Using Polyethyleneimine-modified Fish-scale-based Porous Carbon On Separator For Lithium Sulfur Battery

Lithium-sulfur(Li-S)battery has gained much concern due to its high theoretical capacity and high energy density.However,the practical discharge capacity and cyclic stability of Li-S battery are impaired by the shuttle of soluble polysulfides.In this paper,polyethyleneimine(PEI),which is rich in amine group,was loaded into fish-scale-based porous carbon material(FPC),taking advantage of large specific surface area and highly-developed porous structure of FPC.The voids of pores were filled in the meantime of loading amine group to obtain compact material that was rich in amine group.This material was used for modifying separator of Li-S battery and captured and immobilized polysulfides in both physical and chemical ways.The details of the study are as follows:First,the preparation method of PEI-modified fish-scale-based porous carbon material(PFPC)was studied.The effect of PEI loading on the porous structure of PFPCs was investigated.It is found that with the increase of PEI loading,the nitrogen content of PFPC increased and the specific surface area of PFPC decreased.The highest PEI loading could reach 12.08%,and the corresponding specific surface area was 494.86 g/cm3.Then the functional separator coating with light weight,high wettability and excellent mechanical property was designed and prepared to study the effect of PFPC on polysulfides.The initial discharge capacity of the battery with the modified separator in high discharge plateau was 341.9 mA h/g at the discharge rate of 0.1 C,reaching 81.6%of the theoretical value(419 mA h/g).After 100 cycles,the capacity retention of the battery in high discharge plateau was 82.5%,manifesting that the coating could adsorb and immobilize polysulfides and improve the utilization of active material.The discharge capacity of the battery still remained 638.1 mA h/g after 400 cycles at the rate of 1 C,corresponding to capacity fading of 0.07%per cycle.In the end,the charge/discharge process of the battery was investigated by electrochemical impedance spectroscopy(EIS).It is found that PFPC could effectively reduce the interface impedance and charge transfer impedance,confirming that the modified separator could not only effectively suppress the diffusion of polysulfides and restrained the formation of insulating layer on the surface of the anode,but also improve the wettability of separator,electron conductivity and ion conductivity.