Study On Electrochemical Energy Storage Characteristics Of Sn-based Functional Composites

In recent years,functional composites have attracted widespread attention because of their advantages.In the fields of machinery,electrical appliances,aerospace and other fields,the coexistence of support structure and energy storage device can avoid the complication of equipment due to its mechanical carrying capacity and energy storage capacity.Among them,lithium-ion batteries（LIBs）are the most widely used material in secondary batteries,so it is of great practical significance to improve the lithium storage characteristics of functional composites.Graphite is one of the most popular anode material for LIBs.With the increasing functions of electronic devices,the lower theoretical capacity(372 mAh g^-1)can not meet the current market demand.In contrast,the theoretical capacity of Sn can reach 990 mAh g^-1,which is about 2.67 times that of graphite.The Li_4.4Sn alloy phase formed as a functional anode electrode energy storage material has broad application prospects.However,when Sn is used as energy storage material for functional anode electrodes,huge volume expansion（>360%）will occur during the process of charging and discharging,resulting in irreversible collapse of the structure and rapid decay of the capacity,which ultimately limits the practical application of Sn material.In order to improve the cycling performance of Sn-based anode material,the morphology and composition of the anode material are controlled by adjusting the proportion of drugs and preparation methods.Meanwhile,Sn-based salts,Sn-based porous carbon film oxides and Sn-based carbon cloth composites are introduced to improve the electrochemical properties of the products.In addition,XRD,TEM and other characterization and testing methods are used to analyze the composition and morphology of the sample,and the cycle rate performance of the battery is tested by electrochemical workstation and battery performance tester.The main contents and conclusions of this paper are as follows:1.Preparation of one-dimensional SnC₂O₄ material and study of its battery performance:one-dimensional SnC₂O₄ material is synthesized by one-step stirring at room temperature.By controlling the amount of tin source to adjust the morphology of the sample,the material with different electrochemical structures can be obtained.The special morphology with small radial distance will play an important role in the charging and discharging process,which greatly improves the transmission efficiency of electrons.When the material is applied to the anode electrode material,the capacity of one-dimensional SnC₂O₄ material can maintain above 462 mAh g^-11 after 100 cycles at a current density of0.1 A g^-1.After 230 long cycle cycles,the Coulomb efficiency is 100%,and the capacity can maintain 349.3 mAh g^-1.In addition,SnC₂O₄ material can still obtain the capacity of335.5 mAh g^-11 even at high current density of 2000 mA g^-1,which proves the excellent electrochemical performance.2.Preparation of Sn-based oxide composite with porous structure and study on battery performance:one-dimensional SnC₂O₄ material is used as precursor to synthesize the final product SnO₂@C composite by high temperature annealing and stirring at room temperature.On the one hand,the carbon film on the surface improves the intercalation ability of lithium-ion,on the other hand,it improves the conductivity of the composite and provides buffer space.With the high theoretical capacity of SnO₂(¹492 mAh g^-1),the specific capacity of SnO₂@C composite remains the capacity of 659.4 mAh g^-11 after 100cycles at the current density of 0.1 A g^-11 when the material is used as the anode electrode of LIBs.After 120 cycles,the discharge capacity of SnO₂@C composite could reach 648.7mAh g^-1.At the current density of 2000 mA g^-1,the average discharge capacity is 507.2mAh g^-1.Even under the condition of 500 mA g^-1,the discharge capacity of SnO₂@C composite can still reach 448.3 mAh g^-11 after 500 charge-discharge cycles.3.Preparation of integrated Sn/CC composite and study on battery performance:the Sn/CC composite electrode material based on carbon fiber cloth is prepared by electrochemical deposition.This method has the advantages of simple operation and high efficiency.Compared with the conventional electrode material,the addition of conductive agent and binder is omitted,and the Sn particles are firmly bonded with carbon fiber cloth.As the anode electrode,it has better cycle stability than Sn material and higher capacity than carbon material.After 100 cycles at the current density of 100 mA cm^-2,the discharge capacity can maintain 2.23 mAh cm^-2.What’s more,as anode material for structural lithium-ion batteries（SLIBs）,this value(431.5 mAh g^-1)is almost 3.3 times as high as the capacity of T300 fibers（130 mAh g^-11 at 10 cycles）.The discharge capacity of 1.18 mAh cm^-22 can also be obtained at high current density of 2000 mA cm^-2.