Tailoring MoS2 Ultrathin Sheets Anchored on Graphene Flexible Supports for Superstable Lithium‐Ion Battery Anodes

2D MoS₂ has a significant capacity decay due to the stack of layers during the charge/discharge process, which has seriously restricted its practical application in lithium‐ion batteries. Herein, a simple preform‐in situ process to fabricate vertically grown MoS₂ nanosheets with 8–12 layers anchored on reduced graphene oxide (rGO) flexible supports is presented. As an anode in MoS₂/rGO//Li half‐cell, the MoS₂/rGO electrode shows a high initial coulomb efficiency (84.1%) and excellent capacity retention (84.7% after 100 cycles) at a current density of 100 mA g^?1. Moreover, the MoS₂/rGO electrode keeps capacity as high as 786 mAh g^?1 after 1000 cycles with minimum degradation of 54 µAh g^?1 cycle^?1 after being further tested at a high current density of 1000 mA g^?1. When evaluated in a MoS₂/rGO//LiCoO₂ full‐cell, it delivers an initial charge capacity of 153 mAh g^?1 at a current density of 100 mA g^?1 and achieves an energy density of 208 Wh kg^?1 under the power density of 220 W kg^?1.     

A High‐Performance Anode Material for Li‐Ion Batteries Based on a Vertically Aligned CNTs/NiCo2O4 Core/Shell Structure

3D vertically aligned carbon nanotubes (CNTs)/NiCo₂O₄ core/shell structures are successfully synthesized as binder‐free anode materials for Li‐ion batteries (LIBs) via a facile electrochemical deposition method followed by subsequent annealing in air. The vertically aligned CNTs/NiCo₂O₄ core/shell structures are used as binder‐free anode materials for LIBs and exhibit high and stable reversible capacity (1147.6 mAhg^?1 at 100 mAg^?1), excellent rate capability (712.9 mAh g^?1 at 1000 mAg^?1), and good cycle stability (no capacity fading over 200 cycles). The improved performance of these LIBs is attributed to the unique 3D vertically aligned CNTs/NiCo₂O₄ core/shell structures, which support high electron conductivity, fast ion/electron transport in the electrode and at the electrolyte/electrode interface, and accommodate the volume change during cycling. Furthermore, the synthetic strategy presented can be easily extended to fabricate other metal oxides with a controlled core/shell structure, which may be a promising electrode material for high‐performance LIBs.     

Liquid‐Crystal‐Mediated Self‐Assembly of Porous α‐Fe2O3 Nanorods on PEDOT:PSS‐Functionalized Graphene as a Flexible Ternary Architecture for Capacitive Energy Storage

A novel aqueous‐based self‐assembly approach to a composite of iron oxide nanorods on conductive‐polymer (CP)‐functionalized, ultralarge graphene oxide (GO) liquid crystals (LCs) is demonstrated here for the fabrication of a flexible hybrid material for charge capacitive application. Uniform decoration of α‐Fe₂O₃ nanorods on a poly(3,4‐ethylene‐dioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)‐functionalized, ultralarge GO scaffold results in a 3D interconnected layer‐by‐layer (LBL) architecture. This advanced interpenetrating network of ternary components is lightweight, foldable, and possesses highly conductive pathways for facile ion transportation and charge storage, making it promising for high‐performance energy‐storage applications. Having such structural merits and good synergistic effects, the flexible architecture exhibits a high specific discharge capacitance of 875 F g^?1 and excellent volumetric specific capacitance of 868 F cm^?3 at 5 mV s^?1, as well as a promising energy density of 118 W h kg^?1 (at 0.5 A g^?1) and promising cyclability, with capacity retention of 100% after 5000 charge–discharge (CD) cycles. This synthesis method provides a simple, yet efficient approach for the solution‐processed LBL insertion of the hematite nanorods (HNR) into CP‐functionalized novel composite structure. It provides great promise for the fabrication of a variety of metal‐oxide (MO)‐nanomaterial‐based binder and current collector‐free flexible composite electrodes for high‐performance energy‐storage applications.     

