A Microwave Synthesis of Mesoporous NiCo2O4 Nanosheets as Electrode Materials for Lithium‐Ion Batteries and Supercapacitors

A facile microwave method was employed to synthesize NiCo₂O₄ nanosheets as electrode materials for lithium‐ion batteries and supercapacitors. The structure and morphology of the materials were characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller methods. Owing to the porous nanosheet structure, the NiCo₂O₄ electrodes exhibited a high reversible capacity of 891 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, NiCo₂O₄ 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.     

Mass‐Production of Mesoporous MnCo2O4 Spinels with Manganese(IV)‐ and Cobalt(II)‐Rich Surfaces for Superior Bifunctional Oxygen Electrocatalysis

A mesoporous MnCo₂O₄ electrode material is made for bifunctional oxygen electrocatalysis. The MnCo₂O₄ exhibits both Co₃O₄‐like activity for oxygen evolution reaction (OER) and Mn₂O₃‐like performance for oxygen reduction reaction (ORR). The potential difference between the ORR and OER of MnCo₂O₄ is as low as 0.83 V. By XANES and XPS investigation, the notable activity results from the preferred Mn^IV‐ and Co^II‐rich surface. The electrode material can be obtained on large‐scale with the precise chemical control of the components at relatively low temperature. The surface state engineering may open a new avenue to optimize the electrocatalysis performance of electrode materials. The prominent bifunctional activity shows that MnCo₂O₄ could be used in metal–air batteries and/or other energy devices.     

Green Template‐Free Synthesis of Hierarchical Shuttle‐Shaped Mesoporous ZnFe2O4 Microrods with Enhanced Lithium Storage for Advanced Li‐Ion Batteries

In the work, a facile and green two‐step synthetic strategy was purposefully developed to efficiently fabricate hierarchical shuttle‐shaped mesoporous ZnFe₂O₄ microrods (MRs) with a high tap density of ～0.85 g cm³, which were assembled by 1D nanofiber (NF) subunits, and further utilized as a long‐life anode for advanced Li‐ion batteries. The significant role of the mixed solvent of glycerin and water in the formation of such hierarchical mesoporous MRs was systematically investigated. After 488 cycles at a large current rate of 1000 mA g^?1, the resulting ZnFe₂O₄ MRs with high loading of ～1.4 mg per electrode still preserved a reversible capacity as large as ～542 mAh g^?1. Furthermore, an initial charge capacity of ～1150 mAh g^?1 is delivered by the ZnFe₂O₄ anode at 100 mA g^?1, resulting in a high Coulombic efficiency of ～76 % for the first cycle. The superior Li‐storage properties of the as‐obtained ZnFe₂O₄ were rationally associated with its mesoprous micro‐/nanostructures and 1D nanoscaled building blocks, which accelerated the electron transportation, facilitated Li⁺ transfer rate, buffered the large volume variations during repeated discharge/charge processes, and provided rich electrode–electrolyte sur‐/interfaces for efficient lithium storage, particularly at high rates.     

Wintersweet‐Flower‐Like CoFe2O4/MWCNTs Hybrid Material for High‐Capacity Reversible Lithium Storage

CoFe₂O₄/multiwalled carbon nanotubes (MWCNTs) hybrid materials were synthesized by a hydrothermal method. Field emission scanning electron microscopy and transmission electron microscopy analysis confirmed the morphology of the as‐prepared hybrid material resembling wintersweet flower “buds on branches”, in which CoFe₂O₄ nanoclusters, consisting of nanocrystals with a size of 5–10 nm, are anchored along carbon nanotubes. When applied as an anode material in lithium ion batteries, the CoFe₂O₄/MWCNTs hybrid material exhibited a high performance for reversible lithium storage. In particular, the hybrid anode material delivered reversible lithium storage capacities of 809, 765, 539, and 359 mA h g^?1 at current densities of 180, 450, 900, and 1800 mA g^?1, respectively. The superior performance of CoFe₂O₄/MWCNTs hybrid materials could be ascribed to the synergistic pinning effect of the wintersweet‐flower‐like nanoarchitecture. This strategy could also be applied to synthesize other metal oxide/CNTs hybrid materials as high‐capacity anode materials for lithium ion batteries.     

