Porous Co3O4 nanofibers surface-modified by reduced graphene oxide as a durable, high-rate anode for lithium ion battery

Hierarchical architecture of ZIF-8@ZIF-67-Derived N-doped carbon nanotube hollow polyhedron supported on 2D Ti3C2Tx nanosheets targeting enhanced lithium-ion capacitors

The matching of long cycle life, high power density, and high energy density has been an inevitable requirement for the development of efficient anode materials for lithium-ion capacitors (LICs). Here, we introduce an N-doped carbon nanotube hollow polyhedron structure (Co3O4-CNT-800) with high specific surface area and active sites, which is anchored with two-dimensional (2D) Ti3C2Tx nanosheets with metallic conductivity and abundant surface functional groups by electrostatic adsorption to form a hierarchical multilevel hollow semi-covered framework structure. Benefiting from the synergistic effect between Co3O4-CNT-800 and Ti3C2Tx, the composites exhibit superior energy storage efficiency and long cycling stability. The Co3O4-CNT-800/Ti3C2Tx electrodes exhibit a high specific capacity of 817C/g at a current density of 0.5 A/g under the three-electrode system, and the capacity retention rate is 91 % after 5000 cycles at a current density of 2 A/g. Additionally, we assembled Co3O4-CNT-800/Ti3C2Tx as the anode and Activated carbon (AC) cathode to form LIC devices, which showed an electrochemical test result of 90.01 % capacitance retention after 8000 cycles at 2 A/g, and the maximum power density of the LIC was 3000 W/kg and the maximum energy density was 121 Wh/kg. This work pioneered the combination of N-doped carbon nanotube hollow polyhedron structure with two-dimensional Ti3C2Tx, which provides an effective strategy for preparing LIC negative electrode materials with high specific capacitance and long cycling stability.

3D Porous Co3O4/MXene Foam Fabricated via a Sulfur Template Strategy for Enhanced Li/K-Ion Storage

Co₃O₄ is a potential high-capacity anode material for lithium-ion batteries (LIBs) and potassium-ion batteries (PIBs), but the poor electrical conductivity and large volume fluctuations during long-term cycling severely limit its cycle durability and rate capabilities, especially for PIBs with large K-ion size. Here, we propose a sulfur template route to fabricate an integral 3D porous Co₃O₄/MXene (Ti₃C₂T_x) foam using simple vacuum co-filtrating an aqueous dispersion of Co₃O₄, S and MXene followed by calcining to remove the S template. The 3D porous structure can easily accommodate the large volume changes of Co₃O₄ while maintains electrode structural integrity, allowing to realize outstanding long-term cycle stability when tested as anodes for both LIBs (620.4 mA h g^-1 after 1000 cycles at 1 A g^-1) and PIBs (134.1 mA h g^-1 after 1000 cycles at 0.5 A g^-1). The high metallic conductivity of the 3D porous MXene network further facilitates the electron/ion transmission, resulting in an improved rate capability of 390 mA h g^-1 at 13 A g^-1 for LIBs and 125.3 mA h g^-1 at 1 A g^-1 for PIBs. The robust performance of the 3D porous Co₃O₄/MXene foam reflects its perspective as a high-performance anode material for both LIBs and PIBs.

Advances in Electrochemical Energy Devices Constructed with Tungsten Oxide-Based Nanomaterials

Tungsten oxide-based materials have drawn huge attention for their versatile uses to construct various energy storage devices. Particularly, their electrochromic devices and optically-changing devices are intensively studied in terms of energy-saving. Furthermore, based on close connections in the forms of device structure and working mechanisms between these two main applications, bifunctional devices of tungsten oxide-based materials with energy storage and optical change came into our view, and when solar cells are integrated, multifunctional devices are accessible. In this article, we have reviewed the latest developments of tungsten oxide-based nanostructured materials in various kinds of applications, and our focus falls on their energy-related uses, especially supercapacitors, lithium ion batteries, electrochromic devices, and their bifunctional and multifunctional devices. Additionally, other applications such as photochromic devices, sensors, and photocatalysts of tungsten oxide-based materials have also been mentioned. We hope this article can shed light on the related applications of tungsten oxide-based materials and inspire new possibilities for further uses.

Pure-phase β-Mn2V2O7 interconnected nanospheres as a high-performance lithium ion battery anode

This work primarily exhibits a systematic study of the large-scale hydrothermal synthesis of β-Mn₂V₂O₇ interconnected nanospheres without templates. An optimal combination of hydrothermal/annealing/atmosphere parameters is identified for the pure phase, which exhibits an excellent cycling performance of 760 mA h g^-1 at 0.5 A g^-1 over 120 cycles and a rate capability of 470 mA h g^-1 at 2 A g^-1 as an anode for a lithium ion battery. Guidelines have been provided for the first time for the synthesis of β-Mn₂V₂O₇, which opens broad opportunities for this earth-abundant chemical in electrochemical devices.

Nitrogen-Doped Porous Co3O4/Graphene Nanocomposite for Advanced Lithium-Ion Batteries

A novel approach is developed to synthesize a nitrogen-doped porous Co₃O₄/anthracite-derived graphene (Co₃O₄/AG) nanocomposite through a combined self-assembly and heat treatment process using resource-rich anthracite as a carbonaceous precursor. The nanocomposite contains uniformly distributed Co₃O₄ nanoparticles with a size smaller than 8 nm on the surface of porous graphene, and exhibits a specific surface area (120 m²·g⁻¹), well-developed mesopores distributed at 3~10 nm, and a high level of nitrogen doping (5.4 at. %). These unique microstructure features of the nanocomposite can offer extra active sites and efficient pathways during the electrochemical reaction, which are conducive to improvement of the electrochemical performance for the anode material. The Co₃O₄/AG electrode possesses a high reversible capacity of 845 mAh·g⁻¹ and an excellent rate capacity of 587 mAh·g⁻¹. Furthermore, a good cyclic stability of 510 mAh·g⁻¹ after 100 cycles at 500 mA·g⁻¹ is maintained. Therefore, this work could provide an economical and effective route for the large-scale application of a Co₃O₄/AG nanocomposite as an excellent anode material in lithium-ion batteries.

