Synthesis And Electrochemical Performance Of Sulfur-Contained Cathode Materials For Lithium Sulfur Batteries

With the development of society,develop ing the high-energy density,safe and low-cost electrochemical energy storage devices are becoming more and more important.The traditional lithium-ion battery has low theoretical capacity and high cost with its cathode material,so it is difficult to meet the needs of the society.In recent years,more and more scientific researchers pay attention to lithium-sulfur batteries.The theoretical specific capacity of elemental sulfur is 1675 mAh g-1,which is at least 10 times higher than that of commercial used transition metal phosphates and oxides.In addition,elemental sulfur is resource-rich,low-cost,and environmentally friendly,making lithium-sulfur batteries a promising candidate for high-energy-density energy storage devices that can be used commercially.Although lithium-sulfur batteries have a promising future,they still face many challenges in practical applications.The poor conductivity of sulfur and the dissolution of the polysulfide and the volume expansion of sulfur during lithiation?⁸0%?cause a decline of the specific capacity and instability of the cycle performance in lithium-sulfur battery.This paper designed metal oxygen?sulfide?-carbon materials or metal oxygen?sulfur?-polymers as the sulfur supports.On the one hand,the conductivity of the electrode material can be increased,and on the other hand,the“shuttle effect”of polysulfides can be effectively suppressed.We studied the morphology,structure and electrochemical performance of these materials and achieved the following results:1.We designed the form-like G-TiO₂ as a sulfur supports and then obtained G-TiO₂/S cathode by the method of sulfur melting diffusion.The network structure in which the foamy graphenes crosslink with each other can serve as a fast channel for lithium ions and electrons,providing strong conductivity.TiO₂ nanoparticles can chemically anchor polysulfides and suppress the shuttle effect of polysulfides during charge and d ischarge process.In this paper,we characterized the morphology and structure of G,G-TiO₂ and G-TiO₂/S and studied the effect of different proportions of G and TiO₂ on the electrochemical performance of cathode materials,finding that the G-TiO₂-30%/S cathode has a excellent electrochemical performance.When the current density is 0.1C,the discharge specific capacity of the materials is 990.2 mAh g^-1 after 50 cycles.Even at the current density of 2 C,the discharge specific capacity of the materials can still reach 635.4 mAh g^-1.2.In this paper,the polyaniline coated titanium dioxide coated sulfur nanoparticles?S@TiO₂@PANI?was designed as the cathode materials for lithium sulfur batteries.The TiO₂nanoshell can effectively adsorb polysulfide,at the sametime polyaniline provides a conductive network to promote lithium ion or electron transport.In this paper,we characterized the morphologies and structures of S nanospheres,S@TiO 2 nanospheres and lychee-like S@TiO₂@PANI multishell structures,and studied the effect of different proportions of TiO₂ and PANI on the electrochemical performance of cathode materials.The lychee-like S@TiO₂@PANI-2 multishell structure,which were synthesized from S@TiO₂and aniline with a mass ratio of 5:3,has excellent electrochemical properties.At a current density of 0.1 C,the discharge specific capacity of the materials was 1150.3 mAh g^-1 after100 cycles.Even at a current density of 2 C,the material's specific discharge capacity can still reach 638.1 mAh g^-1.3.We designed CoS@PTh multishell nanoboxes as a sulfur supports and then obtained the multi-shell nanobox S@CoS@PTh cathode by the method of sulfur melting diffusion.The CoS nanobox can effectively suppress the shuttle effect of polysulfide,and polythiophene can improve the conductivity of the electrode material.In this paper,we characterized the structure of CoS nanoboxes,CoS@PTh nanoboxes and S@CoS@PTh multishell nanoboxes and studied the effec t of different proportions of CoS and polythiophene on the electrochemical performance of cathode materials.The multi-shell nanobox S@CoS@PTh-2,which were synthesized from CoS and thiophene with a mass ratio of 4:1,has excellent electrochemical properties.At a current density of 0.2 C,the discharge specific capacity of materials was 751.7 mAh g^-1 after 150 cycles.Even at 2 C current density,the material's discharge specific capacity can still reach 640.1 mAh g^-1...