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© 2017, Tsinghua University Press and Springer-Verlag GmbH Germany. Activated graphene (AG) with various specific surface areas, pore volumes, and average pore sizes is fabricated and applied as a matrix for sulfur. The impacts of the AG pore structure parameters and sulfur loadings on the electrochemical performance of lithium-sulfur batteries are systematically investigated. The results show that specific capacity, cycling performance, and Coulombic efficiency of the batteries are closely linked to the pore structure and sulfur loading. An AG3/S composite electrode with a high sulfur loading of 72 wt.% exhibited an excellent long-term cycling stability (50% capacity retention over 1,000 cycles) and extra-low capacity fade rate (0.05% per cycle). In addition, when LiNO3 was used as an electrolyte additive, the AG3/S electrode exhibited a similar capacity retention and high Coulombic efficiency (∼98%) over 1,000 cycles. The excellent electrochemical performance of the series of AG3/S electrodes is attributed to the mixed micro/mesoporous structure, high surface area, and good electrical conductivity of the AG matrices and the well-distributed sulfur within the micro/mesopores, which is beneficial for electrical and ionic transfer during cycling. [Figure not available: see fulltext.].

Metal fluoride-lithium batteries with potentially high energy densities, even higher than lithium-sulfur batteries, are viewed as very promising candidates for next-generation lightweight and low-cost rechargeable batteries. However, so far, metal fluoride cathodes have suffered from poor electronic conductivity, sluggish reaction kinetics and side reactions causing high voltage hysteresis, poor rate capability, and rapid capacity degradation upon cycling. Herein, it is reported that an FeF3 @C composite having a 3D honeycomb architecture synthesized by a simple method may overcome these issues. The FeF3 nanoparticles (10-50 nm) are uniformly embedded in the 3D honeycomb carbon framework where the honeycomb walls and hexagonal-like channels provide sufficient pathways for the fast electron and Li-ion diffusion, respectively. As a result, the as-produced 3D honeycomb FeF3 @C composite cathodes even with high areal FeF3 loadings of 2.2 and 5.3 mg cm-2 offer unprecedented rate capability up to 100 C and remarkable cycle stability within 1000 cycles, displaying capacity retentions of 95%-100% within 200 cycles at various C rates, and ≈85% at 2C within 1000 cycles. The reported results demonstrate that the 3D honeycomb architecture is a powerful composite design for conversion-type metal fluorides to achieve excellent electrochemical performance in metal fluoride-lithium batteries.

With the porous feature, high aspect ratio and high electronic conductivity, nitrogen-doped one-dimensional carbon nanofibers can effectively shorten ionic transport pathways and enhance the intrinsic electronic conductivity of metal selenides electrodes, showing a great potential as anode material for the next-generation lithium-ion batteries (LIBs). In this work, we have synthesized nitrogen-doped carbon nanofibers encapsulated Cu2-xSe (N-CNFs@Cu2-xSe) with an average particle size of 20 nm, via electrospinning and in-situ selenization process, giving an excellent lithium storage capability. Specifically, such electrodes delivered a specific capacity of 1079.1 mA h g−1 at 0.1 A g−1 after 100 cycles, while 639.4 mA h g−1 at 2 A g−1 after 1000 cycles, exhibiting an ultralong cycle life. The gradually increased capacity was attributed to phase transformation of Cu2-xSe from crystalline to amorphous state, which leads to the capacity improvement from increased capacitive behavior. The in-situ X-ray diffraction harvest at the real time state of battery demonstrated the phase transition of Cu2-xSe with lithium and phase regeneration among cycles, verifying copper selenide has the features of the high reversibility of conversion reaction and superior thermostability. The high capacity and long cycling life of N CNFs@Cu2-xSe make it possible for great application potentials for high-performance lithium-ion batteries.

Sodium-ion batteries (SIBs) are recognized as an alternative to lithium ion batteries due to the abundance of sodium and potentially low cost of the whole battery system. One of the major challenges facing SIBs is to develop suitable anode materials with high capacity and long cycling life. Herein, we report the synthesis of porous carbon nanocage-Sn (PCNCs-Sn) nanocomposites as anodes of SIBs, demonstrating a high capacity of 828 mAh g −1 at 40 mA g −1 . The electrodes also exhibited good rate capabilities (up to 3C) and superior cycling performances (1000 cycles). Post-mortem analyses verified the efficient volume change restriction by carbon nanocages and the well-preserved porous structure. Theoretical calculations indicated that the pulverization of bare Sn electrodes could be ascribed to strong bonds formed between amorphous carbon and the discharge product (Na 15 Sn 4 ), which also deteriorated the conductivity. In contrast, the relatively weak interaction between Na 15 Sn 4 and graphitic carbon can maintain superior conductivity and structural stability for better cycling performance.

