Hydrothermal Coating of Patterned Carbon Nanotube Forest for Structured Lithium-Ion Battery Electrodes

Microwave-Assisted Synthesis as a Promising Tool for the Preparation of Materials Containing Defective Carbon Nanostructures: Implications on Properties and Applications

In this review, we focus on a small section of the literature that deals with the materials containing pristine defective carbon nanostructures (CNs) and those incorporated into the larger systems containing carbon atoms, heteroatoms, and inorganic components.. Briefly, we discuss only those topics that focus on structural defects related to introducing perturbation into the surface topology of the ideal lattice structure. The disorder in the crystal structure may vary in character, size, and location, which significantly modifies the physical and chemical properties of CNs or their hybrid combination. We focus mainly on the method using microwave (MW) irradiation, which is a powerful tool for synthesizing and modifying carbon-based solid materials due to its simplicity, the possibility of conducting the reaction in solvents and solid phases, and the presence of components of different chemical natures. Herein, we will emphasize the advantages of synthesis using MW-assisted heating and indicate the influence of the structure of the obtained materials on their physical and chemical properties. It is the first review paper that comprehensively summarizes research in the context of using MW-assisted heating to modify the structure of CNs, paying attention to its remarkable universality and simplicity. In the final part, we emphasize the role of MW-assisted heating in creating defects in CNs and the implications in designing their properties and applications. The presented review is a valuable source summarizing the achievements of scientists in this area of research.

Sb Nanoparticles Embedded in the N-Doped Carbon Fibers as Binder-Free Anode for Flexible Li-Ion Batteries

Antimony (Sb) is considered a promising anode for Li-ion batteries (LIBs) because of its high theoretical specific capacity and safe Li-ion insertion potential; however, the LIBs suffer from dramatic volume variation. The volume expansion results in unstable electrode/electrolyte interphase and active material exfoliation during lithiation and delithiation processes. Designing flexible free-standing electrodes can effectively inhibit the exfoliation of the electrode materials from the current collector. However, the generally adopted methods for preparing flexible free-standing electrodes are complex and high cost. To address these issues, we report the synthesis of a unique Sb nanoparticle@N-doped porous carbon fiber structure as a free-standing electrode via an electrospinning method and surface passivation. Such a hierarchical structure possesses a robust framework with rich voids and a stable solid electrolyte interphase (SEI) film, which can well accommodate the mechanical strain and avoid electrode cracks and pulverization during lithiation/delithiation processes. When evaluated as an anode for LIBs, the as-prepared nanoarchitectures exhibited a high initial reversible capacity (675 mAh g^-1) and good cyclability (480 mAh g^-1 after 300 cycles at a current density of 400 mA g^-1), along with a superior rate capability (420 mA h g^-1 at 1 A g^-1). This work could offer a simple, effective, and efficient approach to improve flexible and free-standing alloy-based anode materials for high performance Li-ion batteries.

Anisotropic Carbon Nanotube Structures with High Aspect Ratio Nanopores for Li-Ion Battery Anodes

Technological advances in membrane technology, catalysis, and electrochemical energy storage require the fabrication of controlled pore structures at ever smaller length scales. It is therefore important to develop processes allowing for the fabrication of materials with controlled submicron porous structures. We propose a combination of colloidal lithography and chemical vapor deposition of carbon nanotubes to create continuous straight pores with diameters down to 100 nm in structures with thicknesses of more than 300 μm. These structures offer unique features, including continuous and parallel pores with aspect ratios in excess of 3000, a low pore tortuosity, good electrical conductivity, and electrochemical stability. We demonstrate that these structures can be used in Li-ion batteries by coating the carbon nanotubes with Si as an active anode material.

