A molybdenum disulfide (MoS 2 ) nanosheet was grown directly on a surface of reduced graphene oxide (RGO) by using a one-step hydrothermal growth technique. The samples were systematically characterized by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HRTEM). The electrochemical properties were evaluated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy tests in two-electrode cells. The results indicate that the synthesized MoS 2 /RGO composites show excellent electrochemical performance as anode materials for Na-ion batteries. The MoS 2 /RGO composites exhibit an initial discharge capacity of 715.5 mAh g -1 and an initial charge capacity of 440.5 mAh g -1 at a current density of 100 mA g -1 . The composites also exhibit excellent cycling stability with almost no capacity fading after 100 cycles at a current density of 250 mA g -1 compared with only 39.6% of that for pure MoS 2 , and the electrode shows stable highrate performance. The superior electrochemical performance of the MoS 2 /RGO composites as Na-ion battery anodes may be attributed to their loose structure and the excellent conductivity of reduced graphene oxide in MoS 2 /RGO.
A molybdenum disulfide/carbon (MoS2/C) nanocomposite was synthesized by a simple hydrothermal method using glucose as a carbon source followed by carbonization. The sample was systematically investigated by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Electrochemical performances were evaluated in two-electrode cells versus metallic sodium. The synthesized MoS2/C composite exhibits an initial capacity of 475.1 mAh g -1 at a current density of 100 mA g -1 , and a capacity retention of 71% is obtained after 100 cycles at a current density of 250 mA g -1 . The material shows enhanced electrochemical performances compared with pristine MoS2 due to incorporation of the conductive carbon, which suppressed significant volumetric change in MoS2 during the charge/discharge process and increased the electrical conductivity of MoS2.
A porous TiO2 particle is synthesized and used as a sulfur host. The obtained TiO2 material provides a large number of pores that can accommodate sulfur, and the porous structure also enables effective contact between the host material and lithium polysulfides.
The TiO2/S electrode shows excellent electrochemical performance, exhibiting a capacity loss of 0.17% per cycle and a Coulombic efficiency of 97.7% during cycling at 0.5 C. The appealing results are due to the porous characteristics of the TiO2 material and the chemical
adsorption between the TiO2 and lithium polysulfides.
Lithium-sulfur (Li-S) batteries have been widely studied in recent years, but the utilization of sulfur cathode is still limited by the low conductivity of cathode material and dissolution of polysulfides. A polypyrrole (PPy) coated reduced graphene oxide/S (RGO/S@PPy) material was synthesized in this study. It is shown that sulfur is uniformly distributed on RGO sheets, and a PPy layer is homogeneously coated on the surface of the RGO/S composite. The PPy coating relieves the dissolution of polysulfides and improves the utilization of active sulfur. As a result, a discharge capacity of 631 mA h g-1 after 300 cycles at 0.2C and an excellent rate capability are obtained.
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