MoO2@MoS2 Nanoarchitectures for High‐Loading Advanced Lithium‐Ion Battery Anodes

The capacity loading per unit area is of importance as specific capacity while evaluating the lithium‐ion battery anode. However, the low conductivity of several advanced anode materials (such as molybdenum sulfide, MoS₂) prohibits the wide application of materials. Nanostructural engineering becomes a key to overcome the obstacles. A one‐step in situ conversion reaction is employed to synthesize molybdenum oxide (MoO₂)–MoS₂ core–shell nanoarchitectures (MoO₂@MoS₂) by partially sulfiding MoO₂ into MoS₂ using sulfur. The MoO₂@MoS₂ displays a 3D architecture constructed by hundreds of MoS₂ ultrathin sheets with several layers arranged and fixed to an MoO₂ particle vertically with the size in the range of 200–500 nm. MoO₂ acts as the molybdenum source for the synthesis of MoS₂, as well as the conductive substrate. The designed 3D architectures with empty space between MoS₂ layers can prevent the damage originated from volume change of MoS₂ undergoing charge/discharge process. The lithium storage capacities of the MoO₂@MoS₂ 3D architectures are higher and the stability has been significantly improved compared to pure MoS₂. 4 mAh cm^?2 capacity loading of MoO₂@MoS₂ has been achieved with a specific capacity of more than 1000 mAh g^?1.     

Flower-like MoS<Subscript>2</Subscript> supported on three-dimensional graphene aerogels as high-performance anode materials for sodium-ion batteries

Flower-like MoS₂ supported on three-dimensional graphene aerogel (MoS₂/GA) composite has been prepared by a facile hydrothermal method followed by subsequent heat-treatment process. Each of MoS₂ microflowers is surrounded by the three-dimensional graphene nanosheets. The MoS₂/GA composite is applied as an anode material of sodium-ion batteries (SIBs) and it exhibits high initial discharge/charge capacities of 562.7 and 460 mAh g^?1 at a current density of 0.1 A g^?1 and good cycling performance (348.6 mAh g^?1 after 30 cycles at 0.1 A g^?1). The good Na⁺ storage properties of the MoS₂/GA composite could be attributed to the unique structure which flower-like MoS₂ are homogeneously and tightly decorated on the surface of three-dimensional graphene aerogel. Our results demonstrate that as-prepared MoS₂/GA composite has a great potential prospect as anodes for SIBs.     

Synthesis of hierarchical MoS<Subscript>2</Subscript> microspheres composed of nanosheets assembled via facile hydrothermal method as anode material for lithium-ion batteries

A hierarchical MoS₂ architecture composed of nanosheet-assembled microspheres with an expanded interplanar spacing of the (002) planes was successfully prepared via a simple hydrothermal reaction. Electron microscopy studies revealed formation of the MoS₂ microspheres with an average diameter of 230 nm. It was shown that the hierarchical structure of MoS₂ microspheres possesses both the merits of nanometer-sized building blocks and micrometer-sized assemblies, which offer high surface area for fast kinetics and buffers the volume expansion during lithium insertion/deinsertion, respectively. The micrometer-sized assemblies were found to contribute to the enhanced electrochemical stabilities of the electrode materials. The mentioned advantages of the MoS₂ electrode prepared in this work allowed enhanced cyclability and high rate capability of the material. Along with this, the material delivered a high initial discharge capacity of 1206 mAh g^?1 and a reversible discharge capacity of 653 mAh g^?1 after 100 cycles at a current density of 100 mA g^?1. Furthermore, the material delivered a high reversible capacity of 480 mAh g^?1 at a high current density of 1000 mA g^?1.     

