Preparation And Properties Of Cathode Materials For High Performance Lithium Sulfur Battery

In recent years,lithium-sulfur batterises?LSB?have been attrcted many researchers`attention,because of their higher specific capacity(1675 mAh g^-1),excellent theorerical energy density(2600 Wh kg^-1),abundant resources of sulfur and environmental friendliness.However,there are some serious problems have been occurred for its further development and commercial application such as relatively low electrical conductivity of sulfur and Li₂S,large volume expansion of sulfur during charging process,the dissolution of polysulfide intermediates and the resulting shuttling effect.In this paper,the above mentioned problems of lithium-sulfur batteries to be solved by preparing nitrogen-doped mesoporous carbon materials and multi-wall carbon nanotubes-mesoporous carbon materials.?1?nitrogen-doped mesoporous carbon materials as the cathode materials for lithium-sulfur batteries.First,mesoporous carbon has limited the dissolution of polysulfides through capillary action of mesopores,thereby reducing or even eliminating the"shuttle effect"during charge and discharge processes.When the nitrogen-doped carbon acted as the sulfur carrier,which main causes of nitrogen-sulfur bonding can be formed between the nitrogen and sulfur atoms during the process of charging and discharging,thus sulfur was fixed with nitrogen-doped carbon material.In this research investigation,konjic was selected as a carbon source,melamine as a nitrogen source and Potassium hydroxide as an activator,the nitrogen-doped mesoporous carbon materials have been prepared with high specific surface area by high-temperature carbonization.The prepared composite materials exhibit high electrochemical performance that deliver the excellent performance with a discharge capacity of 532 mAh g^-1 at 0.5 C over 200 cycles,and also shows better cycle performance.In addition,the Coulomb efficiency during the cycle is always maintained at about 98%.?2?Multi-wall carbon nanotubes-mesoporous carbon materials as the cathode materials for lithium-sulfur batteries.Carbon nanotubes have good mechanical properties,electrical conductivity and thermal conductivity,that making it can be an excellent conductive additive for lithium-sulfur batteries.In this experiment,multi-wall carbon nanotubes were used as the substrate,coating a layer of hydrothermal carbon on the outer wall of carbon nanotubes by hydrothermal method,subsequently remove the oxygen-containing groups in the hydrothermal carbon by high-temperature treatment,at the same time,mesoporous were formed to obtain multi-wall carbon nanotube-mesoporous carbon materials.Finally,the sublimed sulfur was loaded into the mesopores of the multi-wall carbon nanotube-mesoporous carbon by through hot melt method to obtain a carbon nanotube-mesoporous carbon/sulfur composite material.Mesoporous carbon provides sufficient storage space for sulfur,and carbon nanotubes exert their excellent electrical conductivity that as a conductive bridge,the transmission path of ions and electrons is greatly shortened.The composite materials exhibit high electrochemical performance that deliver the excellent performance with a discharge capacity of 653 mAh g^-1 at 0.2 C over 200 cycles,569mAh g^-1 at 1 C after 200 cycles,shows higher excellent large rate discharge performance.