SiO_<i>x</i>C_<i>y</i> Microspheres with Homogeneous Atom Distribution for a High-Performance Li-Ion Battery

The broad application of silicon-based materials is limited by large volume fluctuation, high preparation costs, and complicated preparation processes. Here, we synthesized SiOxCy microspheres on 3D copper foams by a simple chemical vapor deposition method using a low-cost silane coupling agent (KH560) as precursors. The SiOxCy microspheres are available with a large mass loading (>3 mg/cm2) on collectors and can be directly used as the electrode without any binders or extra conductive agents. As a result, the as-prepared SiOxCy shows a high reversible capacity of ∼1240 mAh g–1 and can be cycled more than 1900 times without decay. Ex situ characterizations show that the volume change of the microspheres is only 55% and the spherical morphology as well as the 3D structure remain intact after cycles. Full-cell electrochemical tests paired with LiFePO4 as cathodes show 87% capacity retention after 500 cycles, better than most reported results, thus showing the commercial potential of the material

Two-Dimensional Ag Nanoparticle Tetramer Array for Surface-Enhanced Raman Scattering Measurements

A two-dimensional Ag nanoparticle tetramer array which served as a hotspot matrix for surface-enhanced Raman scattering detection of rhodamine 6G (R6G) molecules down to a concentration as low as 10^–15 M was successfully fabricated by electrochemical deposition on an anodized aluminum substrate. The high detection sensitivity was attributed to both the electromagetic enhancement at the dense Ag nanoparticle tetramer hotspot matrix and chemical enhancement on the corrugated substrate. A single molecule dynamic adsorption behavior was experimentally sensed by the abrupt changes of the charateristic peak intensity and line shape in the spectroscopy when the R6G concentration was lowered to 10^–15 M. Time-evolved spectroscopies revealed the adsorption behavior of either the single molecule in the nanogaps of 2–5 nm or multiple molecules in the nanogaps of 5–9 nm between the Ag nanoparticles

Gate-Induced Metal–Insulator Transition in MoS₂ by Solid Superionic Conductor LaF₃

Electric-double-layer (EDL) gating with liquid electrolyte has been a powerful tool widely used to explore emerging interfacial electronic phenomena. Due to the large EDL capacitance, a high carrier density up to 10¹⁴ cm^–2 can be induced, directly leading to the realization of field-induced insulator to metal (or superconductor) transition. However, the liquid nature of the electrolyte has created technical issues including possible side electrochemical reactions or intercalation, and the potential for huge strain at the interface during cooling. In addition, the liquid coverage of active devices also makes many surface characterizations and <i>in situ</i> measurements challenging. Here, we demonstrate an all solid-state EDL device based on a solid superionic conductor LaF₃, which can be used as both a substrate and a fluorine ionic gate dielectric to achieve a wide tunability of carrier density without the issues of strain or electrochemical reactions and can expose the active device surface for external access. Based on LaF₃ EDL transistors (EDLTs), we observe the metal–insulator transition in MoS₂. Interestingly, the well-defined crystal lattice provides a more uniform potential distribution in the substrate, resulting in less interface electron scattering and therefore a higher mobility in MoS₂ transistors. This result shows the powerful gating capability of LaF₃ solid electrolyte for new possibilities of novel interfacial electronic phenomena

Effect of Carrier Localization on Electrical Transport and Noise at Individual Grain Boundaries in Monolayer MoS₂

Despite its importance in the large-scale synthesis of transition metal dichalcogenides (TMDC) molecular layers, the generic quantum effects on electrical transport across individual grain boundaries (GBs) in TMDC monolayers remain unclear. Here we demonstrate that strong carrier localization due to the increased density of defects determines both temperature dependence of electrical transport and low-frequency noise at the GBs of chemical vapor deposition (CVD)-grown MoS₂ layers. Using field effect devices designed to explore transport across individual GBs, we show that the localization length of electrons in the GB region is ∼30–70% lower than that within the grain, even though the room temperature conductance across the GB, oriented perpendicular to the overall flow of current, may be lower or higher than the intragrain region. Remarkably, we find that the stronger localization is accompanied by nearly 5 orders of magnitude enhancement in the low-frequency noise at the GB region, which increases exponentially when the temperature is reduced. The microscopic framework of electrical transport and noise developed in this paper may be readily extended to other strongly localized two-dimensional systems, including other members of the TMDC family

Bottom-up Approach toward Single-Crystalline VO₂‑Graphene Ribbons as Cathodes for Ultrafast Lithium Storage

Although lithium ion batteries have gained commercial success owing to their high energy density, they lack suitable electrodes capable of rapid charging and discharging to enable a high power density critical for broad applications. Here, we demonstrate a simple bottom-up approach toward single crystalline vanadium oxide (VO₂) ribbons with graphene layers. The unique structure of VO₂-graphene ribbons thus provides the right combination of electrode properties and could enable the design of high-power lithium ion batteries. As a consequence, a high reversible capacity and ultrafast charging and discharging capability is achieved with these ribbons as cathodes for lithium storage. A full charge or discharge is capable in 20 s. More remarkably, the resulting electrodes retain more than 90% of the initial capacity after cycling more than 1000 times at an ultrahigh rate of 190C, providing the best reported rate performance for cathodes in lithium ion batteries to date

