Preparation Of Tin-based Anode Materials And The Properties In Sodium Ion Batteries

Lithium ion battery has become the most widely used rechargeable battery in the world owing to its high energy density and excellent rate performance.Nowadays,more and more electronic devices in people’s daily life need to be driven by lithium-ion battery.At the same time,with the improvement of social requirements for environmental protection,more and more vehicle s have been driven by electricity instead of traditional fossil energy,that has led to a rapid rise in the demand for lithium resources.As the mining cost of lithium salt is tens of times higher than that of sodium salt,sodium ion battery as a potential low-cost substitute for lithium-ion battery has gradually attracted people’s attention.Tin is one of the most promising anode materials for sodium ion battery,the specific sodium storage capacity of tin can reach to 847 m Ah/g,which is more than twice of graphite in most commercial lithium-ion battery anode materials,its price is relatively low,non-flammable and non-toxic,not harm the environment,and is relatively safe.However,the tin-based material will produce more than 400%volume expansion in the process of charge and discharge,which will lead to the pulverization of the electrode material and the loss of contact with the current collector,thus affecting the cycle performance of the material.In order to solve this problem,this paper explores the preparation methods and corresponding electrochemical properties of two kinds of tin compound carbon-coated materials.A two-step hydrothermal method for the preparation of carbon-coated tin dioxide（SnO₂@C）and its performance as anode materials for sodium ion batteries were investigated.The results show that the synthesized material has complete and uniform spherical morphology,the particle size is distributed from hundreds of nanometers to several micrometers,the materials has good cycle performance and rate performance.the specific capacity of the first charge and discharge is 603.39m Ah/g and 412.39 m Ah/g,respectively,and the initial coulombic efficiency of the first charge and discharge is 68.34%.After 100 cycles and 200 cycles,the coulombic efficiency of the first charge and discharge is 68.34%.The discharge capacity can be maintained at 272.19 m Ah/g and 248.01 m Ah/g,respectively,and the capacity retention rate is 66%and 60.14%,respectively.When the discharge current is 2 A/g,the capacity of the material is 136.15m Ah/g.At the same time,the electrochemical properties of SnO₂@C materials in several different ether electrolytes were investigated.It was found that the electrochemical behavior of the materials in ether electrolytes was different from that of esters.The compositions of SEI on different electrolyte surfaces are obviously different.In DME solution of 1 mol/L Na OTf,the first charge-discharge specific capacity of the materials was 527.25 m Ah/g and439.67 m Ah/g,respectively,and the first coulombic efficiency was 76.83%,which was significantly higher than that of carbonate electrolytes.A tin phosphide Sn₄P₃ was prepared by solvothermal method,the effect of carbon coating content on the performance of the battery was also investigated.It is found that with the increase of carbon coating content,the cycle stability of the material is greatly improved,and the initial coulombic efficiency of the material decreases correspondingly.The capacity retention of the uncoated grou p after 100charge-discharge cycles is only less than 10%.When the ratio of carbon source increased to 40%,the first and 100th discharge specific capacity of Sn₄P₃@C materials are 274.35 m Ah/g and 180.81 m Ah/g,respectively,the capacity retention rate is 65.90%.In addition,a matrix material with composite phase,Sn₄P₃/Sn@C,prepared by a solid phase phosphating method,which has a great improvement in charge-discharge capacity,cyclic stability and rate performance.Compared with Sn₄P₃@C,the first discharge capacity increased to 470.26 m Ah/g after 100 cycles,the capacity remained at 380.60 m Ah/g,and the capacity retention was 83.6%.At the same time,the discharge capacity of the material is about 120 m Ah/g under the current density of 5 A/g.The good electrochemical properties of the materials can be attributed to the mixture of Sn and Sn P_0.94 in the matrix Sn₄P₃ phase,which improve the conductivity and Na ion diffusion rate.