Gram-scale bottom-up flash graphene synthesis.

Most bulk-scale graphene is produced by a top-down approach, exfoliating graphite, which often requires large amounts of solvent with high-energy mixing, shearing, sonication or electrochemical treatment1-3. Although chemical oxidation of graphite to graphene oxide promotes exfoliation, it requires harsh oxidants and leaves the graphene with a defective perforated structure after the subsequent reduction step3,4. Bottom-up synthesis of high-quality graphene is often restricted to ultrasmall amounts if performed by chemical vapour deposition or advanced synthetic organic methods, or it provides a defect-ridden structure if carried out in bulk solution4-6. Here we show that flash Joule heating of inexpensive carbon sources-such as coal, petroleum coke, biochar, carbon black, discarded food, rubber tyres and mixed plastic waste-can afford gram-scale quantities of graphene in less than one second. The product, named flash graphene (FG) after the process used to produce it, shows turbostratic arrangement (that is, little order) between the stacked graphene layers. FG synthesis uses no furnace and no solvents or reactive gases. Yields depend on the carbon content of the source; when using a high-carbon source, such as carbon black, anthracitic coal or calcined coke, yields can range from 80 to 90 per cent with carbon purity greater than 99 per cent. No purification steps are necessary. Raman spectroscopy analysis shows a low-intensity or absent D band for FG, indicating that FG has among the lowest defect concentrations reported so far for graphene, and confirms the turbostratic stacking of FG, which is clearly distinguished from turbostratic graphite. The disordered orientation of FG layers facilitates its rapid exfoliation upon mixing during composite formation. The electric energy cost for FG synthesis is only about 7.2 kilojoules per gram, which could render FG suitable for use in bulk composites of plastic, metals, plywood, concrete and other building materials.

Interactions of iron-oxide filled carbon nanotubes with gas molecules.

This work presents a study on iron-oxide filled carbon nanotubes (CNTs) and their interaction with the surrounding atmosphere. Theoretical and experimental methods were employed to determine the interaction mechanism between the CNTs and some gases, such as O2 and N2. The electrical behavior of these CNTs under different atmospheric conditions was studied through resistance measurements, and for comparison, similar studies were conducted on non-filled carbon nanotubes. The iron-oxide filled CNTs were found to be more sensitive to the presence of O2 than the non-filled carbon nanotubes. This behavior was confirmed by the first-principles simulations based on density functional theory with local spin density approximations for CNTs filled with hematite and magnetite iron-oxides. The theoretical study on the interactions of iron-oxide filled CNTs with gas molecules demonstrated a physisorption regime between the nanotube and the surrounding atmosphere, resulting in modifications of the electronic properties of this material.

Flash Recycling of Graphite Anodes.

The ever-increasing production of commercial lithium-ion batteries (LIBs) will result in a staggering accumulation of waste when they reach their end of life. A closed-loop solution, with effective recycling of spent LIBs, will lessen both the environmental impacts and economic cost of their use. Presently, <5% of spent LIBs are recycled and the regeneration of graphite anodes has, unfortunately, been mostly overlooked despite the considerable cost of battery-grade graphite. Here, an ultrafast flash recycling method to regenerate the graphite anode is developed and valuable battery metal resources are recovered. Selective Joule heating is applied for only seconds to efficiently decompose the resistive impurities. The generated inorganic salts, including lithium, cobalt, nickel, and manganese, can be easily recollected from the flashed anode waste using diluted acid, specifically 0.1 m HCl. The flash-recycled anode preserves the graphite structure and is coated with a solid-electrolyte-interphase-derived carbon shell, contributing to high initial specific capacity, superior rate performance, and cycling stability, when compared to anode materials recycled using a high-temperature-calcination method. Life-cycle-analysis relative to current graphite production and recycling methods indicate that flash recycling can significantly reduce the total energy consumption and greenhouse gas emission while turning anode recycling into an economically advantageous process.

Battery metal recycling by flash Joule heating.

The staggering accumulation of end-of-life lithium-ion batteries (LIBs) and the growing scarcity of battery metal sources have triggered an urgent call for an effective recycling strategy. However, it is challenging to reclaim these metals with both high efficiency and low environmental footprint. We use here a pulsed dc flash Joule heating (FJH) strategy that heats the black mass, the combined anode and cathode, to >2100 kelvin within seconds, leading to ~1000-fold increase in subsequent leaching kinetics. There are high recovery yields of all the battery metals, regardless of their chemistries, using even diluted acids like 0.01 M HCl, thereby lessening the secondary waste stream. The ultrafast high temperature achieves thermal decomposition of the passivated solid electrolyte interphase and valence state reduction of the hard-to-dissolve metal compounds while mitigating diffusional loss of volatile metals. Life cycle analysis versus present recycling methods shows that FJH significantly reduces the environmental footprint of spent LIB processing while turning it into an economically attractive process.

Brushed Metals for Rechargeable Metal Batteries.