© 2016 The Royal Society of Chemistry. Lithium-ion batteries (LIBs) are widely implemented to power portable electronic devices and are increasingly in demand for large-scale applications. One of the major obstacles for this technology is still the low cost-efficiency of its electrochemical active materials and production processes. In this work, we present a novel impregnation-carbothermal reduction method to generate a LiFePO4-carbon paper hybrid electrode, which doesn't require a metallic current collector, polymeric binder or conducting additives to function as a cathode material in a LIB system. A shell of LiFePO4 crystals was grown in situ on carbon fibres during the carbonization of microcrystalline cellulose. The LiFePO4-carbon paper electrode achieved an initial reversible areal capacity of 197 μA h cm-2 increasing to 222 μA h cm-2 after 500 cycles at a current density of 0.1 mA cm-2. The hybrid electrode also demonstrated a superior cycling performance for up to 1000 cycles. The free-standing electrode could be potentially applied for flexible lithium-ion batteries.

This work introduces a simple microwave method for the preparation of α-Fe 2 O 3 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.

Metal molybdates are regarding as promising electrode materials for next-generation lithium-ion batteries (LIBs). However, the poor electronic conductivity and sluggish ion diffusion are the two main obstacles that limit their electrochemical performances. In this work, self-assembled hierarchical Fe2(MoO4)3 microspheres with a thin amorphous shell (FMO-A) were prepared via a morphology-tunable and template-free hydrothermal method as an example of metal molybdates for LIBs. The morphologies were easily tunable by changing experimental parameters, such as the pH value, and reaction time. When applied as anode of LIBs, FMO-A delivered a high reversible capacity of 1138.2 mAh g−1 after 250 cycles at 100 mA g−1 and displayed remarkable rate performances. This is mainly ascribed to the unique hierarchical structure and high surface area of Fe2(MoO4)3 and the thin amorphous shell on providing low Gibbs free energy on redox reactions, reduced grain boundaries, isotropic nature, and buffering volume variations during cycles.

Sodium-ion batteries are emerging as promising candidates for grid energy storage because of the abundant sodium resources and low cost. However, the identification and development of suitable anode materials is far from being satisfactory. Here, it is demonstrated that the Ti

Sodium-ion batteries (SIB) are regarded as the most promising competitors to lithium-ion batteries in spite of expected electrochemical disadvantages. Here a "cross-linking" strategy is proposed to mitigate the typical SIB problems. We present a SIB full battery that exhibits a working potential of 3.3 V and an energy density of 180 Wh kg

The lithium-sulfur battery is considered as one of the most promising energy storage systems and has received enormous attentions due to its high energy density and low cost. However, polysulfide dissolution and the resulting shuttle effects hinder its practical application unless very costly solutions are considered. Herein, a sulfur-rich polymer termed sulfur-limonene polysulfide is proposed as powerful electroactive material that uniquely combines decisive advantages and leads out of this dilemma. It is amenable to a large-scale synthesis by the abundant, inexpensive, and environmentally benign raw materials sulfur and limonene (from orange and lemon peels). Moreover, owing to self-protection and confinement of lithium sulfide and sulfur, detrimental dissolution and shuttle effects are successfully avoided. The sulfur-limonene-based electrodes (without elaborate synthesis or surface modification) exhibit excellent electrochemical performances characterized by high discharge capacities (≈1000 mA h g-1 at C/2) and remarkable cycle stability (average fading rate as low as 0.008% per cycle during 300 cycles).

Achieving rechargeable batteries with high-energy density, long cycle life and excellent rate capability is of significant importance for a vast energy-consuming society. Lithium sulfur (Li–S) batteries, attracting extensive attentions, are regarded as one of the most promising energy storage system. However, Li–S batteries are facing big challenges, owing to the fast capacity degradation, low Coulombic efficiency and poor rate capabilities. By adopting a dual confinement strategy, we successfully synthesized homogenous poly(3,4-ethylenedioxythiophene) (PEDOT) coated multi-chambered micro/mesoporous carbon nanocube encapsulated sulfur (P@CNC-S) composites. Sulfur is impregnated in individual interconnected multi-chambered micro/mesoporous carbon nanocubes, which act as the physical confinement and multilayered reservoirs for soluble lithium polysulfides. The PEDOT conductive polymer provides chemical bondings to soluble lithium polysulfides. When applied as cathodes in Li–S batteries, the P@CNC-S composites exhibited superior performances, including high specific capacities, long cycle life and outstanding high rate capabilities. Ex-situ TEM analysis confirmed the successful confinement of the dissolution of lithium polysulfides and volume expansion of the discharged product (Li2S), which could contribute to the high Coulombic efficiency and excellent cyclabilities.

