Application Of Three-dimensional Graphene Material On Lithium-Sulfur Battery

Battery,which is widely applied in mobile communication,electric automobile and military project,is a kind of portable energy storage system that transforms chemical energy into electrical energy.Up to now,the most commercial battery product is Lithium-ion battery,but there exists little room for the improvement of its energy density,as a result,it would fail to satisfy human needs in the near future.On the contrary,Li-S battery,in which the sulfur serves as active material in the cathode,could offer a theoretical energy density of 2600 Wh kg^-1(the energy density forbattery is 387 Wh kg^-1),besides that,sulfur is abundant in the nature and environmental friendly.However,Li-S battery is suffering from the bad conductivity of elemental sulfur and its polysulfide intermediates.During the charge/discharge process,the polysulfide would partly dissolve in the electrolyte,which would lead to the shuttle effect and deteriorates the battery performances.Aiming to solve the problems above,we start with the graphene-based material,by constructing 3D structures and surface modification,we successfully created graphene-based sulfur composite.Such composite could adsorb sulfur/polysulfide in its structure;its morphology and electrochemical cycling performance are studied in details.?1?Graphene-polypyrrole membrane is synthesized via a hydrothermal-reduction process,sulfur is loaded into the membrane via solvent-method.When directly served as the cathode,the specific capacity of the composite is stabled at 790⁸10mA hg^-1 in the first 50 cycles at 0.2C rate While the polypyrrole-free graphene membrane witnessed a sharp declaration to 500 m A hg^-1.Such mechanism is investigated by EIS,which illustrated that the polypyrrole could effectively adsorb polysulfide,resulting in a more stable cycling performance in the battery.?2?Boron-doped graphene aerogel?BGA?is synthesized via a hydrothermalreduction process,sulfur is loaded into it via heat-melting treatment.The composite serves as cathode and is assembled into Li-S battery,its cycling performance is tested with nitrogen-doped graphene aerogel-sulfur composite?NGA-S?and undoped graphene aerogel-sulfur composite?GA-S?under the same condition.At 0.2C rate,it has a specific capacity of 1290 mA hg^-1 in the first cycle;after cycling for 100 runs,it maintains a capacity of 994 mA hg^-1.When the battery runs at varying rates such as 0.1C,0.2C,0.5C,1C,0.2C;the composite material offers a specific capacity of 1243,1028,938,864,808 mA hg^-1.On the contrary,both the NGA-S and GA-S material fail to exhibit such outstanding performance.The XPS indicates that there exists interaction between BGA material and sulfur/polysulfide,which would help to adsorb polysulfide during the charge/discharge progress.Further EIS investigation is also in accordance with the XPS result,explaining for the better cycling stability of BGA-S material.