Preparation And Performance Study Of Cu_xS(1<x<2) As Cathode Material For Magnesium Ion Batteries

Energy is the foundation of human survival and development.In recent years,with the rapid development of global economy and the continuous increase of fossil energy consumption,energy shortage,environmental pollution and climate warming have become more and more serious.Therefore,the energy structure has also made some adjustment strategies,including reducing the consumption of fossil energy and increasing the proportion of clean energy.At present,widely used clean energy such as solar energy,wind energy and tidal energy generally have the defects of"discontinuity"and"instability"in production.Therefore,the use of large-scale grid energy storage to reasonably regulate energy can greatly improve the utilization rate of clean energy.Magnesium-ion batteries,as a new generation of energy storage devices,have the advantages of high specific capacity,large reserves and environmental friendliness.However,it needs to overcome a high energy barrier during the insertion/extraction of the cathode electrode,due to the excessive polarization of Mg²⁺,which makes it difficult to achieve high reversible capacity and long cycle life.Therefore,cathode electrode material with more stable structure and higher matching degree must be developed in order to meet the needs of large-scale energy storage.At present,copper sulfide（Cu _XS,1<X<2）among the cathode electrode material of magnesium ion batteries is used as a conversion cathode electrode material,which has high theoretical specific capacity and electrical conductivity.However,copper sulfide（Cu _XS,1<X<2）has poor stability at room temperature due to the physical structure of the material,resulting in its inability to fully exert its performance.Studies have shown that more active sites and shorter migration distances can be provided for the reaction of ions by nano-processing the microstructure of the material,thereby improving the actual performance of the material.In this paper,two types of copper sulfides,including nanoflower-like Cu S and nanoporous hollow spherical Cu₂S,were synthesized by a simple method,which showed good magnesium storage properties as cathode electrode materials for magnesium ion batteries.The microstructure and chemical composition of the materials were characterized by X-ray diffractometer（XRD）,scanning electron microscope（SEM）,energy dispersive spectrometer（EDS）,X-ray photoelectron spectroscopy（XPS）and transmission electron microscope（TEM）.The electrochemical properties of the materials were tested by electrochemical workstation and charge-discharge tester.（1）In this paper,the effects of surfactants CATB and PVP on the microscopic morphology of Cu S were investigated,and Cu S with different flower-like structures were synthesized by changing the composition ratio of deionized water and ethylene glycol in the reaction solvent.The study shows that CTAB can modulate the morphology of Cu S,which in turn can substantially improve the electrochemical performance of Magnesium ion battery,and that the synthesized nano-flower-like Cu S-C50 has the most complete structure and the largest specific surface area when the volume ratio of ethylene glycol to pure water in the reaction solvent is 1:1.Performance tests show that the Cu S-C50cathode has discharge specific capacity of 168.89 m Ah g^-1 after 50 cycles at current density of 50 m A g^-1 and can still exceed 200 m Ah g^-1 at high current density of 200 m A g^-1.（2）Nanoporous hollow spherical Cu₂S with diameters ranging from 200 nm to 500nm was synthesized using the Kirkendall effect as a cathode electrode material for Magnesium ion batteries.The electrochemical test results show that the nanoporous hollow spherical Cu₂S material still has a specific discharge capacity of 152 m Ah g^-1 after850 cycles at a high current density of 560 m A g^-1...