Low-cost and sustainable sodium-ion batteries are regarded as a promising technology for large-scale energy storage and conversion. The development of high-rate anode materials is highly desirable for sodium-ion batteries. The optimization of mass transport and electron transfer is crucial in the discovery of electrode materials with good high-rate performances. Herein, we report the synthesis of 3 D interconnected SnO2 /graphene aerogels with a hierarchically porous structure as anode materials for sodium-ion batteries. The unique 3 D architecture was prepared by a facile in situ process, during which cross-linked 3 D conductive graphene networks with macro-/meso-sized hierarchical pores were formed and SnO2 nanoparticles were dispersed uniformly on the graphene surface simultaneously. Such a 3 D functional architecture not only facilitates the electrode-electrolyte interaction but also provides an efficient electron pathway within the graphene networks. When applied as anode materials in sodium-ion batteries, the as-prepared SnO2 /graphene aerogel exhibited high reversible capacity, improved cycling performance compared to SnO2 , and promising high-rate capability.

© 2014 Elsevier B.V. Porous polymer membrane with a sandwich-like architecture has been prepared by coating poly(methyl methacrylate) (PMMA) on poly(vinylidene fluoride-co-hexafluoropylene) (PVDF-HFP) porous membranes. Field emission scanning electron microscopy analysis identified that the PMMA/PVDF-HFP porous polymer membrane consists of the stacking of several porous layers with one layer of large pores in the middle of the membrane. This unique sandwich-like structure provides large porosity and good affinity towards a liquid organic electrolyte, leading to a high electrolyte uptake of 342wt%, excellent electrolyte retention, and enhanced tolerance towards high temperature and fire. The gel polymer electrolyte membrane achieved a high ionic conductivity of 1.31mScm-1 with similar activation energy as the conventional Celgard 2400 separator in liquid electrolyte. The porous polymer electrolyte membrane also has an outstanding thermal and electrochemical stability. When applied in lithium ion batteries with LiFePO4 cathode and lithium metal anode, the PMMA/PVDF-HFP electrolyte membrane demonstrated high discharge capacity, enhanced high rate capability, and extended cycle life. The PMMA/PVDF-HFP porous polymer membrane could be employed as an integrated separator and electrolyte for lithium ion batteries with high safety.

Lithium-ion batteries are receiving considerable attention for large-scale energy-storage systems. However, to date the current cathode/anode system cannot satisfy safety, cost, and performance requirements for such applications. Here, a lithium-ion full battery based on the combination of a Li

Sodium-ion batteries (SIBs) have attracted increasing attention in the past decades, because of high overall abundance of precursors, their even geographical distribution, and low cost. Apart from inherent thermodynamic disadvantages, SIBs have to overcome multiple kinetic problems, such as fast capacity decay, low rate capacities and low Coulombic efficiencies. A special case is sodium super ion conductor (NASICON)-based electrode materials as they exhibit - besides pronounced structural stability - exceptionally high ion conductivity, rendering them most promising for sodium storage. Owing to the limiting, comparatively low electronic conductivity, nano-structuring is a prerequisite for achieving satisfactory rate-capability. In this review, we analyze advantages and disadvantages of NASICON-type electrode materials and highlight electrode structure design principles for obtaining the desired electrochemical performance. Moreover, we give an overview of recent approaches to enhance electrical conductivity and structural stability of cathode and anode materials based on NASICON structure. We believe that this review provides a pertinent insight into relevant design principles and inspires further research in this respect.

Lithium ion capacitors are new energy storage devices combining the complementary features of both electric double-layer capacitors and lithium ion batteries. A key limitation to this technology is the kinetic imbalance between the Faradaic insertion electrode and capacitive electrode. Here, we demonstrate that the Li

A novel single-step microwave-assisted process has been developed to synthesize spherical β-Ni(OH)2 superstructures without using any templates. Structure characterizations show that the spherical β-Ni(OH)2 composed of twisted nanosheets was obtained. The electrochemical properties of the as-prepared materials were evaluated by cyclic voltammetry and chronopotentiometry technology in 2 M KOH solution. Due to the unique morphology, the prepared β-Ni(OH)2 electrode displays a high specific capacitance of 2147 F g−1 at a discharge current of 1 A g−1 and outstanding cycling stability (99.5% capacitance retained after 2000 cycles), suggesting its potential application as an efficient electrode material for high-performance electrochemical capacitors.

Abandoned peanut shells, a common farm waste, have caused tremendous environmental pollution and huge waste deposits through burned and buried disposal approaches. In targeting to enhance the potential value of peanut shells and discover a new alternative candidate for lithium ion batteries, we adopted an easy to scale-up and highly repeated method to treat fresh and dry peanut shells via acid-treatment and pyrolysis, making porous structures on carbonized peanut shells. The pyrolysis process transformed the peanut shells to porous carbon (PC) materials in a quartz tube furnace at a series of temperatures from 500°C to 700°C in N2 under the condition of 40°C gradient temperatures with a heating rate of 2°C min−1. Scanning electron microscopy (SEM) images show that the irregular porous structures and hundreds of micropores are distributed on the PC materials. The cyclic voltammogram (CV) test and particle size analysis are employed to investigate their characteristics of voltammetry and particle size distribution. PC material obtained at 620°C (PC-620) exhibited good particle distribution, porous structure and less agglomerated particles. When applied as anode materials in lithium ion batteries, the PC-620 electrode displayed the high reversible capacity of 608 mAh g−1. Moreover, the cycling performance of PC-620 was the most stable, with a high Coulombic efficiency of 98.9% at the 20th cycle, demonstrating a reversible capacity of 418 mAh g−1, which is higher than the theoretical capacity of graphite. Most importantly, the PC materials harvested from the wastes of natural resources are turned into valuable electrode materials for the high demand energy storage devices, which can significantly reduce severe environmental pollution and alleviate an energy shortage. Open image in new window

