•A novel core-shell Li2S@Li3PS4 composite is reported as cathode for Li-S battery.•It comprises highly crystal nano-Li2S and superionic conducting Li3PS4 coating layer.•The Li2S@Li3PS4/GA electrode shows low potential barrier (2.40 V) and overpotential.•The composite delivers high specific capacity of 934.4 mA h/g at 0.1 C rate.Lithium sulfide as a promising cathode material not only have a high theoretical specific capacity, but also can be paired with Li-free anode material to avoid potential safety issues. However, how to prepare high electrochemical performance material is still challenge. Herein, we present a facile way to obtain high crystal quality Li2S nanomaterials with average particle size of about 55 nm and coated with Li3PS4 to form the nano-scaled core-shell Li2S@Li3PS4 composite. Then nano-Li2S@Li3PS4/graphene aerogel is prepared by a simple liquid infiltration-evaporation coating process and used directly as a composite cathode without metal substrate for lithium-sulfur batteries. Electrochemical tests demonstrate that the composite delivers a high discharge capacity of 934.4 mAh g−1 in the initial cycle and retains 485.5 mAh g−1 after 100 cycles at 0.1 C rate. In addition, the composite exhibits much lower potential barrier (∼2.40 V) and overpotential compared with previous reports, indicating that Li2S needs only a little energy to be activated. The excellent electrochemical performances could be attributed to the tiny particle size of Li2S and the superionic conducting Li3PS4 coating layer, which can shorten Li-ion and electron diffusion paths, improve the ionic conductivity, as well as retarding polysulfides dissolution into the electrolyte to some extent.A novel core-shell Li2S@Li3PS4 composite with highly crystal nano-Li2S particles (ca. 55 nm) and superionic conducting Li3PS4 coating layer is introduced, and it shows low potential barrier (∼2.40 V) and overpotential as cathode for Li–S battery.Download high-res image (245KB)Download full-size image

•Hierarchical MnO2 nanoflakes are conformally deposited on CNTs based textiles.•The electrodeposition mechanism is investigated by time-dependent experiments.•The textiles show excellent flexibility and structural integrity after 2000 cycles.•A slight capacitance decrease even as the textiles vertically folded.In this paper, an ultrathin layer of acid treated multiwalled carbon nanotubes (CNTs) are conformally wrapped on everyday cotton textiles for subsequently controlled electrodeposition of MnO2 nanoflakes. The general morphology and detailed microstructure of the as-prepared composites are characterized and the formation mechanism is investigated by time-dependent experiments. Such conductive textiles show outstanding flexibility and strong adhesion between the CNTs and the textiles of interest. Supercapacitors made from these ternary conductive textiles show high specific capacitance up to 247 F·g−1 at 1 A·g−1. A capacity retention of 94.7% can be maintained at 2000 continuous charge-discharge cycles, after which the textiles electrode essentially maintained its whole structural integrity. The discharge curves remain unchanged with a slight capacitance decrease even under vertical folding condition. All these demonstrate that hybrid flexible electrode of MnO2 and conductive textile is an effective strategy towards high-energy supercapacitors and may provide a promising design direction for optimizing the electrochemical performance of insulating metal oxide based on electrode materials.

•3D porous GA/S nanocrystals are prepared by a one-step hydrothermal method.•The structure is affected by hydrothermal temperature and liquid sulfur’s viscosity.•The hybrid delivers a capacity of 716.2 mA h g−1 after 50 cycles at 100 mA g−1.•The nanosized S, strong adsorbability and intimate contact of GNS are main factors.Lithium–sulfur (Li–S) batteries are receiving significant attention as a new energy source because of its high theoretical capacity and specific energy. However, the low sulfur loading and large particles (usually in submicron dimension) in the cathode greatly offset its advantage in high energy density and lead to the instability of the cathode and rapid capacity decay. Herein, we introduce a one-step hydrothermal synthesis of three-dimensional porous graphene aerogels/sulfur nanocrystals to suppress the rapid fading of sulfur electrode. It is found that the hydrothermal temperature and viscosity of liquid sulfur have significant effects on particle size and loading mass of sulfur nanocrystals, graphitization degree of graphene and chemical bonding between sulfur and oxygen-containing groups of graphene. The hybrid could deliver a specific capacity of 716.2 mA h g−1 after 50 cycles at a current density of 100 mA g−1 and reversible capacity of 517.9 mA h g−1 at 1 A g−1. The performance we demonstrate herein suggests that Li–S battery may provide an opportunity for development of rechargeable battery systems.Figure optionsDownload full-size imageDownload as PowerPoint slide

