Preparation Of Sulfur/Carbon Composite And Its Application Research For Lithium/Sulfur Battery

In recent years, lithium sulfur battery has attracted wide attention for its high theoretical capacity(1675 m Ah/g) and energy density(2600 Wh/kg). Elemental sulfur is rich source, low price and environment friendly but sulfur conductivity is not high and discharge intermediate products and the final products easily dissolve into the electrolyte, so they can lead to attenuation of battery capacity and serious decline of cycle performance. This paper prepared sulfur/carbon nanofibers, sulfur/carbon nanotubes, sulfur/activated carbon composite materials by heating in order to improve the conductivity of elemental sulfur and inhabit the dissolution of the discharge intermediate products and the final products in the electrolyte.Carbon nanofibers were prepared by electrospinning. Precursor solution concentration and the electrospinning process parameters were selected and optimized. Finally, precursor solution was N,N-dimethylformamide(DMF) as solvent and polypropylene nitrile PAN of 7% by mass as solute. Atmospheres of nitrogen and ammonia were used to process the precursor fiber membrane which were heated with sulfur to get sulfur/carbon nanofiber composite materials. The obtained composites were characterized by physical and electrochemical methods. The results showed that sulfur/carbon composites annealed in ammonia atmosphere were better than nitrogen atmosphere. Four samples including pure elemental sulfur, sulfur/carbon nanofiber composites with the mass ratio 7:3、9:1、4:6 of elemental sulfur and carbon nanofibers were studied. The results showed that conductivity of sulfur/carbon nanofiber composites with the mass ratio 7:3 of elemental sulfur and carbon nanofibers was the highest; When the current density was 335 m A/g, the material with mass ratio 7:3of sulfur and carbon fiber performance was the best, which initial discharge capacity was 458 m Ah/g, the discharge capacity after 100 cycles was 133.2 m Ah/g, the minimum polarization and the charge transfer impedance was 17 Ω; The performance of elemental sulfur was the worst, which initial discharge capacity was 385.5 m Ah/g, the discharge capacity after 100 cycles was 2 m Ah/g, maximum polarization and the charge transfer impedance was 800 Ω. Therefore, carbon nanofibers significantly improved the electrochemical properties of elemental sulfur.Sulfur/carbon nanotubes and sulfur/activated composites with the mass ratio 7:3 of elemental sulfur and carbon nanotubes/activated carbon were studied. When the current density was 335 m A/g, discharge capacity of sulfur/carbon nanotubes was 559.5 m Ah/g, the discharge capacity after 100 cycles was 297 m Ah/g, polarization potential was about 0.3 V. Activated carbon used in the experiment was in the micron size. Activated carbon with micron size did little to adsorb elemental sulfur and discharge by-products, so the electrochemical properties of prepared sulfur/activated materials were very poor.