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.     

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.     

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.     

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.     

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.     

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.     

General Synthesis and Lithium Storage Properties of Metal Oxides/MnO2 Hierarchical Hollow Hybrid Spheres

Metal oxides/MnO₂ hierarchical hollow hybrid nanostructures have attracted significant attention because of their wide potential applications. However, the exploration of a general synthetic approach for fabricating hierarchical hollow hybrid nanostructures is still a great challenge. Herein, a “penetration‐carbonization and reduction‐coating–annealing” route is presented for the generalized synthesis of metal oxides/MnO₂ hierarchical hollow hybrid spheres, including NiO/MnO₂, Co₃O₄/MnO₂, and CuO/MnO₂. Because of the unique hierarchical hollow hybrid nanostructures, NiO/MnO₂ nanomaterials possess a desirable capacity (1520 mA h g⁻¹) and outstanding cyclic stability (909 mA h g⁻¹ at the 200th cycle) as Li‐ion battery anode materials. The work reported herein can not only pave the way for the generalized synthetic strategy of metal oxides/MnO₂ hierarchical hollow hybrid nanostructures, but also provide a promising application of NiO/MnO₂ nanomaterials for Li‐ion battery anode.     

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.     

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.     

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.     

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.     

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.     

Improving the cycle stability and rate performance of LiNi0.91Co0.06Mn0.03O2 Ni-rich cathode material by La2O3 coating for Lithium-ion batteries

In this wok, a uniform layer of La₂O₃ is coated on the surface of LiNi_0.91Co_0.06Mn_0.03O₂ Ni-rich cathode material by using a wet coating process. The XPS and EDX analysis confirms the presence of La₂O₃ coating on the surface of NCM. The coated samples deliver the superior electrochemical performance, 0.2 wt % La₂O₃ (LaO-0.2) NCM exhibits discharge capacity of 202.7 mAh g⁻¹ in 1^st cycle and delivered the cycle stability of 87.2% after 100 cycles. Besides, the enhanced capacity retention, LaO-0.2 has delivered very high discharge capacity of 80.3 mAh g⁻¹ at very high C-rate of 5C while the pristine sample shows very low discharge capacity (33.4 mAh g⁻¹). CV results shows the significant suppression in the intensity of H2–H3 which indicates the superior electrochemical stability of LaO-0.2 NCM. Thus, we can confirm that La₂O₃ coating is promising technique to achieve superior electrochemical performance in the long term cycling process.     

Insert Zn Nanoparticles into the 3D Porous Carbon Ultrathin Films as a Superior Anode Material for Lithium Ion Battery

A flexible strategy is exploited to insert Zn nanoparticles into the pores of highly stable 3D network of carbon ultrathin films (P‐Zn/C) that can effectively localize the postformed Zn nanoparticles, thereby solving the problem of structural degradation, and thus achieve improved anode performance. A maximum capacity of 657.3 mA h g⁻¹ at a current density of 200 mA g⁻¹ after 50 cycles is achieved for P‐Zn/C. Even at a high current density of 2 A g⁻¹, a capacity of 653 mA h g⁻¹ is maintained after 1000 cycles, indicating that it could be a promising anode for lithium ion batteries. By comparing the capacitive and diffusion contribution qualitatively and quantitatively, the result reveals that the enhanced electrochemical performance mainly originates from the pseudocapacitance storage mechanism.     

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.     

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.     

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.     

Uniform Mesoporous CoCO3 Nanospindles on Graphite Nanosheets for Highly Efficient Lithium Storage

As anodes for lithium-ion batteries, CoCO₃ has a much higher specific capacity than graphite and can meet the urgent demands of electric vehicles and portable electronics. However, reported CoCO₃ anodes are of micrometer-sized morphology (0.4–10 µm) that severely limits long-term and rate performances (in particular >2.0 A g⁻¹) due to intrinsically low conductivity and high volume expansion. Mesoporous materials have uniform open mesopores to offer sufficient solid/electrolyte contact, rapid Li⁺ transport, and large pore volume. However, it is still challenging to prepare uniform mesoporous CoCO₃ nanostructures. This work reports a urea–NH₄HCO₃–ethylene glycol (EG) solvothermal system to fabricate uniform mesoporous CoCO₃ nanospindles and concurrently composite with multilayered graphite nanosheets. The obtained mesoporous CoCO₃ has a specific surface area of 143.7 m² g⁻¹, 12.4 times that of commercial CoCO₃. The preparation mechanism is studied in-depth, where urea, NH₄HCO₃, EG, and crystal water play essential and respective roles. The synergistic effect of the mesopore and graphite nanosheets facilitates long-term cycling stability (1465 mAh g⁻¹ after 450 cycles at 200 mA g⁻¹ with 101.1% capacity retention) and high-rate performance (1033 mAh g⁻¹ at 2.0 A g⁻¹). The essential roles of mesopores and graphite nanosheets in boosting the kinetic change are investigated.     

Ge Nanoparticles Encapsulated in Interconnected Hollow Carbon Boxes as Anodes for Sodium Ion and Lithium Ion Batteries with Enhanced Electrochemical Performance

A carbothermal reaction route to Ge nanoparticle homogeneously encapsulated hollow carbon boxes from NH₄H₃Ge₂O₆/resorcinol formaldehyde precursors is designed, using NH₄H₃Ge₂O₆ as a Ge precursor from commercial GeO₂ and NH₄OH. The Ge/C hybrid anode for sodium ion battery displays a higher Na⁺ storage capacity of 346 mA h g^?1 after 500 cycles at a current density of 100 mA h g^?1, almost approaching the theoretical capacity of Ge. Furthermore, Ge/C anode shows significantly improved electrochemical performance for Li⁺ storage, showing a higher initial Coulombic efficiency of 85.1% and a superior reversible capacity of 1336 mA h g^?1 at a high current density of 200 mA g^?1 after 150 cycles. An excellent rate capability with a capacity of 825 mA h g^?1 at a current density of 4.0 A g^?1 can be obtained based on Ge/C anodes. The enhanced electrochemical performance can be attributed to the unique microstructures of Ge/C hybrid anode. The internal void space of hollow carbon boxes can accommodate the volume expansion of Ge during lithiation or sodiation process, thus preserving the structural integrity of electrode material. The interconnected carbon shell can increase the electronic conductivity of the electrode, resulting in the high rate capability and cycling stability.     

Electrochemical performances of nano-Co3O4 with different morphologies as anode materials for Li-ion batteries

Three kinds of Co₃O₄ nanomaterials with different morphologies were synthesized controllably by a post-anneal-assisted hydrothermal method in this study. X-ray diffraction and scanning electron microscopy indicated that all three kinds of samples were pure cubic phase of Co₃O₄ with morphologies of nanorods, nanoclusters, and nanoplates. Moreover, the transmission electron microscopy (TEM) and high-resolution TEM showed that the Co₃O₄ nanorods were bamboo-like and highly crystalline structures. When these materials were applied to the lithium-ion batteries (LIBs) as anode materials, the Co₃O₄ of nanorods demonstrated the best performance. It has a stable reversible capacity of 954 mAh g^?1 as the anode of a LIB, much higher than the other two kinds of Co₃O₄ of rod-like nanoclusters and nanoplates, even after 35 cycles. All results showed that the morphology and microstructure take very important roles in the performance of Co₃O₄ as the anode materials in LIBs.