Carbon And Cobalt-based Bimetallic Selenides Composite As Anode Material With High Lithium/sodium Storage Performance

Due to the increasing energy shortage and environment problems,the enthusiasm to find efficient,green and environment-friendly energy storage equipment has been inspired.Recently,lithium ion batteries（LIBs）with high energy density and long cycle life have been widely used in electronic equipment,vehicle and chemical energy storage equipment.In addition,sodium ion batteries（SIBs）have attracted wide attention because of its similar charging and discharging mechanism with lithium ion batteries,abundant sodium resources,low cost,low self-discharge rate and environmental protection.However,on the one hand,as the anode material for LIBs,the specific capacity of traditional graphite is low.On the other hand,because the radius and relative mass of sodium ion are larger than that of lithium ion,the materials suitable for LIBs are not necessarily suitable for SIBs.Therefore,development of high performance anode materials for LIBs/SIBs has important scientific and application value.Metal selenides are promising materials for LIBs/SIBs due to their high theoretical capacity and week metal-selenium bond.Compared with single metal selenide,bimetallic selenide possess bimetallic synergistic effect and more redox active sites,which is more conductive to improve the lithium/sodium ion storage performance.However,the bimetallic selenides still suffer from the poor cycle stability due to the large volume expansion during the charge discharge process.In order to solve the above problems,the strategy of the nano structure control and carbon composite have been combined to alleviate the large volume expansive of the bimetallic selenides,which can improve the lithium/sodium ion storage performance.The main research contents and results are as follows:（1）CoSe₂-MoSe₂hollow microspheres are successfully synthesized by hydrothermal selenidation of the Co Mo-glycerate spheres.Then,the CoSe₂-MoSe₂@C is prepared successfully by adding the dopamine hydrochloride to carbon coated.Hollow structure and carbon coating can effectively alleviate the volume expansion,and the addition of carbon improves the conductivity of electrode materials.As the anode materials of LIBs/SIBs,the CoSe₂-MoSe₂@C delivers high specific capacity as well as excellent rate and cycle performance.When CoSe₂-MoSe₂@C is used as anode of LIBs,its specific capacity remains 1067.2 m Ah g^-1at the current density of 0.1 A g^-1after 100 cycles.Moreover,the discharge capacity of CoSe₂-MoSe₂@C manifests 1059.5 m Ah g^-1under the current density of 1A g^-1after 200 cycles.When the it is applied for SIBs,the reversible capacity of CoSe₂-MoSe₂@C is 337.7 m Ah g^-1at 5 A g^-1.Furthermore,the cyclic voltammetry is tested to analyze the lithium/sodium ion storage mechanism and reaction kinetics of CoSe₂-MoSe₂@C,the results show that the good pseudocapacitance contribution and reaction kinetics can improve the rate performance of the batteries.（2）The r GO/SnSe₂-CoSe₂composites are successfully prepared by physical mixing and high temperature selenidation with CoSn-glycerate spheres and graphene oxide as precursor.The structure of r GO/SnSe₂-CoSe₂not only possesses a large specific surface area,making it fully contact with the electrolyte and accelerating the transportation of sodium ion,but also can improve the conductivity of electrode materials and alleviates the volume expansion during the charge-discharge process.As the anode material of SIBs,the r GO/SnSe₂-CoSe₂delivers the initial capacity of 806.7m Ah g^-1at 0.1 A g^-1and the remained capacity of 919.8 m Ah g^-1after 100 cycles.In addition,the reversible capacity of r GO/SnSe₂-CoSe₂remains 395 m Ah g^-1after 600cycles under the current density of 1 A g^-1.The preliminary results show that r GO/SnSe₂-CoSe₂is a potential sodium-ion electrochemical energy storage material.