Synthesis of Porous NiO Nanorods as High‐Performance Anode Materials for Lithium‐Ion Batteries

1D nanostructured metal oxides with porous structure have drawn wide attention to being used as high‐performance anode materials for lithium‐ion batteries (LIBs). This study puts forward a simple and scalable strategy to synthesize porous NiO nanorods with the help of a thermal treatment of metal‐organic frameworks in air. The NiO nanorods with an average diameter of approximately 38 nm are composed of nanosized primary particles. When evaluated as anode materials for LIBs, an initial discharge capacity of 743 mA h g^?1 is obtained at a current density of 100 mA g^?1, and a high reversible capacity is still maintained as high as 700 mA h g^?1 even after 60 charge–discharge cycles. The excellent electrochemical performance is mainly ascribed to the 1D porous structure.     

Facile Fabrication of Bicomponent CoO/CoFe2O4‐N‐Doped Graphene Hybrids with Ultrahigh Lithium Storage Capacity

A facile strategy is developed to fabricate bicomponent CoO/CoFe₂O₄‐N‐doped graphene hybrids (CoO/CoFe₂O₄‐NG). These hybrids are demonstrated to be potential high‐performance anodes for lithium‐ion batteries (LIBs). The CoO/CoFe₂O₄ nanoplatelets are finely dispersed on the surface of N‐doped graphene nanosheets (CoO/CoFe₂O₄‐NG). The CoO/CoFe₂O₄‐NG electrode exhibits ultrahigh specific capacity with 1172 mA h g^?1 at 500 mA g^?1 and 970 mA h g^?1 at 1000 mA g^?1 as well as excellent cycle stability due to the synergetic effects of N‐doped graphene and CoO/CoFe₂O₄ nanoplatelets. The well‐dispersed bicomponent CoO/CoFe₂O₄ is responsible for the high specific capacity. The N‐doped graphene with high specific surface area has dual roles: to provide active sites for dispersing the CoO/CoFe₂O₄ species and to function as an electrical conducting matrix for fast charge transfer. This method provides a simple and efficient way to configure the hybridized electrode materials with high lithium storage capacity.     

Multi-hierarchical nanosheet-assembled chrysanthemum-structured Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C as electrode materials for high-performance sodium-ion batteries

The structure and morphology of sodium vanadium phosphate (Na₃V₂(PO₄)₃) play a vital role in enhancing the electrochemical performance of sodium-ion batteries due to the inherent poor electronic conductivity of the phosphate framework. In order to improve this drawback, a new chrysanthemum-structured Na₃V₂(PO₄)₃/C material has been successfully assembled with multi-hierarchical nanosheets via a hydrothermal method. Continuous scattering nanosheets in chrysanthemum petals are beneficial in reducing energy consumption during the process of sodium ion diffusion, on which the carbon-coated surface can significantly increase overall conductivity. The as-prepared sample exhibits outstanding electrochemical performance due to its unique structure. It rendered a high initial specific capacity of 117.4?mAh?g^?1 at a current density of 0.05 C. Further increasing the current density to 10 C, the initial specific capacity still achieves 101.3?mAh?g^?1 and remains at 87.5?mAh?g^?1 after 1000 cycles. In addition, a symmetrical sodium-ion full battery using the chrysanthemum-structured Na₃V₂(PO₄)₃/C materials as both the cathode and anode has been successfully fabricated, delivering the capacity of 62?mAh?g^?1 at 1?C and achieving the coulombic efficiency at an average of 96.4% within 100 cycles. These results indicate that the new chrysanthemum-structured Na₃V₂(PO₄)₃/C can provide a new idea for the development of high-performance sodium-ion batteries.     

Wintersweet Branch‐Like C/C@SnO2/MoS2 Nanofibers as High‐Performance Li and Na‐Ion Battery Anodes

Structure and morphology of molybdenum disulfide (MoS₂) play an important role in improving its reversible lithium storage and sodium storage as anodes. In this study, a facile method is developed to prepare C/C@SnO₂/MoS₂ nanofibers with MoS₂ nanoflakes anchoring on the core–shell C/C@SnO₂ nanofibers through hydrothermal reaction. By adjusting the concentration of MoS₂ precursors, the synthesized MoS₂ with different slabs dimensions, size, and morphologies are obtained, constituting budding and blooming wintersweet branch‐like composite structure, respectively. Owing to scattered MoS₂ nanoparticles and sporadic MoS₂ nanoflakes, the budding wintersweet branch‐like composite nanofibers processes less slabs of staking in number and large specific surface area. Benefiting from the exposed C@SnO₂ shell layer, the synergistic effect among SnO₂, carbon, and MoS₂ is strengthened, which maximizes the advantage of each material to exhibit stable specific capacities of 650 and 230 mAh g^?1 for Li‐ion batteries and Na‐ion batteries after 200 cycles.     

