The Fabrication And Electrochemical Characterization Of Freestanding Sulfur/Graphene Film Electrode

At present,the commercial lithium ion batteries have been unable to meet the ever growing demand for long driving range of electric vehicles.It is essential to develop the novel and high energy density battery system.Lithium sulfur battery,with a high theoretical mass energy density of 2600 Wh kg^-1 and volume energy density of 2800 Wh L^-1,is an ideal choice to replace the current commercial lithium ion battery.However,as the active material in cathode of lithium sulfur battery,sulfur is of low conductivity.Moreover,during the electrochemical reaction process,the polysulfides derived from sulfur can shuttle between the cathode and anode,leading to bad rate performance and cyclability.To solve the above issue,many researchers focus their research on the“shuttling effect”of lithium sulfur battery,ignoring the possible decrease of energy density.It is significant of maintaining the high energy density of lithium sulfur battery while alleviating the“shuttling effect”.Due to the introduction of conductive additives and binder,the energy density of battery will decrease.Thus,we adopt the reduction induced self-assembly and filtration to fabricate the flexible sulfur/graphene film.Through changing the stacking way of graphene,the obtained film shows different microstructure.The film fabricated from the reduction induced self-assembly exhibits macro-pores and the continuous conductive framework.The XPS test shows the chemisorption between sulfur and reduced graphene oxide.The electrolyte uptake test shows excellent absorbability of electrode.When cycling at 1.5 A g^-1 for 500 cycles,the capacity retention of film electrode is 78.4%,much better than the traditional coating electrode.More importantly,the film electrode delivers a relatively high energy density of 694kWh kg^-1.But the sulfur packing density in the electrode is only about 0.2 mg cm^-3,leading to a volume energy density of 255.2 Wh L^-1.In contrast,the film obtained by filtration gets a high packing density of 1.25 mg cm^-3.When used as electrode,the film delivers a volume and mass energy density of 1793 Wh L^-1 and 905.5 Wh kg^-1after 1200 cycles at a current density of 2 Ag^-1.