Mesoporous Spherical Li4Ti5O12 as High‐Performance Anodes for Lithium‐Ion Batteries

Porous microspherical Li₄Ti₅O₁₂ aggregates (LTO‐PSA) can be successfully prepared by using porous spherical TiO₂ as a titanium source and lithium acetate as a lithium source followed by calcinations. The synthesized LTO‐PSA possess outstanding morphology, with nanosized, porous, and spherical distributions, that allow good electrochemical performances, including high reversible capacity, good cycling stability, and impressive rate capacity, to be achieved. The specific capacity of the LTO‐PSA at 30 C is as high as 141 mA h g^?1, whereas that of normal Li₄Ti₅O₁₂ powders prepared by a sol–gel method can only achieve 100 mA h g^?1. This improved rate performance can be ascribed to small Li₄Ti₅O₁₂ nanocrystallites, a three‐dimensional mesoporous structure, and enhanced ionic conductivity.     

Facile Synthesis of A 3D Flower‐Like Mesoporous Ni@C Composite Material for High‐Energy Aqueous Asymmetric Supercapacitors

A 3D flower‐like mesoporous Ni@C composite material has been synthesized by using a facile and economical one‐pot hydrothermal method. This unique 3D flower‐like Ni@C composite, which exhibited a high surface area (522.4 m² g^?1), consisted of highly dispersed Ni nanoparticles on mesoporous carbon flakes. The effect of calcination temperature on the electrochemical performance of the Ni@C composite was systematically investigated. The optimized material (Ni@C 700) displayed high specific capacity (1306 F g^?1 at 2 A g^?1) and excellent cycling performance (96.7 % retention after 5000 cycles). Furthermore, an asymmetric supercapacitor (ASC) that contained Ni@C 700 as cathode and mesoporous carbon (MC) as anode demonstrated high energy density (60.4 W h kg^?1 at a power density of 750 W kg^?1).     

Synthesis of Mesoporous Wall‐Structured TiO2 on Reduced Graphene Oxide Nanosheets with High Rate Performance for Lithium‐Ion Batteries

Mesoporous wall‐structured TiO₂ on reduced graphene oxide (RGO) nanosheets were successfully fabricated through a simple hydrothermal process without any surfactants and annealed at 400 °C for 2 h under argon. The obtained mesoporous structured TiO₂–RGO composites had a high surface area (99 0307 m² g^?1) and exhibited excellent electrochemical cycling (a reversible capacity of 260 mAh g^?1 at 1.2 C and 180 mAh g^?1 at 5 C after 400 cycles), demonstrating it to be a promising method for the development of high‐performance Li‐ion batteries.     

2 D Manganese Vanadate Nanoflakes as High‐Performance Anode for Lithium‐Ion Batteries

Nanometer‐sized flakes of MnV₂O₆ were synthesized by a hydrothermal method. No surfactant, expensive metal salt, or alkali reagent was used. These MnV₂O₆ nanoflakes present a high discharge capacity of 768 mA h g^?1 at 200 mA g^?1, good rate capacity, and excellent cycling stability. Further investigation demonstrates that the nanoflake structure and the specific crystal structure make the prepared MnV₂O₆ a suitable material for lithium‐ion batteries.     

Ruthenium‐Oxide‐Coated Sodium Vanadium Fluorophosphate Nanowires as High‐Power Cathode Materials for Sodium‐Ion Batteries

Sodium‐ion batteries are a very promising alternative to lithium‐ion batteries because of their reliance on an abundant supply of sodium salts, environmental benignity, and low cost. However, the low rate capability and poor long‐term stability still hinder their practical application. A cathode material, formed of RuO₂‐coated Na₃V₂O₂(PO₄)₂F nanowires, has a 50 nm diameter with the space group of I4/mmm. When used as a cathode material for Na‐ion batteries, a reversible capacity of 120 mAh g^?1 at 1 C and 95 mAh g^?1 at 20 C can be achieved after 1000 charge–discharge cycles. The ultrahigh rate capability and enhanced cycling stability are comparable with high performance lithium cathodes. Combining first principles computational investigation with experimental observations, the excellent performance can be attributed to the uniform and highly conductive RuO₂ coating and the preferred growth of the (002) plane in the Na₃V₂O₂(PO₄)₂F nanowires.     