Lithium–sulfur batteries are regarded as a promising energy storage system. However, they are plagued by rapid capacity decay, low coulombic efficiency, a severe shuttle effect and low sulfur loading in cathodes. To address these problems, effective carriers are highly demanded to encapsulate sulfur and extend the cycle life. Here, we report an aqueous emulsion approach and in situ sulfur impregnation to synthesize multi-shelled hollow carbon nanosphere-encapsulated sulfur composites with a high percentage of sulfur loading (86 wt%). When applied as cathodes in lithium–sulfur batteries, the composite materials delivered a high specific capacity of 1350 mA h g−1 and excellent capacity retention (92% for 200 cycles). Further measurements at high current densities also demonstrate significantly enhanced cyclability and high rate capability.

Urchin-like NiO nanospheres were synthesised by a microwave hydrothermal method. The as-synthesised NiO nanospheres were characterised by X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. It was found that NiO nanosphere consists of a nanoporous structure and nanosize crystals. When applied as anode materials in lithium-ion batteries, NiO nanospheres exhibited a high reversible specific capacity of 1027 mA h g-1, an excellent cycling performance and a good high rate capability. NiO nanospheres also showed a high specific capacitance as electrode materials for supercapacitors. © 2013 Elsevier B.V. All rights reserved.

Nickel hydroxide nanosheets were synthesized by a simple microwave assisted heating method and investigated as electrochemical pseudo-capacitive materials for supercapacitors. The crystalline structure and morphology of the as-obtained Ni(OH)2 nanosheets were characterized by X-ray diffraction, nitrogen adsorption–desorption isotherms, field emission scanning electron microscopy and transmission electron microscopy. The electrochemical properties of the Ni(OH)2 nanosheets were evaluated by cyclic voltammetry and chronopotentiometry technology in 2 M KOH solution. The nickel hydroxide nanosheet electrode shows a maximum specific capacitance of 2570 F g−1 at a current density of 5 A g−1 and exhibits superior cycling stability. These results suggest its potential application as an electrode material for supercapacitors.

We report a simple synthetic approach to coaxially grow transition metal oxide (TMO) nanostructures on carbon nanotubes (CNT) with ready control of phase and morphology. A thin (~4 nm) sulfonated-polystyrene (SPS) pre-coating is essential for the deposition of transition metal based materials. This layer has abundant sulfonic groups (−SO3−) that can effectively attract Ni2+, Co2+, Zn2+ ions through electrostatic interaction and induce them via hydrolysis, dehydration and recrystallization to form coaxial (NiO, Co3O4, NiCoO2 and ZnCo2O4) shells and a nanosheet-like morphology around CNT. These structures possess a large active surface and enhanced structural robustness when used as electrode materials for lithium-ion batteries (LIBs) and electrochemical capacitors (ECs). As electrodes for LIBs, the ZnCo2O4@CNT material shows extremely stable cycling performance with a discharge capacity of 1068 mAh g−1 after 100 cycles at a current density of 400 mAg−1. For EC applications, the NiCoO2@CNT exhibits a high capacitance of 1360 Fg−1 at current densities of 10 Ag−1 after 3000 cycles and an overall capacitance loss of only 1.4%. These results demonstrate the potential of such hybrid materials meeting the crucial requirements of cycling stability and high rate capability for energy conversion and storage devices.

Silicon has been recognized as the most promising anode material for high capacity lithium ion batteries. However, large volume variations during charge and discharge result in pulverization of Si electrodes and fast capacity loss on cycling. This drawback of Si electrodes can be overcome by combination with well-organized graphene foam. In this work, hierarchical three-dimensional carbon-coated mesoporous Si nanospheres@graphene foam (C@Si@GF) nanoarchitectures were successfully synthesized by a thermal bubble ejection assisted chemical-vapor-deposition and magnesiothermic reduction method. The morphology and structure of the as-prepared nanocomposites were characterized by field emission scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. When employed as anode materials in lithium ion batteries, C@Si@GF nanocomposites exhibited superior electrochemical performance including a high specific capacity of 1,200 mAh/g at the current density of 1 A/g, excellent high rate capabilities and an outstanding cyclability. Post-mortem analyses identified that the morphology of 3D C@Si@GF electrodes after 200 cycles was well maintained. The synergistic effects arising from the combination of mesoporous Si nanospheres and graphene foam nanoarchitectures may address the intractable pulverization problem of Si electrode. [Figure not available: see fulltext.] © 2014 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

