| Energy storage technology has made a breakthrough in recent decades.Lithium-ion battery(LIB)has many advantages,such as high energy density,good cycle stability and so on.It has been used in many aspects of production and life.However,due to the limited supply of lithium resources,its sustainability is affected,and the rising price of lithium also affects the development of lithium ion technology.In order to alleviate these problems,we need to focus on the study of alternative energy storage systems.Among them,sodium and potassium are rich in mineral resources on earth,and the price is far lower than that of lithium.Sodium-ion battery(SIB)and potassium-ion battery(PIB)have similar properties to lithium-ion battery,and they are expected to be excellent substitutes.However,the large atomic radii of sodium and potassium ions hinder their rapid migration,and the volume expansion during the charge discharge process will also destroy the structure of the material.Therefore,it is of great significance to find stable and efficient cathode materials.Titanium disulfide(Ti S2),as one of the earliest cathode materials for lithium-ion batteries,has the advantages of stable layered structure,good intercalation and detachment performance,high theoretical capacity and strong conductivity.However,when Ti S2 is used as the cathode material of sodium-ion battery or potassium-ion battery,its cycle stability and rate performance are poor.In order to solve this problem,the chemical pre-intercalation method is used to embed K+/Na+into the Ti S2layer,which is used to enhance the structural stress of the material,increase the active sites of K+/Na+during the material cycle,and improve the cycle stability of the battery.The morphology and structure of Ti S2 were optimized by annealing reduction method,which further improved its performance.The specific work is divided into the following two aspects.(1)Preparation and electrochemical properties of KxTi S2 microchips by pre-intercalation method.In this work,a chemical method was used to pre-intercalate potassium ions between the layers of Ti S2 micro plates to form KxTi S2 with hexagonal organ like structure,so as to improve the cycle stability and rate performance of the material.This method expands the interlayer spacing,and improves the diffusion kinetics of potassium ions.The initial reversible specific capacity of 102 m Ah/g was obtained at a current density of 0.05 A/g.after 200 cycles,the capacity was 95 m Ah/g,with high retention.Compared with the original sample,the rate performance is significantly improved,and the specific capacity reaches 46m Ah/g at a high current density of 10 A/g.What is more prominent is that sufficient potassium source makes it possible for KxTi S2 to be used as cathode material.It combined with carbon material to form a full cell with high specific capacity and good cycle stability.The test range of the full cell was 0.01-2.7 V,and the initial discharge capacity was 73 m Ah/g.After 100 cycles,the discharge capacity was 37m Ah/g,which has a high cycle retention rate.(2)Preparation of NaxTi S2 micro or nano materials by pre-intercalation method and their Na storage properties.In this work,NaxTi S2 microchips were prepared and their cycling performance was tested.In order to further improve the properties of NaxTi S2 micro or nano materials,the morphology and structure of the micro sheet were optimized.Ti S3 nanowires were reduced to Ti S2 nanowires by high-temperature annealing,so that they have one-dimensional nanoscale structure,which has large specific surface area and provides more active sites for materials.On this basis,NaxTi S2 nanowires were also formed by chemical pre-intercalation method.The coulomb efficiency is close to 100%and the discharge capacity is 159 m Ah/g after500 cycles.What's more,NaxTi S2 nanowires have excellent rate performance,with a high specific capacity of 116 m Ah/g after 500 cycles at 1 A/g high current. |
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