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© 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The development of high energy-density and low-cost energy storage devices requires new chemistry beyond the horizon of current state-of-the-art lithium-ion batteries. Recently, sodium/oxygen (Na/O2) batteries have attracted great attention as one possible battery type among the new generation of rechargeable batteries. They convince with superior energy density, a relatively simple cell reaction, and abundance of sodium. Research on Na/O2 batteries has progressed quickly in recent years. However, a fundamental understanding underpinning the complex chemical/electrochemical side reactions is still insufficient, and many challenges remain unsolved for real practical applications. Herein, recent achievements and remaining issues for the development of rechargeable Na/O2 batteries are summarized. The discussion focuses on cell reaction mechanisms as well as cathode materials, sodium anodes, and electrolytes as key components of this type of battery. Furthermore, perspectives for future research and technological advances of Na/O2 batteries are outlined.

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim As a new family member of room-temperature aprotic metal–O2 batteries, Na–O2 batteries, are attracting growing attention because of their relatively high theoretical specific energy and particularly their uncompromised round-trip efficiency. Here, a hierarchical porous carbon sphere (PCS) electrode that has outstanding properties to realize Na–O2 batteries with excellent electrochemical performances is reported. The controlled porosity of the PCS electrode, with macropores formed between PCSs and nanopores inside each PCS, enables effective formation/decomposition of NaO2 by facilitating the electrolyte impregnation and oxygen diffusion to the inner part of the oxygen electrode. In addition, the discharge product of NaO2 is deposited on the surface of individual PCSs with an unusual conformal film-like morphology, which can be more easily decomposed than the commonly observed microsized NaO2 cubes in Na–O2 batteries. A combination of coulometry, X-ray diffraction, and in situ differential electrochemical mass spectrometry provides compelling evidence that the operation of the PCS-based Na–O2 battery is underpinned by the formation and decomposition of NaO2. This work demonstrates that employing nanostructured carbon materials to control the porosity, pore-size distribution of the oxygen electrodes, and the morphology of the discharged NaO2 is a promising strategy to develop high-performance Na–O2 batteries.

Large over‐potentials owing to the sluggish kinetics of battery reactions have always been the drawbacks of Li−O2 batteries, which lead to short cycle life. Although redox mediators have been intensively investigated to overcome this issue, side‐reactions are generally induced by the solvated nature of redox mediators. Herein, we report an alternative method to achieve more efficient utilization of tetrathiafulvalene (TTF) in Li−O2 batteries. By coordinating TTF+ with LiCl during charging, an organic conductor TTF+Clx− precipitate covers Li2O2 to provide an additional electron‐transfer pathway on the surface, which can significantly reduce the charge over‐potential, improve the energy efficiency of Li−O2 batteries, and eliminate side‐reactions between the lithium metal anode and TTF+. When a porous graphene electrode is used, the Li−O2 battery combined with TTF and LiCl shows an outstanding performance and prolonged cycle life.

© 2016 Lithium-oxygen (Li–O2) batteries have the highest theoretical energy density amongst all rechargeable batteries and have attracted significant attention. However, large over-potentials originating from sluggish reaction kinetics often lead to low round-trip energy efficiency and short cycle life. We report here a novel multi-functional gel co-polymer that efficiently enhances the discharge and charge performances in Li–O2 batteries by intimately connecting the liquid electrolyte and solid cathode nanoparticles. On one hand, the co-polymer material, poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate-co-methyl methacrylate) (P(TMA-MMA)), functions as a binder during the fabrication of the cathode and forms a gel polymer membrane to retain liquid electrolyte and to increase ionic conductivity. On the other hand, the TMA units, containing N–O radical groups that catalyse Li2O2 formation and decomposition during charge and discharge cycles, are distributed throughout the polymer membrane. This allows more effective formation and decomposition of Li2O2 than surface bound catalytic units. The combination of gelable MMA and catalytic TMA moieties enhances the interface between liquid electrolyte and solid cathode by functioning as a medium both to transport Li+ (enhancing discharge process) and to carry electrons (reducing charge over-potential). Consequently, the optimized P(TMA-MMA) co-polymers provide exceptional electrochemical performance in Li–O2 batteries.