W Clusters In Situ Assisted Synthesis of Layered Carbon Nanotube Arrays on Graphene Achieving High-Rate Performance

W atoms/clusters are employed to in situ assist the development of layered vertically aligned carbon nanotube arrays (VACNTs) through hot-filament-assisted chemical vapor deposition (HFCVD) with liquid binary Fe₃O₄/AlO_x catalysts. The hot W filament was utilized to in situ evaporate atomic W and form W clusters on Fe catalysts, which have a strong impact on the growth of layered VACNT arrays. The migration and Ostwald ripening of Fe catalysts are found to be suppressed immediately with more W clusters deposition during CNT growth. Through controlling the deposition of W clusters, the electrochemical energy storage performance of as-prepared layered VACNT arrays is also tunable as electrodes of ion-based supercapacitors. The layered VACNT arrays can achieve a high capacity of 83.1 mF cm^-2 and possess desirable rate performance due to the suitable hot filament condition (55 W for 90 s). This work provides a new perspective to in-depth understand the behavior of W filament during HFCVD and the significant role of the in situ generated W clusters on the growth of CNTs by maintaining the catalytic activity and structure of catalysts.

High electrochemical performance of Fe2O3@OMC for lithium-ions batteries

Fe₂O₃@OMC (ordered mesoporous carbon) is synthesized using Fe-MOFs (metal-organic frameworks). The Fe₂O₃@OMC pore size is mostly concentrated at approximately 2-4 nm. Compared to traditional OMC or carbonized Fe-MOFs, Fe₂O₃@OMC demonstrates a higher capacity (the capacity remains at 1176.6 mAh g^-1 after 500 cycles under a current density of 0.1 A g^-1) and a longer cycle life. The first cycle capacity of Fe₂O₃@OMC is ultrahigh at 2448.6 mAh g^-1, and the reversible capacity is 1294.1 mAh g^-1. Fe₂O₃@OMC maintains a good performance under current densities of 0.1 A g^-1, 0.2 A g^-1, 0.5 A g^-1, 1 A g^-1, 2 A g^-1, and 5 A g^-1, with electric capacities of 1100.8 mAh g^-1, 1017.6 mAh g^-1, 849.3 mAh g^-1, 690.7 mAh g^-1, 506.7 mAh g^-1, and 272.1 mAh g^-1, respectively. Thus, the material has good rate performance. Combining iron oxide and MOFs is helpful to improve the capacity performance.

Bicontinuous phase separation of lithium-ion battery electrodes for ultrahigh areal loading

Ultrathick battery electrodes are appealing as they reduce the fraction of inactive battery parts such as current collectors and separators. However, thick electrodes are difficult to dry and tend to crack or flake during production. Moreover, the electrochemical performance of thick electrodes is constrained by ion and electron transport as well as fast capacity degradation. Here, we report a thermally induced phase separation (TIPS) process for fabricating thick Li-ion battery electrodes, which incorporates the electrolyte directly in the electrode and alleviates the need to dry the electrode. The proposed TIPS process creates a bicontinuous electrolyte and electrode network with excellent ion and electron transport, respectively, and consequently achieves better rate performance. Using this process, electrodes with areal capacities of more than 30 mAh/cm² are demonstrated. Capacity retentions of 87% are attained over 500 cycles in full cells with 1-mm-thick anodes and cathodes. Finally, we verified the scalability of the TIPS process by coating thick electrodes continuously on a pilot-scale roll-to-roll coating tool.

Honeycomb-shaped carbon nanotube supports for BiVO4 based solar water splitting

Advances in the synthesis and assembly of nanomaterials offer a unique opportunity to purposefully design structures according to the requirements of the targeted applications. This paper shows a process to create robust 3D carbon nanotube (CNT) structures, which provide an electrically conductive support for nanoparticle coating. We describe a process to reliably fabricate robust honeycomb structures with walls made out of aligned CNTs. We present a design of experimental analysis of this fabrication process and discuss methods to coat these honeycombs with BiVO₄ for solar fuel applications. The proposed honeycomb structure allows for an efficient transport of electrons through the electrode, as well as an enhanced light-electrode interaction. Finally, we demonstrate that the developed CNT electrodes can survive harsh BiVO₄ synthesis conditions and can subsequently be used as photoelectrodes for solar water splitting.