Preparation Of Metal Sulfides Confined In Porous Carbon As Anodes For Lithium/Sodium Ion Storage

Lithium ion battery is widely used in electric vehicles and portable equipment owning to its advantages of high energy density and long cycle life.However,when as the anode material of lithium ion battery,graphite electrode has low capacity,which cannot meet the increasing demand and limit the large-scale application of lithium ion battery.Therefore,it is particularly important to develop new electrode materials with excellent electrochemical properties.In addition,lithium resources in the earth's crust are limited and expensive,which greatly limits its application in large-scale energy storage systems.In view of this,sodium ion batteries with abundant reserves of sodium resources in the earth's crust and similar energy storage mechanism are considered as an important supplement to lithium ion batteries and have a great development prospect.However,due to the large radius of sodium ions and poor reaction kinetics,there are few electrode materials suitable for the stable extraction and embedding of sodium ions.Therefore,the development of high-capacity electrode materials capable of rapidly and stably storing lithium/sodium is a problem to be solved urgently now.Transition metal sulfides?such as FeS,CoS,MoS₂,etc.?have higher theoretical capacity,weaker metal-sulfur bonds,and suitable redox potentials.They have attracted much attention as anode materials for lithium/sodium ion batteries.However,metal sulfides have poor electrical conductivity,large volume changes and slow diffusion rates during the ion extraction/intercalation process,causing rapid capacity decay and poor rate performance,which severely restricts their use in the field of electrochemical energy storage.To deal with the problem of transition metal sulfide,this paper prepared transition metal sulfide and carbon composite materials.Using carbon materials to limit the size of sulfide,and improve its electrical conductivity.The nanostructure suitable for lithium/sodium ion transport can effectively shorten the ion/electron diffusion distance,make the active material and electrolyte fully contact,thus accelerating the reaction kinetics,and obtain the anode material of lithium/sodium ion battery with excellent performance.The main research contents are as follows:1.FeS/porous carbon nanosheets composite material was prepared through metal salt-assisted high-temperature carbonization and sulfurization processes.FeS nanoparticles are evenly distributed on the surface of carbon nanosheets,which is beneficial to shorten the ion/electron diffusion distance,and accelerating the electrochemical reaction rate.At the same time,the structure of carbon-coated FeS nanoparticles can effectively buffer the volume expansion of FeS particles during charging/discharging.When investigated as an anode for lithium ion batteries,the as-prepared FeS@PCSs electrode exhibits a high reversible capacity(1026.2 mAh g^-1 at 0.1A g^-1),and excellent rate capability(561.1 mAh g^-1 at 10 A g^-1).2.When the Co?OH?₂ as precursor and sodium citrate as carbon source,CoS_x@porous carbon nanosheets material was prepared.Sodium citrate is carbonized into porous carbon nanosheets,and Co?OH?₂ sheets are transformed into nanoparticles through a simple carbonization and vulcanization process,which are uniformly dispersed on the surface of the carbon nanosheets.In this process,the strong interaction between the nanoparticles and the carbon material is achieved.Thereby,it would achieve the purpose of limiting the range of movement of the nanoparticles.Finally,nano-structured cobalt sulfide composite is prepared through a vulcanization process.When used as anode electrode material for lithium-ion batteries,CoS_x@porous carbon nanosheets material possesses a high reversible specific capacity of 1243.3 mAh g^-1 after 110 cycles at a current density of 0.1 A g^-1,and exhibiting good rate performance and excellent cyclic stable performance.3.3D porous carbon structure was prepared using trisodium citrate as a raw material.CoS/porous carbon nanosheets composite was prepared by using a carbon material and Co?OH?₂ nanosheets as precursors through a hydrothermal method and a sulfurization process.Furthermore,a double carbon-coated CoS composite material was prepared.by in-situ polymerization of polydopamine and a secondary vulcanization process.After a series of processes,CoS nanoparticles are evenly distributed on the surface of the three-dimensional porous carbon,and the surface is coated with a layer of amorphous carbon.The three-dimensional network structure effectively relieves the mechanical stress and improves electron transmission.The structure of carbon-coated nanoparticles effectively shortens the diffusion path of sodium ions and eases volume changes.When used as anode electrode material,it can still maintain a reversible capacity of 322.8 mAh g^-1 after 100cycles at current density of 0.1 A g^-1.