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.     

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 Facile Method for Synthesis of Porous NiCo2O4 Nanorods as a High‐Performance Anode Material for Li‐Ion Batteries

Porous electrode materials with large specific surface area, relatively short diffusion path, and higher electrical conductivity, which display both better rate capabilities and good cycle lives, have huge benefits for practical applications in lithium‐ion batteries. Here, uniform porous NiCo₂O₄ nanorods (PNNs) with pore‐size distribution in the range of 10–30 nm and lengths of up to several micrometers are synthesized through a convenient oxalate co‐precipitation method followed by a calcining process. The PNN electrode exhibits high reversible capacity and outstanding cycling stability (after 150 cycles still maintain about 650 mA h g^?1 at a current density of 100 mA g^?1), as well as high Coulombic efficiency (>98%). Moreover, the PNNs also exhibit an excellent rate performance, and deliver a stable reversible specific capacity of 450 mA h g^?1 even at 2000 mA g^?1. These results demonstrate that the PNNs are promising anode materials for high‐performance Li‐ion batteries.     

A Dual Component Catalytic System Composed of Non‐Noble Metal Oxides for Li–O2 Batteries with Enhanced Cyclability

One of the great challenges in the development of lithium–oxygen batteries (Li–O₂ batteries) is to synthesize cost‐effective and efficient electrocatalysts to overcome several issues such as high charge overpotential and poor cycle life. Here, an efficient method is reported to fabricate a dual component electrocatalyst made of MnO₂ nanoparticles supported on 1D Co₃O₄ nanorods (MnO₂–Co₃O₄), and its electrochemical behavior as a non‐noble metal cathode catalyst is demonstrated in Li–O₂ batteries. It is found that the as‐made MnO₂–Co₃O₄ catalyst exhibits an enhanced electrochemical performance, such as increased specific capacity (increase to 4023 mA h g^?1 from 2993 mA h g^?1), low charge overpotential (reduce 350 mV), high rate performance, and superior cyclability up to 150 cycles. The excellent electrochemical performance is attributed to the synergistic effects of the dual component catalytic system.     

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.     

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.     

Template‐Free Fabrication of Hollow NiO–Carbon Hybrid Nanoparticle Aggregates with Improved Lithium Storage

Hollow NiO–carbon hybrid nanoparticle aggregates are fabricated through an environmental template‐free solvothermal alcoholysis route. Controlled hollow structure is achieved by adjusting the ratio of ethylene glycol to water and reaction time of solvothermal alcoholysis. Amorphous carbon can be loaded on the NiO nanoparticles uniformly in the solvothermal alcoholysis process, and the subsequent calcination results in the formation of hollow NiO–C hybrid nanoparticle aggregates. As anode materials for lithium‐ion batteries, it exhibits a stable reversible capacity of 622 mAh g^?1, and capacity retention keeps over 90.7% after 100 cycles at constant current density of 200 mA g^?1. The NiO–C electrode also exhibits good rate capabilities. The unique hollow structures can shorten the length of Li‐ion diffusion and offer a sufficient void space, which sufficiently alleviates the mechanical stress caused by volume change. The hybrid carbon in the particles renders the electrode having a good electronic conductivity. Here, the hollow NiO‐C hybrid electrode exhibits excellent electrochemical performance.     

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.     

Resin‐Derived Ni3S2/Carbon Nanocomposite for Advanced Rechargeable Aqueous Zn‐Based Batteries

The exploration of high‐energy and stable cathode materials is highly desirable and challenging for the development of advanced Zn‐based batteries. In this work, a facile pyrolysis method is reported to synthetize Ni₃S₂/carbon nanocomposite as high‐performance cathode by employing ion exchange resin as a precursor. Attributing to the abundant active sites and enhanced conductivity from well binding between Ni₃S₂ and carbon, a markedly high capacity of 234.3 mA h g^?1 is obtained for this Ni₃S₂/carbon at a high current density of 6.9 A g^?1. Moreover, a Zn‐based battery is demonstrated by using the Ni₃S₂/carbon as a cathode and Zn plate as an anode, which delivers a maximum power density of 58.6 kW kg^?1, together with a peak energy density of 356 W h kg^?1 and 93.7% capacity retention after 5000 charging–discharging cycles. This simple synthetic strategy to achieve robust Ni‐based composite electrodes may open up new opportunities to design other transition metal–based electrodes for energy storage applications.     

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.     

