Stable dispersion of carbon nanotubes in a molten salt of KNO3-NaNO3-NaNO2-LiNO3-LiOH.

Carbon nanotubes (CNTs) have excellent mechanical and electrical properties; however, they suffer from dispersion problems in various applications. Traditional dispersing strategies of CNTs mostly use oxidation with strong acids or mechanical milling with high energy, which causes serious damage to the intrinsic structures and properties of CNTs. Therefore, it is important to develop new methods for dispersing CNTs without destroying their structures. This paper proposes to disperse CNTs in low-temperature molten salts composed of KNO3-NaNO3-NaNO2-LiNO3-LiOH. By adjusting the composition ratio of molten salts and alkaline, the interaction between charged ions and CNT electrons in the molten salt is studied. The alkaline molten salts can stably disperse CNTs and do not destroy their lengths, thereby offering better electric conductivity. This work will provide a new yet effective method for dispersing CNTs with high aspect ratios, which are important for the application of CNTs and other nanocarbons.

Unraveling the Fundamental Mechanism of Interface Conductive Network Influence on the Fast-Charging Performance of SiO-Based Anode for Lithium-Ion Batteries.

HIGHLIGHTS: Influence of interface conductive network on ionic transport and mechanical stability under fast charging is explored for the first time. The mitigation of interface polarization is precisely revealed by the combination of 2D modeling simulation and Cryo-TEM observation, which can be attributed to a higher fraction formation of conductive inorganic species in bilayer SEI, and primarily contributes to a linear decrease in ionic diffusion energy barrier. The improved stress dissipation presented by AFM and Raman shift is critical for the linear reduction in electrode residual stress and thickness swelling. Progress in the fast charging of high-capacity silicon monoxide (SiO)-based anode is currently hindered by insufficient conductivity and notable volume expansion. The construction of an interface conductive network effectively addresses the aforementioned problems; however, the impact of its quality on lithium-ion transfer and structure durability is yet to be explored. Herein, the influence of an interface conductive network on ionic transport and mechanical stability under fast charging is explored for the first time. 2D modeling simulation and Cryo-transmission electron microscopy precisely reveal the mitigation of interface polarization owing to a higher fraction of conductive inorganic species formation in bilayer solid electrolyte interphase is mainly responsible for a linear decrease in ionic diffusion energy barrier. Furthermore, atomic force microscopy and Raman shift exhibit substantial stress dissipation generated by a complete conductive network, which is critical to the linear reduction of electrode residual stress. This study provides insights into the rational design of optimized interface SiO-based anodes with reinforced fast-charging performance.

Conversion of coal into N-doped porous carbon for high-performance SO2 adsorption.

The large-scale burning of coal has led to increasingly serious SO2 environmental pollution problems. The SO2 adsorption and removal technology based on porous carbons has the advantages of less water consumption, no secondary pollution, recycling of pollutants, and renewable utilization of adsorbents, in contrast to the wet desulfurization process. In this work, we developed a series of N-doped coal-based porous carbons (NCPCs) by calcining a mixture of anthracite, MgO, KOH and carbamide at 800 °C. Among them, the NCPC-2 sample achieves a high N-doped amount of 1.29 at%, and suitable pores with a specific surface area of 1370 m2 g-1 and pore volume of 0.62 cm3 g-1. This N-doped porous carbon exhibits excellent SO2 adsorption capacity as high as 115 mg g-1, which is 3.47 times that of commercial coal-based activated carbon, and 2 times that of NCPC-0 without N-doping. Theoretical calculations show that the active adsorption sites of SO2 are located at the edges and gaps of carbon materials, and surface N doping enhances the adsorption affinity of carbon materials for SO2. In addition, the NCPCs prepared in this work are rich in raw materials and cheap, which meets the needs of industrial production, having excellent SO2 adsorption capacity.

Self-Supported Porous Ni-Fe-W Hydroxide Nanosheets on Carbon Fiber: A Highly Efficient Electrode for Oxygen Evolution Reaction.