Synthesis of free-standing MnO<Subscript>2</Subscript>/reduced graphene oxide membranes and electrochemical investigation of their performances as anode materials for half and full lithium-ion batteries

MnO₂ nanotubes/reduced graphene oxide (MnO₂/RGO) membranes with different MnO₂ contents are successfully synthesized by a facile two-step method including vacuum filtration and subsequent thermal reduction route. The MnO₂ nanotubes obtained are 38 nm in diameter and homogeneously imbedded in RGO sheets as spacers. The synthesized MnO₂/RGO membranes exhibit excellent mechanical flexibilities and free-standing properties. Using the membranes directly as anode materials for lithium batteries (LIBs), the membranes for half LIBs show superb cycling stabilities and rate performances. Importantly, the electrochemical performances of MnO₂/RGO membranes show a strong dependence on the MnO₂ nanotube contents in the hybrids. In addition, our results show that the hybrid membranes with 49.0 wt% MnO₂ nanotube in half LIBs achieve a high reversible capacity of 1006.7 mAh g^?1 after 100 cycles at a current density of 0.1 A g^?1, which is higher lithium storage capacity than that of reported MnO₂-carbon electrodes. Furthermore, the synthesized full cell (MnO₂/RGO//LiCoO₂) system also exhibit excellent electrochemical performances, which can be attributed to the unique microstructures of MnO₂ and GRO, coupled with the strong synergistic interaction between MnO₂ nanotubes and GRO sheets.     

Porous NiO hollow quasi-nanospheres derived from a new metal-organic framework template as high-performance anode materials for lithium ion batteries

Porous hollow metal oxides derived from nanoscaled metal-organic framework (MOF) have drawn tremendous attention due to their high electrochemical performance in advanced Li-ion batteries (LIBs). In this work, porous NiO hollow quasi-nanospheres were fabricated by an ordinary refluxing reaction combination of a thermal decomposition of new nanostructured Ni-MOF, i.e., {Ni₃(HCOO)₆·DMF}_n. When evaluated as an anode material for lithium ion batteries, the MOF derived NiO electrode exhibits high capacity, good cycling stability and rate performance (760 mAh g^?1 at 200 mA g^?1 after 100 cycles, 392 mAh g^?1 at 3200 mA g^?1). This superior lithium storage performance is mainly attributed to the unique hollow and porous nanostructure of the as-synthesized NiO, which offer enough space to accommodate the dramstic volume change and alleviate the pulverization problem during the repeated lithiation/delithiation processes, and provide more electro-active sites for fast electrochemical reactions as well as promote lithium ions and electrons transfer at the electrolyte/electrode interface.     

Titanium Dioxide/Germanium Core–Shell Nanorod Arrays Grown on Carbon Textiles as Flexible Electrodes for High Density Lithium‐Ion Batteries

Three‐dimensional (3D) titanium dioxide@germanium (TiO₂@Ge) core–shell nanorod arrays on carbon textiles are fabricated by a facile two‐step method and further investigated as flexible electrode for Li‐ion batteries (LIBs). The synthesis of TiO₂@Ge composite involves the hydrothermal growth of TiO₂ nanorod arrays on carbon textiles and a subsequent coat with a thin layer of germanium with radio frequency (RF) magnetron sputtering. The TiO₂ nanorod arrays can effectively not only increase the unit mass loading as a role of skeleton but also remarkably enhance the electrical conductivity via control the lithiation/delithiation voltage in the range of 0.01–1.0 V, where TiO₂ can be in situ lithiated to Li_xTiO₂ after the first discharge cycle. Moreover, each TiO₂@Ge nanorod has enough space to accommodate the large volume expansion of Ge during charge and discharge cycles. Benefiting from unique electrode architectures, this additive free, self‐supported electrode exhibits the high reversible capacity, outstanding rate capability, and the extremely long cycling stability even at a high rate (700.3 mAh g^?1 is still retained at 5 A g^?1 after 600 cycles).     