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Nitrogen-doped porous carbon nanosheets were prepared from eucalyptus tree leaves by simply mixing the leaf powders with KHCO3 and subsequent carbonisation. Porous carbon nanosheets with a high specific surface area of 2133 m2g-1 were obtained and applied as electrode materials for supercapacitors and lithium ion batteries. For supercapacitor applications, the porous carbon nanosheet electrode exhibited a supercapacitance of 372 Fg-1 at a current density of 500 mAg-1 in 1m H2SO4 aqueous electrolyte and excellent cycling stability over 15000 cycles. In organic electrolyte, the nanosheet electrode showed a specific capacitance of 71 Fg-1 at a current density of 2 Ag-1 and stable cycling performance. When applied as the anode material for lithium ion batteries, the as-prepared porous carbon nanosheets also demonstrated a high specific capacity of 819 mAhg-1 at a current density of 100 mAg-1, good rate capability, and stable cycling performance. The outstanding electrochemical performances for both supercapacitors and lithium ion batteries are derived from the large specific surface area, porous nanosheet structure and nitrogen doping effects. The strategy developed in this paper provides a novel route to utilise biomass-derived materials for low-cost energy storage systems.

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Sodium-ion batteries (NIBs) are an emerging technology, which can meet increasing demands for large-scale energy storage. One of the most promising cathode material candidates for sodium-ion batteries is Na3V2(PO4)3 due to its high capacity, thermal stability, and sodium (Na) Superionic Conductor 3D (NASICON)-type framework. In this work, the authors have significantly improved electrochemical performance and cycling stability of Na3V2(PO4)3 by introducing a 3D interconnected conductive network in the form of carbon fiber derived from ordinary paper towel. The free-standing Na3V2(PO4)3-carbon paper (Na3V2(PO4)3@CP) hybrid electrodes do not require a metallic current collector, polymeric binder, or conducting additives to function as a cathode material in an NIB system. The Na3V2(PO4)3@CP cathode demonstrates extraordinary long term cycling stability for 30 000 deep charge–discharge cycles at a current density of 2.5 mA cm−2. Such outstanding cycling stability can meet the stringent requirements for renewable energy storage.

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Large over-potentials owing to the sluggish kinetics of battery reactions have always been the drawbacks of Li−O2 batteries, which lead to short cycle life. Although redox mediators have been intensively investigated to overcome this issue, side-reactions are generally induced by the solvated nature of redox mediators. Herein, we report an alternative method to achieve more efficient utilization of tetrathiafulvalene (TTF) in Li−O2 batteries. By coordinating TTF+ with LiCl during charging, an organic conductor TTF+Clx− precipitate covers Li2O2 to provide an additional electron-transfer pathway on the surface, which can significantly reduce the charge over-potential, improve the energy efficiency of Li−O2 batteries, and eliminate side-reactions between the lithium metal anode and TTF+. When a porous graphene electrode is used, the Li−O2 battery combined with TTF and LiCl shows an outstanding performance and prolonged cycle life.

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. We hereby report carbon-coated LiFePO4 cathode materials prepared by industrial ball milling and a solid-state reaction with Li2CO3, NH4H2PO4, and FeC2O4⋅2H2O as starting materials. Soluble starch as the primary carbon source was investigated for its capability of generating a highly graphitic carbon coating, whilst sufficiently controlling the crystal growth of LiFePO4. XRD analysis, Raman spectroscopy, and electrochemical testing revealed the significant impact of the amount of starch added to the pre-sintered precursor on phase purity, carbon quality, and electrochemical performance of the final LiFePO4/C composite. The optimum soluble starch content to achieve a highly sp2-coordinated carbon coating is 10wt%, which enabled our LiFePO4/C composite to achieve competitive reversible capacities as well as improved rate performance.

