Preparation Of Telluride Composites Supported On Three-dimensional Porous Carbon And Study On Electrochemical Energy Storage

In recent years,the rapid development of energy storage equipment such as portable electronic equipment and electric vehicles has promoted the development of chemical energy technology.Lithium-Ion Capacitor（LIC）combines the advantages of lithium-ion batteries and supercapacitors and has become the most advanced at present One of the energy storage devices.Although the development of LIC has achieved world-renowned achievements,there is still a dynamic imbalance between battery-type anode and capacitor-type cathode,which limits the overall performance of LIC.Therefore,choosing a suitable anode material with fast storage kinetics is a promising strategy to improve the overall electrochemical performance of LIC.It is understood that the"embedded"anode material has a lower lithium storage capacity and a smaller potential range,resulting in lower energy density."Alloyed"anode materials have extremely high theoretical capacity,but the volume expansion of this type of material is huge,so there is still a big gap for practical applications.The"conversion"anode material not only has a higher theoretical capacity,but also its volume expansion is much smaller than that of the"alloyed"anode material.In view of this,the research work of this thesis selects tellurides（Fe Te₂,Co Te₂）in transition metal chalcogen compounds for research,and then develops high-performance lithium-ion capacitors.This thesis addresses a series of problems such as poor ion/electronic conductivity of transition metal tellurides（Fe Te₂,Co Te₂）,large volume expansion after lithium insertion,and dissolution of multiple tellurides.To construct micro-nano-sized carbon-modified transition metal tellurides to form a composite three-dimensional electrode structure.To achieve the study of adjusting the microstructure of the substance and then optimizing its electrochemical performance.The main research contents are as follows:（1）In this chapter,for the first time,ferric ammonium sulfate and tellurium powder are used as Fe source and Te source respectively,Fe Te₂ nanocrystals are synthesized by one-step hydrothermal method,and three-dimensional N-doped porous carbon microspheres（NPCM）derived from small molecule polymerization are used as carbon matrix.By exploring the different ratios of Fe Te₂ and NPCM to optimize its electrochemical performance,the prepared Fe Te₂-NPCM-2 composite electrode has a specific discharge capacity of 554 m Ah g^-1 after 200cycles at 0.1 A g^-1.Next,we performed a dynamic analysis on the Fe Te₂-NPCM-2 sample by calculating its pseudo-capacitive contribution,diffusion coefficient and EIS impedance test.In addition,by comparing the scan images before and after the cycle of Fe Te₂,Fe Te₂-NPCM-1and Fe Te₂-NPCM-2,it is found that only the morphology of Fe Te₂-NPCM-2 remains intact,which also proves the successful improvement of its volume expansion problem from the side.Moreover,we used mung bean shell-derived three-dimensional porous carbon（HPC）as the cathode,and tested by assembling button half-cells.The discharge specific capacity is 140 m Ah g^-1 after 2 000 cycles at 2.0 A g^-1.Based on the excellent electrochemical performance of the cathode and anode,we use Fe Te₂-NPCM-2 as the anode and HPC as the cathode.The assembled lithium-ion capacitor has ultra-high energy density(228.29 Wh kg^-1)and excellent power density(10 k W kg^-1)and good cycling retention rate.Therefore,we hope that lithium-ion capacitors with transition metal telluride as the anode have broad application prospects in the fields of new energy 3C electronic products and hybrid vehicles.（2）In this work,we propose a strategy to use MOF-derived carbonaceous materials to modify Co-based nanoparticle anodes,so as to achieve heteroatom doping,structure and electronic properties of composite electrode materials in one step.In more detail,this article uses the cobalt-based metal-organic framework（ZIF-67）as the precursor matrix to synthesize Co,Co₃O₄,and Co Te₂ nano-particles embedded in carbon nanocubes composite electrode materials through carbonization,oxidation and tellurization reactions in sequence.Then,we used XRD,XPS,BET,SEM and TEM to perform in-depth phase/chemical composition/microstructure characterization of the three composite electrode materials.Furthermore,electrochemical experiments and test results show that the reversibility of Li-ion storage of the half-cell Co Te₂@N-C composite is significantly enhanced,and it has a higher rate capacity,ultra-fast charging capability and long cycle stable life.On this basis,we built the Co Te₂@N-C//HPC lithium-ion capacitor for the first time,which achieves a high energy density of 144.5 Wh kg^-1 while maintaining a high-power density of 10 k W kg^-1.At the same time,the device exhibits excellent electrochemical structural stability,and can still maintain an original capacity of 90.95%after 1 000 charge-discharge cycles.Thus,the rational design and development of partially coated nanoparticle structures derived from MOF is of great significance for improving the energy density and power density of advanced energy storage devices.