Nitrogen‐Doped Mesoporous Carbon‐Encapsulated MoO2 Nanobelts as a High‐Capacity and Stable Host for Lithium‐Ion Storage

N‐doped mesoporous carbon‐capped MoO₂ nanobelts (designated as MoO₂@NC) were synthesized and applied to lithium‐ion storage. Owing to the stable core–shell structural framework and conductive mesoporous carbon matrix, the as‐prepared MoO₂@NC shows a high specific capacity of around 700 mA h g⁻¹ at a current of 0.5 A g⁻¹, excellent cycling stability up to 100 cycles, and superior rate performance. The N‐doped mesoporous carbon can greatly improve the conductivity and provide uninhibited conducting pathways for fast charge transfer and transport. Moreover, the core–shell structure improved the structural integrity, leading to a high stability during the cycling process. All of these merits make the MoO₂@NC to be a suitable and promising material for lithium ion battery.     

CNT@Fe3O4@C Coaxial Nanocables: One‐Pot,Additive‐Free Synthesis and Remarkable Lithium Storage Behavior

By using carbon nanotubes (CNTs) as a shape template and glucose as a carbon precursor and structure‐directing agent, CNT@Fe₃O₄@C porous core/sheath coaxial nanocables have been synthesized by a simple one‐pot hydrothermal process. Neither a surfactant/ligand nor a CNT pretreatment is needed in the synthetic process. A possible growth mechanism governing the formation of this nanostructure is discussed. When used as an anode material of lithium‐ion batteries, the CNT@Fe₃O₄@C nanocables show significantly enhanced cycling performance, high rate capability, and high Coulombic efficiency compared with pure Fe₂O₃ particles and Fe₃O₄/CNT composites. The CNT@Fe₃O₄@C nanocables deliver a reversible capacity of 1290 mA h g^?1 after 80 cycles at a current density of 200 mA g^?1, and maintain a reversible capacity of 690 mA h g^?1 after 200 cycles at a current density of 2000 mA g^?1. The improved lithium storage behavior can be attributed to the synergistic effect of the high electronic conductivity support and the inner CNT/outer carbon buffering matrix.     

Facile Synthesis of Ge@C Core–Shell Nanocomposites for High‐Performance Lithium Storage in Lithium‐Ion Batteries

Herein, we report a facile and “green” synthetic route for the preparation of Ge@C core–shell nanocomposites by using a low‐cost Ge precursor. Field‐emission scanning electron microscopy and transmission electron microscopy analyses confirmed the core–shell nanoarchitecture of the Ge@C nanocomposites, with particle sizes ranging from 60 to 100 nm. Individual Ge nanocrystals were coated by a continuous carbon layer, which had an average thickness of 2 nm. When applied as an anode materials for lithium‐ion batteries, the Ge@C nanocomposites exhibited a high initial discharge capacity of 1670 mAh g^?1 and superior rate capability. In particular, Ge@C nanocomposite electrodes maintained a reversible capacity of 734 mAh g^?1 after repeated cycling at a current density of 800 mA g^?1 over 100 cycles.     

Scalable Room‐Temperature Synthesis of Mesoporous Nanocrystalline ZnMn2O4 with Enhanced Lithium Storage Properties for Lithium‐Ion Batteries

In this work, we put forward a facile yet efficient room‐temperature synthetic methodology for the smart fabrication of mesoporous nanocrystalline ZnMn₂O₄ in macro‐quality from the birnessite‐type MnO₂ phase. A plausible reduction/ion exchange/re‐crystallization mechanism is tentatively proposed herein for the scalable synthesis of the spinel phase ZnMn₂O₄. When utilized as a high‐performance anode for advanced Li‐ion battery (LIB) application, the as‐synthesized nanocrystalline ZnMn₂O₄ delivered an excellent discharge capacity of approximately 1288 mAh g^?1 on the first cycle at a current density of 400 mA g^?1, and exhibited an outstanding cycling durability, rate capability, and coulombic efficiency, benefiting from its mesoporous and nanoscale structure, which strongly highlighted its great potential in next‐generation LIBs. Furthermore, the strategy developed here is very simple and of great importance for large‐scale industrial production.     