Recent Progress of Electrochemical Energy Devices: Metal Oxide–Carbon Nanocomposites as Materials for Next-Generation Chemical Storage for Renewable Energy

With the importance of sustainable energy, resources, and environmental issues, interest in metal oxides increased significantly during the past several years owing to their high theoretical capacity and promising use as electrode materials for electrochemical energy devices. However, the low electrical conductivity of metal oxides and their structural instability during cycling can degrade the battery performance. To solve this problem, studies on carbon/metal-oxide composites were carried out. In this review, we comprehensively discuss the characteristics (chemical, physical, electrical, and structural properties) of such composites by categorizing the structure of carbon in different dimensions and discuss their application toward electrochemical energy devices. In particular, one-, two-, and three-dimensional (1D, 2D, and 3D) carbon bring about numerous advantages to a carbon/metal-oxide composite owing to the unique characteristics of each dimension.

Self-supporting Co3O4/Graphene Hybrid Films as Binder-free Anode Materials for Lithium Ion Batteries

A self-supporting Co₃O₄/graphene hybrid film has been constructed via vacuum filtration of Co(OH)₂ nanosheet and graphene, followed by a two-step thermal treatment. Within the hybrid film, Co₃O₄ nanoparticles with size of 40~60 nm uniformly in-situ grew on the surface of graphene, forming a novel porous and interleaved structure with strong interactions between Co₃O₄ nanoparticles and graphene. Such fascinating microstructures can greatly facilitate interfacial electron transportation and accommodate the volume changes upon Li ions insertion and extraction. Consequently, the binder-less hybrid film demonstrated extremely high reversible capacity (1287.7 mAh g⁻¹ at 0.2 A g⁻¹), excellent cycling stability and rate capability (1110 and 800 mAh g⁻¹ at 0.5 and 1.0 A g⁻¹, respectively).

3D plum candy-like NiCoMnO4@graphene as anodes for high-performance lithium-ion batteries

3D plum candy-like NiCoMnO₄ microspheres have been prepared via ultrasonic spraying and subsequently wrapped by graphene through electrostatic self-assembly. The as-prepared NiCoMnO₄ powders show hollow structures and NiCoMnO₄@graphene exhibits excellent electrochemical performances in terms of rate performance and cycling stability, achieving a high reversible capacity of 844.6 mA h g⁻¹ at a current density of 2000 mA g⁻¹. After 50 cycles at 1000 mA g⁻¹, NiCoMnO₄@graphene delivers a reversible capacity of 1045.1 mA h g⁻¹ while the pristine NiCoMnO₄ only has a capacity of 143.4 mA h g⁻¹. The hierarchical porous structure helps to facilitate electron transfer and Li-ion kinetic diffusion by shortening the Li-ion diffusion length, accommodating the mechanical stress and volume change during the Li-ion insertion/extraction processes. Analysis from the electrochemical performances reveals that the enhanced performances could be also attributed to the reduced charge-transfer resistance and enhanced Li-ion diffusion kinetics because of the graphene-coating. Moreover, Schottky electric field, due to the difference in work function between graphene and NiCoMnO_4, might be favorable for the redox activity of the NiCoMnO₄. In light of the excellent electrochemical performance and simple preparation, we believe that 3D plum candy-like NiCoMnO₄@graphene composites are expected to be applied as a promising anode materials for high-performance lithium ion batteries.

3D plum candy-like NiCoMnO₄ microspheres have been prepared via ultrasonic spraying and subsequently wrapped by graphene through electrostatic self-assembly.

Direct Electrophoretic Deposition of Binder-Free Co3O4/Graphene Sandwich-Like Hybrid Electrode as Remarkable Lithium Ion Battery Anode

Co₃O₄ is emerging as a promising anode candidate for lithium ion batteries (LIBs) with high theoretical capacity (890 mAh g^-1) but suffers from poor electrochemical cycling stability resulting from the inferior intrinsic electronic conductivity and large volume changes during electrochemical cycling. Here, a new electrophoretic deposition Co₃O₄/graphene (EPD Co₃O₄/G) hybrid electrode is developed to improve the electrochemical performance. Through EPD, Co₃O₄ nanocubes can be homogeneously embedded between graphene sheets to form a sandwich-like structure. Owing to the excellent flexibility of graphene and a large number of voids in this sandwich-like structure, the structural integrity and unobstructed conductive network can be maintained during cycling. Moreover, the electrode kinetics has proved to be a fast surface-controlled lithium storage process. As a result, the Co₃O₄/G hybrid electrode exhibits high specific capacity and excellent electrochemical cycling performance. The Co₃O₄/G hybrid electrode was also further studied by in situ electrochemical XRD to understand the relationship of its structure and performance: (1) The observed Li_xCo₃O₄ indicates an intermediate of possible small volume change in the first discharging. (2) The theoretical capacity achievement of the Co₃O₄ in hybrid electrode was evidenced. (3) The correlation between the electrochemical performance and the structural evolution of the Co₃O₄/G hybrid electrode was discussed detailedly.