Application Of Molybdenum Disulfide/Carbon Composite In Sodium-ion Batteries

With the widespread use of lithium-ion batteries,lithium resources are in short supply,so sodium-ion batteries have entered the field of vision as a replacement for lithium-ion batteries.Traditional graphite is used as a negative electrode material in sodium ion batteries.Its specific capacity is too low to achieve the expected effect.Therefore,it is very important to find a suitable negative electrode material for sodium ion batteries.Molybdenum disulfide(MoS₂)has a two-dimensional layered structure similar to graphite and a high theoretical specific capacity(669 mAh g^-1).Besides,it is rich in resources and environmentally friendly.However,MoS₂ is poor in conductivity,and MoS₂ has the severe volume expansion caused by the charging and discharging process.These questions affect the rate performance and cycle performance of the battery.Therefore,it is critical to consider the reasonable structural design of MoS₂ and compound it with carbon materials.Then assemble into a sodium ion battery,and test its electrochemical performance.First,a nanofiber material CF@MoS₂@Al₂O₃ with a large layer spacing and a three-dimensional porous structure was designed.MoS₂ was grown on porous carbon fibers with a diameter of 500 nm.The surface was covered with a thin layer of Al₂O₃,which can maintain the stability of the SEI film and prevent MoS₂ from breaking during the charging and discharging process.The internal carbon fiber has a three-dimensional pore structure,which can shorten the ion diffusion path,speed up the reaction,and improve the rate performance and cycle performance of the battery.The large interlayer distance(0.94 nm)of MoS₂ is beneficial to reduce the diffusio n resistance of sodium ions between layers and improve the electrochemical performance of the battery.CF@MoS₂@Al₂O₃ has excellent electrochemical performance.The reversible specific capacity of CF@MoS₂@Al₂O₃ at a current density of 50 mA g^-1 is 443 mAh g^-1,and CF@MoS₂@Al₂O₃ still has a high reversible specific capacity at a large current.The capacity retention rate of CF@MoS₂@Al₂O₃is 83.3%at 500 mA g^-1 after 500 cycles.Then a nano-material FeCo@C@MoS₂ with magnetic and core-shell cubic structure was designed.The inside of the material is magnetic particles FeCo,which can improve the electronic conductivity and ion transport capacity of the material,and can also inhibit the growth of metal dendrites.The core-shell structure can alleviate volume changes during charge and discharge.The middle carbon layer can maintain the stability of the cubic structure,and at the same time can improve the conductivity of the material.These advantages improve the rate performance and cycle performance of the material.FeCo@C@MoS₂ exhibits excellent rate performance and cycle performance.During the first charge and discharge,the reversible specific capacity was 566 mAh g^-1,and the Coulomb efficiency was 76%.The reversible specific capacities at current densitie s of 50 mA g^-1,100 mA g^-1,150mA g^-1,200 mA g^-1and 500 mA g^-1 are 482 mAh g^-1,457 mAh g^-1,441 mAh g^-1,428mAh g^-1 and 380 mAh g^-1.FeCo@C@MoS₂ also has a high reversible specific capacity at high currents.The constant current charge and discharge test was conducted at a current density of 500 mA g^-1.After 500 cycles,the reversible specific capacity of FeCo@C@MoS₂ was 89%.