S-doped mesoporous graphene modified separator for high performance lithium-sulfur batteries

Due to their low cost,environmental friendliness and high energy density,the lithium-sulfur batteries(LSB)have been regarded as a promising alternative for the next generation of rechargeable battery systems.However,the practical application of LSB is seriously hampered by its short cycle life and high self-charge owing to the apparent shuttle effect of soluble lithium polysulfides.Using MgSO_(4)@MgO composite as both template and dopant,template-guided S-doped mesoporous graphene(SMG)is prepared via the fluidized-bed chemical vapor deposition method.As the polypropylene(PP)modifier,SMG with high specific surface area,abundant mesoporous structures and moderate S doping content offers a wealth of physical and chemical adsorptive sites and reduced interfacial contact resistance,thereby restraining the serious shuttle effects of lithium polysulfides.Consequently,the LSB configured with mesoporous graphene(MG)as S host material and SMG as a separator modifier exhibits an enhanced electrochemical performance with a high average capacity of 955.64 mA h g^(-1) at 1C and a small capacity decay rate of 0.109%per cycle.Additionally,the density functional theory(DFT)calculation models have been rationally constructed and demonstrated that the doped S atoms in SMG possess higher binding energy to lithium polysulfides than that in MG,indicating that the SMG/PP separator can effectively capture soluble lithium polysulfides via chemical binding forces.This work would provide valuable insight into developing a versatile carbon-based separator modifier for LSB.

Structural evolution of mesoporous graphene/LiNi_(1/3)Co_(1/3)Mn_(1/3)O_(2) composite cathode for Li-ion battery

Layered LiMO_(2)(M=Ni,Co,and Mn) is a type of promising cathode materials for high energy density and high work voltage lithium-ion batteries.However,the poor rate performance and low power density hinder its further applications.The capacity fade is related to the structural transformation in the layered LiMO_(2).In this work,the structural changes of bi-material cathode composed of mesoporous graphene and layered LiNi_(1/3)Co_(1/3)Mn_(1/3)O_(2)(NCM) were studied via in situ X-ray diffraction(XRD).During different C-rate charge-discharge test at the voltage range of 2.5-4.1 V,the composite cathode of NCM-graphene(NCM-G) reveals better rate performances than pure NCM cathode.The NCM-G composite electrode displays a higher rate capability of 76.7 mAh·g^(-1) at 5 C rate,compared to the pure NCM cathode of 69.8 mAh·g^(-1)discharge capacity.The in situ XRD results indicate that a reversible phase transition from hexagonal H1 to hexagonal H2 occurs in layered NCM material during 1 C chargedischarge process.With the current increasing to 2 C/5 C,the structure of layered NCM material for both electrodes reveals few changes during charge and discharge processes,which indicates the less utilization of NCM component at high C-rates.Hence,the improved rate performance for bi-material electrode is attributed to the highly conductive mesoporous graphene and the synergistic effect of mesoporous graphene and NCM material.

Constructing a multifunctional mesoporous composite of metallic cobalt nanoparticles and nitrogen-doped reduced graphene oxides for high-performance lithium-sulfur batteries

Electrochemical properties of lithium-sulfur(Li-S)batteries are mainly hindered by both the insulating nature of elemental sulfur(i.e.,molecular S8)and the shuttling effect or sluggish redox kinetics of lithium polysulfide intermediates(Li_(2)S_(n),3≤n≤8).In this paper,a three-dimensional mesoporous reduced graphene oxide-based nanocomposite,with the embedding of metallic Co nanoparticles and the doping of elemental N(Co/NrGO),and its simply ground mixture with powdered S at a mass ratio of 1:6(Co/NrGO/S)are prepared and used as cathode-/separator-coated interlayers and working electrodes in assembled Li-S cells,respectively.One of the effective cell configurations is to paste composite Co/NrGO onto both the S-loading cathode and separator,showing good cycling stability(1070mAh g^(−1) in the 100th cycle at 0.2 C),highrate capability(835mAh g^(−1),2.0 C),and excellent durability(905mAh g^(−1) in the 250th cycle at 0.5 or 0.2 C).Compared with the experimental results of Co-absent NrGO,electrochemical properties of various Co/NrGO-based cell configurations clearly show multiple functions of Co/NrGO,indicating that the absence of Co/NrGO coatings and/or Co nanoparticles may be inadequate to achieve superior S availability of assembled Li-S batteries.

