Study On Preparation Of Lithium/Sulfur Battery With Carbon/Sulfur-modified Cathode

On account of sulfur’s high abundance，low cost，non-pollution and safety，lithium/sulfur battery with high energy density has been researched for many years.However，lithium/sulfur battery is actually difficult to be applied in practical use for itspoor conductivity and the loss of polysulfide in the liquid organic electrolyte. In this study，making use of the metal’s good electrical conductivity and high specific surface area，stable chemical performance of carbon material，a carbon nanofiber/nickel compositematerial was prepared. Morphology and the structure of composite fiber material werecharacterized by scanning electron microscopy，X-ray diffraction and energy dispersivespectrometer separately， the electrochemical properties of assembled batteries weremeasured by cycle test and electrochemical workstation.Uniform nickel layer on chemical fiber was prepared by electroless Ni plating，eliminate fiber structure to get hollow nickel fiber which the diameter is about10μm byusing the SEM. Carbon nanofiber(CNF) were deposited on hollow nickel fiber atappropriate hydro-carbon scale and temperature conditions in chemical vapor depositiondevice，carbon film was deposited on the fiber with the appropriate microwave power andcarbon content. When the microwave power is500W，H2/CH4ratio is100/6，the pressureis4.0KPa at chemical vapor deposition process，carbon nanofibers are uniform depositedouter and inner port of the hollow nickel fiber，the average diameter of fiber is about50nm，thickness of carbon film is about3μm，the depth of fiber at inner port can bereached10μm. XRD results showed that the composition of composite fibers includeCNF，Ni3P，Nickel and the structure of carbon nanofiber is graphite phase.A variety of sulfur-containing cathode with different additive amount of compositedfiber were prepared，Results show that the discharge performance is improved when thecontent of composite fiber is above5%. When mass content of CNF/Ni composite fiber is7%and current density is200mA/g，initial discharge specific capacity of the electrode is1059.9mAh/g and then decrease to750.5mAh/g after30cycles. Moreover，the electrodeexhibits preferable discharge performance at0.5C. The composite material which has covered with carbon nanofiber improve the performance of own conduction andadsorption，hollow tube structure can offer expansion volume for active material of storagespace.The impedance spectra at different discharge/charge of depth are taken byelectrochemical workstation，then using equivalent circuit to analysis the changes of Re、Rs，Rct respectively. Results show that the cycle discharge performance is mainly affect bypolysulfide solvent in electrolyte solution and non-conductive insoluble Li2S，adding thecomposite fiber in cathode can improve the battery performance.