Preparation And Performance Research Of Sulfur And Sulfide Copper Cathode Materials

With the development of electronic technology and the emergence of hybrid and all-electric vehicles, people put forward higher requirements on lithium secondary battery for environmental protection, high efficiency, high energy and safety. Sulfur and copper sulfide as cathode materials of lithium ion battery became hot spot research by people for their high theoretical specific capacity, environmental friendly, low prices, abundant raw materials and high security. but the volume change and polysulphide dissolution in the process of circulation always restricts its further utility progress. Therefore, with sulfur, copper sulfide as the activity of lithium storage material, the methods of coating, infiltration on the modification and preparation technology was studied, the morphology, structure, composition and the relationship between the lithium storage properties in this thesis, the related laws were obtained, the performance of sulfur and sulfide copper in lithium storage material were optimized, specific results are as follows:(1) Polyacrylonitrile were used as carbon source, sublimed sulfur were used as sulfur source, S/C composite materials were obtained by heat treatment in high pressure reaction kettle, the influence of heat treatment temperature was investigated by electrochemical performance, it shows that the composite with 155?×6 h, and then 180?×6 h, the battery has good cycle stability: the first discharge capacity is 756 mAh/g, and reversible capacity is 337 mAh/g after 50 cycles under the current density of 100 mAh/g, capacity retention is 44.6%. Polypyrrole were coated on the S/C composites with method in situ, Results show that when the dosage of polypyrrole design for 10 wt.%, the composite material has excellent electrochemical performance of lithium storage: the first discharge capacity is 846 mAh/g, and reversible capacity is 387 mAh/g after 50 cycles under the current density of 100mAh/g, capacity retention is 46%, PPy coating promote the electrical conductivity of the composite materials and inhibit the dissolution of the reaction intermediate disulfide, The composite material have good electrochemical performance.(2) Polyacrylonitrile were used as carbon source and potassium hydroxide were used as expanding agent, porous carbon were prepared with method of pyrolysis, sulfur / porous carbon composites were prepared by melt impregnation process with sublimation sulfur, the sulfur content in composite materials were optimizationed, physical and electrochemical performance were researched, The results show that: When sulfur content is low(< 60 wt. %), the sulfur can be stable in the porosity of the porous carbon materials, when the high sulfur content(> 60 wt. %), part of the sulfur in composite materials exist in the porosity of porous carbon materials, and there will be a part of the sulfur exist on the surface of the porous carbon materials. When the dosage of sulfur is 59.5wt.%, the composite material has excellent electrochemical performance: the first discharge capacity is 694 mAh/g, and reversible capacity is 394mAh/g after 50 cycles under the current density of 100 mAh/g, capacity retention is 56.8%. Superior electrochemical performance benefit from the sulfur uniform dispersion in porous carbon materials, porous carbon improved the electrical conductivity of the composites and also increased the contact area between electrolyte and sulfur, improved the utilization rate of active materials. In order to improve the cycle stability of sulfur / porous carbon composites different polypyrrole were coated on the composites, Results show that when the dosage of polypyrrole design for 15 wt.%, the composite material has excellent electrochemical performance of lithium storage: the first discharge capacity is 744 mAh/g, and reversible capacity is 387mAh/g after 50 cycles under the current density of 100 m Ah/g, capacity retention is 41.9%, Polypyrrole coated are beneficial to the comprehensive electrochemical properties of composites, but too much of the polypyrrole coated will reduce the content of active substance sulfur, lead to low capacity of composite materials.(3) S/CuS composite materials were obtained with method of precipitation, then different qualities of polyaniline were coated on it, then copper sulfide/carbon composites were acquired by high temperature carbonization. The influence of composition, morphology and structure of the composites by heat treatment is studied. Results show: elemental S can be removed from the materials by heat treatment and CuS were evenly dispersed in C materials. The electrochemical performance were tested, results indicate: when the dosage of polyaniline design for 25 wt.%, the composite material has excellent electrochemical performance of lithium storage: the first discharge capacity is 1334 mAh/g, and reversible capacity is 653 mAh/g after 100 cycles under the current density of 100 m Ah/g, capacity retention is 49%, it shows good cycle stability. Superior electrochemical performance benefit from heat treatment removed sulfur from the composite and porous structure were fromed, the porosity can be a very good adaption to the volume expansion of CuS during charge and discharge, it also good inhibition of intermediate disulfide dissolved.