Study On Controlled Synthesis And Electrochemical Performance Of Tin-Based Nanomaterials

With the increase of energy consumption and the gradual deterioration of human living environment,the current social demand for new clean energy is increasing.As one of the most efficient and clean energy storage systems,lithium ion battery is the most widely used secondary battery with the largest market share.Compared with other batteries,lithium ion battery has the advantages of high energy density,large rated voltage,no memory effect and low self-discharge rate,and is the most potential energy supply equipment for electric vehicles and hybrid electric vehicles that have attracted much attention.However,in order to meet the current requirements of power and mileage of electric vehicles,it is necessary to research and develop electrode materials with larger capacity and better rate performance.In addition,due to the increasing market demand for lithium ion batteries,the scarcity of global lithium resources gradually begins to emerge.To solve this problem,the development of new,cheap and resource-rich alternative battery systems is also one of the most urgent tasks.Tin is one of the key anode materials for lithium ion batteries.Its theoretical capacity is up to 994 m A h g^-1,about three times that of graphite.In addition,tin-based materials can be used as anode materials for sodium ion batteries and potassium ion batteries.For them,the large volume change during charging and discharging process is the main problem.During cycling processes,the pulverization and detachment of the electrode materials will easily lead to the failure of the whole battery.This seriously restricts the popularization,application and industrialization of tin-based electrode materials in alkaline ion secondary batteries.Studies have shown that controlling the structure and composition of tin-based materials can effectively improve their electrochemical properties.In this paper,on the one hand,we synthesized a series of tin-based nanomaterials with controllable size and structure by a simple colloidal synthesis method,and studied the influence of nano-size and hollow/core-shell structure on the performance of tin-based materials in lithium/sodium ion batteries.On the other hand,we also prepared a variety of high-capacity tin phosphide-carbon composite materials by combining a variety of methods,and used them as new type of anode materials for potassium ion batteries,showing excellent electrochemical potassium storage performance.At the same time,we also studied the phase transformation and morphological evolution during charging and discharging,and further explained the reaction mechanism of electrochemical potassium storage,which is of great significance for promoting the development of metal phosphide based anode materials for potassium ion batteries.We first prepared Sn nanoparticles and amorphous SnO_x nanoparticles by a colloidal method.As the anode material of lithium ion battery,Sn nanoparticle electrode has reversible capacities of 471.8 m A h g^-1 and 416.4 m A h g^-1 after 300 and 400 cycles,respectively,when the current density is 200 m A g^-1 and 500 m A g^-1.Similarly,the SnO_x hollow nanospheres maintain a high capacity retention of 81.3%for 400 cycles at a current density of 500 m A g^-1and exhibit excellent rate performance.We believe that these excellent electrochemical properties are mainly due to the small size of nanoparticles and the formation of Li₂O matrix on the particle surface,which are benefical to regulate the mechanical stress of the active material and prevent Sn agglomeration.In addition,the hollow and amorphous structure of SnO_x hollow nanospheres can also adjust the volume change of the electrode material and shorten the diffusion distance of lithium ions.On the basis of our previous work,we prepared monodisperse SnSe nanoparticles with unique yolk-shell structure using tin nanocrystals as template by a colloidal method,and studied their electrochemical properties as negative electrode materials for sodium ion batteries.The results showed that the prepared SnSe electrode had good sodium-storage performance,and could show an initial discharge capacity of 355.8 m A h g^-1 at the current density of 500 m A g^-1,and still maintain 72.5%of initial capacity after 150 cycles.In addition,the prepared SnSe electrode also has excellent rate performance.Notably,we determined that capacitive contribution is dominant when SnSe nanoparticles were used as the negative electrode for sodium ion batteries,which is also the main reason for their superior rate performance.Tin phosphite is a promising anode material for potassium ion batteries because it has higher theoretical capacity,better conductivity and lower volume expansion rate than phosphorus.Here,we developed a simple colloidal method to prepare hexagonal SnP_0.94nanoplates.Then,graphene oxide(GO)-coated SnP_0.94@GO composite was prepared by a chitosan-assisted method.Due to the high theoretical capacity of SnP_0.94 and the important role of GO nanosheets in buffering volume change,accelerating charge transfer and reducing the contact between electrode materials and electrolytes,SnP_0.94@GO composite material has shown excellent electrochemical potassium storage performance compared with the single SnP_0.94 nanoplates.These results can be used for reference in the future research on the high-capacity metal phosphide based anode of potassium ion batteries.As an anode material of potassium ion battery,phosphorus has a theoretical capacity as high as 2594 m A h g^-1.Therefore,for tin phosphide,higher phosphorus content means higher theoretical capacity.A series of more phosphorus-rich SnP₃/C composites were prepared by a ball milling method,and their electrochemical potassium storage properties as new anode materials for potassium ion batteries were studied.The results show that the electrochemical reversibility and cyclic stability of SnP₃ can be greatly improved by combining SnP₃ with high theoretical capacity and carbon materials with excellent electrical conductivity.When used as the anode material of potassium ion battery,SnP₃/C-20%electrode can show a reversible capacity of 337 m A h g^-1 after 100 cycles at the current density of 500 m A g^-1.Even at the current density of 1000 m A g^-1 for 150 cycles,SnP₃/C-20%electrode can still provide a reversible capacity of 190 m A h g^-1,corresponding to an initial Coulombic efficiency greater than 70%and a capacity retention of 88%.Compared with the current literature reports,the SnP₃/C composite prepared by us shows better electrochemical potassium storage performance.