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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.

This article reports a facile preparation of NiO/graphene composite by the combination of a controlled refluxing method with water based solvent in the presence of cetyltrimethylammonium bromide and subsequent annealing. X-ray diffraction and scanning electron microscopy reveal that the graphene nanosheets are uniformly wrapped by hierarchical porous NiO spheres with three-dimension hierarchical structure in the product. The composite shows highly improved electrochemical performance as electrode material for supercapacitor. The three-dimension hierarchical structure NiO/graphene composite delivers a first discharge capacitance of 555 F g −1 and remains a reversible capacitance up to 504 F g −1 after 2000 cycles at a current of 1 A g −1 in three-electrode system. Contrarily, the pure NiO shows only a first discharge capacitance of 166 F g −1 and remains only a reversible capacitance of 107 F g −1 after 2000 cycles. The NiO/graphene composite also exhibits ameliorative rate capacitance of 402.9 F g −1 at the current density of 5 A g −1 . The enhanced electrochemical performances are ascribed to the higher surface area, the stable three-dimension hierarchical structure and the synergistic effects between the conductive graphene and porous NiO spheres.

Lithium-sulfur battery has attracted notable attention because of its high special capacity (1675 mAh g−1). However, polysulfide dissolution and low electronic conductivity of sulfur cathode usually cause significant capacity fading during cycling. In this paper, we introduce a double-shelled structure of reduced graphene oxide@polyaniline@sulfur (rGO@PANI@S) composite, which not only can prevent volume expansion at sulfur charge/discharge process, inhibit lithium polysulfides dissolution and shuttle in the electrolyte, and also ensure a good electro-conductibility for sulfur cathode materials. The microstructure and electrochemical performance of the rGO@PANI@S cathode are investigated systematically. The results show that polyaniline inner shell with thickness of about 27.5 nm is coated uniformly on the surface of S submicron particles and few-layered reduced graphene oxide sheets are chemically bonded at the outer surface with a high sulfur content (74 wt%). When used as cathode for lithium-sulfur battery, the rGO@PANI@S composite shows an initial capacity of 1482.7 mAh g−1 at a rate of 100 mA g−1 and retains reversible capacity of 812.1 mAh g−1 over 100 cycles. This all-solution-based process is scalable and the double-shell wrapping structure has promising candidate in designing rechargeable sulfur cathode for application.

In this study, a nanorod-like Fe2O3/graphene nanocomposite is synthesized by a facile template-free hydrothermal method and a following calcination in air at 300 °C for 2 h. The Fe2O3 nanorods with diameter of 15–30 nm and length of 120–300 nm are homogenous distributed on both sides of graphene. The morphologies of intermediates at different hydrothermal reaction times are investigated by transmission electron microscopy (TEM) characterization, and a possible growth mechanism of this one-dimensional structure is proposed. It is shown that the α-FeOOH rodlike precursors are formed through a rolling-broken-growth (RBG) model, then the α-FeOOH is transformed into α-Fe2O3 nanorods during calcinations, preserving the same rodlike morphology. Electrochemical characterizations demonstrate that the Fe2O3 nanorod/graphene composites exhibit a very large reversible capacity of 1063.2 mAh/g at the charge/discharge rate of 0.1 C.

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.