Facile Synthesis of Nitrogen‐Containing Mesoporous Carbon for High‐Performance Energy Storage Applications

Porous carbon with high specific surface area (SSA), a reasonable pore size distribution, and modified surface chemistry is highly desirable for application in energy storage devices. Herein, we report the synthesis of nitrogen‐containing mesoporous carbon with high SSA (1390 m² g^?1), a suitable pore size distribution (1.5–8.1 nm), and a nitrogen content of 4.7 wt % through a facile one‐step self‐assembly process. Owing to its unique physical characteristics and nitrogen doping, this material demonstrates great promise for application in both supercapacitors and encapsulating sulfur as a superior cathode material for lithium–sulfur batteries. When deployed as a supercapacitor electrode, it exhibited a high specific capacitance of 238.4 F g^?1 at 1 A g^?1 and an excellent rate capability (180 F g^?1, 10 A g^?1). Furthermore, when an NMC/S electrode was evaluated as the cathode material for lithium–sulfur batteries, it showed a high initial discharge capacity of 1143.6 mA h g^?1 at 837.5 mA g^?1 and an extraordinary cycling stability with 70.3 % capacity retention after 100 cycles.     

Electrochemical and Structural Study of Layered P2‐Type Na2/3Ni1/3Mn2/3O2 as Cathode Material for Sodium‐Ion Battery

P2‐type Na_2/3Ni_1/3Mn_2/3O₂ was synthesized by a controlled co‐precipitation method followed by a high‐temperature solid‐state reaction and was used as a cathode material for a sodium‐ion battery (SIB). The electrochemical behavior of this layered material was studied and an initial discharge capacity of 151.8 mA h g^?1 was achieved in the voltage range of 1.5–3.75 V versus Na⁺/Na. The retained discharge capacity was found to be 123.5 mA h g^?1 after charging/discharging 50 cycles, approximately 81.4 % of the initial discharge capacity. In situ X‐ray diffraction analysis was used to investigate the sodium insertion and extraction mechanism and clearly revealed the reversible structural changes of the P2‐Na_2/3Ni_1/3Mn_2/3O₂ and no emergence of the O2‐Ni_1/3Mn_2/3O₂ phase during the cycling test, which is important for designing stable and high‐performance SIB cathode materials.     

Hierarchical ZnCo2O4@NiCo2O4 Core–Sheath Nanowires: Bifunctionality towards High‐Performance Supercapacitors and the Oxygen‐Reduction Reaction

Increasing energy demands and worsening environmental issues have stimulated intense research on alternative energy storage and conversion systems including supercapacitors and fuel cells. Here, a rationally designed hierarchical structure of ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires synthesized through facile electrospinning combined with a simple co‐precipitation method is proposed. The obtained core–sheath nanostructures consisting of mesoporous ZnCo₂O₄ nanowires as the core and uniformly distributed ultrathin NiCo₂O₄ nanosheets as the sheath, exhibit excellent electrochemical activity as bifunctional materials for supercapacitor electrodes and oxygen reduction reaction (ORR) catalysts. Compared with the single component of either ZnCo₂O₄ nanowires or NiCo₂O₄ nanosheets, the hierarchical ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires demonstrate higher specific capacitance of 1476 F g^?1 (1 A g^?1) and better rate capability of 942 F g^?1 (20 A g^?1), while maintaining 98.9 % capacity after 2000 cycles at 10 A g^?1. Meanwhile, the ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires reveal comparable catalytic activity but superior stability and methanol tolerance over Pt/C as ORR catalyst. The impressive performance may originate from the unique hierarchical core–sheath structures that greatly facilitate enhanced reactivity, and faster ion and electron transfer.     

Two‐Dimensional Cobalt‐/Nickel‐Based Oxide Nanosheets for High‐Performance Sodium and Lithium Storage

Two‐dimensional (2D) nanomaterials are one of the most promising types of candidates for energy‐storage applications due to confined thicknesses and high surface areas, which would play an essential role in enhanced reaction kinetics. Herein, a universal process that can be extended for scale up is developed to synthesise ultrathin cobalt‐/nickel‐based hydroxides and oxides. The sodium and lithium storage capabilities of Co₃O₄ nanosheets are evaluated in detail. For sodium storage, the Co₃O₄ nanosheets exhibit excellent rate capability (e.g., 179 mA h g^?1 at 7.0 A g^?1 and 150 mA h g^?1 at 10.0 A g^?1) and promising cycling performance (404 mA h g^?1 after 100 cycles at 0.1 A g^?1). Meanwhile, very impressive lithium storage performance is also achieved, which is maintained at 1029 mA h g^?1 after 100 cycles at 0.2 A g^?1. NiO and NiCo₂O₄ nanosheets are also successfully prepared through the same synthetic approach, and both deliver very encouraging lithium storage performances. In addition to rechargeable batteries, 2D cobalt‐/nickel‐based hydroxides and oxides are also anticipated to have great potential applications in supercapacitors, electrocatalysis and other energy‐storage‐/‐conversion‐related fields.     

