Preparation And Performance Of MoS₂ Thin Film As Anode For Lithium-ion Batteries

With the rapid development of portable devices and new energy vehicles,the demand for high-performance lithium-ion batteries has been increasing in recent years.The traditional graphite anode material has been unable to meet the market’s demand for high energy density and high power density of power batteries due to the limitation of theoretical capacity.So the research and development of new anode materials with high specific energy density and long cycle stability have become the focus of current lithium ion battery research.MoS₂ has the graphene-like layered structure,high theoretical specific capacity,unique physical and chemical properties,which makes it a great potential for commercial application as the anode material for lithium ion batteries.However,on the one hand,MoS₂ has a large volume change（volume expansion rate of 106%）during the charge/discharge process,which is likely to cause powdering and peeling of the anode material;on the other hand,the lower ion and electronic conductivity of MoS₂ leads to the poor rate performance.For the above-mentioned problems,researchers mainly improve the electrochemical performance of MoS₂ by nanometerizing materials and preparing composite materials.In this paper,pure MoS₂ films and MoS₂-Cu composite films with different Cu content were prepared by RF magnetron sputtering technology.The morphology,structure,composition and electrochemical performance of the MoS₂ films were studied and the main results are as follows:Firstly,the sputtering time was changed to prepare MoS₂ films with different thicknesses.The results show that as the film thickness decreases,the stress of the MoS₂ film produced during the charging/discharging process decreases and the structure stability is more better during cycling,leading to the more superior cycling performance.At the same time,the MoS₂films with S-rich has the more excellent cycle stability.To further study the effect of S-rich on the electrochemical performance of MoS₂ films,a series of S-rich amorphous MoS₂ films were prepared with different targer powers by RF magnetron method.The results show that the elemental S phase exists in the MoS₂ film.During the initial 20 cycling process,the capacity of the MoS₂ films rapidly decays.And at the same time,due to the reaction of the elemental S and Li⁺,the lithium polysulfide formed has a shuttle effect and causes irreversible dissolution.The elemental S is continuously worn out to form a uniformly distributed porous structure in situ.The porous structure not only can effectively relieve the volume expansion of the films during the subsequent cycling process,but also increase the specific surface area of the active material,which are conducive to improving the specific capacity and cycling performance of the films.When the target power is 100 W,the cycling performance of the MoS₂ film electrode is more excellent.The specific discharge capacity of MoS₂ film with target power of 100W is 429.8 mAh·g^-1 after 20 cycling process and the specific discharge capacity remains 413.2 mA·g^-1 after 160 cycling process.The research results of MoS₂-Cu composite films show that the addition of Cu element can not only reduce the volume change of the material during the cycling process,but also improve the conductivity of the MoS₂-Cu composite films.As the Cu content increases,the cycle stability of the MoS₂-Cu composite films increase constantly.In this study,when the Cu content was added to 25.18 at.%,the film shows excellent cycle stability.The first discharge capacity is 860.7 mAh·g^-1,after 300 cycles,the specific capacity of the film was 580.2mAh·g^-1,and the capacity retention rate was 67.4%.The electrochemical impedance spectroscopy（EIS）results show that with the increase of Cu content,the interface contact resistance of the MoS₂-Cu composite films keeps decreasing.When the Cu content was added to 25.18 at.%,the film has the lowest interface contact resistance.And the rate performance of the film is more excellent than pure MoS₂ film.