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Hybrid electric storage systems that combine capacitive and faradaic materials need to be well designed to benefit from the advantages of batteries and supercapacitors. The ultimate capacitive material is graphite (GR), yet high capacitance is usually not achieved due to restacking of its sheets. Therefore, an appealing approach to achieve high power and energy systems is to embed a faradaic 2D material in between the graphite sheets. Here, a simple one‐step approach was developed, whereby a faradaic material [layered double hydroxide (LDH)] was electrochemically formed inside electrochemically exfoliated graphite. Specifically, GR was exfoliated under negative potentials by CoII and, in the presence of MnII, formed GR‐CoMn‐LDH, which exhibited a high areal capacitance and energy density. The high areal capacitance was attributed to the exfoliation of the graphite at very negative potentials to form a 3D foam‐like structure driven by hydrogen evolution as well as the deposition of CoMn‐LDH due to hydroxide ion generation inside the GR sheets. The ratio between the CoII and MnII in the CoMn‐LDH was optimized and analyzed, and the electrochemical performance was studied. Analysis of a cross‐section of the GR‐CoMn‐LDH confirmed the deposition of LDH inside the GR layers. The areal capacitance of the electrode was 186 mF cm−2 at a scan rate of 2 mV s−1. Finally, an asymmetric supercapacitor was assembled with GR‐CoMn‐LDH and exfoliated graphite as the positive and negative electrodes, respectively, yielding an energy density of 96.1 μWh cm−3 and a power density of 5 mW cm−3. [ABSTRACT FROM AUTHOR]

Abstract Despite many efforts devoted to explore novel electrode materials for lithium ion hybrid supercapacitors, the obtainable long-life cycling of existing anode materials are still inadequate for promising applications. This report demonstrates a new nanocomposite with TiNb 2 O 7 network nanostructure in situ anchored onto the holey graphene, which is designed as anode material for lithium ion hybrid supercapacitors. Impressively, electrochemical analyses show that the good rate performance (capacity retention of 73.5% from 0.05 to 5 A g−1) and long cycle life up to 1000 cycles at 1 A g−1 (a capacity retention of 91.5%) are attained. Furthermore, the lithium ion hybrid supercapacitor device consisting of this nanocomposite and activated carbon exhibits excellent cycling stability (90.2% of initial capacity after 3000 cycles), high energy density of 86.3 W h kg−1 (at 237.7 W kg−1) and high power density of 3.88 kW kg−1 (at 28.7 W h kg−1). This study ascribes the unprecedented performance to the high conductive holey graphene with abundant mesopores, the uniformly distributed TiNb 2 O 7 network nanostructure and the synergetic effect between them. Based on these findings, the presented nanocomposite has great potential in high performance lithium ion hybrid supercapacitors. Graphical abstract Image 1 Highlights • A novel composite of TiNb 2 O 7 network nanostructure and holey graphene was fabricated. • The long-term life with 91.5% capacity retention after 1000 cycles was obtained. • The Li-HSC device exhibits high energy density and excellent cycling stability. [ABSTRACT FROM AUTHOR]

Abstract: A novel high-performance electrode material based on fibrillar polyaniline (PANI) doped with graphene oxide sheets was synthesized via in situ polymerization of monomer in the presence of graphene oxide, with a high conductivity of 10Scm−1 at 22°C for the obtained nanocomposite with a mass ratio of aniline/graphite oxide, 100:1. Its high specific capacitance of 531F/g was obtained in the potential range from 0 to 0.45V at 200mA/g by charge–discharge analysis compared to 216F/g of individual PANI. The doping and the ratio of graphene oxide have a pronounced effect on the electrochemical capacitance performance of the nanocomposites. [Copyright &y& Elsevier]

Highlights: [•] CoMoO4/Graphene composites were prepared via one-step hydrothermal method. [•] The composites have high surface/body ratios and large electroactive regions. [•] The composites present better electrochemical properties than pure-CoMoO4. [•] The composite achieves a capacitance of 394.5Fg−1 at 1mVs−1. [ABSTRACT FROM AUTHOR]

Abstract Sandwich-like ZIF-8 nanocrystal derived N-doped carbon decorated graphene sheets are developed through in-situ growth and followed by a thermal annealing treatment. The sandwich-like N-doped carbon decorated graphene sheets (NCGs) contain graphene substrate and the carbon nanoparticles with 30–50 nm in size. The sandwich-like NCGs generate a large specific surface area of 816.4 m2 g−1. With the high surface area and nitrogen doping, the as-fabricated NCGs as electrode materials for supercapacitor exhibit high specific capacitance of 225.0 F g−1 at 0.5 A g−1, an enhanced rate capability and excellent electrochemical stability with 96.8% retention after 10000 cycles even at 10 A g−1. The symmetry supercapacitor based on NCGs delivers an energy density of 12.7 Wh kg−1 at a specific power of 447 W kg−1. When the power density increases to 15126 W kg−1, the energy density can still keep 6.5 W h kg−1. Furthermore, the symmetry supercapacitor shows an excellent cycle stability with 96.6% capacitance retention at 2 A g−1 after 10000 cycles. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

To enhance the energy density of supercapacitors, an asymmetric supercapacitor was prepared by well-matched graphene@MnO 2 nanosheets (G@MnO 2 ) as cathode material and porous graphene as anode material. The hierarchical MnO 2 ultrathin nanosheets uniformly decorating on graphene sheets were prepared by polyaniline-assisted growth method. The obtained G@MnO 2 composite can provide fast electron transfer rate and efficient space to decrease the length of ion diffusion during energy storage. Therefore, the G@MnO 2 electrode exhibits a high specific capacitance reaching 245.0 F g −1 at 0.5 A g −1 , 74.5% of retention ratio at 20 A g −1 . Meanwhile the assembled asymmetric supercapacitor delivers a high energy density of 30.6 W h kg −1 , and a remarkable energy density of 7.9 W h kg −1 at ultrahigh power density of 11,804 W kg −1 due to the well-assembly of G@MnO 2 and porous graphene with the similar capacitance and rate performance. Moreover, the asymmetric supercapacitor also shows an excellent cycle life with 8.5% loss of the initial specific capacitance after 10,000 cycles. The excellent electrochemical performance of the asymmetric supercapacitor of G@MnO 2 //porous graphene makes it an attractive candidate for high power and energy storage systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Graphene/SnO2/PEDOT composites were obtained via one-pot synthesis method. [•] No obvious capacitance loss was found for the composite at 1Ag−1 after 5000 cycles in 1M H2SO4. [•] The composites present the enhanced capacitance and energy density in both acidic and neutral electrolytes. [ABSTRACT FROM AUTHOR]