Fabrication Of Transition Metal Sulfide As Electrode Material And Application For Lithium Ion Capacitor

The efficient and versatile energy conversion and storage（ECS）has become a major endeavor of science and technology in recent years.From small portable energy storage equipment to large-scale power storage system,there is an urgent need to develop new energy storage devices with a high energy density,a high-power density and long cycle life.Lithium-ion capacitors（LIC）,with their high energy and power densities,can combine both the advantages of supercapacitors and lithium-ion batteries,which is considered to be one of the most potential energy storage devices.In addition,transition metal sulfides（TMSs）have received extensive attention in energy storage systems due to their many advantages,while research in LIC systems is relatively poor.In this article,for the purpose of constructing high-performance LICs,three different dimensions of single and double TMSs were designed as anode materials for LICs by different methods.We have characterized the morphology and structure of the material,the Li storage performance of the electrode material and the electrochemical performance of the lithium ion capacitor were evaluated and analyzed by electrochemical means.The specific research contents are as follows:（1）A MoS₂ electrode material with a typical two-dimensional layered structure was prepared by using a thermal decomposition system.There are many voids between the layers to provide multiple diffusion channels for Li⁺,which facilitates the rapid insertion and extraction of lithium ions.Electrochemical analysis shows that:this material has considerable Li⁺storage properties.The lithium ion capacitor constructed of this material and activated carbon（AC）has a large voltage window of4 V,a maximum energy density of 79.2 W h/kg and a maximum power density of8000 W/kg,and good cycle performance,the capacity retention rate after 5,000 cycles is 80%.（2）The porous interconnected bimetallic sulfide of CoMoS₄ nanoparticles were prepared by chemical coprecipitation system.The loose porous structure facilitated the transport and diffusion of lithium ions in the electrolyte.Electrochemical study and kinetic analysis showed that:this material with a similar energy storage behavior as pseudocapacitive.can exhibit 391 m Ah/g specific discharge capacity after 500cycles at a current density of 0.1 A/g.In addition,a hierarchical porous structure biochar material（FCS）with a large specific surface area and typical electric double layer energy storage behavior was successfully prepared,and the CoMoS₄//FCS device has a large voltage window of 3.6 V.The highest energy density is 81.7 W h/kg,the maximum power density is 7200 W/kg,with the capacity retention rate is up to95%after 10,000 cycles.（3）A 3D self-assembled hierarchical structure of CoS nanosheets were first synthesized by a simple and efficient hydrothermal system and applied to LICs for the first time.Kinetic analysis and electrochemical studies have shown that:this material has a conversion-type Li⁺storage mechanism dominated by diffusion control behavior,and can exhibit 434 mA h/g specific discharge capacity after 300 cycles at 0.1 A/g.In addition,the CoS//FCS device constructed in combination with the hierarchical porous structure biochar material（FCS）cathode exhibits a large voltage window of3.6 V and has both high-energy and large-power characteristics,when the energy density is 125.2 W h/kg,the device exhibits a power density of 160 W/kg;the device can retain an energy density of 60.8 W h/kg even at a high-power density of 6400W/kg,as well as an extremely excellent cycle life of 81.75%after 40000 cycles at a current density of 1 A/g.