Battery designs are swiftly changing from metal-ion to rechargeable metal batteries. Theoretically, metals can deliver maximum anode capacity and enable cells with improved energy density. In practice, these advantages are only possible if the parasitic surface reactions associated with metal anodes are controlled. These undesirable surface reactions are responsible for many troublesome issues, like dendrite formation and accelerated consumption of active materials, which leads to anodes with low cycle life or even battery runaway. Here, a facile and solvent-free brushing method is reported to convert powders into films atop Li and Na metal foils. Benefiting from the reactivity of Li metal with these powder films, surface energy can be effectively tuned, thereby preventing parasitic reaction. In-operando study of P2 S5 -modified Li anodes in liquid electrolyte cells reveals a smoother electrode contour and more uniform metal electrodeposition and dissolution behavior. The P2 S5 -modified Li anodes sustain ultralow polarization in symmetric cell for >4000 h, ≈8× longer than bare Li anodes. The capacity retention is ≈70% higher when P2 S5 -modified Li anodes are paired with a practical LiFePO4 cathode (≈3.2 mAh cm-2 ) after 340 cycles. Brush coating opens a promising avenue to fabricate large-scale artificial solid-electrolyte-interphase directly on metals without the need for organic solvent.

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/AlOx 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.

Laser-Induced Silicon Oxide for Anode-Free Lithium Metal Batteries.

The development of a rechargeable Li metal anode (LMA) is an important milestone for improved battery technology. Practical issues hindering LMAs are the formation of Li dendrites and inactive Li during plating and stripping processes, which can cause short circuits, thermal runaway, and low coulombic efficiency (CE). Here, the use of a laser-induced silicon oxide (LI-SiOx ) layer derived from a commercial adhesive tape to improve the reversibility of Li metal batteries (LMBs) is studied. The silicone-based adhesive of the tape is converted by a commercial infrared laser into a homogeneous porous SiOx layer deposited directly over the current collector. The coating results in superior performance by suppressing the formation of Li dendrites and inactive Li and presenting higher average CE of 99.3% (2.0 mAh cm-2 at 2.0 mA cm-2 ) compared to bare electrodes. The thickness and morphology of the deposited Li is investigated, revealing a different mechanism of Li deposition on coated electrodes. The laser coating affords a method that is fast and avoids the use of toxic organic solvents and extensive drying times. The improved performance with the SiOx coating is demonstrated in LMB with a zero-excess ("anode-free") configuration where a 100% improved performance is verified.

Suppressing Li Metal Dendrites Through a Solid Li-Ion Backup Layer.

The growing demand for sustainable and off-grid energy storage is reviving the attempts to use Li metal as the anode in the next generation of batteries. However, the use of Li anodes is hampered due to the growth of Li dendrites upon charging and discharging, which compromises the life and safety of the battery. Here, it is shown that lithiated multiwall carbon nanotubes (Li-MWCNTs) act as a controlled Li diffusion interface that suppresses the growth of Li dendrites by regulating the Li+ ion flux during charge/discharge cycling at current densities between 2 and 4 mA cm-2 . A full Li-S cell is fabricated to showcase the versatility of the protected Li anode with the Li-MWCNT interface, where the full cells could support pulse discharges at high currents and over 450 cycles at different rates with coulombic efficiencies close to 99.9%. This work indicates that carbon materials in lithiated forms can be an effective and simple approach to the stabilization of Li metal anodes.

Three-Dimensional Rebar Graphene.

Free-standing robust three-dimensional (3D) rebar graphene foams (GFs) were developed by a powder metallurgy template method with multiwalled carbon nanotubes (MWCNTs) as a reinforcing bar, sintered Ni skeletons as a template and catalyst, and sucrose as a solid carbon source. As a reinforcement and bridge between different graphene sheets and carbon shells, MWCNTs improved the thermostability, storage modulus (290.1 kPa) and conductivity (21.82 S cm-1) of 3D GF resulting in a high porosity and structurally stable 3D rebar GF. The 3D rebar GF can support >3150× the foam's weight with no irreversible height change, and shows only a ∼25% irreversible height change after loading >8500× the foam's weight. The 3D rebar GF also shows stable performance as a highly porous electrode in lithium ion capacitors (LICs) with an energy density of 32 Wh kg-1. After 500 cycles of testing at a high current density of 6.50 mA cm-2, the LIC shows 78% energy density retention. These properties indicate promising applications with 3D rebar GFs in devices requiring stable mechanical and electrochemical properties.

The total chemical synthesis of polymer/graphene nanocomposite films.

A versatile and room temperature synthesis of thin films of polymer/graphene is reported. Drastically differing from other methods, not only the polymer but also the graphene are completely built from their simplest monomers (thiophene and benzene) in a one-pot polymerization reaction at a liquid-liquid interface. The materials were characterized and electronic properties are presented.

Transparent and conductive thin films of graphene/polyaniline nanocomposites prepared through interfacial polymerization.

This communication reports a simple, one-pot procedure for the synthesis and processing of transparent and conductive thin films of graphene/polyaniline nanocomposites based on an interfacial polymerization. Thin films presenting transmittance of 89% and sheet resistance of 60.6 Ω sq(-1) are spontaneously obtained and can be easily transferred to suitable substrates.