Structural and compositional modulation of low-cost hydroxide is important for making efficient electrocatalysts of the oxygen evolution reaction (OER), and it is an ongoing challenge. Here, Ni-Fe-W hydroxide complex by incorporation of tungsten into nickel-iron layered double hydroxide was proposed and investigated. As-formed Ni-Fe-W hydroxide nanosheets are highly porous and self-supported on the carbon fiber substrates, which promote the exposure of the active metal sites for significantly enhanced OER activity. Moreover, the as-introduced tungsten is evidenced to be in a W6+ oxidation state which can facilitate charge transfer and electron capture and thereby decrease the critical conversion barrier of the absorbed OH- to O radical in OER. A series of Ni-Fe-W hydroxides were prepared, with the best molar ratio of Ni-Fe-W sources being 6:2:1. The optimal Ni6Fe2W-LDH@carbon fiber electrode delivers a low overpotential of 264 mV at 10 mA cm-2 and high stability (only 1.6% of the potential increase after 10 h) in alkaline electrolyte. Moreover, the structure of the constructed Ni-Fe-W hydroxide is evidenced to be stable and important for the electrocatalytically stable. The study is expected to open a new avenue in developing multiple hydroxides for low-cost and efficient electrocatalysts.

Capacitive Sodium-Ion Storage Based on Double-Layered Mesoporous Graphene with High Capacity and Charging/Discharging Rate.

Sodium-ion batteries (SIBs) are regarded as an ideal alternative to lithium-ion batteries, but the larger radius of Na+ compared with Li+ results in lower energy density, shorter cycle life, and sluggish kinetics of SIBs. Therefore, it is of significant importance to explore appropriate Na+ storage materials with high capacity and fast Na+ transport kinetics. Herein, doublelayered mesoporous graphene nanosheets codoped with oxygen and nitrogen (O,N-MGNSs) were developed as a new cathode material with high Na+ storage capacity and fast ion-transport kinetics for SIBs. The codoping of MGNSs with oxygen and nitrogen by in situ chemical vapor deposition endowed them with a hierarchical porous network, robust structures, good conductivity, and abundant functional groups. The O,N-MGNSs could host Na+ in two ways: surface adsorption and surface redox reaction, and this endowed them with high Na+ storage capacity and fast charging/discharging rates in SIBs. Electrochemical results revealed that the O,N-MGNSs delivered a reversible capacity of 156 mAh g-1 at a current density of 0.5 A g-1 (corresponding to a rate of 3 C) between 1.5 and 4.2 V and exhibited a high cycling stability (95 % capacity retention at 1 A g-1 for more than 1000 cycles).

Tuning Microstructures of Graphene to Improve Power Capability of Rechargeable Hybrid Aqueous Batteries.

Low conductivity and structural degradation of LiMn2O4 lead to poor power capability and severe capacity fading of hybrid aqueous Zn/LiMn2O4 battery. Here, we propose an effective strategy by tuning the microstructures of graphene to optimize its electrical and interfacial properties and electrode dynamics of LiMn2O4/graphene cathodes, which successfully prompt significant improvements in electrical conductivity and structural stability, thus essentially leading to a promising electrochemical performance. More importantly, it reveals different electrochemical properties prompted by different conductivity, which mainly depends on the microstructures of graphene. This dependence is due to the influence of electronic channels and conductive paths on the conductivity of LiMn2O4/graphene electrodes. A well-designed mesoporous graphene composed of about two graphene-layers exhibits an excellent high-rate performance; even after 300 cycles, a highly reversible capacity of 75 mAh g-1 is retained at 4C rate. The results of this study suggest that the structural tuning of electronic channels of graphene can be used as an effective means to improve the performance of LiMn2O4 cathodes in hybrid aqueous batteries.

Advances in Production and Applications of Carbon Nanotubes.

Recent decades have witnessed many breakthroughs in research on carbon nanotubes (CNTs), particularly regarding controllable synthesis, production scale-up, and application advances for this material. This sp 2-bonded nanocarbon uniquely combines extreme mechanical strength, exceptionally high electrical conductivity, as well as many other superior properties, making it highly attractive for fundamental research and industrial applications. Synthesis and mass production form the solid basis for high-volume applications of CNTs. During recent decades, CNT production capacity has reached more than thousands of tons per year, greatly decreasing the price of CNTs. Although the unique physiochemical properties of an individual CNT are stated repeatedly, manifestation of such unique properties in a macroscopic material, e.g., realization of high-strength CNT fibers, remains a great challenge. If such challenges are solved, many critical applications will be enabled. Herein we review the critical progress in the development of synthesis and scaled-up production methods for CNTs, and discuss advances in their applications. Scientific problems and technological challenges are discussed together.

Aerosol-Assisted Heteroassembly of Oxide Nanocrystals and Carbon Nanotubes into 3D Mesoporous Composites for High-Rate Electrochemical Energy Storage.