A new porous graphene/NiO has been prepared successfully by hydrothermal method with graphene oxide solution, Ni(NO3)2·6H2O and urea as raw materials. The as-prepared composite is characterized by X-ray diffraction, Raman, FT-IR, SEM, TEM and nitrogen adsorption/desorption. It is shown that graphene sheets are well decorated by the NiO nanoparticles to form a hierarchical nanostructures with rich porosity (ca. 2–5 nm) and large specific surface area (174.1 m2 g−1). Electrochemical characterization demonstrates that the mesoporous graphene/NiO are capable of delivering a specific capacitance of 429.7 F g−1 at the current density of 200 mA g−1 and offer good capacitance retention of 86.1% at 1 A g−1 after 2000 continuous charge–discharge cycles. These rich and evenly distributed porosity could reduce the transportation distance and offer a robust sustentation of OH− ions due to its “ion-buffering reservoirs”, ensuring that sufficient Faradaic reactions can take place at the surfaces of electroactive NiO nanoparticles. It suggests that the hierarchical nanostructure is helpful in improving the electrochemical performance of the oxide.Graphical abstractHighlights► Graphene porous NiO nanocomposite is prepared by hydrothermal method. ► The hierarchical nanostructures possess rich porosity and large specific surface area. ► The rich and evenly distributed porosity offers a robust sustentation of OH− ions and reduce transportation distance during charge/discharge process. ► The composite delivers a capacitance of 342.9 F g−1 at 1 A g−1 with capacity retention of 86.1% after 2000 cycles.

Chemical lithiation of amorphous FePO4 with LiI in acetonitrile is performed to form amorphous LiFePO4. The amorphous FePO4·2H2O precursor is synthesized by co-precipitation method from equimolar aqueous solutions of FeSO4·7H2O and NH4H2PO4, using H2O2 (hydrogen peroxide) as the oxidizing agent. The nanocrystalline LiFePO4/C is obtained by annealing the amorphous LiFePO4 and in situ carbon coating with sucrose in a reducing atmosphere. The particle size of FePO4·2H2O precursor decreases with increasing reaction temperature. The final LiFePO4/C products completely maintain the shape and size of the precursor even after annealing at 700 °C for 2 h. The excellent electrochemical properties of these nanocrystalline LiFePO4/C composites suggest that to decrease the particle size of LiFePO4 is very effective in enhancing the rate capability and cycle performance. The specific discharge capacities of LiFePO4/C obtained from the FePO4·2H2O precursor synthesized at 75 °C are 151.8 and 133.5 mAh g−1 at 0.1 and 1 C rates, with a low capacity fading of about 0.075 % per cycle over 50 cycles at 0.5 C rate.