Reduced Graphene Oxide decorated with Manganese Cobalt Oxide as Multifunctional Material for Mechanically Rechargeable and Hybrid Zinc–Air Batteries

Spinel MnCo₂O₄ nanoparticles on nitrogen‐doped reduced graphene oxide (MnCo₂O₄/NGr) are synthesized for advanced zinc–air batteries with remarkable cyclic efficiency and stability. The synthesized MnCo₂O₄/NGr exhibits good oxygen‐reduction reaction (ORR) activity with half‐wave potential E _1/2 of 0.85 V (vs reversible hydrogen electrode (RHE)), comparable to commercial Pt/C with E _1/2 of 0.88 V (vs RHE) along with superior oxygen electrode activity ΔE = 0.91 V for the ORR/OER (oxygen‐evolution reaction) in alkaline media. Durability tests confirm that MnCo₂O₄/NGr is more stable than Pt/C in alkaline environment. MnCo₂O₄/NGr functions with stable discharge profile of 1.2 V at 20 mA cm^?2, large discharge capacity of 707 mAh g^?1_Zn at 40 mA cm^?2 and a high energy density of 813 Wh kg^?1_Zn in a mechanically rechargeable zinc–air battery. The electrically rechargeable MnCo₂O₄/NGr zinc–air battery displays hybrid behavior with both Faradaic and oxygen redox charge–discharge characteristics, operating at higher voltage and providing higher power density and excellent cyclic efficiency of 86% for over 100 cycles compared to Pt/C with efficiency of around 60%. Moreover, hybrid zinc–air battery operates with a stable and energy efficient profile at different current densities.     

Effects of Al doping for Li[Li0.09Mn0.65*0.91Ni0.35*0.91]O2 cathode material

Li-rich Mn-based Li[Li_0.09Mn_{0.65*(0.91???x)} Ni_{0.35*(0.91???x)} Al _x ]O₂ cathode materials have been prepared by traditional solid-state reaction. The lattice parameters a, c, and V have decreased, but c/a increased with the increase of Al doping. All the samples show analogy morphology of a quasi-spherical shape. Li[Li_0.09Mn_0.591Ni_0.319]O₂ sample shows a higher initial discharge capacity of 239.4 mAh?g^?1 at 20 mA?g^?1, while Li[Li_0.09Mn_0.582Ni_0.314Al_0.015]O₂ sample presents a higher discharge capacity of 170.1 mAh?g^?1 and ratio of 72.0 % with 200 vs. 20 mA?g^?1. The solid electrolyte interface resistance (R _SEI) and charge transfer process resistance (R _ct ) values are relatively smaller for Al-doped samples than those of non-doped samples. Almost no reduction is observed after 24-time cycles in different discharge rates for the samples prepared.     

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.     

Sulfur Immobilized in Hierarchically Porous Structured Carbon as Cathodes for Lithium–Sulfur Battery with Improved Electrochemical Performance

In order to overcome the main obstacles for lithium–sulfur batteries, such as poor conductivity of sulfur, polysulfide intermediate dissolution, and large volume change generated during the cycle process, a hard‐template route is developed to synthesize large‐surface area carbon with abundant micropores and mesopores to immobilize sulfur species. The microstructures of the C/S hybrids are investigated using field emission scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Raman spectroscopy, X‐ray photoelectron spectroscopy, nitrogen adsorption–desorption isotherms, and electrochemical impedance spectroscopy techniques. The large surface and porous structure can effectively alleviate large strain due to the lithiation/delithiation process. More importantly, the micropores can effectively confine small molecules of sulfur in the form of S_2–4, avoiding loss of active S species and dissolution of high‐order lithium polysulfides. The porous C/S hybrids show significantly enhanced electrochemical performance with good cycling stability, high specific capacity, and rate capability. The C/S‐39 hybrid with an optimal content of 39 wt% S shows a reversible capacity of 780 mA h g^?1 after 100 cycles at the current density of 100 mA g^?1. Even at a current density of 5 A g^?1, the reversible capacity of C/S‐39 can still maintain at 420 mA h g^?1 after 60 cycles. This strategy offers a new way for solving long‐term reversibility obstacle and designing new cathode electrode architectures.     

Structure Dependence of Fe‐Co Hydroxides on Fe/Co Ratio and Their Application for Supercapacitors

Fe‐Co hydroxides with different Fe/Co atomic ratios grown on nickel foams are synthesized by one‐step electrochemical deposition. The prepared samples are characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. It was found that the influence of initial Fe/Co ratios in the precursor solutions on the structure and electrochemical performance of electrodeposited products is significant. Fe(OH)₃ shows particle shape with average diameter of 200 nm. With addition of Co ions, frame‐like structure consisting of smaller particles is formed for Fe‐Co hydroxides. Based on the morphology of Co(OH)₂, it is deduced that Co(OH)₂ serves as a network former constructing a tridimensional frame network structure. Fe‐Co hydroxide with Fe/Co ratio of 1:1 exhibits two types of structure features: nanoflake‐like network structure overall and nanoparticle structure with numerous mesoporous microscopically. As the supercapacitor electrode materials, the as‐prepared Fe‐Co hydroxide electrode with Fe/Co ratio of 1:1 exhibits highest specific capacitance of 2255.6 F g^?1 at the current density of 1 A g^?1 and also shows good cycling performance of 73.5% capacity retention at current density of 10 A g^?1 after 2000 cycles. This work provides a facile method to produce promising Fe‐Co hydroxide electrode materials with high performance for supercapacitors.     

