Silicon (Si) has been regarded as one of the most promising anodes for next-generation lithium-ion batteries (LIBs) due to its exceptional capacity, appropriate voltage profile, and reliable operation safety. However, poor cyclic stability and moderate rate performance have been critical drawbacks to hamper the practical application of Si-based anodes. It has been one of the central issues to develop new strategies to improve the cyclic and rate performance of the Si-based lithium-ion battery anodes. In this work, super-small metal nanoparticles (2.9 nm in diameter) are in situ synthesized and homogeneously embedded in the in situ formed nitrogen-doped carbon matrix, as demonstrated by the Si/Ag/C nanohybrid, where epoxy resin monomers are used as solvent and carbon source. With tiny amount of silver (2.59% by mass), the Si/Ag/C nanohybrid exhibits superior rate performance compared to the bare Si/C sample. Systematic structure characterization and electrochemical performance tests of the Si/Ag/C nanohybrids have been performed. The mechanism for the enhanced rate performance is investigated and elaborated. The temperature-dependent I-V behavior of the Si/Ag/C nanohybrids with tuned silver contents is measured. Based on the model, it is found that the super-small silver nanoparticles mainly increase charge carrier mobility instead of the charge carrier density in the Si/Ag/C nanohybrids. The evaluation of the total electron transportation length provided by the silver nanoparticles within the electrode also suggests significantly enhanced charge carrier mobility. The existence of tremendous amounts of super-small silver nanoparticles with excellent mechanical properties also contributes to the slightly improved cyclic stability compared to that of simple Si/C anodes.

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MoS2 is widely used in many fields including spin-valleytronics, logic transistors, light emitting devices, clean energy and biology. However, controllable synthesis of two-dimensional MoS2 sheets remains a great challenge. We report the formation of round-shaped monolayer MoS2 domains with a tunable size and the shape transformation from triangle to round. A qualitative interpretation of the formation mechanism is presented and the process can be controlled by either a thermodynamic or a kinetic growth regime depending on the growth rate. The round-shaped MoS2 domains show a high electron mobility of 1.39 cm(2) V(-1) s(-1), comparable to the mechanically exfoliated counterparts. Our study reveals the dominant factors that influence the synthesis of MoS2 and improves our understanding of the nucleation and growth mechanisms of MoS2, towards fine control over the synthesis of MoS2 and other TMDs.

Niobium dioxide (NbO 2 ) features a high theoretical capacity and an outstanding electron conductivity, which makes it a promising alternative to the commercial graphite negative electrode. However, studies on NbO 2 based lithium-ion battery negative electrodes have been rarely reported. In the present work, NbO 2 nanoparticles homogeneously embedded in a carbon matrix are synthesized through calcination using a dental resin monomer (bisphenol A glycidyl dimethacrylate, Bis-GMA) as the solvent and a carbon source and niobium ethoxide (NbETO) as the precursor. It is revealed that a low Bis-GMA/NbETO mass ratio (from 1:1 to 1:2) enables the conversion of Nb (V) to Nb (IV) due to increased porosity induced by an alcoholysis reaction between the NbETO and Bis-GMA. The as-prepared NbO 2 /carbon nanohybrid delivers a reversible capacity of 225 mAh g −1 after 500 cycles at a 1 C rate with a Coulombic efficiency of more than 99.4% in the cycles. Various experimental and theoretical approaches including solid state nuclear magnetic resonance, ex situ X-ray diffraction, differential electrochemical mass spectrometry, and density functional theory are utilized to understand the fundamental lithiation/delithiation mechanisms of the NbO 2 /carbon nanohybrid. The results suggest that the NbO 2 /carbon nanohybrid bearing high capacity, long cycle life, and low gas evolution is promising for lithium storage applications.intercalation behavior and to reveal the fundamental mechanisms of NbO 2 based lithium-ion battery negative electrodes. A size reduction to the nanoscale range is identified of being crucial to demonstrate electrochemical activity toward lithium intercalation, where micrometer and sub-micrometer-sized particles only possess very limited actual capacities. [2e] The deposition of nanosized Nb 2 O 5 particles onto a carbon foam followed by high-temperature annealing in a reducing atmosphere proved to be an effective way to synthesize NbO 2 nanoparticles bearing a reasonable electrochemical performance in lithium microbatteries. [4b] Nevertheless, the limited amount of NbO 2 nanoparticles within the carbon foam resulted in a low total energy output, which made it only suitable for microbatteries. Hydrothermal reaction was applied to synthesize NbO 2 / carbon core shell nanocomposites, which showed a good electrochemical performance in super capacitors. [4a] However, an application as lithium-ion battery negative electrode was not addressed. Besides, the suggested synthetic method will be difficult to scale up, which renders this approach from the literature to be nonfeasible for practical applications.In our previous work, a new concept was developed to synthesize intercalation negative electrode in a facile scalable way. TiO 2 /C and Li 4 Ti 5 O 12 /C nanohybrid particles with super-small-sized TiO 2 or Li 4 Ti 5 O 12 nanoparticles were in situ formed and homogeneously embedded in a carbon matrix. [5] The dental resin monomers of bisphenol A glycidyl dimethacrylate (Bis-GMA) and triethylene glycol dimethacrylate ...

