The development of high-performance silicon anodes for the next generation of lithium ion batteries (LIBs) evokes increasing interest in studying its lithiated counterpart-lithium silicide (LixSi). In this paper we report a systematic study of three thermodynamically stable phases of LixSi (x = 4.4, 3.75, and 2.33) plus nitride-protected Li4.4Si, which are synthesized via the high-energy ball-milling technique. All three LixSi phases show improved performance over that of unmodified Si, where Li4.4Si demonstrates optimum performance with a discharging capacity of 3306 (mA h)/g initially and maintains above 2100 (mA h)/g for over 30 cycles and above 1200 (mA h)/g for over 60 cycles at the current density of 358 mA/g of Si. A fundamental question studied is whether different electrochemical paradigms, that is, delithiation first or lithiation first, influence the electrode performance. No significant difference in electrode performance is observed. When a nitride layer (LixNySiz) is created on the surface of Li4.4Si, the cyclability is improved to retain the capacity above 1200 (mA h)/g for more than 80 cycles. By increasing the nitridation extent, the capacity retention is improved significantly from the average decrease of 1.06% per cycle to 0.15% per cycle, while the initial discharge capacity decreases due to the inactivity of Si in the LixNySiz layer. Moreover, the Coulombic efficiencies of all LixSi-based electrodes in the first cycle are significantly higher than that of a Si electrode (∼90% vs 40-70%).

Converting iron pyrite (FeS2) from a non-cyclable to a cyclable cathode material for lithium ion batteries has been an ongoing challenge in recent years. Herein we report a promising mitigation strategy: wet-chemistry based conformal encapsulation of synthetic FeS2 nanocrystals in a resilient carbon (RC) matrix (FeS2@RC). The FeS2@RC composite was fabricated by dispersing autoclave-synthesized FeS2 nanocrystals in an aqueous glucose solution, polymerizing the glucose in a hydrothermal reactor, and finally heating the polymer/FeS2 composite in a tube furnace to partially carbonize the polymer. The FeS2@RC electrodes showed superior cyclability compared with the FeS2 electrodes, that is, 25% versus 1% of retention at the 20th cycle. Based on electrochemical analysis, XRD study, and SEM characterization, the performance enhancement was attributed to RC's ability to accommodate volume fluctuation, enhance charge transfer, alleviate detrimental side reactions, and suppress loss of the active material. Furthermore, the remaining issues associated with the current system were identified and future research directions were proposed.

We present a scalable, single-step, non-thermal plasma synthesis technique for the growth of sub5 nm, hydrogenated amorphous carbon (a-C:H) coated 3C-SiC nanoparticles (NPs). In a tubular flow reactor, we first nucleate and grow c-Si NPs upstream in a SiH4/Ar plasma. These c-Si NPs are then transported by gas flow to a downstream C2H2/Ar plasma, and carburized in-flight by carbon-containing radicals and ions to 3C-SiC NPs. X-ray diffraction and transmission electron microscopy indicate an NP size of similar to 4 nm. X-ray photoelectron spectroscopy analysis confirms that the c-Si NPs are completely carburized to 3C-SiC. Fourier transform infrared spectroscopy shows that the surface of the 3C-SiC NPs is coated with a-C: H with some alkenyl termination, which can facilitate further solution-based surface functionalization for biomedical applications.

Colloidal iron pyrite nanocrystals (or FeS2 NC inks) are desirable as active materials in lithium ion batteries and photovoltaics and are particularly suitable for large-scale, roll-to-roll deposition or inkjet printing. However, to date, FeS2 NC inks have only been synthesized using the hot-injection technique, which requires air-free conditions and may not be desirable at an industrial scale. Here, we report the synthesis of monodisperse, colloidal, spherical, and phase-pure FeS2 NCs of 5.5 +/- 0.3 nm in diameter via a scalable solvothermal method using iron diethyldithiocarbamate as the precursor, combined with a postdigestive ripening process. The phase purity and crystallinity are determined using X-ray diffraction, transmission electron microscopy, far-infrared spectroscopy, and Raman spectroscopy techniques. Through this study, a hypothesis has been verified that solvothermal syntheses can also produce FeS2 NC inks by incorporating three experimental conditions: high solubility of the precursor, efficient mass transport, and sufficient stabilizing ligands. The addition of ligands and stirring decrease the NC size and led to a narrow size distribution. Moreover, using density functional theory calculations, we have identified an acid-mediated decomposition of the precursor as the initial and critical step in the synthesis of FeS2 from iron diethyldithiocarbamate.