Nickel oxide nanosheets have been successfully synthesized by a facile ethylene glycol mediated hydrothermal method. The morphology and crystal structure of the nickel oxide nanosheets were characterized by X-ray diffraction, field-emission SEM, and TEM. When applied as electrode materials for lithium-ion batteries and supercapacitors, nickel oxide nanosheets exhibited a high, reversible lithium storage capacity of 1193 mA h g-1 at a current density of 500 mA g-1, an enhanced rate capability, and good cycling stability. Nickel oxide nanosheets also demonstrated a superior specific capacitance of 999 F g-1 at a current density of 20 A g-1 in supercapacitors. Between the sheets: NiO nanosheets were synthesized by a facile ethylene glycol mediated hydrothermal method (see picture). The NiO nanosheets exhibited a high, reversible lithium storage capacity of 1193 mA h g-1 at a current density of 500 mA g-1 for lithium-ion batteries and a superior specific capacitance of 999 F g-1 at a current density of 20 A g-1 in supercapacitors. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fe 2 O 3 –CNT–graphene nanosheet (Fe 2 O 3 –CNT–GNS) hybrid materials were synthesized using a chemical vapor deposition method. The as-prepared materials consist of Fe 2 O 3 nanorings, bamboo-like carbon nanotubes and graphene nanosheets, which form an open three-dimensional architecture . For the first time, we observed the growth of bamboo-like carbon nanotubes with open tips, which were catalyzed by iron nanorings. When applied as anode materials in lithium ion batteries, the Fe 2 O 3 –CNT–GNS hybrid materials exhibited a high specific capacity of 984 mAh g −1 with a superior cycling stability and high rate capability. This could be ascribed to short Li + diffusion path of bamboo-like CNTs, more active reaction sites provided by graphene layers inside CNTs, flexible and highly conductive graphene nanosheets, and an open three-dimensional structure.

Typical layered transition‐metal chalcogenide materials, in particular layered molybdenum disulfide (MoS2) nanocomposites, have attracted increasing attention in recent years due to their excellent chemical and physical properties in various research fieldsHere, a general overview of synthetic MoS2 based nanocomposites via different preparation approaches and their applications in energy storage devices (Li‐ion battery, Na‐ion battery, and supercapacitor) is presented. The relationship between morphologies and the electrochemical performances of MoS2‐based nanocomposites in the three typical and promising rechargeable systems is also discussed. Finally, perspectives on major challenges and opportunities faced by MoS2‐based materials to address the practical problems of MoS2‐based materials are presented.

Tinegraphene nanocomposites are prepared by a combination of microwave hydrothermal synthesis and a one-step hydrogen gas reduction. Altering the weight ratio between tin and graphene nanosheets has critical influences on their morphologies and electrochemical performances. Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) analysis confirm the homogeneous distribution of tin nanoparticles on the surface of graphene nanosheets. When applied as an anode material in lithium ion batteries, tinegraphene nanocomposite exhibits a high lithium storage capacity of 1407 mAh g

Sodium-ion batteries are emerging as promising candidates for grid energy storage because of the abundant sodium resources and low cost. However, the identification and development of suitable anode materials is far from being satisfactory. Here, it is demonstrated that the Ti2 Nb2 O9 nanosheets with tunnel structure can be used as suitable anode materials for sodium-ion batteries. Ti2 Nb2 O9 nanosheets are synthesized by liquid exfoliation combined with topotactic dehydration, delivering a high reversible capacity of 250 mAh g-1 at 50 mA g-1 at a suitable average voltage of ≈0.7 V. It is found that a low energy diffusion barrier, enlarged interlayer spacing, and exceptional nanoporosity together give rise to high rate performance characterized by pseudocapacitive behavior. The observed high reversible capacity, excellent rate capability, and good cyclability of Ti2 Nb2 O9 nanosheets make this material competitive when compared to other sodium insertion anode materials.

This paper reports the preparation and Li-storage properties of graphene nanosheets(GNS), GNS supported Sn–Sb@carbon (50–150 nm) and Sn–Sb nanoparticles (5–10 nm). The best cycling performance and excellent high rate capabilities were observed for GNS-supported Sn–Sb@carbon core-shell particles, which exhibited initial capacities of 978, 850 and 668 mAh/g respectively at 0.1C, 2C and 5C (1C=800 mA/g) with good cyclability. Besides the GNS support, the carbon skin around Sn–Sb particles is believed to be a key factor to improve electrochemical properties of Sn–Sb. Keywords: Core-shell nanostructure, Graphene nanosheets, Lithium-ion battery, Sn-Sb