Hierarchical Co<Subscript>3</Subscript>O<Subscript>4</Subscript>@C hollow microspheres with high capacity as an anode material for lithium-ion batteries

Three-dimensional hierarchical Co₃O₄@C hollow microspheres (Co₃O₄@C HSs) are successfully fabricated by a facile and scalable method. The Co₃O₄@C HSs are composed of numerous Co₃O₄ nanoparticles uniformly coated by a thin layer of carbon. Due to its stable 3D hierarchical hollow structure and uniform carbon coating, the Co₃O₄@C HSs exhibit excellent electrochemical performance as an anode material for lithium-ion batteries (LIBs). The Co₃O₄@C HSs electrode delivers a high reversible specific capacity, excellent cycling stability (1672 mAh g^?1 after 100 cycles at 0.2 A g^?1 and 842.7 mAh g^?1 after 600 cycles at 1 A g^?1), and prominent rate performance (580.9 mAh g^?1 at 5 A g^?1). The excellent electrochemical performance makes this 3D hierarchical Co₃O₄@C HS a potential candidate for the anode materials of the next-generation LIBs. In addition, this simple synthetic strategy should also be applicable for synthesizing other 3D hierarchical metal oxide/C composites for energy storage and conversion.     

Co3O4 Hollow Nanoparticles and Co Organic Complexes Highly Dispersed on N‐Doped Graphene: An Efficient Cathode Catalyst for Li‐O2 Batteries

Rechargeable Li‐O₂ batteries are promising candidates for electric vehicles due to their high energy density. However, the current development of Li‐O₂ batteries demands highly efficient air cathode catalysts for high capacity, good rate capability, and long cycle life. In this work, a hydrothermal‐calcination method is presented to prepare a composite of Co₃O₄ hollow nanoparticles and Co organic complexes highly dispersed on N‐doped graphene (Co–NG), which acts as a bifunctional air cathode catalyst to optimize the electrochemical performances of Li‐O₂ batteries. Co–NG exhibits an outstanding initial discharge capacity up to 19 133 mAh g^?1 at a current density of 200 mA g^?1. In addition, the batteries could sustain 71 cycles at a cutoff capacity of 1000 mAh g^?1 with low overpotentials at the current density of 200 mA g^?1. Co–NG composites are attractive as air cathode catalysts for rechargeable Li‐O₂ batteries.     

Graphene‐Based Phosphorus‐Doped Carbon as Anode Material for High‐Performance Sodium‐Ion Batteries

Graphene‐based phosphorus‐doped carbon (GPC) is prepared through a facile and scalable thermal annealing method by triphenylphosphine and graphite oxide as precursor. The P atoms are successfully doped into few layer graphene with two forms of P–O and P–C bands. The GPC used as anode material for Na‐ion batteries delivers a high charge capacity 284.8 mAh g^?1 at a current density of 50 mA g^?1 after 60 cycles. Superior cycling performance is also shown at high charge?discharge rate: a stable charge capacity 145.6 mAh g^?1 can be achieved at the current density of 500 mA g^?1 after 600 cycles. The result demonstrates that the GPC electrode exhibits good electrochemical performance (higher reversible charge capacity, super rate capability, and long‐term cycling stability). The excellent electrochemical performance originated from the large interlayer distance, large amount of defects, vacancies, and active site caused by P atoms doping. The relationship of P atoms doping amount with the Na storage properties is also discussed. This superior sodium storage performance of GPC makes it as a promising alternative anode material for sodium‐ion batteries.     