Ultrathin surface coatings to enhance cycling stability of LiMn2O4 cathode in lithium-ion batteries

Spinel LiMn₂O₄ suffers from severe dissolution when used as a cathode material in rechargeable Li-ion batteries. To enhance the cycling stability of LiMn₂O₄, we use the atomic layer deposition (ALD) method to deposit ultrathin and highly conformal Al₂O₃ coatings (as thin as 0.6–1.2 nm) onto LiMn₂O₄ cathodes with precise thickness control at atomic scale. Both bare and ALD-coated cathodes are cycled at a specific current of 300 mA g^?1 (2.5 C) in a potential range of 3.4–4.5 V (vs. Li/Li⁺). All ALD-coated cathodes exhibit significantly improved cycleability compared to bare cathodes. Particularly, the cathode coated with six Al₂O₃ ALD layers (0.9 nm thick) shows the best cycling performance, delivering an initial capacity of 101.5 mA h?g^?1 and a final capacity of 96.5 mA h?g^?1 after 100 cycles, while bare cathode delivers an initial capacity of 100.6 mA h?g^?1 and a final capacity of only 78.6 mA h?g^?1. Such enhanced electrochemical performances of ALD-coated cathodes are ascribed to the high-quality ALD oxide coatings that are highly conformal, dense, and complete, and thus protect active material from severe dissolution into electrolytes. Besides, cycling performances of coated cathodes can be easily optimized by accurately tuning coating thickness via varying ALD growth cycles.     

Hierarchically Porous NaCoPO4–Co3O4 Hollow Microspheres for Flexible Asymmetric Solid‐State Supercapacitors

A template‐free hydrothermal method is developed to prepare hierarchical hollow precursors. An inside‐out Ostwald ripening mechanism is proposed to explain the formation of the hollow structure. After the calcination in the air, hierarchically meso/macroporous NaCoPO₄–Co₃O₄ hollow microspheres can easily be obtained. When being evaluated as electrode materials for a supercapacitor, the hierarchically porous NaCoPO₄–Co₃O₄ hollow microspheres electrode shows a specific capacitance of 268 F g^?1 at 0.8 A g^?1 and offers a good cycle life. More importantly, the obtained materials are successfully applied to fabricate flexible solid‐state asymmetric supercapacitors. The device exhibits a specific capacitance of 28.6 mF cm^?2 at 0.1 mA cm^?2, a good cycling stability with only 5.5% loss of capacitance after 5000 cycles, and good mechanical flexibility under different bending angles, which confirms that the hierarchically porous NaCoPO₄–Co₃O₄ hollow microspheres are promising active materials for the flexible supercapacitor.     

3D Array of Bi2S3 Nanorods Supported on Ni Foam as a Highly Efficient Integrated Oxygen Electrode for the Lithium‐Oxygen Battery

Bismuth sulfide nanorod array is directly grown on nickel foam (R‐Bi₂S₃/NF) to serve as a completely carbon and binder‐free 3D porous oxygen electrode material for lithium‐oxygen (Li‐O₂) batteries. The synergistic effect of the fast kinetics of electron transport and gas and electrolyte diffusion provided by the continuous free‐standing network structure and the excellent electrocatalytic activity of the bismuth sulfide nanorod array enables outstanding performance of the oxygen electrode. Li‐O₂ battery with the free‐standing R‐Bi₂S₃/NF oxygen electrode exhibits high energy efficiency (78.7%), good rate capability (4464 mA h g⁻¹ at 1500 mA g⁻¹), as well as excellent cyclability (146 cycles) while maintaining a moderate specific capacity of 1000 mA h g⁻¹. The effect of cathodes with different reactant (O₂) and intermediate (LiO₂) adsorbability on the product (Li₂O₂) growth model is studied by first‐principle calculations. The strong O₂ adsorption and weak LiO₂ adsorption on Bi₂S₃ drives the growth of large‐size Li₂O₂ particles via solution growth model. Remarkably, the large‐area pouch‐type Li‐O₂ battery delivers an energy density of 330 Wh kg⁻¹. The present results open up a promising avenue toward developing novel electrode architecture for high‐performance Li‐O₂ batteries through controlling morphology and functionality of porous electrodes.     

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.     

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.