Preparation And Electrochemical Performance Of Cobalt Selenide Composites For Cathode Catalysis Of Lithium-Sulfur Battery

Lithium-sulfur battery stands out among many energy storage devices and is expected to replace lithium-ion battery because of its high energy density,green environmental protection and low price.However,the large-scale application of lithium-sulfur battery still faces some severe challenges.Generally speaking,there are three main points:During the operation of the battery,the slow sulfur conversion kinetics results in the dissolution of a large number of polysulfides,which leads to serious shuttle effect,resulting in capacity attenuation and low Coulomb efficiency;The volume changes greatly after sulfur is completely converted to Li2S;The low conductivity of S/LiPS/Li2S results in poor electronic conductivity.In order to overcome the above problems,researchers are committed to extensive and in-depth research on the cathode structure design of sulfur-based materials.Various forms of carbon materials are used as skeletons for physical sulfur fixation,while increasing the electrical conductivity of sulfur.;Adding polar materials for chemisorption and sulfur fixation of lithium polysulfide;The catalytic material of lithium-sulfur battery was added to accelerate the kinetics of redox reaction.Combined with the existing related reports,this paper focuses on the catalytic material of CoSe2 lithium-sulfur battery,because as a transition metal selenide semiconductor,it is rich in reserves and simple in chemical synthesis.In this paper,CoSe2/CNT were designed and used as cathode catalytic materials for lithium-sulfur batteries to study their effects on the electrochemical performance of sulfur.A layer of Co3O4 nanoparticles was grown on carboxylated carbon nanotubes by a simple solvothermal method,and the effect of Co3O4(the precursor for the preparation of CoSe2)on the electrochemical performance of lithium-sulfur batteries was studied.A layer of Co3O4 nanoparticles was grown on carboxylated carbon nanotubes by a simple solvothermal method.A kind of Co3O4 modified CNT material(COCNT)was designed to add the cathode of lithium-sulfur battery.Polar oxide Co3O4 particles inhibit the dissolution and shuttle of lithium polysulfide by chemical adsorption to achieve sulfur immobilization.However,because of its low conductivity,the effect of Co3O4 content in COCNT on the performance of cathode was investigated.Too much Co3O4 will decrease the electron transport rate and slow down the redox kinetics,but too little will not work.Finally,the battery prepared with COCNT-10 sample has the best electrochemical performance,and its performance is much better than that of pure CNT sample.The specific capacity of 0.2 C is 821 mAh g-1,and the specific capacity retention of 0.5 C after 200 cycles is 81.7%.On the basis of the above research,using three samples with different Co3O4 content as precursors,CoSe2/CNT composites were obtained by further selenization and calcination in a tube furnace.The cobalt oxide(Co3O4)in the precursor is used as the template for the synthesis of CoSe2,which realizes the strong interaction with carbon nanotubes and the particle size control of CoSe2.On this basis,the electrochemical performance of CoSe2/CNT as a catalytic material was explored.Carbon nanotubes can weaken the volume expansion of sulfur reaction during discharge,and CoSe2 can increase the electrochemical catalytic activity.CoSe2/CNT alleviates the shuttle effect of LiPS by chemisorption LiPS and catalytic redox kinetics,and improves the electrochemical performance of S cathode.In addition,the effect of CoSe2 content in CoSe2/CNT on the performance of cathode was explored.The electrochemical performance of S cathode increases at first and then decreases with the increase of CoSe2 content.Finally,the battery prepared with CoSe2/CNT-10 sample has the best electrochemical performance,and its performance is much better than that of COCNT material.The maximum specific capacity at 0.2 C is 954 mAh g-1,and the specific capacity retention of 0.5 C after 200 cycles is 86.0%.Finally,phosphorus doping was carried out on the basis of CoSe2/CNT-10,and the catalytic performance of P-doped cobalt selenide modified carbon nanotube material(P-CoSe2/CNT)in the positive stage of lithium-sulfur battery was studied.After doping,CoSe2 changes from cubic phase to orthorhombic phase,which proves the successful doping of phosphorus.And P-doping accelerates the redox kinetics of lithium-sulfur battery and reduces the shuttle effect.Furthermore,it is found that the amount of P-doping in P-CoSe2/CNT materials has a certain effect on the electrochemical performance,a small amount of doping has a limited effect on the catalytic performance,and excessive doping is not conducive to improve the catalytic activity.Finally,the catalytic activity of P-CoSe2/CNT-10 sample is the highest.The specific capacitance of the battery can reach 1266 mAh g-1 at 0.2 C,and the cycle performance is obviously improved.The specific capacitance of 0.5 C after 200 cycles retains 92.9%.