Synthesis Of Electrode Materials For Potassium Ion Batteries And Research Of Their Potassium Storage Performance

With the rapid development of the Society in the 21st Century,more and more demands for energy were increased.The fossil energy,the use of which accompanied by serious environmental pollution,will be exhausted in 100 years.Thus,storage and conversion of intermittent clean energy becomes particularly important.And the large-scale energy storage system is one of the strong candidates to store this kind of clean energy.However,the decrease of lithium resources leads to the rising cost of battery energy storage system.In order to reduce costs,many researchers have turned their attention to other alkaline metals ion batteries,such as sodium ion and potassium ion batteries,which have abundant and inexpensive raw materials.Nowadays,many researchers are trying their best to research and develop sodium ion batteries.However,due to the unique advantages of potassium ion batteries compared with sodium ion batteries,some researchers also have focused their attention on potassium ion batteries.For example,the standard electrode potential of Na⁺/Na?-2.71 V vs.SHE?is higher than that of K⁺/K?-2.93 V vs.SHE?.In addition,in some electrolytes,the standard electrode potential of Li⁺/Li is even higher than that of K⁺/K,which gives the potassium ion batteries an advantage in voltage output.Secondly,since the potassium ion has the weakest Lewis acidity,it can form solvated ions smaller than lithium ion and sodium ion,which makes a better ionic conductivity.Moreover,smaller solvation ions mean lower dissolvation energy,allowing potassium ions to diffuse more rapidly across the electrode and electrolyte interface.At the same time,potassium ion batteries can be inserted and extracted with commercial graphite anodes,but sodium ion batteries cannot.Therefore,it is essential to research and development potassium ion battery.Currently,cathode materials of potassium ion batteries mainly include Prussian blue analogues,polyanion compounds,layered transition metal oxides and organic matter etc.Correspondingly,the anode materials are mainly concentrated in graphite carbon materials,metal alloy compounds,layered materials,conversion anodes and other materials.However,due to the larger ion radius of potassium ion,some problems,like volume expansion occurred,it resulted in unsatisfactory battery performance when potassium ions are electrochemically inserted and extracted in these materials.For this reason,it is significance to develop and design cathode and anode materials for potassium ion batteries with good performance.According to the literatures,Prussian blue analogues have achieved excellent electrochemical performance when used as the cathode electrode materials of lithium ion batteries and sodium ion batteries respectively.In addition,in order to further reduce the cost of electrode materials,this work selection in low-cost and resource-rich iron and titanium are used as metal ions of Prussian blue analogues and the potassium storage properties of the iron-titanium-based Prussian blue analogs have been studied.In addition,in order to improve the capacity of the anode material for potassium ion batteries,we selected the iron-based sulfide with low cost and high theoretical capacity as the anode material for potassium ion batteries.Finally,due to the special structure of the layered material,stable lattice,and special physical and chemical properties,it has attracted the research interest of many researchers.In this paper,a layered selenide was synthesized and its sodium storage and potassium storage properties were studied.On the basis of reviewing the latest research progress of potassium ion batteries,some innovative potassium ion batteries electrode materials have been prepared in this paper.It improves the current situation of the shortage in electrode materials of potassium ion batteries and provides a new idea for the development of electrode materials for potassium ion batteries with good performance.Moreover,the morphology,structure and properties of the synthesized materials were characterized in this paper,and the effects of material structure on their properties and the electrochemical reaction mechanism were analyzed.The specific works are as follows:1.The cubic iron-titanium-based Prussian blue analogues (K_0.3Ti_0.75Fe_0.25[Fe?CN?₆]_0.95·2.8H₂O) were synthesized by co-precipitation method for the first time and used as cathode materials for potassium ion batteries.Their electrochemical performance was tested and excellent electrochemical performance was obtained.It shows a specific capacity of 136 mAh g^-1 at the voltage range of 1-4.5V at50 mA g^-1.The addition of titanium expands the voltage window of the material and increases the mass energy density of the material.2.The FeS₂@C nanoparticle cubes were prepared by a series of treatments on the Prussian blue precursor and used as an anode electrode material for potassium ion batteries.It possesses an excellent electrochemical performance due to the carbon layer externally coated on the material and the smaller nano-size of iron disulfide in the internal cavity.The FeS₂@C nanoparticles inside the cube facilitate the migration of potassium ions and shorten the migration path of ions;the internal loosely distributed nanoparticles and the externally coated carbon layer can buffer volume expansion and stabilize the material structure during electrode cycling.Finally,the outer surface coated carbon and the inner particle coated carbon can increase the conductivity of the material.3.NbSe₂,a micron layered selenide,was synthesized by ball milling method and applied to the anode materials of potassium ion and sodium ion batteries for the first time.Next,the electrochemical reaction process in sodium ion batteries was further explored by using ex-situ XRD.In summary,we synthesized three materials through different synthetic methods.This work enriches the electrode materials of potassium ion batteries,improves the current situation of the lack of electrode materials for potassium ion batteries,and provides a new idea and direction for the development of potassium ion battery electrode materials.