In this paper, graphene-modified Li3V2(PO4)3 composites have been developed as Li-ion battery cathode materials with high specific capacity and excellent cycling stability. The composites are prepared by spray–drying process using graphene oxide nanosheet and citric acid as carbon source. X-ray diffraction patterns demonstrate that the as-prepared samples are well crystallized with orderly monoclinic structures. SEM and TEM images reveal that the 3D network graphene and Li3V2(PO4)3 primary nanoparticles interlace with each other. The citric acid-derived amorphous carbon species interrupt the stacking of graphene sheets and minimize in-plane anisotropy of electronic migration within graphene layers, which would facilitate fast electron migration and Li+ diffusion throughout the micro-sized spherical secondary particles. The discharge capacity of the composite could respectively achieve 131.4 and 181.5 mAh g−1 in the voltage range 3.0–4.3 V and 3.0–4.8 V at 0.1C discharge rate, which almost reach the theoretical capacity of the cathode material. Both of them nearly showed no capacity decay at 0.1C charging and discharging rate after long cycles.Graphical abstractHighlights► Graphene-modified Li3V2(PO4)3 composites are produced by spray–drying process. ► 3D network graphene and Li3V2(PO4)3 primary nanoparticles interlace with each other. ► The citric acid-derived amorphous carbon interrupts the stacking of GNS and minimizes in-plane anisotropy of electronic migration within graphene layers. ► LVP/(G + C) sample exhibits the best electrochemical performances.

A novel ordered mesoporous carbon hybrid composite, CoO/CMK-3, is prepared by an infusing method using Co(NO3)2·6H2O as the cobalt source. The products are characterized by X-ray diffraction, transmission electron microscopy and N2 adsorption–desorption analysis techniques. It is observed that the CoO nanoparticles are loaded in the channels of mesoporous carbon. The mesopore structure of CMK-3 is destroyed gradually with increasing of the CoO content. The electrochemical properties of samples as the anode materials for lithium-ion batteries are studied by galvanostatic method. The results show that the CoO/CMK-3 composites have higher reversible capacities (more than 700 mAh g−1) and better cycle performance in comparison with the pure mesoporous carbon (CMK-3). Based on the above results, a mechanism is proposed to explain the reason of such a substantial improvement of electrochemical performance in the CoO/CMK-3 composites.

Graphene has aroused intensive interest because of its unique structure, superior properties, and various promising applications. Graphene nanostructures with significant disorder and defects have been considered to be poor materials because disorder and defects lower their electrical conductivity. In this paper, we report that highly disordered graphene nanosheets can find promising applications in high-capacity Li ion batteries because of their exceptionally high reversible capacities (794−1054 mA h/g) and good cyclic stability. To understand the Li storage mechanism of graphene nanosheets, we have prepared graphene nanosheets with structural parameters tunable via different reduction methods including hydrazine reduction, low-temperature pyrolysis, and electron beam irradiation. The effects of these parameters on Li storage properties were investigated systematically. A key structural parameter, Raman intensity ratio of D bands to G bands, has been identified to evaluate the reversible capacity. The greatly enhanced capacity in disordered graphene nanosheets is suggested to be mainly ascribed to additional reversible storage sites such as edges and other defects.

•GO-separator is used as a shuttle inhibitor of the Li–S battery.•Excellent polysulfide-diffusion inhibiting effect and cycle life are observed.•Much less sulfur and polysulfide species are tested in separator and electrolyte.•GO film still maintains 3D flexible porous structure with a few insoluble particles.•Less sulfate species, lithium salts and polysulfides are detected on the cathode.In this paper, graphene oxide (GO) is integrated on commercial polypropylene separator by tape casting method and sandwiched between a sulfur cathode and the separator as a shuttle inhibitor of the Li-S battery. The issues of lithium polysulfides dissolution and shuttle effect are inhibited distinctly, and significant improvements not only in the active material utilization but also in capacity retention are observed. What's more, the improvement mechanism is studied in detail. The results demonstrate that the sulfur and polysulfide species in separator and electrolyte for the cell with GO-coating separator are much less than that with the pristine separator. The GO membrane still maintains three-dimensional porous and flexible structure with a few lithium polysulfides and Li2S2/Li2S nanoparticles anchored on the surface and inter-layers of GO sheets after long cycles. And the active materials are significantly localized within the cathode structure after GO-coating. In addition, less sulfate species, lithium salts, polysulfides and other insoluble species are identified on the cathode and separator after long-term cycling.Graphene oxide coating separator is used to inhibit the shuttle effect of Li–S battery with improved electrochemical performance, and the improvement mechanism is studied.