Study On Preparation And Modification Of Tin-Based Thin Film Anode Materials For Lithium Ion Batteries

Tin anode materials for lithium ion batteries have the advantages of good conductivity,high theoretical specific capacity（992 m Ah/g）,and suitable operating voltage（0.3-0.6 V）,making them ideal materials to replace graphite anode materials.However,during the charging and discharging process,the tin anode material will expand in volume,causing large stress,leading to particle pulverization,damaging structural stability and mechanical integrity,and rapidly reducing the electrode capacity.Aiming at the problem of poor cycle stability of tin negative electrodes,this topic has made relevant research and obtained the following results:1.Pure Sn thin film electrodes were prepared by magnetron sputtering method,and their initial discharge capacity was 952 m Ah/g at a current density of 200 m A/g.After 50 cycles,the capacity retention rate was only3%.Tin copper alloy targets were prepared by arc melting method,and tin copper alloy thin film electrodes were obtained by magnetron sputtering method.At the same time,a group of samples were prepared using Sn-Cu（70:30）alloy targets with increasing sputtering power of 20 W,40 W,60W,80 W,110 W,etc.The effect of magnetron sputtering power on thin film electrodes was investigated.The experimental results show that with the increase of sputtering power,the crystallinity and crystal integrity of the film are improved,the particle size of the film increases,and the spacing between particles decreases,becoming more dense.When the sputtering power is too low,the capacity of the electrode is very small.As the power is increased,the capacity of the electrode can be improved,but the cyclic stability of the electrode is not significantly improved.Among them,the Sn-Cu（70:30）alloy thin film electrode obtained by sputtering at60 W power for 10 minutes has a first discharge capacity of 449 m Ah/g at a current density of 200 m A/g,and a capacity retention rate of 16%after70 cycles.2.Sn-Cu（60:40）and Sn-Cu（50:50）targets with higher copper content were prepared by arc melting method.Then,tin copper alloy thin film electrodes were deposited for 10 minutes using magnetron sputtering method at different sputtering powers,and the effect of tin copper alloy ratio on the thin film electrode was investigated.The experimental results show that with the increase of copper content,the main phase components in the film change from Cu₆Sn₅ to Cu₃Sn,while the specific capacity of the electrode decreases and the cycling stability improves.Among them,the initial discharge capacity of Sn-Cu（60:40）alloy thin film electrode obtained by sputtering at 60 W power for 10 minutes is 731 m Ah/g,and the capacity retention rate reaches 50%after 70 cycles.Sn-Cu（50:50）alloy thin film electrodes were deposited at a power of 60 W for 10 minutes,with a first discharge capacity of 439 m Ah/g and a capacity retention rate of 22%after 200 cycles.3.Using magnetron sputtering method,different target materials were sputtered in two steps to obtain multi-layer thin film electrodes.After depositing a pure Sn film at a power of 40 W for 5 minutes,a multi-layer thin film electrode was obtained by sputtering a Sn-Cu（50:50）alloy target at a power of 60 W for 10 minutes.The initial discharge capacity was 621m Ah/g,and after 70 cycles,it retained 29%of the capacity.After preparing Sn-Fe（70:30）alloy targets using the same method,thin film electrodes were deposited at 30 W power for 10 minutes,with a first discharge capacity of 411 m Ah/g and a capacity retention of 55%after 70 cycles.After depositing a pure Sn thin film layer on top of it,the first discharge capacity of the multi-layer thin film electrode obtained was 690 m Ah/g,and the capacity retention rate also reached 54%after 70 cycles.