Preparation Of Copper Selenide Micro-nanocrystals With Different Morphology And Study On Its Electrochemical Properties

The development of renewable and high-efficiency energy conversion materials is essential to meet the ever-increasing energy consumption and environmental protection.A battery with polyhedral electrodes is one of the ideal power supply devices.Its high specific surface area,high material loading capacity and unique crystal structure can effectively increase the energy and power density of the battery.At present,the research on copper selenide mainly focuses on zero-dimensional quantum dots,one-dimensional nanorods,nanotubes,two-dimensional nanosheets,and nanofilms.The synthesis of polyhedral copper selenide crystals is rarely reported.How to synthesize polyhedral copper selenide crystals stably and efficiently still requires continuous scientific research.In addition,the research on crystal structure batteries mostly focuses on the experimental design of electrode structure and the optimization of materials,and the theoretical simulation and analysis that can help to comprehensively and in-depth understand the dynamic characteristics of the battery and the evolution of the electrode structure has been overlooked.This article first summarizes the general law of nanocrystal growth,designs and synthesizes polyhedral CuSe₂micro-nanocrystals,adopts microwave-assisted polyol growth method,and changes the amount of adsorbent,reducing agent,reactant ratio,solvent dosage,and reaction temperature.For the first time synthesis of cube,octahedron,rhombic dodecahedron,pentagonal dodecahedron,tetradecahedron,icosahedron morphology of single crystal,polycrystal,twin crystal structure of polyhedral CuSe₂micro-nanocrystals,and use XRD,SEM and TEM to characterize the crystal form and morphology of the product.Secondly,by observing the growth process of different morphologies of polyhedral CuSe₂micro-nano crystals,the growth and morphological transformation of polyhedral CuSe₂micro-nano crystals with different morphologies,CuSe₂micro-nano crystal derivatives,grafted structures,and twin crystals were clarified.mechanism.Then,the electrochemical properties of the polyhedral CuSe₂micro-nanocrystals with different morphologies were studied.Through cyclic voltammetry,AC impedance,and constant current charge and discharge experiments,the electrode reaction process kinetics were measured,and the electrode reaction mechanism was discussed.Research indicates:（1）The competition between the reduction of selenium element and the capping effect of PVP at the crystal interface plays a crucial role in the formation and morphology control of CuSe₂nanocrystals;CTAB reduces the surface energy of the binding surface through specific adsorption of halide counterions,Forming a controlled morphology.Surfactants also have a significant effect on the surface energy of the copper selenide crystal plane.Surfactants can selectively change the surface energy of the CuSe₂crystal plane,and by adjusting the crystal surface energy and growth kinetics,they can grow into CuSe₂crystal materials with different crystal plane structures.（2）Micro-nanocrystals with different morphologies have different growth kinetics of morphological evolution,including morphological transformation and the self-assembly effect of nanocrystals.In the morphology transformation,the capping effect of PVP and the reduction of selenium elements play a major role in crystal growth.PVP can selectively stabilize the{111}plane of CuSe₂and is formed when the cap layer on the{111}plane is dominant.Octahedral nanocrystals,the introduction of CTAB,the synergistic effect of PVP,CTA⁺hydrocarbon chain and Br^-ions can transform the octahedron into cubic CuSe₂micro-nanocrystals.When selenium element reduction is dominant on the{111}plane,the octahedron can be transformed into rhombohedral nanocrystals.When the internal elastic deformation of the octahedron is caused by the mismatch of crystal angles,it can transform into an icosahedron with twin boundary defects on the surface.At the same time,the icosahedral surface defects are also conducive to the adsorption of selenium atoms and the pentagonal dodecahedron.change.In the self-assembly effect,the hexagonal CuSe nanocrystals self-assemble perpendicular to the surface layer,which may lead to a strong tendency to form a multilayer structure.In the combination of triangular CuSe nanoplates,the dipole moment is distributed along the side of the nanocrystal.Van der Waals interaction depends on the distance between the two substances.The interaction between the two can form octahedral CuSe micro-nanocrystals with a certain spatial configuration.In the process of these morphological transformations,due to the influence of anisotropy and expansion rate,some derivative structure CuSe₂micro-nano crystals are formed.（3）The morphology has a significant influence on the kinetics of the electrode reaction process.The cyclic voltammetry test shows that the electrode reaction kinetics of CuSe₂micro/nano crystals is controlled by surface adsorption,and the oxidation peak current of CuSe₂electrodes with different morphologies gradually increases with the increase of CuSe₂micro/nano crystal geometry.Through the EIS patterns of different voltages and different electrolyte concentrations,it is shown that the semicircle in the high frequency region mainly reflects the electronic contact resistance between CuSe₂crystal particles,between CuSe₂/current collector,and the adsorption and desorption impedance of Li+on the surface of CuSe₂crystals.Impedance.the semicircle in the intermediate frequency region mainly reflects the charge exchange impedance of Li⁺on the electrode surface and the impedance of the interface film formed by the decomposition of the electrolyte on the CuSe₂surface.With the increase of the CuSe₂crystal geometry,the CuSe₂crystal particles,CuSe₂/current collector The electrical contact resistance between them is reduced.In addition,the charge-discharge platform potential difference of the CuSe₂electrode gradually decreases with the increase of the crystal geometry,and the smaller the charge-discharge platform potential difference,the stronger the reversibility of the electrode reaction,and the better the CuSe₂electrode performance.The morphologies transformation models and their morphologies transformation mechanism established in this paper can explain and predict the synthesis of polyhedral nanocrystals with different crystalline surfaces.The reaction mechanism of CuSe₂microcrystalline electrode with different morphology was discussed by measuring the reaction kinetics of CuSe₂microcrystalline electrode.The research on the surface and structure regulation and electrochemical properties of copper selenide nanocrystals,for the synthesis of transition metal chalcogenides with different morphologies of single crystal,polycrystalline,and twin crystal structures,and research on anode materials for sodium/lithium-ion batteries And application provides an important basis and reference.