Study On Preparation Of Nickel Sulfur Based Composite Cathode Material

The rechargeable lithium-sulfur （Li/S） battery system, based on the mental lithium asanode and sulfur as cathode, is increasingly attractive due to its high theoretical specificcapacity and high theoretical specific energy. In addition, sulfur also has the advantage ofabundance, low cost, environment friendly. So Li/S battery system is the most promisecandidate for high specific energy rechargeable lithium battery. However, the insulatingnature of sulfur and discharge products and the loss of polysulfides in the electrolyteduring the charge-discharge processes result in low positive active material utilization andpoor cycle stability, which restricts the practical applications of lithium/sulfur battery.In this study, hollow nickel fiber tube was prepared by free-palladium electrolessplating and hydrogen plasma reducing method. Nickel fiber tube/sulfur composite positivematerial was prepared by means of adding mental nickel fiber tube into sulfur positive,which can adsorb and load active mass sulfur. In addition, different sulfur cathodecomposite materials were prepared by adding directly, heating treatment and immersionmethod. Surface morphology, composition and structure of sulfur positive compositematerials were characterized by scanning electron microscopy （SEM）, energy dispersiveX-ray spectrometry （EDAX） and X-ray diffraction （XRD）, respectively. Electrochemicalproperties of composite materials sulfur positive were analyzed by charge-discharge test,cycle performance test and alternating current impedance spectroscopy test.Hollow nickel fiber tube, which prepared by free-palladium electroless plating andhydrogen plasma reducing method, owns rough and micropore tube wall. The diameter ofthe tube and the thickness of wall are10¹5μm and0.7μm approximately, respectively.In this study, nickel fiber tube/sulfur composite cathode was prepared by addingdirectly and heating treatment. Electrochemical properties of nickel fiber tube/sulfurcomposite cathode, prepared by adding directly, were investigated under different nickelcontent and different discharge current density. The results indicate that nickel fibertube/sulfur composite cathode presents high discharge specific capacity and fine cycledischarge features. When discharge current density is0.2mA/cm², initial discharge specificcapacity of nickel fiber tube/sulfur composite cathode is954.5mAh/g and the dischargespecific capacity remains537.3mAh/g after30cycles. With the increase of nickel content, electrochemical properties of sulfur positive of the relevant content increase and thendecrease. Nickel content around15%is proper. At the condition of different dischargecurrent density, electrochemical properties of sulfur positive of nickel content around15%were further investigated. The results reveal sulfur cathode can endure large currentdischarge and display good cycle stability. Simultaneously, that different preparingmethods have an effect on electrochemical properties of lithium/sulfur battery wasinvestigated. By comparison, the study found that cycle ability of nickel fiber tube/sulfurcathode prepared by heating treatment was much better, but its capacity deceasedobviously.In this study, sulfur sol was fabricated though the reaction of Na₂S₂O₃and HClsolution. Sulfur/carbon fiber cloth composite material was prepared by immersion methodand its electrochemical performances were discussed. The results display that sulfur, in theform of nano-particle, is adhered on the surface of carbon fiber cloth. Under the conditionof o.2mA/cm²charge-discharge current density, initial discharge specific capacity ofcarbon fiber cloth/sulfur composite material cathode is965.2mAh/g and the dischargespecific capacity remains689.1mAh/g after30cycles, and the capacity retention is71.4%,which shows a good cycle performance.