Preparation Of Polymer Porous Carbon And Performance Study Of Lithium Sulfur Battery

After two decades of development,lithium-ion batteries(LIBs)based on intercalation compounds are approaching their energy density limit,and unable to meet the ever-growing demands of the requirements of the electronics industry and electric vehicles.New battery systems with higher energy densities are urgently required for the rapidly evolving markets.Due to the eye-catching features of high theoretical energy density(2600 Wh-kg-1),low cost and environmental compatibility,lithium sulfur(Li-S)battery been considered as very promising candidates for the next-generation of rechargeable batteries.However,the practical application of Li-S batteries is still suffering from several problems of the sulfur cathode,including the low conductivity of sulfur,the large volumetric change of sulfur during lithiation/delithiation process,and the capacity loss induced by the dissolution of intermediate products in the electrolyte.electrode,In this thesis,in order to solve the major problem of sulfur,The modification of sulfur based cathode materials was adopted to improve their electrochemical performance.It is a quotable reference for the broad application of Li-S batteries.The main results are shown asfollows:The research in this thesis mainly focused on the high-performance carbon/sulfur composite cathodes,and the development of novel polymer porous carbon materials as the sulfur support to improve the electrochemical-performances of the sulfur cathode.The main results and new findings in this work are summarized as follows:1.Polymer porous carbon(PPC500)with abundant interconnected channels,large surface areas were synthesized by a simple method.Sulfur loaded sample with a high sulfur content of 75 wt%,SPPC500,is fabricated by melt impregnating method.The loaded sulfur homogeneously disperses in SPPC500 without large aggregates.Electrochemical tests reveal that the SPPC500 composite shows high rate capability and long cycling stability as cathode materials.It showed high initial capacity of 1397.3 mAh-g-1 at 0.2 C,which is 83.4%of the theoretical value of sulfur.And at 0.5 C,it shows 0.074%decay rate per cycle over 1000 cycles,2.Nitrogen-doped polymer porous carbon(NPPC)with abundant micropores and mesopores structure was obtained by a facile polymerization reaction,and sulfur-NPPC composite based on NPPC was synthesized for Li-S batteries by a melt-diffusion method.Nitrogen doping could assist polymer porous carbon to suppress the shuttling phenomenon,possibly via an enhanced surface interaction between the basic nitrogen functionalities and polysulfide species.Nitrogen doping only within an appropriate level(4.06 wt.%)can improve the electronic conductivity of the carbon matrix.As the cathode of rechargeable Li-S batteries,the SNPPC composites with the sulfur content of 72 wt%exhibit a long cycle life exceeding 600 cycles and an extremely low capacity decay rate(0.06%per cycle)at 0.5 C rate.The rate performance test shows that capacity of 547.9 mAh·g-1 is obtained even at 2C.When the current density turn back to 0.1C rate,the discharge capacity of 732.0 mAh·g-1 is remained.Good cycle and rate performance is achieved by using the composite material of SNPPC.