SnO2/nitrogen-doped graphene nanohybrids have been synthesized by an in situ hydrothermal method, during which the formation of SnO2 nanocrystals and nitrogen doping of graphene occur simultaneously. The as-prepared SnO2/nitrogen-doped graphene nanohybrids exhibit enhanced electrochemical performance for sodium-ion batteries compared to SnO2/graphene nanocomposites. A systematic comparison between SnO2/nitrogen-doped graphene nanohybrids and the SnO2/graphene counterpart as anode materials for sodium-ion batteries has been conducted. The comparison is in a reasonable framework, where SnO2/nitrogen-doped graphene nanohybrids and the SnO2/graphene counterpart have the same SnO2 ratio, similar SnO2 crystallinity and particle size, close surface area and pore size. The results clearly manifest that the improved electron transfer efficiency of SnO2/nitrogen-doped graphene due to nitrogen-doping plays a more important role than the increased electro-active sites within graphene network in enhancing the electro-activity of SnO2/nitrogen-doped graphene nanohybrids compared to the SnO2/graphene counterpart. In contrast to the previous reports which often ascribe the enhanced electro-activity of nitrogen-doped graphene based composites to two nitrogen-doping effects (improving the electron transfer efficiency and increasing electro-active sites within graphene networks) in one single declaration, this work is expected to provide more specific information for understanding the effects of nitrogen-doping into graphene on improving the electrochemical performance of graphene based composites.

Mesoporous Co3O4 nanoflakes with an interconnected architecture were successfully synthesized using a microwave-assisted hydrothermal and low-temperature conversion method, which exhibited excellent electrochemical performances as anode materials in lithium ion batteries and as catalysts in the oxygen evolution reaction (OER). Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) observations showed the unique interconnected and mesoporous structure. When employed as anode materials for lithium ion batteries, mesoporous Co3O4 nanoflakes delivered a high specific capacity of 883 mAh/g at 0.1C current rate and stable cycling performances even at higher current rates. Post-mortem analysis of ex situ FESEM images revealed that the mesoporous and interconnected structure had been well maintained after long-term cycling. The mesoporous Co3O4 nanoflakes also showed both OER active properties and good catalytic stability. This could be attributed to both the stability of unique mesoporous structure and highly reactive facets.

Graphene-Co3O4 composite with a unique sandwich-architecture was successfully synthesized and applied as an efficient electrocatalyst for oxygen evolution reaction. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses confirmed that Co3O4 nanocrystals were homogeneously distributed on both sides of graphene nanosheets. The obtained composite shows enhanced catalytic activities in both alkaline and neutral electrolytes. The onset potential towards the oxygen evolution reaction is 0.406 V (vs. Ag/AgCl) in 1 M KOH solution, and 0.858 V (vs. Ag/AgCl) in neutral phosphate buffer solution (PBS), respectively. The current density of 10 mA/cm2 has been achieved at the overpotential of 313 mV in 1 M KOH and 498 mV in PBS. The graphene-Co3O4 composite also exhibited an excellent stability in both alkaline and neutral electrolytes. In particular, no obvious current density decay was observed after 10 hours testing in alkaline solution and the morphology of the material was well maintained, which could be ascribed to the synergistic effect of combining Co3O4 and graphene.

Lithium ion capacitors are new energy storage devices combining the complementary features of both electric double-layer capacitors and lithium ion batteries. A key limitation to this technology is the kinetic imbalance between the Faradaic insertion electrode and capacitive electrode. Here, we demonstrate that the Li3 VO4 with low Li-ion insertion voltage and fast kinetics can be favorably used for lithium ion capacitors. N-doped carbon-encapsulated Li3 VO4 nanowires are synthesized through a morphology-inheritance route, displaying a low insertion voltage between 0.2 and 1.0 V, a high reversible capacity of ≈400 mAh g-1 at 0.1 A g-1 , excellent rate capability, and long-term cycling stability. Benefiting from the small nanoparticles, low energy diffusion barrier and highly localized charge-transfer, the Li3 VO4 /N-doped carbon nanowires exhibit a high-rate pseudocapacitive behavior. A lithium ion capacitor device based on these Li3 VO4 /N-doped carbon nanowires delivers a high energy density of 136.4 Wh kg-1 at a power density of 532 W kg-1 , revealing the potential for application in high-performance and long life energy storage devices.

To address the challenge of huge volume change and unstable solid electrolyte interface (SEI) of silicon in cycles, causing severe pulverization, this paper proposes a "double-shell" concept. This concept is designed to perform dual functions on encapsulating volume change of silicon and stabilizing SEI layer in cycles using double carbon shells. Double carbon shells coated Si nanoparticles (DCS-Si) are prepared. Inner carbon shell provides finite inner voids to allow large volume changes of Si nanoparticles inside of inner carbon shell, while static outer shell facilitates the formation of stable SEI. Most importantly, intershell spaces are preserved to buffer volume changes and alleviate mechanical stress from inner carbon shell. DCS-Si electrodes display a high rechargeable specific capacity of 1802 mAh g-1 at a current rate of 0.2 C, superior rate capability and good cycling performance up to 1000 cycles. A full cell of DCS-Si//LiNi0.45 Co0.1 Mn1.45 O4 exhibits an average discharge voltage of 4.2 V, a high energy density of 473.6 Wh kg-1 , and good cycling performance. Such double-shell concept can be applied to synthesize other electrode materials with large volume changes in cycles by simultaneously enhancing electronic conductivity and controlling SEI growth.

