The Construction Of Carbon-Based Transition Metal Chalcogenides And Their Sodium Storage Properties

In order to meet the growing demand for energy storage and conversion,it is urgent to improve the energy density and power density of electrochemical energy storage devices in nowsdays society.Sodium ion hybrid capacitors（SICs）have attracted considerable attentions due to their high-energy density of batteries and high-power output of supercapacitors.However,the slow Na⁺diffusion kinetics greatly hinder the high-performance output of the SICs.Carbon materials are very promising anode materials accompanied with excellent electronic conductivity,high chemical stability,as well as cost-efficient property.Designing the hierarchical structure of porous carbon can optimize the Na⁺transport procedure to achieve its good rate performance.Besides,on account of the low capacity carbon materials,porous carbon can also be used as a carrier material to anchor transmition metal compositions.The anodes with high capacity and stability can be obtained by using the high capacity of transmition metal compositions and the stability of carbon material.But in terms of the current research technology,the synthetic methods of porous carbon and carbon-based transmition metal composites are complicated,and it is difficult to construct the high-stability carbon-based transmition metal composites.Therefore,based on the above questions of porous carbon and carbon-based metal composites electrodes,the purpose of this article is to fabricate the high-performance carbon-based transmition metal chalcogenides composites by the simple,low-cost and sustainability methods,and study the electrode performance and sodium ion storage mechanism of these anode materials by the electrochemical analysis,in-situ structure characterization and DFT theory.The specific research results are as follows:（1）A gas expansion and chemical etching method is proposed to prepare 3D nitrogen and sulfur co-doped porous carbon nanosheet（PCNS）using the low-cost soybean protein was used as the precursor because it contains abundant peptide bonds（–CO–NH–）and disulfide bonds（–S–S–）.The obtained PCNS exhibits a regular 3D interconnected framework with a large specific surface area.Meanwhile,the N and S atoms can offer more electrochemical active sites and improve the electronic conductivity,promoting the diffusion and adsorption of Na⁺.As an anode material of SIBs,the PCNS shows an outstanding rate capability with a high reversible capacity of 205 m Ah g^-1 at 0.5 A g^-1,and delivers a specific capacity of 96 m Ah g^-1 at 20 A g^-1.Besides,it possesses an excellent cycle performance of 180 m Ah g^-1 at 7 A g^-1 after 10000 cycles with no decay.A dual-carbon SIC（PCNS//HPC）is assembled by battery-type anode material（PCNS）and capacitive-type cathode material（HPC）.This device exhibits high energy densities of 119 Wh kg^-1 and 53 Wh kg^-1 at power densities of 200 W kg^-1 and 20 k W kg^-1,respectively.Besides,it possesses a superior cycle life of 82%capacity retention after 8000cycles.Moreover,this work provides a new idea for the synthesis of porous carbon materials as high-performance SICs anode materials.（2）The 2D few-layer Mo Se₂ embedded in nitrogen-doped carbon sheets（Mo Se₂@NCS）anode electrodes were prepared by a sacrificial template approach.Specifically,graphitic carbon nitride was carried as the sacrificial template to prepare the Mo₂C@NCS composite.Then 2D nanosheets structure Mo Se₂@NCS composites were gained by the subsequent selenizaiton procedure at high temperature,which avoid the agglomeration of Mo Se₂.Besides,the density functional theory（DFT）calculations were performed to construct the atomic structure model,which simulate the Na adsorption and transport paths in this model.The results showed that the Mo Se₂@NCS exhibits the fast Na⁺diffusion rate,high electronic conductivity,and low volume variation.Consequently,the Mo Se₂@NCS shows the good rate performance,which delivers a high specific capacity of 398.9 m Ah g^-1 at 0.1 A g^-1,and still maintains a specific capacity of 229 m Ah g^-1 at 5 A g^-1.Meanwhile,it has an outstanding long cyclic stability with high capacity of 225.2 m Ah g^-1 is maintained after 1000 cycles at 1 A g^-1.By matching with activated carbon（AC）,the as-assembled Mo Se₂@NCS//AC SIC is exhibits the high energy densities of 122.8 Wh kg^-1 and 65.3 Wh kg^-1at the power densities of 105 W kg^-1and 10500 W kg^-1 and the splendid cyclic performance.（3）A dual-carbon protected Zn Se-based anode material（Zn Se@NC/r GO）was prepared vai a two-step carbonization method at inert gas.Firstly,Zn Se@NC was obtained by the selenization of ZIF-8,and wrapped with graphene sheets in subsequent sintering.The researches showed that nitrogen-doped carbon（NC）can restrain the volume variation to relieve the pulverization of Zn Se.Meanwhile,the r GO can facilitate the ion transport and enhance electrical conductivity.Therefore,the Zn Se@NC/r GO anode shows nice rate capability.It delivers a high specific capacity of 455.3 m Ah g^-1 at 0.1 A g^-1,and a superior rate capability of195.1 m Ah g^-1 at 5 A g^-1.Besides,it exhibits a high capacity of 170.1 m Ah g^-1 after 500 cycles at 5 A g^-1,indicating its outstanding long cyclic stability.By matching with AC cathode,an as-assembled Zn Se@NC/r GO//AC SIC delivers a high energy density of 117.8 Wh kg^-1 at 105 W kg^-1,and a long lifespan of 86.4%capacity retention after 3000 cycles.（4）A general approach was designed to fabricate a series carbon-supported Co-based chalcogenide compounds nanostructured anode materials.Firstly,Co nanoparticles embedded in nitrogen-doped carbon frameworks（Co@NC）were obtained by a carbonization reduction process using the ZIF-67 as a precursor.Then,different kinds of carbon-supported Co-based chalcogenide compounds composites were synthesized through graphene encapsulation and subsequent processes of sulfidation,selenization,and tellurization（Co X₂@NC/r GO,X=S、Se、Te）.The researches showed that the hierarchical hybrid nanoarchitecture can increase sodium storage active sites and shorten electron/ion diffusion rates,and the carbon substrate in the composite material can also increase the electronic conductivity of the material.The sodium ion storage performance and mechanism of a series of anode materials were investigated in this article,the Co S₂@NC/r GO exhibits more superior rate performance and cycling performance.Co S₂@NC/r GO shows a high specific capacity of 140.4 m Ah g^-1 at a current density of 5 A g^-1.It can also deliver a high capacity of 264.3 m Ah g^-1 over 200 cycles at a current density of 0.2A g^-1.The Co S₂@NC/r GO//AC SIC device displays the high energy densities of 114.7 Wh kg^-1and 64.2 Wh kg^-1 at the power densities of 105 W kg^-1 and 4200 W kg^-1,respectively.Meanwhile,it outputs a good long cyclic performance(capacity retention of 72%at 1 A g^-1after 1500 cycles).