Structure Optimization Design And Properties Study Of High Energy Tin Based Composite Films

In recent years,with the widespread use of new energy vehicles and portable electronic devices,there is an increasing demand for lithium-ion batteries（LIBs）in terms of energy density and cycle life.However,graphite,as a traditional anode material,has limited room for improvement,which severely limits the development of new Li-ion batteries.Tin-based materials have become one of the new candidate materials with the advantages of high theoretical specific capacity of 994 m Ah/g,first discharge potential and lower price.However,tin itself has a large volume change,and the process of lithium removal/embedding suffers from irreversible lithium consumption and particle coarsening,which in turn affects the battery performance.Therefore,the search for methods to alleviate the volume expansion and improve the conductivity of tin-based materials has become a hot research topic.To address the above issues,this paper firstly applies Materials Studio（MS）software to construct a structural model of tin,and then based on this,doping specific atoms/molecules into tin to construct a new modified material model.The optimal solution is calculated by using the first nature principle and spin density generalized function theory（DFT）.Meanwhile,the tin-based composite films are prepared and verified and analyzed under the guidance of simulation results.The main research work in this paper is as follows:（1）Coral-like pure Sn films were prepared by magnetron sputtering using a pure Sn target as the sputtering source and adjusting the parameters of sputtering temperature,power and time,and the XRD structural characterization and constant-current charge-discharge cycle performance tests were performed to derive the optimal process parameters for the synthesis of pure Sn films.The pure Sn films prepared according to the optimal process parameters had a first discharge specific capacity of 951.2 m Ah/g at a multiplicity of 99.4 m A/g with multiple charge/discharge plateaus.（2）The introduction of nitrogen atoms is used to inhibit the irreversible reaction of tin in the process of lithium removal/embedding and to reduce the number of its charging and discharging platforms.Firstly,the structural models of tin doped with different amounts of nitrogen atoms are constructed on the basis of the pure tin structure.Then the energy bands and density of states are calculated to analyze the effects of the introduction of different amounts of nitrogen atoms on the tin structure.Guided by the results of this simulation,tin nitride（Sn N）thin films were prepared by magnetron sputtering in a mixed atmosphere of argon and nitrogen using a tin target as the sputtering source.The analysis of its properties revealed that the introduction of N improved the specific capacity of the material to a certain extent,and the discharge specific capacity of the Sn N film was 1100.6 m Ah/g after 50charge/discharge tests at 0.1 C,while exhibiting excellent multiplicative performance.（3）The electrical conductivity of the material was improved by introducing manganese dioxide（Mn O₂）molecules into the tin material.The structural model of tin-manganese dioxide（Sn-Mn O₂）was first constructed on the basis of the pure tin structure,and then the energy band and density of states were calculated.After adding Mn O₂,the density near the Fermi energy level increases significantly,indicating an improved conductivity.Guided by this simulation result,tin-manganese oxide composite（Sn-Mn O₂）films were prepared by magnetron sputtering using a tin target and a manganese dioxide powder target as sputtering sources.The successful doping of Mn O₂ enhanced the diffusion and transport rate of lithium ions in the tin-based films and improved the electrical conductivity and cycling stability of the Sn-Mn O₂ composite films.At a multiplicity of 1 C,the Sn-Mn O₂ composite film exhibits a high discharge specific capacity（1502.8 m Ah/g）and can be stably cycled for 150 cycles.