Ionic Liquid Assisted Synthesis Of Porous Carbon Materials For Lithium–sulfur Batteries

With the decreased fossil resources,and increased demand of EV and hybrid devices,high-energy storage batteries are in gread need.Lithium-sulfur?Li-S?batteries have been regarded as one of the promising energy storage systems due to their high theoretical specific capacity(1675 mA h g^-1)and energy density(2600 W h kg^-1)as well as the low cost and environmental friendliness of sulfur element.However,some disadvantages restricted their practical applications,such as the poor conductivity of the S and its discharge products?Li₂S/Li₂S₂?,the severe volume expansion?about 80%?of cathode materials during the electrochemical process and the“shuttle effect”of the lithium polysulfides?Li₂S_x,4?x?8?.In order to alleviate the problem,numerous strategies have been proposed to improve the cathode material and improve its electrochemical performance in Li-S batteries.Ionic liquid?IL?assisted synthesis methods have been studied in various areas for the excellent chemical and thermal stability,wide polarity and designable structure of ionic liquids.Based on that,in this thesis,carbon/sulfur composite cathode materials for lithium-sulfur batteries were prepared by ionic liquid assisted method,and their physical characteristics and electrochemical properties were characterized.The main research contents and results are as follows:?1?Ionic liquid assisted Pickering emulsion synthesis of graphene-based composite for Lithium sulfur batteries.In this chaper,we designed a porous carbon wrapped graphene-based nanosheet?M-GN?via a facile IL-microemulsion method.During the Pickering emulsion emulsification process,graphene oxide?GO?is used as a surfactant and a template,while the hydrophobic ionic liquid[BMIm]FeCl₄ serves as a stabilizer for GO and forms a stable emulsion environment.The strong electrostatic interaction between the negatively charged graphene oxide and the positively charged cation 1-butyl-3-methylimidazole?BMIm⁺?helps to form a stable microemulsion system,which can promote the uniform growth of the porous carbon layer on the GO surface.The S/M-GN cathode was prepared to provide a high discharge capacity of1331 mA h g^-1at 0.1 C and 757 mA h g^-1after 100 cycles at 0.5 C.?2?High performance carbon nanotube-based one-dimensional nanocomposites for lithium sulfur batteries.In this part,a W/IL system was formed to synthesize carbon nanotube-based one-dimensional nanocomposite C@CNT-IL.During the synthesis process,the hydrophobic ionic liquid?[BMIm]FeCl₄?plays a great role as a dispersing agent for carbon nanotubes.The prepared S/C@CNT-IL composite delivers a capacity of 1188 mA h g^-11 at the current rate of0.1 C,and 563 mA h g^-11 at the high current rate of 2 C.When tested at 0.5 C for 100 cycles,it stiu maintains a capacity of 610 mA h g^-1.