Structure Optimization And Electrochemical Performance Study Of Polymer-based Composites As Cathode Materials

Due to its high theoretical energy density(2600 Wh/kg)and high theoretical specific capacity(1675 mAh/g),lithium-sulfur batteries have attracted much attention.However,widespread practical applications for rechargeable lithium-sulfur batteries are plagued with many problems,such as low utilization rate,poor cycle life and rate performance,poor safety.To solve the above problems,the research now is focusing on modification of the cathode composite materials with high conductivity.Polypyrrole(PPy)is a typical conductive polymer owing to its show better properties in charge transportation after proper doping.It has potential and broad application prospects in sensor,capacitor,conductive composites and solar cells.However,its poor thermal stability and processability limit the applications of polypyrrole.The fabrication of PPy using various templates becomes a researching focus in order to promote the conductivities and processability of the PPy.This paper used conducting polypyrrole composited with elemental sulfur as the cathode and the electrochemical properties of cathode materials were also characterized.The main research contents are summarized as follows:1.In this paper,PPy with various morphology were synthesized via different concentration CTAB surfactant as soft templates.Results presented that the formation of polypyrrole appears particle-like,ring-like and network-like with increasing CTAB concentration from 1 to 12 cmc.Especially,the specific surface area and pore volume of the PPy with ring-like is maximum.Mixed with sulfur,the cathode showed best electrochemical properties.The initial discharge capacity was 1080.6 mAh/g and the discharge capacity was retained at 900.3 mAh/g after 50 cycles.2.In this paper,the effects of different amount of the sulfur mixing on the real sulfur content and electrochemical properties of PPy/S composite cathode materials were discussed.Results presented that with the increase in the amount of sulfur mixing,the real sulfur content is also increasing,but the conductivity is degraded.When the PPy:S=1:2(mass ratio),indicating an excellent cycle and rate performance of PPy/S composite cathode.The initial discharge capacity was 1080.6 mAh/g,and after 50 cycles of testing,the discharge capacity of this material still protected at about 83.3% in retention.3.In this paper,the different process of mixing sulfur effects on PPy/S composite materials and the electrochemical performance of PPy/S composite materials were studied.The experimental results show that the PPy/S composite via ball-milling is more uniform than manual milling,because the sulfur particles are more evenly embedded in the pores of the PPy surface to increase the utilization of the active material.The initial discharge capacity was 1200.2 mAh/g,and showed good cycle performance.