vulcanization processes.First,ZIF-67 and thioacetamide were prepared by solvothermal method to obtain Co3S4 hollow nanocubes.Then,MoS2 nanosheets are grown on the surface of the Co3S4 nanocube,thereby forming a Co3S4/MoS2 hollow honeycomb composite material.The outer flakes of MoS2 are intertwined to form a honeycomb structure.Compared with a single Co3S4 or MoS2,the combination of Co3S4 and MoS2 significantly improves its electrochemical performance.The honeycomb sheet-like MoS2 alleviates the volume expansion during the discharge/charge process and stabilizes the internal Co3S4 nanocube structure.At the same time,it also provides more active sites for the insertion/extraction of Li+and Na+,increases the contact area between the electrode material and the electrolyte,and shortens the ion diffusion distance.5.In this work,polyacrylic acid(PAA)microspheres are used as templates,and Co(OH)2 particles are first loaded on the surface.Through calcination and vulcanization treatment,a composite product of CoS2 nanoparticles dispersed in N-doped hollow nanospheres(N-HCS)was prepared.Experiments have found that during the calcination process,S will penetrate into the PAA balls and be embedded in the graphite layer along with the carbonization process.During the discharge/charge process,S in the carbon layer will gradually dissolve out,thereby forming new ion diffusion channels in the carbon spheres and exposing more CoS2 active sites,thereby gradually increasing the discharge specific capacity.When CoS2/N-HCS is used as anode electrode material for sodium-ion batteries,it still has a high specific capacity of 729.6 mAh g-1 after being cycled for 500 cycles at a current density of 1 A g-1.After 3000 cycles at high current densities of 5 and 10 A g-1,the specific capacity of the electrode material can still be maintained at 498.4 and 459.4 mAh g-1.Through in-situ electrochemical impedance spectroscopy,ex-situ X-ray diffraction,capacitance performance evaluation and constant current intermittent titration technology,the sodium storage mechanism and reaction kinetics of the material were further explored.