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.     

High Rate and Long Cycle Life of a CNT/rGO/Si Nanoparticle Composite Anode for Lithium‐Ion Batteries

Si nanoparticle (Si‐NP) composite anode with high rate and long cycle life is an attractive anode material for lithium‐ion battery (LIB) in hybrid electric vehicle (HEV)/pure electric vehicle (PEV). In this work, a carbon nanotube (CNT)/reduced graphene oxide (rGO)/Si nanoparticle composite with alternated structure as Li‐ion battery anode is prepared. In this structure, rGO completely wraps the entire Si/CNT networks by different layers and CNT networks provide fast electron transport pathways with reduced solid‐state diffusion, so that the stable solid‐electrolyte interphase layer can form on the whole surface of the matrix instead of on single Si nanoparticle, which ensure the high cycle stability to achieve the excellent cycle performance. As a result, the CNT/rGO/Si‐NP anode exhibits high performances with long cycle life (≈455 mAh g^?1 at 15 A g^?1 after 2000 cycles), high specific charge capacity (≈2250 mAh g^?1 at 0.2 A g^?1, ≈650 mAh g^?1 at 15 A g^?1), and fast charge/discharge rates (up to 16 A g^?1). This nanostructure anode with facile and low‐cost synthesis method, as well as excellent electrochemical performances, makes it attractive for the long life cycles at high rate of the next generation LIB applications in HEV/PEV.     

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.     

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.     

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.     

Synthesis of Li3V2(PO4)3/reduced graphene oxide cathode material with high-rate capability

The Li₃V₂(PO₄)₃/reduced graphene oxide (LVP/rGO) composite is successfully synthesized by a conventional solid-state reaction with a high yield of 10 g, which is suitable for large-scale production. Its structure and physicochemical properties are investigated using X-ray diffraction, Raman spectra, field-emission scanning electron microscopy, transmission electron microscopy, and electrochemical methods. The rGO content is as low as ~3 wt%, and LVP particles are strongly adhered to the surface of the rGO layer and/or enwrapped into the rGO sheets, which can facilitate the fast charge transfer within the whole electrode and to the current collector. The galvanostatic charge–discharge tests show that the LVP/rGO electrode delivers an initial discharge capacity of 177 mAh g^?1 at 0.5 C with capacity retention of 88 % during the 50th cycle in a wide voltage range of 3.0–4.8 V. A superior rate capability is also achieved, e.g., exhibiting discharge capacities of 137 and 117 mAh g^?1 during the 50th cycle at high C rates of 2 and 5 C, respectively.     

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.     

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.     

Three‐Dimensional Multilayer Assemblies of MoS2/Reduced Graphene Oxide for High‐Performance Lithium Ion Batteries

Three‐dimensional (3D) multilayer molybdenum disulfide (MoS₂)/reduced graphene oxide (RGO) nanocomposites are prepared by a solution‐processed self‐assembly based on the interaction using different sizes of MoS₂ and GO nanosheets followed by in situ chemical reduction. 3D multilayer assemblies with MoS₂ wrapped by large RGO nanosheets and good interface are observed by transmission electron microscopy. The interaction of Na⁺ ions with oxygen‐containing groups of GO is also investigated. The measurement of lithium ion batteries (LIBs) shows that MoS₂/RGO anode nanocomposite with a weight ratio of MoS₂ to GO of 3:1 exhibits an excellent rate performance of 750 mAh g^?1 at 3 A g^?1 outperforming many previous studies and a high reversible capacity up to ≈1180 mAh g^?1 after 80 cycles at 100 mA g^?1. Good rate performance and high capacity of MoS₂/RGO with 3D unique layered‐structures are attributed to the combined effects of continuous conductive networks of RGO, good interface facilitating charge transfer, and strong RGO sheets preventing the volume expansion. Results indicate that 3D multilayer MoS₂/RGO prepared by a facile solution‐processed assembly can be developed to be an excellent nanoarchitecture for high‐performance LIBs.     

Facile Construction of 3D Reduced Graphene Oxide Wrapped Ni3S2 Nanoparticles on Ni Foam for High‐Performance Asymmetric Supercapacitor Electrodes

3D reduced graphene oxide (rGO)‐wrapped Ni₃S₂ nanoparticles on Ni foam with porous structure is successfully synthesized via a facile one‐step solvothermal method. This unique structure and the positive synergistic effect between Ni₃S₂ nanoparticles and graphene can greatly improve the electrochemical performance of the NF@rGO/Ni₃S₂ composite. Detailed electrochemical measurements show that the NF@rGO/Ni₃S₂ composite exhibits excellent supercapacitor performance with a high specific capacitance of 4048 mF cm^?2 (816.8 F g^?1) at a current density of 5 mA cm^?2 (0.98 A g^?1), as well as long cycling ability (93.8% capacitance retention after 6000 cycles at a current density of 25 mA cm^?2). A novel aqueous asymmetric supercapacitor is designed using the NF@rGO/Ni₃S₂ composite as positive electrode and nitrogen‐doped graphene as negative electrode. The assembled device displays an energy density of 32.6 W h kg^?1 at a power density of 399.8 W kg^?1, and maintains 16.7 W h kg^?1 at 8000.2 W kg^?1. This outstanding performance promotes the as‐prepared NF@rGO/Ni₃S₂ composite to be ideal electrode materials for supercapacitors.     

