Fabrication And Electrochemical Performanceof C-S/PANI Cathode Material

The lithium-sulfur(Li-S) battery has been paid close attention due to its high theoretical specific energy, environmental friendliness and its potential uses as an energy storage system that can substitute for the limited energy density of currently widely used lithium-ion battery. However, the poor conductivity of elemental sulfur and its discharge product Li2 S lower the utilization of active materials. Moreover, the high solubility of Li2Sx(2<x<8) intermediates in organic electrolyte can result in lower coulombic efficiency. In this thesis, The modification of sulfur based cathode materials was adopted to improve their electrochemical performance. It is a quotable reference for the broad application of Li-S batteries. The main results are shown as follows:Acetylene black-sulfur and carbon nanofibers-sulfur composites were obtained through a high energy ball milling method. The effect of rotation speed and sulfur loading on the electrochemical properties of acetylene black-sulfur and carbon nanofibers-sulfur cathode materials were studied. It is found that the best cycle performance of the two cathode materials with 50 wt% S was recieved at 0.5 C when rotation speed is 600 rpm. After 200 cycles, the reversible capacities of Acetylene black-sulfur and carbon nanofibers-sulfur composites were 611.4 and 691.1 m Ah·g-1, respectively. The big specific surface area could guarantee the full contact between cathode material and electrolyte. When rotation speed increase, the combination of sulfur and carbon could be enhanced, which may improve conductivity of sulfur cathode and activity of sulfur.Acetylene black-sulfur and carbon nanofibers-sulfur composites were modifide through acidification, The effect of acidification on the electrochemical performance of acetylene black-sulfur and carbon nanofibers-sulfur cathode materials were studied. The two cathode material with 50 wt% S was measured at 0.5 C. As a result, after 200 cycles, the reversible capacity of acetylene black-sulfur was 631.5 m Ah·g-1, 20.1 m Ah·g-1 larger than that of the cathode without acidification and the reversible capacity of carbon nanofibers-sulfur composites were and 708.6, 17.5 m Ah·g-1 larger than that of the cathode without acidification. The –OH and –COOH groups were induced on the surface of carbon materials after acidification. Meanwhile, the surface area also increased. It could trap the diffused intermediates and remit the shuttle effect. And then the specific capacity, cycle performance could be further improved.Acetylene black-sulfur and carbon nanofibers-sulfur composites were coated by PANI via in-situ deposition method to further improve their cycle performance. The effect of PANI coating on the electrochemical properties of acetylene black-sulfur and carbon nanofibers-sulfur cathode materials were studied. As a result, after 200 cycles, the reversible capacities of acetylene black-sulfur and carbon nanofibers-sulfur composites were 651.8 and 716.1 m Ah·g-1, respectively. Stable three-dimensional conductive network structure was obtained after PANI coating, which could increase the conductivity and stablity of sulfur cathode, relieve the diffusion of intermediates and improve cycle performance of sulfur based cathodes.