Continuous batch synthesis with atmospheric-pressure microwave plasmas

Plasmas under atmospheric pressure offer a high-temperature environment for material synthesis, but electrode ablation compromises purity. Here, we introduce an atmospheric-pressure microwave plasma (AMP) operated without electrodes to overcome the existing limitations in pure material synthesis. The distribution of the electrostatic field intensity inside a waveguide during AMP excitation was examined via electrostatic field simulations. The lateral and radial gas temperature distributions were also studied using optical emission spectroscopy. The AMP exhibited a uniform ultrahigh temperature (9,000 K), a large volume (102-104 cm3), and a response time on the millisecond level. AMP efficiently synthesized silicon nanoparticles, graphene, and graphene@Si-Fe core-shell nanoparticles within tens of milliseconds, ensuring purity and size control. We propose the "heat impulse" metric for evaluating the plasma characteristics (n a, T g, and t) in material synthesis, extended to other high-temperature plasmas. AMP is compact, cost-effective, and easy to assemble, promising for eco-friendly mass production of pure materials.

Wrapping silicon microparticles by using well-dispersed single-walled carbon nanotubes for the preparation of high-performance lithium-ion battery anode

Silicon microparticles (SiMPs) show considerable promise as an anode material in high-performance lithium-ion batteries (LIBs) because of their low-cost starting material and high capacity. The failure issues associated with the intrinsically low conductivity and significant volume expansion of Si have largely been resolved by designing silicon/carbon composites using carbon nanotubes (CNTs). The CNTs are important in terms of stress dissipation and the conductive network in Si/CNT composites. Here, we synthesized a SiMP/2D CNT sheet wrapping composite (SiMP/CNT wrapping) via a facile freeze-drying method with the use of highly dispersed single-walled CNTs. In this work, the well-dispersed CNTs are easily mixed with Si, resulting in effective CNT wrapping on the SiMP surface. During freeze-drying, the CNTs are self-assembled into a segregated 2D CNT sheet morphology via van der Waals interactions. The resulting CNT wrapping shows a unique wide range of conductive networks and mesh-like CNT sheets with void spaces. The SiMP/CNT wrapping 9 : 1 electrode exhibits good rate and cycle performance. The first charge/discharge capacity of SiMP/CNT wrapping 9 : 1 is 3160.7 mA h g^-1/3469.1 mA h g^-1 at 0.1 A g^-1 with superior initial coulombic efficiency of 91.11%. After cycling, the SiMP/CNT wrapping electrode shows good structural integrity with preserved electrical conductivity. The superior electrochemical performance of the SiMP/CNT wrapping composite can be explained by an extensive conductive CNT network on the SiMPs and facile lithium-ion diffusion via mesh-like CNT wrapping.

Graphene-Induced Performance Enhancement of Batteries, Touch Screens, Transparent Memory, and Integrated Circuits: A Critical Review on a Decade of Developments

Graphene achieved a peerless level among nanomaterials in terms of its application in electronic devices, owing to its fascinating and novel properties. Its large surface area and high electrical conductivity combine to create high-power batteries. In addition, because of its high optical transmittance, low sheet resistance, and the possibility of transferring it onto plastic substrates, graphene is also employed as a replacement for indium tin oxide (ITO) in making electrodes for touch screens. Moreover, it was observed that graphene enhances the performance of transparent flexible electronic modules due to its higher mobility, minimal light absorbance, and superior mechanical properties. Graphene is even considered a potential substitute for the post-Si electronics era, where a high-performance graphene-based field-effect transistor (GFET) can be fabricated to detect the lethal SARS-CoV-2. Hence, graphene incorporation in electronic devices can facilitate immense device structure/performance advancements. In the light of the aforementioned facts, this review critically debates graphene as a prime candidate for the fabrication and performance enhancement of electronic devices, and its future applicability in various potential applications.

Metal (Cu/Fe/Mn)-Doped Silicon/Graphite Composite as a Cost-Effective Anode for Li-Ion Batteries

Silicon is a worthy substitute anode material for lithium-ion batteries because it offers high theoretical capacity and low working potentials vs. Li⁺/Li. However, immense volume changes and the low intrinsic conductivity of Si hampers its practical applications. In this study, nano/micro silicon particles are achieved by ball milling silicon mesh powder as a scalable process. Subsequent metal (Cu/Fe/Mn) doping into nano/micro silicon by low-temperature annealing, followed by high-temperature annealing with graphite, gives a metal-doped silicon/graphite composite. The obtained composites were studied as anodes for Li-ion batteries, and they delivered high reversible capacities of more than 1000 mAh g^-1 with improved Li⁺ diffusion properties. The full cells from these composite anodes vs. LiCoO₂ cathodes delivered suitable energy densities for Li⁺ storage applications. The enhanced electrochemical properties are accredited to the synergistic effect of metal doping and graphite addition to silicon and exhibit potential for suitable Li⁺ energy storage applications.

Research Progress on Coating Structure of Silicon Anode Materials for Lithium-Ion Batteries

Silicon, which has been widely studied by virtue of its extremely high theoretical capacity and abundance, is recognized as one of the most promising anode materials for the next generation of lithium-ion batteries. However, silicon undergoes tremendous volume change during cycling, which leads to the destruction of the electrode structure and irreversible capacity loss, so the promotion of silicon materials in commercial applications is greatly hampered. In recent years, many strategies have been proposed to address these shortcomings of silicon. This Review focused on different coatings materials (e. g., carbon-based materials, metals, oxides, conducting polymers, etc.) for silicon materials. The role of different types of materials in the modification of silicon-based material encapsulation structure was reviewed to confirm the feasibility of the protective layer strategy. Finally, the future research direction of the silicon-based material coating structure design for the next-generation lithium-ion battery was summarized.