Hierarchical nanostructure CuO with peach kernel-like morphology as anode material for lithium-ion batteries

Copper oxide particles with different morphology (flower-like, peach kernel-like, and dandelion-like) are prepared with hydrothermal method by adjusting chitosan ((C₆H₁₁NO₄)_n) concentration in aqueous mixed solutions of ammonia and Cu(NO₃)₂. Various morphologies of porous cupric oxide (CuO) particles are formed by agglomerated nanosheet primary particles and lead to different electrochemical performance of electrodes. The peach kernel-shaped CuO exhibits high reversible capacity and rate capability. The reversible capacity is 722.7 mAh g^?1 at 0.1 C in the first cycle and 339 mAh g^?1 after 50 cycles at 0.2, 0.5, 1.0, and 2.0 C ratio. The higher reversible capacities and good cycling performance are attributed to the larger specific surface area, leading to better contact between CuO and electrolyte.     

A simple approach to synthesize nanosized sulfur/graphene oxide materials for high-performance lithium/sulfur batteries

We report on a simple and facile synthesis route for the sulfur/graphene oxide composite via ultrasonic mixing of the nano-sulfur and graphene oxide aqueous suspensions followed by a low-temperature heat treatment. High-resolution transmission and scanning electronic microscopy observations revealed the formation of a highly porous structure consisting of sulfur with uniform graphene oxide coating on its surface. The resulting sulfur/graphene oxide (S/GO) composite exhibited high and stable specific discharge capacities of 591 mAh g^?1 after 100 cycles at 0.1 C and good rate capability. This enhanced electrochemical performance could be attributed to the effective confining the polysulfides dissolution and accommodation of the volume changes during the Li-S electrochemical reaction by the functional groups on the graphene oxide coating layer. Furthermore, the highly developed porous structure of S/GO composite favors the enhanced ion transport and electrolyte diffusion.     

Highly Dispersed ZnSe Nanoparticles Embedded in N‐Doped Porous Carbon Matrix as an Anode for Potassium Ion Batteries

Advanced nanostructured functional materials obtained from the precursors of metal–organic frameworks show several unique advantages, including plentiful porous structures and large specific surface areas. Based on this, designed and constructed are highly dispersed ZnSe nanoparticles anchored in a N‐doped porous carbon rhombic dodecahedron (ZnSe@NDPC) by a sequential high‐temperature pyrolysis and selenization method. The specific synthesis process involves a two‐step heat treatment of the template‐engaged reaction between zinc‐based zeolitic imidazolate framework (ZIF‐8) and selenium power. By optimizing the calcination temperature, the as‐synthesized ZnSe@NDPC‐700 as an advanced anode of potassium ion batteries demonstrates the best electrochemical performance, including a high capacity (262.8 mA h g^?1 over 200 cycles at 100 mA g^?1) and a good rate capability (109.4 mA h g^?1 at 2000 mA g^?1 and 52.8 mA h g^?1 at 5000 mA g^?1). Moreover, the capacitance and diffusion mechanisms are also investigated by the qualitative and quantitate analysis, finally accounting for the superior K storage.     

Epitaxial Growth of Urchin‐Like CoSe2 Nanorods from Electrospun Co‐Embedded Porous Carbon Nanofibers and Their Superior Lithium Storage Properties

A facile synthesis of porous graphitic carbon nanofibers (CNFs) with encapsulated Co nanoparticles (denote as Co@CNFs) via electrospinning and subsequent annealing is reported. The in situ generated Co nanoparticles (NPs) promote the CNF graphitization under a low temperature of 700 °C, which simultaneously results in the porous structure of the Co@CNFs with a large surface area (416 m² g^?1). Furthermore, urchin‐like CoSe₂ nanorods are epitaxially grown from the Co@CNFs via a facile hydrothermal selenation, in which the embedded Co NPs serve as directing seeds and sacrificial Co‐source, and CoSe₂ nanorods are rooted into the CNFs (denote as CoSe₂@CNFs). When used as anode materials for lithium ion batteries, the CoSe₂@CNFs demonstrate superior lithium storage properties, delivering a high reversible capacity of 1405 mA h g^?1 after 300 cycles at a current density of 200 mA g^?1. The enhanced lithium storage performance can be attributed to the novel hybrid structure, namely, the porous and graphitic CNFs can not only facilitate the charge/ion transfer but also buffer the volume changes of the electrode during lithiation/delithiation processes. More importantly, a general strategy is provided to graphitize amorphous carbon materials via the use of in situ generated transition metal nanoparticles as catalyst.     