Transition metal dichalcogenides such as MoS2 and WS2 quantum dots (QDs) have been found to show a dramatic enhancement of photoluminescence (PL) quantum efficiency as compared with their planar sheet counterparts. However, the mechanisms of PL enhancement remain not to be very clear. In this work, MoSe2 QDs with the size ranging from about 5.30 nm to 1.55 nm were prepared by a probe-assistant ultrasonication exfoliation approach. The as-prepared MoSe2 QDs are strongly fluorescent, suggesting the existence of quantum confinement effects, and show two distinct PL emissions in the ultraviolet and visible ranges, which are attributed to a band-edge state and a surface related defect state, respectively. We observed blue shifts of the PL peak position and the absorption band edge with the change in the QD size, and the discrepancy of the shifted energies between the PL emission and the estimation based on documented models is briefly addressed.

We report the photoluminescence (PL) characteristics of a van der Waals (vdW) heterojunction constructed by simply depositing an organic semiconductor of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) onto a two-dimensional MoS2 monolayer. The crystallinity of PTCDA on MoS2 is significantly improved due to the vdW epitaxial growth. We observe an enhanced PL intensity and PL peak shift of the MoS2/PTCDA heterojunction compared with the solo MoS2 and PTCDA layer. The synergistic PL characteristics are believed to originate from the hybridization interaction between the MoS2 and the PTCDA as evidenced by density functional theory calculations and Raman measurements. The hybridization interfacial interaction is found to be greatly influenced by the crystalline ordering of the PTCDA film on the 2D MoS2. Our study opens up a new avenue to tune the PL of vdW heterojunctions consisting of TMDs and organic semiconductors for optoelectronic applications.

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LiTiO (LTO) is regarded as a promising lithium-ion battery anode due to its stable cyclic performance and reliable operation safety. The moderate rate performance originated from the poor intrinsic electron and lithium-ion conductivities of the LTO has significantly limited its wide applications. A facile scalable synthesis of hierarchical LiTiO/C nanohybrids with supersmall LTO nanoparticles (ca. 17 nm in diameter) homogeneously embedded in the continuous submicrometer-sized carbon matrix is developed. Difunctional methacrylate monomers are used as solvent and carbon source to generate TiO/C nanohybrid, which is in situ converted to LTO/C via a solid-state reaction procedure. The structure, morphology, crystallinity, composition, tap density, and electrochemical performance of the LTO/C nanohybrid are systematically investigated. Comparing to the control sample of the commercial LTO composited with carbon, the reversible specific capacity after 1000 cycles at 175 mA g and rate performance at high current densities (875, 1750, and 3500 mA g) of the LiTiO/C nanohybrid have been significantly improved. The enhanced electrochemical performance is due to the unique structure feature, where the supersmall LTO nanoparticles are homogeneously embedded in the continuous carbon matrix. Good tap density is also achieved with the LTO/C nanohybrid due to its hierarchical micro-/nanohybrid structure, which is even higher than that of the commercial LTO powder.