Mesoporous WO_3-graphene photocatalyst for photocatalytic degradation of Methylene Blue dye under visible light illumination

Advanced oxidation technologies are a friendly environmental approach for the remediation of industrial wastewaters. Here, one pot synthesis of mesoporous WO3 and WO3-graphene oxide（GO） nanocomposites has been performed through the sol–gel method. Then, platinum（Pt） nanoparticles were deposited onto the WO3 and WO3-GO nanocomposite through photochemical reduction to produce mesoporous Pt/WO3 and Pt/WO3-GO nanocomposites. X-ray diffraction（XRD） findings exhibit a formation of monoclinic and triclinic WO3 phases. Transmission Electron Microscope（TEM） images of Pt/WO3-GO nanocomposites exhibited that WO3 nanoparticles are obviously agglomerated and the particle sizes of Pt and WO3 are ~ 10 nm and 20–50 nm, respectively. The mesoporous Pt/WO3 and Pt/WO3-GO nanocomposites were assessed for photocatalytic degradation of Methylene Blue（MB） as a probe molecule under visible light illumination.The findings showed that mesoporous Pt/WO3, WO3-GO and Pt/WO3-GO nanocomposites exhibited much higher photocatalytic efficiencies than the pure WO3. The photodegradation rates by mesoporous Pt/WO3-GO nanocomposites are 3, 2 and 1.15 times greater than those by mesoporous WO3, WO3-GO, and Pt/WO3, respectively. The key factors of the enhanced photocatalytic performance of Pt/WO3-GO nanocomposites could be explained by the highly freedom electron transfer through the synergetic effect between WO3 and GO sheets, in addition to the Pt nanoparticles that act as active sites for O2 reduction, which suppresses the electron hole pair recombination in the Pt/WO3-GO nanocomposites.

Preparation of few-layer reduced graphene oxide-wrapped mesoporous Li4Ti5O12 spheres and its application as an anode material for lithium-ion batteries

A three-dimensional few-layer reduced graphene oxide-wrapped mesoporous Li4TisO12 （m-LTO@FL- RGO） electrode is produced using a simple solution fabrication process. When tested as an anode for Li- ion batteries, the m-LTO@FL-RGO composite exhibits excellent rate capability and superior cycle life. The capacity of m-LTO@FL-RGO reaches 165.4 mA h g 1 after 100 cycles between I and 2.5 V at a rate of 1 C. Even at a rate of 30 C, a high discharge capacity of 115.1 mA h g 1 is still obtained, which is three times higher than the pristine mesoporous Li4TisO12 （m-LTO）. The graphene nanosheets are incorporated into the m-LTO microspheres homogenously, which provide a high conductive network for electron transportation.

Sandwich-type ordered mesoporous carbon/graphene nanocomposites derived from ionic liquid

Sandwich-type ordered mesoporous carbon/graphene nanocomposites were successfully synthesized using 2D ordered mesoporous silica/graphene nanocomposites as the hard template and an ionic liquid as a N-rich carbon source. We used an ionic liquid of 1-(3-cyanopropyl)-3-methylimidazolium dicyanamide containing nitrile groups (–CN) in the cation and anion as a carbon precursor for the preparation of the nanocomposites. Nitriles do not decompose under thermal treatment in an inert gas atmosphere, but leave significant amounts of N-rich carbon materials. The nanocomposites had a large surface area (1,316 m2·g–1), an average pore diameter of 5.9 nm, and high electrical conductivity. The nanocomposite electrode showed a high specific capacitance of 190 F·g–1at 0.5 A·g–1in 1 M TEABF4/AN electrolyte and a good rate capability between 0 and 2.7 V for supercapacitor (or ultracapacitor) applications. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.