© 2015 Elsevier B.V. All rights reserved. This work introduces a simple microwave method for the preparation of α-Fe2O3 nanoparticles with two different sizes. Both the materials were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller methods. The lithium storage properties were evaluated and compared in terms of their reversible capacity, rate capability and cycling performance. Interestingly, the electrode made of large particles (200-300 nm) show the reversible capacity of 1012 mA h g-1, better rate capability and excellent cycling stability than those of the small particles (20-30 nm). The poor electrochemical performances of small particles can be ascribed to their agglomeration during repeated charging and discharge process. The agglomeration of small particles may substantially decrease the surface area, which results in the lack of sufficient electro active sites for electrochemical reaction.

© 2015 Wiley-VCH Verlag GmbH & Co. KGaA , Weinheim. A facile microwave method was employed to synthesize NiCo2O4 nanosheets as electrode materials for lithium-ion batteries and supercapacitors. The structure and morphology of the materials were characterized by X-ray diffraction, fieldemission scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller methods. Owing to the porous nanosheet structure, the NiCo2O4 electrodes exhibited a high reversible capacity of 891 mAhg-1 at a current density of 100 mAg-1, good rate capability and stable cycling performance. When used as electrode materials for supercapacitors, NiCo2O4 nanosheets demonstrated a specific capacitance of 400 Fg-1 at a current density of 20 Ag-1 and superior cycling stability over 5000 cycles. The excellent electrochemical performance could be ascribed to the thin porous structure of the nanosheets, which provides a high specific surface area to increase the electrode-electrolyte contact area and facilitate rapid ion transport.

© The Royal Society of Chemistry. Graphene-based semiconductor photocatalysis has been regarded as a promising technology for solar energy storage and conversion. In this review, we summarized recent developments of graphene-based photocatalysts, including preparation of graphene-based photocatalysts, typical key advances in the understanding of graphene functions for photocatalytic activity enhancement and methodologies to regulate the electron transfer efficiency in graphene-based composite photocatalysts, by which we hope to offer enriched information to harvest the utmost fascinating properties of graphene as a platform to construct efficient graphene-based composite photocatalysts for solar-to-energy conversion.

Gamma-ray line emission from the radioactive decay of 26Al reflects nucleosynthesis in massive stars and supernovae. We use INTEGRAL 26Al measurements to characterize the distribution and characteristics of 26Al source regions throughout the Galaxy. We detect the 26Al line from the inner Galaxy at 28��significance. The line appears narrow, and we constrain broadening in the source regions to 5deg., 13 pages, 12 figures, accepted for the publication in A&A

The search for gamma-ray line emission from the radioactive decay of 60Fe figures among the prime scientific objectives of the INTEGRAL mission. 60Fe is believed to be primarily produced in core-collapse supernovae, although other sites, such as carbon deflagration supernovae or intermediate mass AGB stars have also been suggested. We present first results of our search for the 1173 and 1332 keV gamma-ray lines of 60Fe decay in the SPI data of the first mission year. So far we can only report upper flux limits whose levels are determined by systematic uncertainties in the treatment of the instrumental background. Once we understand the background uncertainties better, the SPI data should provide stringent constraints on 60Fe nucleosynthesis in our Galaxy., Comment: 5 pages, to appear in the Proceedings of the 5th INTEGRAL Workshop (Munich, Germany)

