Electrochemical Energy Storage Of Carbon-sulfur Cathode Material Modified By Conductive Polymer Containing Nitrogen And Sulfur

In recent years,the new energy industry has developed rapidly,and the development of new energy storage devices has gradually become a research hotspot in the current energy industry.Lithium-sulfur batteries with elemental sulfur as the active material have become one of the choices for next-generation energy storage systems.Due to their higher theoretical specific energy(2600 Wh kg-1).In addition,sulfur is rich in resources,low in cost,and environmentally friendly.Account the above advantages,the current research on lithium-sulfur batteries has attracted widespread attention.There are still some defects that hinder its practical application in the commercialization process,such as the low conductivity of active material sulfur and its discharge products,and the shuttle of polysulfides.The effect causes the loss of active material,the volume expansion of the electrode during charge and discharge,and so on.In recent years,scientific researchers have tried to use carbon materials,metal oxides,sulfides,conductive polymers to modify lithium-sulfur battery cathode materials.This paper aims to use conductive polymers containing nitrogen and sulfur heteroatoms to modify common commercial conductive carbon materials,which can improve the conductivity of the sulfur electrode and the cycle performance of the battery.Mainly include the following aspects:(1)Select the common commercial conductive carbon material(AB)and elemental sulfur to obtain the carbon/sulfur composite material(AB/S).Two nitrogen-containing materials conductive polymers(PANI,PPy)are used to modify the surface of basic cathode materials.Then,explore the effects of nitrogen-containing conductive polymers with different molecular structures on the microscopic morphology and polysulfide adsorption capacity.The results show that the first discharge specific capacity of PANI and PPy modified cathode materials are 905 mAh g-1 and 905 mAh g-1 at room temperature 0.1 C.They remain 407 mAh g-1 and 370.7 mAh g-1 after one hundred cycles.The specific discharge capacity shows better electrochemical performance.Due to the difference in the molecular structure of the nitrogen atoms of the two nitrogen-containing conductive polymers,the difference in the polymer structure is calculated by simulation theory to affect the lithium ion transmission energy barrier and the ability to adsorb polysulfides.(2)Two other conductive polymers containing sulfur atoms(PTh and PEDOT)were selected to modify the AB/S composite cathode material.Use chemical in-situ polymerization to obtain PTh@AB/S and PEDOT@AB/S two modified cathode materials.The results show that the first discharge specific capacity of PEDOT@AB/S and PEDOT@AB/S composite electrode is 1005 mAh g-1 and 872.4 mAh g-1.The remaining capacity is 483.1 mAh g-1 and 370.7 mAh g-1 after 100 cycles.The sulfur element contained in the molecular structure of the sulfur-containing conductive polymer increases the specific discharge capacity of the battery.At the same time uses the additional conductive path provided by the coating layer to improve the electron ion transmission efficiency,thereby improving the cycle rate performance of the battery.By constructing a theoretical calculation model,the difference between the adsorption capacity of sulfur for polysulfides and that of sulfur is obtained,and the effects of the two elements in the battery are compared.(3)Select the nitrogen-containing polymer PPy and the sulfur-containing polymer PTh with better performance in the above comparative studies to copolymerize and modify the improved basic cathode material SP/S to prepare the PPy-PTh@SP/S composite cathode material.We explore the influence of hydrochloric acid concentration and monomer ratio on the modification effect of copolymerized products during polymerization.The electrochemical performance test results show that the PPy-PTh@SP/S-3:7 sample prepared when the N:S is 3:7 at a concentration of 1 M hydrochloric acid has the most excellent electrochemical performance.The first discharge capacity of 0.1 C is 1295.2 mAh g-1.It shows 423.8 mAh g-1 remains after one hundred cycles.The reason is that the copolymer layer of the sample is a uniform film with a thickness of about 10 nm,and the coating is uniform.It has the modification characteristics of nitrogen and sulfur atoms.