Nanostructured composites built from ordinary building units have attracted much attention because of their collective properties for critical applications. Herein, we have demonstrated the heteroassembly of carbon nanotubes and oxide nanocrystals using an aerosol spray method to prepare nanostructured mesoporous composites for electrochemical energy storage. The designed composite architectures show high conductivity and hierarchically structured mesopores, which achieve rapid electron and ion transport in electrodes. Therefore, as-synthesized carbon nanotube/TiO2 electrodes exhibit high rate performance through rapid Li(+) intercalation, making them suitable for ultrafast energy storage devices. Moreover, the synthesis process provides a broadly applicable method to achieve the heteroassembly of vast low-dimensional building blocks for many important applications.

Building robust carbon nanotube-interweaved-nanocrystal architecture for high-performance anode materials.

Rational design of electrode materials is essential but still a challenge for lithium-ion batteries. Herein, we report the design and fabrication of a class of nanocomposite architecture featured by hierarchically structured composite particles that are built from iron oxide nanocrystals and carbon nanotubes. An aerosol spray drying process was used to synthesize this architecture. Such nanoarchitecture enhanced the ion transport and conductivity that are required for high-power anodes. The large volume changes of the anodes during lithium insertion and extraction are accommodated by the particle's resilience and internal porosity. High reversible capacities, excellent rate capability, and stable performance are attained. The synthesis process is simple and broadly applicable, providing a general approach toward high-performance energy storage materials.

A novel method to enhance the conductance of transitional metal oxide electrodes.

Transitional metal oxides hold great potential for high capacity anodes. However, the low electron conductivity of such materials leads to poor cycling stability and inferior rate capability. We reported herein the use of a novel hydrogen plasma technology to improve the conductance of metal oxides, which leads great success in improving the rate performance of CuO nanotube based anodes. This method has the potential to be widely adopted in the field of lithium ion batteries and supercapacitors.

Building robust architectures of carbon and metal oxide nanocrystals toward high-performance anodes for lithium-ion batteries.

Design and fabrication of effective electrode structure is essential but is still a challenge for current lithium-ion battery technology. Herein we report the design and fabrication of a class of high-performance robust nanocomposites based on iron oxide spheres and carbon nanotubes (CNTs). An efficient aerosol spray process combined with vacuum filtration was used to synthesize such composite architecture, where oxide nanocrystals were assembled into a continuous carbon skeleton and entangled in porous CNT networks. This material architecture offers many critical features that are required for high-performance anodes, including efficient ion transport, high conductivity, and structure durability, therefore enabling an electrode with outstanding lithium storage performance. For example, such an electrode with a thickness of ∼35 µm could deliver a specific capacity of 994 mA h g(-1) (based on total electrode weight) and high recharging rates. This effective strategy can be extended to construct many other composite electrodes for high-performance lithium-ion batteries.

High-performance sodium-ion pseudocapacitors based on hierarchically porous nanowire composites.

Electrical energy storage plays an increasingly important role in modern society. Current energy storage methods are highly dependent on lithium-ion energy storage devices, and the expanded use of these technologies is likely to affect existing lithium reserves. The abundance of sodium makes Na-ion-based devices very attractive as an alternative, sustainable energy storage system. However, electrodes based on transition-metal oxides often show slow kinetics and poor cycling stability, limiting their use as Na-ion-based energy storage devices. The present paper details a new direction for electrode architectures for Na-ion storage. Using a simple hydrothermal process, we synthesized interpenetrating porous networks consisting of layer-structured V(2)O(5) nanowires and carbon nanotubes (CNTs). This type of architecture provides facile sodium insertion/extraction and fast electron transfer, enabling the fabrication of high-performance Na-ion pseudocapacitors with an organic electrolyte. Hybrid asymmetric capacitors incorporating the V(2)O(5)/CNT nanowire composites as the anode operated at a maximum voltage of 2.8 V and delivered a maximum energy of ∼40 Wh kg(-1), which is comparable to Li-ion-based asymmetric capacitors. The availability of capacitive storage based on Na-ion systems is an attractive, cost-effective alternative to Li-ion systems.

High-performance energy-storage architectures from carbon nanotubes and nanocrystal building blocks.

High-performance energy-storage architectures are fabricated by forming conformal coatings of active nanocrystal building blocks on preformed carbon nanotube conductive scaffolds for lithium ion electrodes. This unique structure offers effective pathways for charge transport, high active-material loading, structure robustness, and flexibility. This general approach enables the fabrication of a new family of high-performance architectures for energy storage and many other applications.

Direct growth of flexible LiMn2O4/CNT lithium-ion cathodes.

Flexible, binder-free LiMn(2)O(4)/CNT nanocomposites with good reversible capability and cycling stability were fabricated by in-situ hydrothermal growth for flexible lithium battery applications.