Research On Construction Of Energy Storage System With New Type Chalcogenide Materials And Its Electrochemical Performance

The energy storage device with high energy density and power density is the goal of commercial production.The lithium sulfur battery with high theoretical energy density(2600 Wh kg-1)and lithium-selenium hybrid capacitor that combines the high power density of supercapacitor and the high energy density of sulfur-based materials were studied in this paper.To solve the problems such as poor conductivity,serious shuttle effect and volume effect of sulfur cathode,we designed hollow cobalt sulfide microspheres and constructed TiO2 nanometers on the Ti3C2 surface as host materials for sulfur,which can achieve sulfur fixation to significantly improve the electrochemical performance.For lithium ion capacitors,capacitive cathode materials have relatively lower energy density than anode materials,selenium is doped into the activated carbon as the cathode material to improve the high area capacity and power performance.The research content includes the following three aspects:(1)In chapter 3,the hollow structure CoS/C/CNT materials were prepared by spray drying method.This kind of hollow porous host materials can play a role of physical confinement to provide enough space to buffer volume expansion of sulfur in the process of charging and discharging,and the chemical confinement of CoS can promote the catalytic conversion of polysulfides.The adsorption experiments and density functional theory(DFT)prove CoS has sulfur fixation effect by calculating the adsorption energy of CoS and Li2S6(2)In Chapter 4,We etched the layered Ti3AlC2 with HF solution(wt 20%)to form Ti3C2Tx substance containing-OH and F-groups.NaOH solution was used to remove the F-group from the surface of Ti3C2Tx and then calcined at 600℃ for 1 hour in argon atmosphere.TiO2 nano dots were obtained on the surface of Ti2C3Tx.The formation of sulfur and selenium compounds can make up for the "chemical inertness"of sulfur.At the same time,this proposed strategy of constructing TiO2 on the surface of Ti2C3Tx can be readily extended to promote the chemisorption of lithium polysulfide.The electrode with 80%high sulfur content still has excellent electrochemical performance,and there is no agglomeration of sulfur in the process of charging and discharging.(3)In Chapter 5,In order to achieve high energy and power density in energy storage devices,a new concept of lithium-selenium hybrid capacitor is proposed.Pre-lithiated graphite was used as anode material,and active carbon(AC/Se)composite electrode with a small amount of Se were used as cathode.Lithium-selenium hybrid capacitor not only shows the dissociation/adsorption of anions on the electrode surface,but also exhibits the redox chemical behavior of sulfur which finally obtains stable high capacity,excellent rate performance and good cycle efficiency.