The precision measurement of the 1809 keV gamma-ray line from Galactic $^{26}$Al is one of the goals of the SPI spectrometer on INTEGRAL with its Ge detector camera. We aim for determination of the detailed shape of this gamma-ray line, and its variation for different source regions along the plane of the Galaxy. Data from the first part of the core program observations of the first mission year have been inspected. A clear detection of the \Al line at about 5--7 $\sigma$ significance demonstrates that SPI will deepen \Al studies. The line intensity is consistent with expectations from previous experiments, and the line appears narrower than the 5.4 keV FWHM reported by GRIS, more consistent with RHESSI's recent value. Only preliminary statements can be made at this time, however, due to the multi-component background underlying the signal at \about 40 times higher intensity than the signal from Galactic $^{26}$Al., Comment: 5 pages, 8 figures; accepted for publication in A&A (special INTEGRAL volume)

The shape of the gamma-ray line from radioactive 26Al, at 1808.7 keV energy in the frame of the decaying isotope, is determined by its kinematics when it decays, typically 10^6 y after its ejection into the interstellar medium from its nucleosynthesis source. Three measurements of the line width exist: HEAO-C's 1982 value of (0+3) keV FWHM, the GRIS 1996 value of (5.4 +/- 1.3) keV FWHM, and the recent RHESSI value of (2.0 +/- 0.8) keV FWHM, suggesting either "cold", "hot", or "warm" 26Al in the ISM. We model the line width as expected from Galactic rotation, expanding supernova ejecta, and/or Wolf-Rayet winds, and predict a value below 1 keV (FWHM) with plausible assumptions about 26Al initial velocities and expansion history. Even though the recent RHESSI measurement reduces the need to explain a broad line corresponding to 540 km/s mean 26Al velocity through extreme assumptions about grain transport of 26Al or huge interstellar cavities, our results suggest that standard 26Al ejection models produce a line on the narrow side of what is observed by RHESSI and INTEGRAL. Improved INTEGRAL and RHESSI spatially-resolved line width measurements should help to disentangle the effects of Galactic rotation from the ISM trajectories of 26Al., Comment: 5 pages, 4 figures, accepted for publication in A&A

The observation of the interstellar 1.809 MeV decay-line of radioactive 26Al by the imaging gamma-ray telescope COMPTEL have let to the conclusion, that massive stars and their subsequent core-collapse supernovae are the dominant sources of the interstellar 26Al abundance. Massive stars are known to affect the surrounding interstellar medium by their energetic stellar winds and by the emission of ionising radiation. We present a population synthesis model allowing the correlated investigation of the gamma-ray emission characteristics with integrated matter, kinetic energy and extreme ultra-violet radiation emission of associations of massive stars. We study the time evolution of the various observables. In addition, we discuss systematic as well as statistical uncertainties affecting the model. Beside uncertainties in the input stellar physics such as stellar rotation, mass loss rates or internal mixing modifications due to a unknown binary component may lead to significant uncertainties., Comment: 10 pages, 7 figures, to appear in Proc. "Influence of Binaries on Stellar Population Studies", eds. Vanbeveren & Van Rensbergen, Brussels, Aug. 2000

The COMPTEL map of the 1.809 MeV gamma-ray line, which is attributed to the radioactive decay of 26Al, shows significant excess emission in the Cygnus region. Cygnus is a region of recent star formation activity, which is rich in massive, early-type stars concentrated in OB associations. We perform population synthesis studies of this region to model the production and distribution of 26Al, which is predominantly synthesized in massive stars and distributed through stellar winds and core-collapse supernovae. Our simulations of the Cygnus OB associations determine the time-dependent production rate of 26Al. We also estimate the associated production of radioactive 60Fe, which is primarily synthesized in core-collapse supernovae. Gamma-ray line emission from this isotope has yet to be detected. We also track the temporal evolution of the mechanical "luminosity" due to the kinetic energy of stellar winds and supernova ejecta, and the ionizing EUV emission from early-type stars. Together with a simple one-dimensional model of the superbubble driven into the ISM by this energy flux one can constrain key parameters of the stellar associations in the Cygnus region., Comment: 5 pages, 5 figures, accepted for publication in the proceedings of the 4th INTEGRAL workshop, to appear in ESA-SP series