A novel method to synthesize SnP<Subscript>2</Subscript>O<Subscript>7</Subscript> spherical particles for lithium-ion battery anode

For the urgent demand of higher capacity of lithium-ion battery anode, tin pyrophosphate has attracted more and more attention because of its high theoretical capacity, cheapness, and no toxicity. However, production of stable mesoporous sphere structure and improvement of electrochemical performance remain a challenge. Here, SnP₂O₇ spherical particles were successfully prepared through spray drying method with SnCl₄·5H₂O and C₂H₈O₇P₂. Crystallization and microstructure were investigated by TG-DSC, XRD, SEM, and TEM. With the obtained mesoporous SnP₂O₇ particles after carbon coating, it demonstrates a high initial capacity reaching up to 1218 mAh g^?1 and a significantly stable cycling performance with 620 mAh g^?1 after 80 deep electrochemical 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.     

Carbon‐Coated Supraballs of Randomly Packed LiFePO4 Nanoplates for High Rate and Stable Cycling of Li‐Ion Batteries

One of the key strategies used to obtain high‐rate Li‐ion battery is the reduction of the Li‐ion path length inside the active materials and the enhancement of the ionic diffusion outside the active materials. It is demonstrated that electrochemical performance can be improved significantly at high C‐rates using carbon‐coated spherical aggregates or “supraballs” of randomly packed olivine LiFePO₄ (LFP) nanoplates as cathode active materials. 258 nm LFP nanoplates with 30 nm thickness are synthesized through a high‐temperature solvothermal method, in which short lithium‐ion channels are formed perpendicular to the top or bottom planes. These thin nanoplates are formed into carbon‐coated “supraballs” through a spray‐drying and thermal annealing process, in which nanoplates are not stacked but randomly packed due to relatively fast drying. Internal and external nanoplate ion diffusion is therefore enhanced simultaneously due to the optimal molecular crystalline structure and interparticle pore structures of the nanoplates. Indeed, the initial capacity of the carbon‐coated supraballs is 162 mAh g^?1 (173.34 mAh cm^?3) at 0.1 C and more than 80% is retained (≈130.91 mAh g^?1) at 50 C. Furthermore, they offer durable cycling stability (>500 cycles) at 1 C without compromising their capacity.     

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.     

Hydrothermal synthesis of carbon- and reduced graphene oxide-supported CoMoO4 nanorods for supercapacitor

Hybrid CoMoO₄ nanorods with carbon (C) and graphene oxide (rGO) are successfully synthesized via one-step hydrothermal process. Hybrid α-CoMoO₄ nanorods have shown excellent electrochemical performances compared to pristine CoMoO₄ in alkaline electrolyte. Specifically, CoMoO₄/C nanorod exhibits a maximum specific capacitance of 451.6 F g^?1 at the current density of 1 A g^?1, whereas CoMoO₄/rGO shows high specific capacitance of 336.1 F g^?1 at the same current density. Both the hybrid nanorods show good rate capability even at high current density of 20 A g^?1 and long-term cyclic stability. The observed electrochemical features of the hybrid CoMoO₄ nanostructure could be attributed to the presence of highly conductive carbonaceous material on unique one-dimensional nanorod microstructure which enhances the electrical conductivity of the nanorods thereby allowing faster electrolyte ion diffusion during the redox process.     

Enhanced lithium storage performance of a self-assembled hierarchical porous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/VGCF hybrid high-capacity anode material for lithium-ion batteries

A Co₃O₄/vapor-grown carbon fiber (VGCF) hybrid material is prepared by a facile approach, namely, via liquid-phase carbonate precipitation followed by thermal decomposition of the precipitate at 380 °C for 2 h in argon gas flow. The material is characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller specific surface area analysis, and carbon elemental analysis. The Co₃O₄ in the hybrid material exhibits the morphology of porous submicron secondary particles which are self assembled from enormous cubic-phase crystalline Co₃O₄ nanograins. The electrochemical performance of the hybrid as a high-capacity conversion-type anode material for lithium-ion batteries is investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic discharge/charge methods. The hybrid material demonstrates high specific capacity, good rate capability, and good long-term cyclability, which are far superior to those of the pristine Co₃O₄ material prepared under similar conditions. For example, the reversible charge capacities of the hybrid can reach 1100–1150 mAh g^?1 at a lower current density of 0.1 or 0.2 A g^?1 and remain 600 mAh g^?1 at the high current density of 5 A g^?1. After 300 cycles at 0.5 A g^?1, a high charge capacity of 850 mAh g^?1 is retained. The enhanced electrochemical performance is attributed to the incorporated VGCFs as well as the porous structure and the smaller nanograins of the Co₃O₄ active material.