Preparation Of Porous Starch Based Porous Carbon Materials And Their Applications In Lithium Sulfur Battery

The lithium-ion battery based on the principle of lithium intercalation electrochemistry has dominated the battery market of portable electronic equipment since its inception.Nowadays,the energy density of lithium-ion battery is difficult to meet the requirements of new power vehicles.At this time,lithium sulfur battery have attracted much attention owing to high theoretical capacity(1675 mAhg^-1)、high power density(2567 Whkg^-1)and low cost.However,the low conductivity of active materials,the"shuttle effect"and the volume expansion during reaction caused by the intermediate products easily soluble in the electrolyte seriously degrade the electrochemical performance of lithium sulfur battery.In order to further improve the performance of lithium sulfur battery,starch is used as carbon source to prepare various carbon/sulfur composite structures for battery positive materials,and the different groups of starch based carbon materials are compared to explore the influence factors to the performance of the battery in this thesis.The anode material（Na₂SO₄-C/S）with high load of small size active substance and porous carbon based material（NS-1）with nitrogen and sulfur co-doped are synthesized with starch,sodium sulfate and KOH which is used as carbon source and activators,respectively.Compared with the pure sulfur electrode,the initial specific capacity in the lithium sulfur battery of Na₂SO₄-C/S and NS-1/S is 797 mAhg^-1 and 690 mAhg^-1 at 0.5C,respectively.After 200 cycles,the discharge specific capacity is kept at 419and 413mAhg^-11 with a low capacity decay rate of 0.23%and 0.14%per cycle,respectively.The excellent electrochemical performance of Na₂SO₄-C/S and NS-1 are further verified under the condition of 2 C high current.In order to further simplify the complex process in the assembly of lithium sulfur battery and avoid the"shuttle effect"caused by the"fragmentation"of the carbon powder,The Carbon Cloth@Nitrogen and Sulfur co-doped porous carbon（CC@NS）has been prepared.Starch derived carbon material and carbon cloth compound by simple dip method while the Starch gel is used as binder.Three-dimensional carbon material with the appropriate weight ratio of starch:thiourea:KOH（6:1:12）yields the optimized performance of lithium sulfur battery.Under the condition of constant current charge and discharge,the initial discharge specific capacity of CC@NS-1 is 1250mAhg^-1.Moreover,a capacity of 752 mAhg^-1（0.5 C）is maintained over 350 cycles with excellent Coulombic efficiency maintaining in the range of 96-97%at a decay rate of0.11%.Even at high current density 2 C,the specific discharge capacity of CC@NS-1can obtain 666 mAhg^-1.The excellent electrochemical performance of CC@NS-1 is further verified by cyclic voltammetry and impedance test.In addition,the excellent adsorption of CC@NS-1 on polysulfide ions is characterized by UV-vis absorption measurements.Based on the successful prepared composite structure of CC@NS-1,the interlayer and CC@NS-1 used as cathode material are used to test the performance of lithium sulfur battery under the condition of high load.The excellent long cycle stability shows the double layer structure of carbon material CC@NS-1 improves the performance for lithium sulfur battery.