Preparation And Electrochemical Properties Of Cathode Materials For Lithium/sulfur Battery Based On Porous Polypyrrole

Nowadays,energy density of cathode materials for traditional lithium ion batteries limits their application especially in rapidly developing electric vehicle and intelligent power grid,which demand high energy density.Lithium/sulfur?Li/S?battery has attracted much attention due to its high theoretical specific capacity of sulfur(1672 mAh g^-1)and theoretical energy density(2600 Wh kg^-1).Nevertheless,the commercial applications of the Li/S battery still has several challenges,such as the low ionic/electronic conductivity of S,large volume change during the charge/discharge process and a low utilization of active material.To overcome the above drawbacks by improving the electrochemical performance of cathode materials for Li/S battery,a novel three-dimensionally?3D?ordered hierarchically macro-mesoporous polypyrrole?HMPPy?and 3D ordered mesoporous polypyrrole?OMPPy?are successfully synthesized via a simple chemical polymerization method with the silica crystals as hard templates.The HMPPy/S composites and OMPPy/S composites are prepared by infusing sulfur into HMPPy and OMPPy and studied as cathode materials for Li/S battery.The influences of different current collectors on the electrical properties of HMPPy/S composite cathodes for Li/S battery were investigated.The effects of different S-doped methods on the sulfur content and electrochemical performance of OMPPy/S composite were studied,to develop the OMPPy/S composite cathodes for Li/S battery with high sulfur content and specific capacity.The related work mainly includes the following:1.Preparation and electrochemical properties of HMPPy/S composites.The HMPPy/S composite is prepared by infusing sulfur into HMPPy via a melting synthesis process,which possesses uniform pore size distribution and is a macroporous material with mesoporous and microporous.The characterization results showed that the content of S in the HMPPy/S composite is calculated to be about 66 wt.%,and the sulfur is distributed uniformly on the surface and pores of the HMPPy.The study on the electrochemical performance for HMPPy/S composites coating on different current collectors shows that the Ni foam current collector with HMPPy/S composite has stable cycle performance and excellent rate performance.The HMPPy/S composite exhibits an initial specific discharge capacity of 1374 mAh g^-1 at 0.1 C.The capacity of the HMPPy/S composite keeps 906mAh g^-1 for the 100 cycles.When the cell operated at 2 C rate,the HMPPy/S composite electrode delivered a capacity of 702 mAh g^-1.2.Preparation and electrochemical properties of OMPPy/S composites.The characterization results showed that the content of S in the OMPPy/S composite synthesized by melting method is approximately 62 wt.%,and the sulfur is distributed uniformly on the mesoporous of the OMPPy.The content of S in the OMPPy/S composite synthesized by ball milling method is approximately 48 wt.%and the distribution of sulfur in the OMPPy/S composite is not uniform because the 3D ordered structure of OMPPy/S composite was damaged by the mechanical force.The study on the electrochemical performance of OMPPy/S composite for Li/S battery shows that the melting method is more suitable for mesoporous materials to load S.Electrochemical tests reveal that the OMPPy/S cathode synthesized by melting method shows a good cycle performance of 903mAh g^-11 after 100 cycles at 0.1 C,corresponding to about 86%capacity retention.When the cell operated at 1 C and 2 C rates,the OMPPy/S composite electrode synthesized by melting method delivers capacities of 727 and 618 mAh g^-1,respectively,revealing the high rate property.