Study On Controllable Preparation Of Copper-based Sulfide/Hydroxide Array And Its Zinc Storage Performance

In recent years,the excessive consumption of coal,oil and natural gas has led to the depletion of fossil fuels.Therefore,it is urgent to develop renewable resources,such as solar energy,wind energy,geothermal energy,tidal energy and other energy.Aqueous zinc ion batteries have high application prospects in large-scale energy storage due to their advantages of low cost,environmental friendliness and fast ion transport.Among the traditional cathode materials,manganese based materials have high theoretical specific capacity and ideal discharge platform.However,due to low intrinsic conductivity,inevitable phase transition and Mn dissolution,manganese based materials have poor magnification performance and fast capacity decay.Vanadium has rich valence states of+2～+5,which means that vanadium-based materials can realize multi-electron transfer and exhibit high zinc storage capacity during charging and discharging.However,during the cycling process,especially at low current density,due to the dissolution of vanadium and the instability of its structure,it has a significant capacity decay.More importantly,vanadium based materials are highly toxic,which limits their practical application in production and life.Therefore,the development of new cathode materials is an important way to promote the development of zinc ion batteries.The research shows that copper-based materials have the advantages of high theoretical capacity,safety,non-toxicity,low cost and good conductivity,and are widely used in energy storage fields such as lithium-ion batteries and supercapacitors.In recent years,copper based materials as zinc storage electrodes have also attracted researchers’attention.Cu⁺based materials such as Cu I,Cu₂S and Cu₂O show excellent energy storage performance through conversion reaction in aqueous zinc ion batteries.Through this conversion mechanism,Cu⁺-based materials have high capacity,which can greatly improve the energy density of aqueous zinc ion batteries.In addition,transition metal sulfides have high electrochemical activity and low electronegativity,so it is necessary and meaningful to develop and study copper-based sulfides.At present,the research of copper based sulfide materials faces the following challenges:（1）most of the preparation methods of copper-based sulphides are traditional hydrothermal methods.This method requires strict equipment and takes a long time.There are few reports on a more convenient and efficient method.（2）The low actual capacity and poor cycle stability of copper-based sulfide hinder its further development.The construction of hierarchical structure can accelerate ion diffusion,increase active sites,and expand the contact area between electrolyte and electrode material,which is one of the effective ways to modify the material.This paper mainly starts with copper foam,designs and synthesizes Cu₇S₄ nanosheet array electrode material through rapid in-situ corrosion strategy,and builds Cu₇S₄@M-OH（M=Cu,Ni,Co）hierarchical structure on the basis of Cu₇S₄ material,our work first explored the zinc storage mechanism of Cu₇S₄ electrode and its composite structure materials.The main research contents are as follows:（1）Preparation of Cu₇S₄ nanosheet array and its electrochemical performance research:Cu₇S₄ nanosheet arrays were successfully prepared on copper foam substrate by using a rapid in-situ conversion strategy through the interaction of S powder and Na₂S solution,and the energy storage mechanism of Cu₇S₄ in different electrolytes was explored.It has been found that the joint action of S powder and Na₂S on the substrate is a key factor for the success of the Cu₇S₄ nanosheet array.The results show that when saturated Zn（CF₃SO₃）₂ is used as the electrolyte,the electrochemical behavior of Cu₇S₄material during charging and discharging is mainly the removal of zinc ions.At the current density of 1 m A cm^-2,the reversible discharge capacity is 2.23 m Ah cm^-2.At the high current density of 10 m A cm^-2,the capacity can reach 0.169 m Ah cm^-2,and the capacity retention rate is 93.2%after 4000 cycles,which has excellent cycle stability.In 1M KOH electrolyte,the electrochemical behavior of Cu₇S₄ is mainly redox reaction with OH^-in the electrolyte,which also leads to easy dissolution of the material.At the current density of 5 m A cm^-2,the discharge capacity is 3.85 m Ah cm^-2.At the high current density of 50 m A cm^-2,the capacity can reach 0.27 m Ah cm^-2,and there is still 0.168 m Ah cm^-2 considerable capacity after 4700 cycles.（2）Preparation and electrochemical zinc storage mechanism of Cu₇S₄@M-OH（M=Cu,Ni,Co）hierarchical structure:At room temperature,Cu₇S₄ nanosheet array was used as precursor,and was constructed in situ in KOH/and H₂O₂ mixed solution,Ni Cl₂solution and Co Cl₂ solution respectively Cu₇S₄@M-OH hierarchical structure.The research shows that Cu₇S₄@Cu（OH）₂ is mainly due to the removal of zinc ions during the charging and discharging process.The synergistic effect of Cu₇S₄ and Cu（OH）₂ provides a large number of active sites for the removal of zinc ions,which shows excellent zinc storage performance.For example,at a current density of 1 m A cm^-2,Cu₇S₄@Cu（OH）₂reversible discharge capacity is 2.58 m Ah cm^-2,while Cu₇S₄@Ni（OH）₂ and Cu₇S₄@Co（OH）₂ discharge capacity is only 1.61 m Ah cm^-2 and 1.52 m Ah cm^-2.At a high current density of 10 m A cm^-2,Cu₇S₄@Cu（OH）₂ capacity up to 0.213 m Ah cm^-2,which with good rate performance.Besides,the capacity retention rate is 92.5%after 8000 cycles,with excellent cycle stability.