Preparation And Electrochemical Performance Of Porous Carbon Fiber For Lithium-sulfur Battery Cathode

Soaring demand for efficient and economic electric energy storage system has intensively promoted the development of rechargeable batteries with high energy density and long cycle life.At present,the lithium-sulfur(Li-S)battery shows a great potential due to the use of sulfur as the electrochemical active material endowing the Li-S batteries with the high theoretical capacity of 1675 mAh/g and the energy density of 2567 Wh/kg.Moreover,sulfur is one of the most abundant and nonpoisonous elements on the earth.However,the insulation of sulfur and the insolubility of the discharged products lead to the low sulfur utilization,and the high solubility of the intermediate polysulfide results in the irreversible capacity fading and low coulombic efficiency.Finally,large volumetric change(80%)during redox process causes the instability of the cathodes and shortens the cycle life.In order to solve the above problems,we reported the method of preparing sulfur-embeded porous carbon nanofibers as the cathode material for Li-S batteries via a simple electro-blown spinning technique of poly(acrylonitrile)(PAN)/polystyrene(PS)solution and following thermal treatment.PAN was used as the carbon precursor due to its high carbon yield,good thermal stability,and spinnability.PS can be used as a pore-making agent to create void spaces in the carbon fibers.The PCFs contained large amount of mesoporous and macroporous due to the phase separated of incompatible PAN and PS and the thermal decomposition of the PS.Finally,the sulfur was embed into the PCFs by high temperature sublimation.The cathode material performed outstanding cycle stability and high coulombic efficiency.The effects of different ratios of PAN:PS on the morphology of the fibers were analyzed by SEM,TEM,FTIR,BET,TGA et.al.The cyclic charge and discharge tests of the S-PCFs were used to analyze the pore structure and conductivity on the electrochemical performance of batteries at different ratio of PAN:PS.The results showed that different spinning solutions were prepared with different ratios of PAN and PS,and they were independent due to the separatio of micro-phases.The porous carbon fibers were obtained by decomposition of the PS during the carbonization treatment.As the ratio of PAN/PS increased from 5:0 to 5:5,the diameter of the fibers gradually increased,from 0.605 increased to 1.716 ?m.The proportion of the fiber to 3:5,the diameter of the fiber was gradually reduced,from 1.716 decreased to 1.045?m.After carbonization,the specific surface area of porous carbon fiber was 56.686 m2/g.In addition,porous carbon fiber has excellent electrical conductivity and more than 1×105 S/m.The results of electrochemical tests showed that the porous carbon fiber exhibited excellent cyclic stability.When PAN/PS ratio was 5:1,the positive electrode had the highest initial specific capacity of 1135.8 mAh/g.After 300 cycles,the cycle loss of the positive electrode material per cycle was only 0.03%.Thus,porous carbon fiber has good application prospects in the field of lithium-sulfur batteries.