Carbon‐Encapsulated Tube‐Wire Co3O4/MnO2 Heterostructure Nanofibers as Anode Material for Sodium‐Ion Batteries

This study presents a general approach for the synthesis of carbon‐encapsulated wire‐in‐tube Co₃O₄/MnO₂ heterostructure nanofibers (Co₃O₄/MnO₂@C) via electrospinning followed by calcination. The as‐synthesized Co₃O₄/MnO₂@C is investigated as the sodium‐ion batteries anode material, which not only exhibits a high reversible capacity of 306 mAh g⁻¹ at 100 mA g⁻¹ over 200 cycles, but also shows a cycling stability of 126 mAh g⁻¹ after 1000 cycles at a high current density of 800 mA g⁻¹. The excellent electrochemical performance can be ascribed to the contribution from carbon‐encapsulated outer‐tube Co₃O₄ and inner‐wire MnO₂ heterostructures, which offer a large internal space and good electrical conductivity. The present work can be helpful in providing new insights into heterostructures for sodium‐ion batteries and other applications.     

Electrospinning Synthesis of Porous NiCoO2 Nanofibers as High‐Performance Anode for Lithium‐Ion Batteries

Nanostructured ternary/mixed transition metal oxides have attracted considerable attentions because of their high‐capacity and high‐rate capability in the electrochemical energy storage applications, but facile large‐scale fabrication with desired nanostructures still remains a great challenge. To overcome this, a facile synthesis of porous NiCoO₂ nanofibers composed of interconnected nanoparticles via an electrospinning–annealing strategy is reported herein. When examined as anode materials for lithium‐ion batteries, the as‐prepared porous NiCoO₂ nanofibers demonstrate superior lithium storage properties, delivering a high discharge capacity of 945 mA h g^?1 after 140 cycles at 100 mA g^?1 and a high rate capacity of 523 mA h g^?1 at 2000 mA g^?1. This excellent electrochemical performance could be ascribed to the novel hierarchical nanoparticle‐nanofiber assembly structure, which can not only buffer the volumetric changes upon lithiation/delithiation processes but also provide enlarged surface sites for lithium storage and facilitate the charge/electrolyte diffusion. Notably, a facile synthetic strategy for fabrication of ternary/mixed metal oxides with 1D nanostructures, which is promising for energy‐related applications, is provided.     

Metal Oxide Nanomaterials with Nitrogen‐Doped Graphene‐Silk Nanofiber Complexes as Templates

Fabricating electrode materials with superior electrochemical performance remains a challenge. Here, a simple but effective strategy for the formation of metal oxide nanomaterials with superior performance has been developed. Silk protein nanofibers adhered on reduced graphene oxide (rGO) sheets are used as templates to regulate the formation of nanostructured iron oxide composites, achieving porous nanorod structures that could not be attained in control experiments. These porous nanorods demonstrate superior electrochemical performance as electrodes with retention of a capacity of 1495 mAh g^?1 after 180 cycles at 0.2 C and a rate capability of 900 mAh g^?1 at 2 C discharge rate. These new rGO/silk composite templates provide a more controllable environment for Fe₂O₃ fabrication, resulting in improved nanostructures and superior electrical performance. The strategy developed here should also be more broadly applicable in the design of metal oxide nanomaterials with specialized structures and useful performance.     

Fracture‐induced nanoscrolls from CVD‐grown monolayer molybdenum disulfide

We report a simple and effective way of fabricating molybdenum disulfide (MoS₂) nanoscrolls by self‐rolling up fractured monolayer CVD‐grown MoS₂ microflakes. Morphological results reveal that MoS₂ nanoscrolls are formed only at newly formed edges, owing to an orientation‐specific fracture behavior. Using Raman spectroscopy, we show that the E¹_2g Raman peak (A_1g peak) for MoS₂ nanoscrolls significantly red‐shifts (blue‐shifts), indicating structural change. The proposed mechanism is that the newly formed edges induced by fracture behavior self‐roll up to nanoscrolls to minimize the surface free energy, meanwhile, the serious lattice contradiction of upper sulfur plane controls the rolling directions. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)