Preparation Of Cobalt-tin Bimetal Oxide Compound/Carbon Composite And Its Application In Lithium Sulfur Batteries

To achieve commercialization,it is necessary for lithium-sulfur batteries（LSBs）to solve the‘shuttle effect’in the process of battery charging and discharging,electrode volume expansion and other problems.In order to solve the problems of poor conductivity,volume expansion,and easy dissolution of lithium polysulfide in the cathode materials of LSBs,co-precipitation method,one-pot method,annealing method,electrospinning method and other methods were used to prepare cobalt-tin bimetal oxide combined with carbon composite materials.They have the advantages of good conductivity,many active sites,and strong adsorption capacity to sulfur.These advantages are due to the combination of carbon materials and doping of nitrogen atoms,which provide more ion transmission channels and active sites,and enhances adsorption capacity to sulfur.The main work is divided into the following three parts:1.Co-precipitation method was used to prepare CoSn（OH）₆nanotubes wrapped with carboxylated carbon nanotubes（CoSn（OH）₆/CNTs）.After annealing,stable CoSn O₃/CNTs composites were obtained and used as lithium sulfur cathode material.The composition,structure and electrochemical energy storage of CoSn O₃/CNTs were studied.The results show that the sulfur storage capacity of CoSn O₃/CNTs is 64.93 wt%.At 0.2 C rate,the initial discharge capacity is 435.2 m Ah g^-1.After 500 charge-discharge cycles,the discharge capacity of the lithium-sulfur battery is still 402.5 m Ah g^-1.During the same rate cycle,the specific capacity of the battery changes relatively little,and the coulomb efficiency is also around 100%.The good electrochemical performance is attributed to the unique composite structure,more electron transport channels and more surface area.2.‘One-pot method’was used to synthesize the bimetallic oxide coated with polyethylene glycol as the precursor,and the Co O/Sn O₂@NC composite was obtained by subsequent.Phase analysis,morphology,structure and electrochemical properties of Co O/Sn O₂@NC composites were studied.The unique Co O/Sn O₂@NC core-shell structure is used as a carrier for LSBs.The initial discharge specific capacity is 395.15m Ah g^-1at 0.2 C,after 400 cycles,it remains at 312.11 m Ah g^-1.The specific discharge capacity of Co O/Sn O₂@NC at 0.5 C was 295.2 m Ah g^-1in the first cycle,and the specific capacity was stable after 150 cycles.Its good stability can be attributed to the unique core-shell structure,which enhances the adsorption of lithium polysulfide.3.With CoSn（OH）₆as the precursor,CoSn O₃@CNFs/S was prepared by electrospinning,calcination and melting of sulfur,and the electrochemical properties of CoSn O₃@CNFs/S as the cathode electrode of lithium sulfur battery were studied.The results show that CoSn O₃@CNFs/S as the positive electrode material has a discharge specific capacity of 554.9 m Ah g^-1at the first cycle of 0.2 C.After 100 charge-discharge cycles,the specific discharge capacity of the material is 332.2 m Ah g^-1,and the coulomb efficiency is 99.42%.After charging and discharging cycles at different rates,the battery can return to the original specific capacity.Therefore,CoSn O₃@CNFs/S as a positive electrode material for LSBs has good rate performance.Its good electrochemical stability is attributed to carbon nanofiber structure,high conductive network,improved adsorption of lithium polysulfide,which effectively relieves the volume expansion and enhances the cycle performance of the lithium-sulfur battery.