Preaperation And Electrochemical Performance Of Co₃O₄/Carbon Nanofibers Composites

Lithium-sulfur(Li-S)batteries have a high theoretical capacity(1672 m Ah g^-1)and energy density(2600 Wh kg^-1).Sulfur has the advantages of abundant reserves,low price and environmental friendliness,which has attracted widespread attention from researchers.However,Li-S batteries still have some problems in practical applications.For example,the insulating properties of sulfur severely reduce the utilization of active materials.In addition,lithium polysulfide(Li PS)generated during cycling is dissolved in the electrolyte and shuttles between the electrodes,resulting in poor cycling stability of batteries.In order to improve the electrochemical performance of Li-S batteries,this work starts from the design of sulfur cathode materials,and uses the electrospinning process to synthesize tricobalt tetraoxide/carbon nanofibers composites.The main research contents are as follows:1.Porous nitrogen-doped carbon nanofibers materials(NCFs)were synthesized by electrospinning.The microstructure,graphitization degree,specific surface area,and electrochemical performance of NCFs were characterized.The results show that when the carbonization temperature was 900?and maintained for 2 h,the carbon nanofibers have the highest degree of graphitization,which have good electrical conductivity and effectively promote the mass transfer of electrons and ions;when the mass ratio of the polyacrylonitrile(PAN)to polymethyl methacrylate(PMMA)is 1:0.4,the obtained NCFs-2 material has a large specific surface area and pore volume;the initial discharge specific capacity of S/NCFs-2 can reach 1123 m Ah g^-1,and it can maintain 741 m Ah g^-1after 100 cycles.2.An electrospinning process was used to synthesize a carbon nanofibers matrix grown carbon nanotube-cobalt tetroxide material(Co₃O₄-CNT@NCFs),and its composition,morphology,and electrochemical properties were characterized.The experimental results showed that hierarchical structure of Co₃O₄-CNT@NCFs material ensures long/short range conductivity of electrons;UV spectra and theoretical calculations results indicate Co₃O₄nanoparticles have strong chemisorption on polysulfides;symmetrical battery cyclic voltammetry(CV)and linear scanning voltammetry(LSV)curves confirm that Co₃O₄greatly promotes the kinetic conversion process of catalytic polysulfides;the first discharge specific capacity of S/Co₃O₄-CNT@NCFs composite cathode can reach 1274 m Ah g^-1,and it can maintain 999 m Ah g^-1after 100 cycles.3.A metal-organic framework-derived tricobalt tetroxide-porous carbon nanofibers material(Co₃O₄@ZNCFs)was synthesized by electrostatic spinning,and the morphology,phase composition,and electrochemical performance of the Co₃O₄@ZNCFs were characterized.The experimental results showed that when the carbonization temperature is900?,ZIF-67 can well maintain the porous polyhedral framework structure and uniformly load ultrafine Co₃O₄nanoparticles;when the mass ratio of PAN and ZIF-67 was2:1,uniformly encapsulated Co₃O₄@ZNCFs-2 is obtained after carbonization.The initial discharge specific capacity of S/Co₃O₄@ZNCFs-2 composite cathode can reach 1245 m Ah g^-1,and it can maintain 908 m Ah g^-1after 100 cycles.