Study On Cathode Performance Of Li-S Battery With Sorghum Rice Porous Carbon

Lithium-sulfur(Li-S)batteries have attracted wide attention from researchers due to their high energy density and low cost.However,the development of the Li-S battery is limited for some weaknesses of the poor electrical conductivity of sulfur and shuttle effect of polysulfide compounds.Researchers generally believe that the porous conductive framework with the confined effect of pores could retard the shuttling effect of intermediate polysulfides,which improve the utilization of elemental sulfur.Therefore,porous carbons(SPC)were prepared by potassium hydroxide activating sorghum in this work.Effect of carbonization temperature,activation temperature and alkali-to-carbon ratio on the pore structure of SPC was syspemly studied,and a composite cathode(SPC/S)was prepared by sulfur infilitrated into SPC.Furthermore,the effects of sulfur loading and pore structure on the cycle performance were investigated.Moreover,N-SPC and Ni-SPC were prepared by dopping melamine and nickel chloride into SPC,respectively.And then,two composite cathode of N-SPC/S and Ni-SPC/S were made by infiltrated sulfur into N-SPC and Ni-SPC.Final,the electrochemical properties of the two composite electrodes were investigated.The main research results are follows:The optimal investigation find that the maximal specific surface area and pore volume of SPC achieves 759.134m~2/g and 0.482cm~3/g under the carbonization temperature of 400?,the activation temperature of 700?,and the alkali-to-carbon ratio of 1:4.When the sulfur loading is 53%,the specific discharge capacity of the first cycle reaches 660.4m Ah/g,and it decrease to 361.5m Ah/g after 50 circles,and coulomb efficiency remains above 97%.These results suggest the cathode of the SPC/S exhibits the better cycle performance.Nitrogen doped into SPC leads to increasing significantly of the specific surface area and pore volume of porous carbon.The cathode of nitrogen doped-porous carbon/sulfur(N-SPC/S)with a sulfur loading of 50% shows the smallest charge transfer resistance of 13.06?.Moreover,N-SPC/S exhibits the high initial capacity about 1152 m Ah/g under 0.1C in contrast with other sulfur loading.After 100 circulations,the discharge capacity is 518.4m Ah/g.Rate test results show that the capacities are respectively 901.6m Ah/g,735.5m Ah/g and 661.6m Ah/g under 0.2C,0.5C and 1C.When the current density recovers to 0.1C again,the capacity is777 m Ah/g.These results suggest the cathode of N-SPC/S achieves excellent rate and regression performance.The cycling performance of the Li-S battery is significantly improves as metallic Ni doped into SPC(Ni-SPC/S)to as the cathode electrode.The initial discharge capacity reaches 733 m Ah/g in 0.1C,and the reversible capacity reduces to434.8m Ah/g after 100 circulations.The capacity maintained of Ni-SPC/S is 21%higher than it of SPC/S.