Preparation Of Three Transition Metal(Mn,Fe And Cu) Compounds And Study Of Their Potassium Storage Properties

With the rapid development of the world,energy has become more and more important in human life.Lithium ion batteries are dominant in the application of energy storage systems such as electric vehicles and grid energy storage because of their high energy density and high cycle stability.However,due to problems of rare lithium resource and uneven distribution,the manufacturing cost of lithium ion batteries has increased year by year.In order to reduce costs and continue to develop battery energy storage systems,sodium ion batteries and potassium ion batteries are gradually being studied by researchers.First,potassium resources and sodium resources are abundant,which is of great significance for reducing the cost of battery energy storage systems.Second,the standard electrode potential of K⁺/K is-2.93 V vs.SHE,which is very close to the standard electrode potential of Li⁺/Li（-3.04 V vs.SHE）,and the standard electrode potential of Na⁺/Na is-2.71 V vs.SHE,which is slightly higher than the standard electrode potential of Li⁺/Li and K⁺/K.Even in some electrolytes,the standard electrode potential of K⁺/K is lower than the standard electrode potential of Li⁺/Li,enabling potassium ion batteries to provide an energy density comparable to or higher than that of lithium ion batteries.Furthermore,for Lewis acidity,the potassium ion has extremely low Lewis acidity,so the solvated ions are smaller and the desolvation energy is also smaller,resulting in faster diffusion of potassium ions.In comparison,potassium ion batteries have unique advantages over sodium/lithium ion batteries.Therefore,the development of potassium ion batteries is an important choice for future energy storage systems.At present,the cathode materials of potassium ion batteries mainly include transition metal oxides,polyanionic compounds,Prussian blue and its analogues,organic compounds,etc.In terms of anode materials,there are mainly transition metal sulfides,organic materials,alloy compounds and so on.Now the reported anode materials for potassium ion batteries are generally of low specific capacity and unstable cycle performance,which can’t meet the practical application.So researchers are prompted to explore anode materials in potassium ion batteries.As we all know,manganese based materials are widely used in many fields because of their simple preparation and low cost,including lithium-ion batteries.At the same time,transition metal chalcogenides have high specific capacity and are widely used as anode in lithium ion batteries and sodium ion batteries.However,there are few reports about the above materials in potassium ion batteries,so studying their application in potassium ion batteries is of great significance to both potassium ion batteries and materials themselves.Based on this idea,a series of new anode materials for potassium ion batteries are synthesized in this paper by simple method,and the electrochemical performances are studied.The main contents of this paper are as follows:（1）Ca₂Mn₂O₅ material with network structure has been synthesized by a two-step calcination method,and has been used as anode in potassium ion batteries.The material shows good electrochemical performance.At the current density of 100 mA g^-1,the discharge specific capacity of the first cycle is 202 mA h g^-1.After 40 cycles,the discharge specific capacity is maintained at 79 mA h g^-1.（2）Cu₂S@C composite with sheet structure has been synthesized directly by a simple method.In this material,the Cu₂S with sheet structure is embedded in the carbon skeleton.The composite is used as anode of potassium ion batteries and its electrochemical performance is tested.The experimental results show that,after 400cycles at high current density of 2000 mA g^-1,the composite shows good cycling performance.The corresponding specific capacity is 206 mA h g^-1,and the decay rate of each cycle is about 0.13%.（3）FeSe@C composite supported by three-dimensional porous open carbon skeleton has been synthesized with environmentally friendly raw materials and applied to the anode system of potassium ion battery.When the current density is 500 mA g^-1 and the voltage window is 0.01-3.0 V,the specific discharge capacity of FeSe@C electrode is298 mA h g^-1 after 200 cycles.At the same time,the possible mechanism of potassium storage and potassium ion diffusion coefficient of the material in potassium ion batteries have also been studied.In summary,in this paper,potassium storage properties of three new anode materials have been studied.The three kinds of anode materials are the first application in potassium ion batteries,and all of them show good electrochemical performance.This paper not only contributes to the research on the anode system of potassium ion batteries,but also lays some foundation for further exploration of related anode materials in the future.