One-Step Cooperative Growth of High Reaction Kinetics Composite Homogeneous Core-Shell Heterostructure.

Reaction kinetics can be improved by the enhanced electrical contact between different components growing symbiotically. But so far, due to the necessity for material synthesis conditions match, the component structures of cooperative growth are similar, and the materials are of the same type. The collaborative growth of high-reaction kinetics composite homogeneous core-shell heterostructure between various materials is innovatively proposed with different structures in one step. The NiCo-LDH and PPy successfully symbiotically grow on activated carbon fiber fabric in one step. The open channel structure of the NiCo-LDH nanosheets is preserved while PPy effectively wrapped around the NiCo-LDH. The well-defined nanostructure with abundant active sites and convenient ion diffusion paths is favorable for electrolyte entry into the entire nanoarrays. In addition, owing to the enhanced electronic interaction between different components through XPS analysis, the NiCo-LDH@PPy electrode shows outstanding reaction kinetics and structural stability. The as-synthesized NiCo-LDH@PPy exhibited excellent super-capacitive storage capabilities, robust capacitive activity, and good rate survival. Furthermore, an asymmetric supercapacitor (ASC) device made of NiCo-LDH@PPy and activated carbon (AC) is able to maintain a long cycle life while achieving high power and energy densities.

Revealing the influence of conversion-type Co3O4 dimensionality on cyclic and rate performance for lithium storage.

Cobalt tetraoxide (Co3O4) is regarded as a promising anode material for Li-ion batteries owing to its high theoretical capacity (890 mAh g-1), simple preparation, and controllable morphology. Nanoengineering has been proven to be an effective method for producing high-performance electrode materials. However, systematic research on the influence of material dimensionality on battery performance is lacking. Herein, we prepared Co3O4 with various dimensionalities (one-dimensional (1D) Co3O4 nanorod (NR), two-dimensional (2D) Co3O4 nanosheet (NS), three-dimensional (3D) Co3O4 nanocluster (NC), and 3D Co3O4 nanoflower (NF)) using a simple solvothermal heat treatment method, and their morphologies were controlled by varying the precipitator type and solvent composition. The 1D Co3O4 NR and 3D samples (3D Co3O4 NC and 3D Co3O4 NF) exhibited poor cyclic and rate performances, respectively, while the 2D Co3O4 NS exhibited the best electrochemical performance. The mechanism analysis revealed that the cyclic stability and rate performance of the Co3O4 nanostructures are closely related to their intrinsic stability and interfacial contact performance, respectively, and the 2D thin-sheet structure can achieve an optimal balance between the two, resulting in the best performance. This work presents a comprehensive study on the effect of dimensionality on the electrochemical performance of Co3O4 anodes, providing a new concept for the nanostructure design of conversion-type materials.

Design and synthesis of cellulose nanofiber-derived CoO/Co/C two-dimensional nanosheet toward enhanced and stable lithium storage.

Nano-sized two-dimensional carbonaceous materials have been widely used as the matrix for alloying-type and conversion-type anode materials for Li-ion batteries (LIBs) to improve structural stability and rate performance. However, relevant synthesis usually requires rigorous conditions and chronic reaction processes. Herein, we have designed a simple solvothermal reaction and heat treatment to prepare a novel CoO/Co/C two-dimensional nanosheet (CoO/Co/C 2DNS) by adopting cellulose nanofibers (CNFs) as the precursor. The unique characteristics of CNFs facilitate the uniform distribution of active materials on the surface and the construction of two-dimensional nanostructure via self-assembly. It is worth noting that CoO/Co/C 2DNS exhibits a striking synergistic effect since the porous 2D carbon framework offers additional pseudo-capacitance and enhances the electronic conductivity, while the ultrafine active materials encapsulated inside shorten the Li-ions diffusion pathways and relieve the volume change. Benefit from the unique structure, the composite anode delivered outstanding rate performance (∼500 mAh g-1 at 10 A g-1) and superior long-range cycling performance up to 800 cycles even at 2 A g-1. This work provides a new strategy for the synthesis of nano-sized 2D composite, offering a promising route to construct high performance conversion-type anodes for next-generation LIBs.

Tailoring conductive network nanostructures of ZIF-derived cobalt-decorated N-doped graphene/carbon nanotubes for microwave absorption applications.

Confronted with microwave pollution issues, there is an urgent need for microwave absorption materials that possess optimal combinations of dielectric loss and magnetic loss properties. While a variety of studies focus on the components, the construction of nanostructure is rarely studied, which is of equivalent significance to microwave absorber design. In this work, Co-ZIF-67 was adopted as self-template to grow N-doped graphene/carbon nanotube interlinked conductive networks in-situ under a one-step carbonization process with tailored microwave absorption properties. Diverse microwave absorption performance could be achieved by directly adjusting the proportions among ingredients and the calcination temperature, obtaining a maximum value of reflection loss of -65.45 dB at 17.5 GHz with a sample thickness of just 1.5 mm. The effective absorption bandwidth could be tailored from 3.75 to 18 GHz among different thickness as required. The nanostructures had an apparent impact on the corresponding microwave absorption performance, in which the N-doped carbon-based conductive networks, ferromagnetic cobalt atoms, and interfaces among heterostructure strengthened the dipolar polarization and conductivity loss, magnetic loss, and interfacial polarization, respectively. This synthesis strategy offers a promising pathway for integrating nanostructures and functions, catering to requirements for designing and optimizing prospective microwave absorbers.