Ascorbic Acid‐Assisted Synthesis of Mesoporous Sodium Vanadium Phosphate Nanoparticles with Highly sp2‐Coordinated Carbon Coatings as Efficient Cathode Materials for Rechargeable Sodium‐Ion Batteries

Herein, mesoporous sodium vanadium phosphate nanoparticles with highly sp²‐coordinated carbon coatings (meso‐Na₃V₂(PO₄)₃/C) were successfully synthesized as efficient cathode material for rechargeable sodium‐ion batteries by using ascorbic acid as both the reductant and carbon source, followed by calcination at 750 °C in an argon atmosphere. Their crystalline structure, morphology, surface area, chemical composition, carbon nature and amount were systematically explored. Following electrochemical measurements, the resultant meso‐Na₃V₂(PO₄)₃/C not only delivered good reversible capacity (98 mAh g^?1 at 0.1 A g^?1) and superior rate capability (63 mAh g^?1 at 1 A g^?1) but also exhibited comparable cycling performance (capacity retention: ≈74 % at 450 cycles at 0.4 A g^?1). Moreover, the symmetrical sodium‐ion full cell with excellent reversibility and cycling stability was also achieved (capacity retention: 92.2 % at 0.1 A g^?1 with 99.5 % coulombic efficiency after 100 cycles). These attributes are ascribed to the distinctive mesostructure for facile sodium‐ion insertion/extraction and their continuous sp²‐coordinated carbon coatings, which facilitate electronic conduction.     

Highly Ordered Mesoporous Cobalt Oxide Nanostructures: Synthesis,Characterisation, Magnetic Properties,and Applications for Electrochemical Energy Devices

Highly ordered mesoporous Co₃O₄ nanostructures were prepared using KIT‐6 and SBA‐15 silica as hard templates. The structures were confirmed by small angle X‐ray diffraction, high resolution transmission electron microscopy, and N₂ adsorption–desorption isotherm analysis. Both KIT‐6 cubic and SBA‐15 hexagonal mesoporous Co₃O₄ samples exhibited a low Néel temperature and bulk antiferromagnetic coupling due to geometric confinement of antiferromagnetic order within the nanoparticles. Mesoporous Co₃O₄ electrode materials have demonstrated the high lithium storage capacity of more than 1200 mAh g^?1 with an excellent cycle life. They also exhibited a high specific capacitance of 370 F g^?1 as electrodes in supercapacitors.     

Hermetically Coated and Well‐Separated Co3O4 Nanophase within Porous Graphitic Carbon Nanosheets: Synthesis,Confinement Effect,and Improved Lithium‐Storage Capacity and Durability

Considerable lithium‐driven volume changes and loss of crystallinity on cycling have impeded the sustainable use of transition metal oxides (MOs) as attractive anode materials for advanced lithium‐ion batteries that have almost six times the capacity of carbon per unit volume. Herein, Co₃O₄ was used as a model MO in a facile process involving two pyrolysis steps for in situ encapsulation of nanosized MO in porous two‐dimensional graphitic carbon nanosheets (2D‐GCNs) with high surface areas and abundant active sites to overcome the above‐mentioned problems. The proposed method is inexpensive, industrially scalable, and easy to operate with a high yield. TEM revealed that the encaged Co₃O₄ is well separated and uniformly dispersed with surrounding onionlike graphitic layers. By taking advantage of the high electronic conductivity and confinement effect of the surrounding 2D‐GCNs, a hierarchical GCNs‐coated Co₃O₄ (Co₃O₄@GCNs) anode with 43.5 wt % entrapped active nanoparticles delivered a remarkable initial specific capacity of 1816 mAh g^?1 at a current density of 100 mA g^?1. After 50 cycles, the retained capacity is as high as 987 mAh g^?1. When the current density was increased to 1000 mA g^?1, the anode showed a capacity retention of 416 mAh g^?1. Enhanced reversible rate capability and prolonged cycling stability were found for Co₃O₄@GCN compared to pure GCNs and Co₃O₄. The Co₃O₄@GCNs hybrid holds promise as an efficient candidate material for anodes due to its low cost, environmentally friendly nature, high capacity, and stability.