A mesoporous flake-like manganese-cobalt composite oxide (MnCo2O4) is synthesized successfully through the hydrothermal method. The crystalline phase and morphology of the materials are characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller methods. The flake-like MnCo2O4 is evaluated as the anode material for lithium-ion batteries. Owing to its mesoporous nature, it exhibits a high reversible capacity of 1066 mA h g(-1), good rate capability, and superior cycling stability. As an electrode material for supercapacitors, the flake-like MnCo2O4 also demonstrates a high supercapacitance of 1487 F g(-1) at a current density of 1 A g(-1), and an exceptional cycling performance over 2000 charge/discharge cycles.

A facile microwave method was employed to synthesize NiCo2 O4 nanosheets as electrode materials for lithium-ion batteries and supercapacitors. The structure and morphology of the materials were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller methods. Owing to the porous nanosheet structure, the NiCo2 O4 electrodes exhibited a high reversible capacity of 891 mA h g(-1) at a current density of 100 mA g(-1) , good rate capability and stable cycling performance. When used as electrode materials for supercapacitors, NiCo2 O4 nanosheets demonstrated a specific capacitance of 400 F g(-1) at a current density of 20 A g(-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.

Graphene-Co₃O₄ composite with a unique sandwich-architecture was successfully synthesized and applied as an efficient electrocatalyst for oxygen evolution reaction. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses confirmed that Co₃O₄ nanocrystals were homogeneously distributed on both sides of graphene nanosheets. The obtained composite shows enhanced catalytic activities in both alkaline and neutral electrolytes. The onset potential towards the oxygen evolution reaction is 0.406 V (vs. Ag/AgCl) in 1 M KOH solution, and 0.858 V (vs. Ag/AgCl) in neutral phosphate buffer solution (PBS), respectively. The current density of 10 mA/cm(2) has been achieved at the overpotential of 313 mV in 1 M KOH and 498 mV in PBS. The graphene-Co₃O₄ composite also exhibited an excellent stability in both alkaline and neutral electrolytes. In particular, no obvious current density decay was observed after 10 hours testing in alkaline solution and the morphology of the material was well maintained, which could be ascribed to the synergistic effect of combining Co₃O₄ and graphene.

Highly porous NiCo2O4 nanoflakes and nanobelts were synthesized by using a hydrothermal technique, followed by calcination of the NiCo2O4 precursors. The as-synthesized materials were analyzed by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and Brunauer-Emmett-Teller methods. The NiCo2O4 nanoflakes and nanobelts were applied as anode materials for lithium-ion batteries. Owing to the unique porous structural features, the NiCo2O4 nanoflakes and nanobelts exhibited high specific capacities of 1033 and 1056 mA h g(-1), respectively, and good cycling stability and rate capability. These exceptional electrochemical performances could be ascribed to the remarkable structural feature with a high surface area and void spaces within the surface of nanoflakes and nanobelts, which provide large contact areas between electrolyte and active materials for electrolyte diffusion and cushion the volume variation during the lithium-ion insertion/extraction process.

3D mesoporous hybrid NiCo2O4@graphene nanoarchitectures were successfully synthesized by a combination of freeze drying and hydrothermal reaction. Field-emission scanning electron microscopy (FESEM) and TEM analyses revealed that the NiCo2O 4@graphene nanostructures consist of a hierarchical mesoporous sheet-on-sheet nanoarchitecture with a high specific surface area of 194 m 2 g-1. Ultrathin NiCo2O4 nanosheets, with a thickness of a few nanometers and mesopores ranging from 2 to 5 nm, were wrapped in graphene nanosheets and hybrid nanoarchitectures were formed. When applied as electrode materials in supercapacitors, the hybrid NiCo 2O4@graphene nanosheets exhibited a high capacitance of 778 F g-1 at a current density of 1 A g-1, and an excellent cycling performance extending to 10000 cycles at a high current density of 10 A g-1. This journal is © the Partner Organisations 2014.