Thickness-Tunable Growth of Composition-Controllable Two-Dimensional Fe_<i>x</i>GeTe₂

Two-dimensional (2D) magnetic materials provide an ideal platform for investigating novel magnetism and spin behavior in low-dimensional systems while being restricted by the deficiency of accurate bottom-up synthesis. To overcome this difficulty, a facile and universal flux-assisted growth (FAG) method is proposed to synthesize the multicomponent FexGeTe2 (x = 3–5) with different Fe contents and even alloyed with hetero metal atoms. This one-to-one method ensures the stoichiometry consistency from the FexGeTe2 and MyFe5–yGeTe2 (M = Co, Ni) bulk crystal precursors to the 2D nanosheets, with controllable composition. Tuning the growth temperatures can provide thickness-tunable products. Changeable magnetic properties of FexGeTe2 and alloyed CoyFe5–yGeTe2 are substantiated by the superconducting quantum interference device and reflective magnetic circular dichroism. This method generates thickness-tunable high-crystallinity FexGeTe2 samples without phase separation and exhibits a high tolerance to different substrates and a large temperature window, providing a new avenue to synthesize and explore such multicomponent 2D magnets and even the alloyed ones

Bottom-up Approach toward Single-Crystalline VO₂‑Graphene Ribbons as Cathodes for Ultrafast Lithium Storage

Although lithium ion batteries have gained commercial success owing to their high energy density, they lack suitable electrodes capable of rapid charging and discharging to enable a high power density critical for broad applications. Here, we demonstrate a simple bottom-up approach toward single crystalline vanadium oxide (VO₂) ribbons with graphene layers. The unique structure of VO₂-graphene ribbons thus provides the right combination of electrode properties and could enable the design of high-power lithium ion batteries. As a consequence, a high reversible capacity and ultrafast charging and discharging capability is achieved with these ribbons as cathodes for lithium storage. A full charge or discharge is capable in 20 s. More remarkably, the resulting electrodes retain more than 90% of the initial capacity after cycling more than 1000 times at an ultrahigh rate of 190C, providing the best reported rate performance for cathodes in lithium ion batteries to date

Active Light Control of the MoS₂ Monolayer Exciton Binding Energy

Plasmonic excitation of Au nanoparticles deposited on a MoS₂ monolayer changes the absorption and photoluminescence characteristics of the material. Hot electrons generated from the Au nanoparticles are transferred into the MoS₂ monolayers, resulting in n-doping. The doping effect of plasmonic hot electrons modulates the dielectric permittivity of materials, resulting in a red shift of both the absorption and the photoluminescence spectrum. This spectroscopic tuning was further investigated experimentally by using different Au nanoparticle concentrations, excitation laser wavelengths, and intensities. An analytical model for the photoinduced modulation of the MoS₂ dielectric function and its exciton binding energy change is developed and used to estimate the doping density of plasmonic hot electrons. Our approach is important for the development of photonic devices for active control of light by light

Boron- and Nitrogen-Doped Graphene Quantum Dots/Graphene Hybrid Nanoplatelets as Efficient Electrocatalysts for Oxygen Reduction

The scarcity and high cost of platinum-based electrocatalysts for the oxygen reduction reaction (ORR) has limited the commercial and scalable use of fuel cells. Heteroatom-doped nanocarbon materials have been demonstrated to be efficient alternative catalysts for ORR. Here, graphene quantum dots, synthesized from inexpensive and earth-abundant anthracite coal, were self-assembled on graphene by hydrothermal treatment to form hybrid nanoplatelets that were then codoped with nitrogen and boron by high-temperature annealing. This hybrid material combined the advantages of both components, such as abundant edges and doping sites, high electrical conductivity, and high surface area, which makes the resulting materials excellent oxygen reduction electrocatalysts with activity even higher than that of commercial Pt/C in alkaline media

High-Entropy Laminates with High Ion Conductivities for High-Power All-Solid-State Lithium Metal Batteries

Solid-state electrolytes (SSEs) are crucial to high-energy-density lithium metal batteries, but they commonly suffer from slow Li+ transfer kinetics and low mechanical strength, severely hampering the application for all-solid-state batteries. Here, we develop a two-dimensional (2D) high-entropy lithium-ion conductor, lithium-containing transition-metal phosphorus sulfide, HE-LixMPS3 (Lix(Fe1/5Co1/5Ni1/5Mn1/5Zn1/5)PS3) with five transition-metal atoms and lithium ions (Li+) dispersed into [P2S6]2– framework layers, exhibiting high lattice distortions and a large amount of cation vacancies. Such unique features enable to efficiently accelerate the migration of Li+ in 2D [P2S6]2– interlamination, delivering a high ionic conductivity of 5 × 10–4 S cm–1 at room temperature. Moreover, the HE-LixMPS3 laminate can be employed as a building block to construct an ultrathin SSE film (∼10 μm) based on strong C–S bonding between HE-LixMPS3 and nitrile-butadiene rubber. The SSE film delivers a strong mechanical robustness (6.0 MPa, 310% elongation) and a high ionic conductivity of 4 × 10–4 S cm–1, showing a long cycle stability of 800 h in lithium symmetric cells. Coupled with LiFePO4 cathode and lithium anode, the all-solid-state battery presents a high Coulombic efficiency of 99.8% within 2000 cycles at 5.0 C