Preparation And Modification Of Carbon/Sulfur Composites Cathode Materials For Lithium Sulfur Batteriesf

The increase of energy demand in modern industry,the decrease of fossil energy reserves,the worsening of living environment and many other problems appear,and the continuous popularity of mobile phones,computers and other portable electronic devices makes people's demand for energy are increasing.The corresponding energy storage and conversion devices and technologies are also facing growing requirements.The key to this problem is to develop new electrode materials with high specific capacity and high energy density.After decades of development,the traditional lithium-ion battery still can not meet the market demand.Lithium-sulfur?Li-S?batteries are one of the next generation of rechargeable batteries due to the advantages of high theoretical specific capacity?1675 m Ah/g?and theoretical energy density?2600Wh/Kg?.Moreover,sulfur has the advantages of abundance,low cost and environmental friendliness.However,Li-S batteries still has some disadvantages that make it difficult to be commercialized,such as poor electronic conductivity of sulfur,significant volumetric changes upon the formation of Li₂S,and dissolution of lithium polysulfides into the organic electrolyte which leads to the shuttle effect.These problems lead to poor coulumbic efficiency and severe capacity decay.In view of the above problems,this work aim at designing Sulfur load time,carbon matrix materials,and adding oxides,sulfides and MOF materials to improve the electrochemical performance of Li-S battery.The contents are as follows:1.Porous carbon as lithium sulfur batteries host material was prepared with Ca NO₃ as template and gelatin carbonized at high temperature.The sublimated sulfur and porous carbon host were combined by melting diffusion method to obtain lithium sulfur battery cathodes material.The results show that the specific surface area of porous carbon host prepared by gelatin carbonization is 647.5466m²/g.The sulfur content of the S@PC12h composite is 64.53%.The S@pc12h electrode delivers an initial discharge capacity of 1471 m Ah/g at 0.1C rate,a super rate capacity of 790m Ah/g at 1C,an excellent long cycle stsbility at 1C with a capacity of 578 m Ah/g,a capacity retention of ca.73.1%and an average capacity decay of ca.0.12%per cycle after 220cycles,and,a capacity of 379m Ah/g,a capacity retention of ca.47.9%and an acerage capacity decay of ca.0.1%per cycle after 500 cycles.For all the samples studied,the optimal melting time is 12h.2.The composite electrode material was obtained by combining sublimated sulfur with different host materials by melting diffusion method.It is found that the initial discharge capacity of the Nis₂@r-Go/S electrode composite reaches1447.1 m Ah/g at 0.1C,and still has 751.1 m Ah/g at 0.1C after 50 cycles,and619.7 m Ah/g at 1C rate.For the samples studied in this experiment,Nis₂@r-Go/S electrode composite has better specific capacity,cycling performance and rate performance.3.A composite electrode material supported by Ce O₂ and MOF was successfully prepared by the method of one-pot hydrothermal treatment and melting diffusion.The research shows that the sulfur content of Ce O₂&MOF-74@r-GO/S composite material is 67.43%.The initial discharge capacity is 1239.8 m Ah/g 0.1C rate,and is 771.8 m Ah/g after 50 cycles.It delivers a high specific diacharge capacity as high as 621.9 m Ah/g at the rate of1C during rate test.Compared with the electrode material sample unloaded with r-GO,the performance of Ce O₂&MOF-74@r-GO/S composite material has been greatly improved.