Lithium-sulfur batteries have been plagued for a long time by low Coulombic efficiency, fast capacity loss, and poor high rate performance. Here, the synthesis of 3D hyperbranched hollow carbon nanorod encapsulated sulfur nanocomposites as cathode materials for lithium-sulfur batteries is reported. The sulfur nanocomposite cathodes deliver a high specific capacity of 1378 mAh g-1 at a 0.1C current rate and exhibit stable cycling performance. The as-prepared sulfur nanocomposites also achieve excellent high rate capacities and cyclability, such as 990 mAh g-1 at 1C, 861 mAh g -1 at 5C, and 663 mAh g-1 at 10C, extending to more than 500 cycles. The superior electrochemical performance are ascribed to the unique 3D hyperbranched hollow carbon nanorod architectures and high length/radius aspect ratio of the carbon nanorods, which can effectively prevent the dissolution of polysulfides, decrease self-discharge, and confine the volume expansion on cycling. High capacity, excellent high-rate performance, and long cycle life render the as-developed sulfur/carbon nanorod nanocomposites a promising cathode material for lithium-sulfur batteries. 3D hyperbranched carbon nanorod-sulfur nanocomposites are synthesized and applied as cathode materials for lithium-sulfur batteries. The composite materials deliver high specific capacity, excellent high rate capability, and extended cycle life. The superior performance is attributed to the nanomaze architecture and high aspect ratio of carbon nanorods, which suppress the dissolution of polysulfides and confine volume expansion. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The electrochemical performance of lithium-oxygen (Li-O2) batteries awaits dramatic improvement in the design of porous cathode electrodes with sufficient spaces to accommodate the discharge products and discovery of effective cathode catalysts to promote both oxygen reduction reactions and oxygen evolution reactions. Herein, we report the synthesis of porous graphene with different pore size architectures as cathode catalysts for Li-O2 batteries. Porous graphene materials exhibited significantly higher discharge capacities than that of nonporous graphene. Furthermore, porous graphene with pore diameter around 250 nm showed the highest discharge capacity among the porous graphene with the small pores (about 60 nm) and large pores (about 400 nm). Moreover, we discovered that addition of ruthenium (Ru) nanocrystals to porous graphene promotes the oxygen evolution reaction. The Ru nanocrystal-decorated porous graphene exhibited an excellent catalytic activity as cathodes in Li-O2 batteries with a high reversible capacity of 17,700 mA h g(-1), a low charge/discharge overpotential (about 0.355 V), and a long cycle life up to 200 cycles (under the curtaining capacity of 1000 mAh g(-1)). The novel porous graphene architecture inspires the development of high-performance Li-O2 batteries.

Lithium ion batteries have shown great potential in applications as power sources for electric vehicles and large-scale energy storage. However, the direct uses of flammable organic liquid electrolyte with commercial separator induce serious safety problems including the risk of fire and explosion. Herein, we report the development of poly(vinylidene difluoride-co-hexafluoropropylene) polymer membranes with multi-sized honeycomb-like porous architectures. The as-prepared polymer electrolyte membranes contain porosity as high as 78%, which leads to the high electrolyte uptake of 86.2 wt%. The PVDF-HFP gel polymer electrolyte membranes exhibited a high ionic conductivity of 1.03 mS cm(-1) at room temperature, which is much higher than that of commercial polymer membranes. Moreover, the as-obtained gel polymer membranes are also thermally stable up to 350 °C and non-combustible in fire (fire-proof). When applied in lithium ion batteries with LiFePO4 as cathode materials, the gel polymer electrolyte demonstrated excellent electrochemical performances. This investigation indicates that PVDF-HFP gel polymer membranes could be potentially applicable for high power lithium ion batteries with the features of high safety, low cost and good performance.

Graphene/MnO2 hybrid nanosheets were prepared by incorporating graphene and MnO2 nanosheets in ethylene glycol. Scanning electron microscopy and transmission electron microscopy analyses confirmed nanosheet morphology of the hybrid materials. Graphene/MnO2 hybrid nanosheets with different ratios were investigated as electrode materials for supercapacitors by cyclic voltammetry (CV) and galvanostatic charge-discharge in 1 M Na2SO4 electrolyte. We found that the graphene/MnO2 hybrid nanosheets with a weight ratio of 1:4 (graphene:MnO2) delivered the highest specific capacitance of 320 F g-1. Graphene/MnO2 hybrid nanosheets also exhibited good capacitance retention on 2000 cycles. © 2013 Elsevier B.V. All rights reserved.

Na-ion batteries have been attracting intensive investigations as a possible alternative to Li-ion batteries. Herein, we report the synthesis of SnS2 nanoplatelet@graphene nanocomposites by using a morphology-controlled hydrothermal method. The as-prepared SnS2/graphene nanocomposites present a unique two-dimensional platelet-on-sheet nanoarchitecture, which has been identified by scanning and transmission electron microscopy. When applied as the anode material for Na-ion batteries, the SnS2/graphene nanosheets achieved a high reversible specific sodium-ion storage capacity of 725 mA h g(-1), stable cyclability, and an enhanced high-rate capability. The improved electrochemical performance for reversible sodium-ion storage could be ascribed to the synergistic effects of the SnS2 nanoplatelet/graphene nanosheets as an integrated hybrid nanoarchitecture, in which the graphene nanosheets provide electronic conductivity and cushion for the active SnS2 nanoplatelets during Na-ion insertion and extraction processes.