Controllable Synthesis、Modification Of Multinary Metal Selenides And Their Applications In Energy Conversion And Storage Devices

In recent years,with the growth of population and the increase of human demand,the demand for various types of energy in society will increase significantly.Therefore,it will bring more demand for energy storage and transportation.Metal chalcogenide nanomaterials have unique physical and chemical properties and have great application potential in the field of energy storage.we attempts to prepare metal chalcogenides nanocrystals with uniform morphology and a narrow size distribution using a hot injection synthesis method.In addition,we also try to develop efficient modification methods to improve the electrochemical performance.This article explore their practical applications in the field of energy storage.In-depth study of the optimization of the properties of such materials will play a more important and comprehensive practical role in solving energy and environmental problems.In this paper,three new types of metal selenides and corresponding modified materials were prepared by improving the synthesis conditions.These materials are applied to lithium ion battery,lithium-sulfur battery and dye-sensitized solar cell.The first chapter introduces the synthesis methods of metal chalcogenide nanomaterials,the modification methods of metal chalcogenide nanomaterials,the applications of metal chalcogenide nanomaterials as energy materials and the importance of this project.In the second chapter,wurtzite Cu₉Sn₂Se₉（designated as CTSe hereafter）NPs with uniform morphology and a narrow size distribution are designed and synthesized by a simple colloidal synthesis method.Subsequently,MPA-CTSe NPs are achieved through colloidal quantum dot（CQD）ligand engineering process and employed as the major constituent of anode materials in a LIB device for characterizations.Mercaptopropionic acid-capped wurtzite Cu₉Sn₂Se₉nanocrystals deliver a high specific capacity,excellent rate performance and good stable cycling.The material has an outstanding reversible capacity of 979.8 mAh g^-1 at a current density of 100mAg^-1 after 100 cycles.In addition,a novel electrochemical reaction mechanism of Sn-based electrodes is established and investigated.Unlike most metal sulfides or selenides,it possesses a step-wise intercalation mechanism during the lithiation/delithiation cycles which is beneficial to buffer against volume variation of the alloy electrode materials and improve the performance of battery.The material exhibits potential application as li-ion battery electrode material,and the experiment provides new strategy for the design and manufacture of high-performance lithium-ion batteries.In the third chapter,sphalerite Cu₂SnSe₃ NPs with uniform morphology and a narrow size distribution are designed and synthesized by a simple hot-injection synthesis method.Subsequently,Cu₂SnSe₃@C-N are prepared through introducing nitrogen-doped porous carbon and employed as the major constituent of anode materials in a LIB device for characterizations.Cu₂SnSe₃@C-N nanocrystals deliver a high specific capacity,excellent rate performance and good stable cycling.The material has an outstanding reversible capacity of 723.4 mAh g^-1 at a current density of 100 mAg^-1 after 100 cycles.In addition,S/Cu₂SnSe₃@C-N nanocrystals are prepared and employed as the cathode materials in a Li-S battery device for characterizations.S/Cu₂SnSe₃@C-N nanocrystals deliver a high specific capacity and good stable cycling.The material has an outstanding reversible capacity of 605.7 mAh g^-1 at 1 C after 300 cycles,higher than S/C-N composites under the same conditions.The material exhibits potential application in the fields of lithium ion batteries and lithium sulfur batteries.In the fourth chapter,we report a simple strategy for the synthesis of quaternary wurtzite Cu₃InSnSe₅ nanoparticles with uniform morphology and narrow size distribution.And the morphology and size of nanomaterials was tuned by changing the amount of surfactant.Subsequently,high-quality Pt/Au-Cu₃InSnSe₅ heteronanostructures were produced on the epitaxial growth of previously synthesized Pt/Au nanocrystals that acted as seeds in the precursor solution.We employed spin-coating method to produce pristine Cu₃InSnSe₅,Pt-and Au-Cu₃InSnSe₅ nanoparticle films onto Mo-coated glass substrate as counter electrodes for DSSCs.As a result,the counter electrodes made of Cu₃InSnSe₅ nanoparticles films,Pt-Cu₃InSnSe₅ and Au-Cu₃InSnSe₅ heteronanostructured films achieved a power conversion efficiency of 5.82%,7.66%and 6.43%respectively（the power conversion efficiency of Pt-based counter electrode was 7.91%under the same condition）.The power conversion efficiency of Au-Cu₃InSnSe₅ and Cu₃InSnSe₅ materials was stable at 5.0%and 4.4%after twenty days.As-prepared Cu₃InSnSe₅NPs has a great application potential as counter electrodes for DSSCs and the construction of the metal-semiconductor heterostructures imposes a substantial effect on optimization of the performance of the DSSCs.The last chapter is the summary and outlook of the three research systems in this dissertation.