A one-step hydrothermal method, followed by calcination at 300 °C in an argon atmosphere, has been developed to synthesize TiO2-B nanoparticles/double-walled nanotubes (NP/DWNT) and TiO2-B nanoparticles/multiple-walled nanotubes (NP/MWNT). To the best of our knowledge, this is the first synthesis of TiO2-B NP/NT hierarchical structures. Both NP/DWNT and NP/MWNT show high performance as anode materials for lithium-ion batteries, superior to their counterparts of DWNT and MWNT, respectively. Among all the four materials studied herein, NP/DWNT demonstrates the highest discharge-charge capacity, rate capability, and cycling stability. The enhancement due to the NP loading results from the increased surface areas, the improved kinetics, and the decreased transport distance for both electrons and Li ions. The charge capacity at high rates lies in the intercalation pseudocapacitance originating from fast Li-ion transport through the infinite channels in TiO2-B. The superiority of DWNT materials versus MWNT materials is ascribed to the thinner walls, which provide a shorter distance for Li-ion transport through the radial direction.

Silver (Ag) and silver oxide (Ag2O) colloidal nanocrystals are easily interconvertable and important for many similar applications; however, they have not been synthesized using the same method. Here we report a simple and effective method for synthesizing well-dispersed, hydrophilic, and colloidal Ag, Ag2O, and Ag–Ag2O mixed nanocrystals, which are 10–50 nm in diameter, sphere-like, and passivated with the same stabilizer polyvinylpyrrolidone (PVP). The method is denoted as alternating voltage induced electrochemical synthesis (AVIES). It involves only a transformer, two pieces of identical Ag wires, a stirring plate, and a PVP-containing electrolyte solution. The control of Ag and/or Ag2O nanocrystals is achieved by tuning the electrolyte identity, the stirring rate, and the applied voltage. Toward exploring practical applications of heterogeneous catalysis and antibacterial therapy, we have employed the synthesized NCs to catalyze the reduction of 4-nitrophenol and fabricated Ag NCs-loaded electrospun carbon fibers, respectively. Moreover, the revealed crystal-formation mechanism is surprising and interesting: the intermediate states for producing Ag nanocrystals are Ag2O nano-islands formed in situ on the electrode, and not the Ag+ ions in solution formed in situ through electrochemical etching.

N-Bromosuccinimide based bromination is proven to be an effective and mild intermediate step to produce surface functionalized, red-emitting, colloidal SiQDs.

Iron pyrite (p-FeS2) has been widely utilized as a commercial cathode material for lithium ion batteries (LIBs) for 30+ years, due to its high charge capacity, natural abundance, low cost, and non-toxicity. Industrialized versions include both non-rechargeable Li/FeS2 batteries at ambient temperatures (-40 – 60 °C) and rechargeable Li/FeS2 batteries at high temperatures (400 – 450 °C). However, FeS2 cathodes suffer from very poor cyclability at room temperature. Four specific reasons have been identified for this problem: 1) Volume fluctuations during cycling, resulting in pulverization of large particles and a subsequent loss of contact to the current collector; 2) poor electrical conductivity of the lithiation product, lithium sulfide; 3) detrimental reactions between the electrolyte solution and the active materials (FeS2and its subsequent derivatives); 4) the loss of materials due to the formation of soluble lithium polysulfides. In this presentation, we will outline our strategy to address all of the above challenges for FeS2 through the encapsulation of FeS2 nanoparticles in an elastic carbon (EC) matrix. Two carbon sources are explored to produce an ideal EC matrix, which is chemically and mechanically stable, elastic, and conductive. These unique properties allow accommodation of the volume fluctuation, enhance the charge transfer, and protect the FeS2 from damaging chemical reactions. The obtained FeS2@EC composites present significantly improved cyclability over bare FeS2 nanoparticles. Scanning electron microscopy, Raman spectroscopy, electrochemical impedance spectroscopy, and cyclability studies are utilized to confirm the structure-performance relationship.

The synthesis of colloidal nanocrystals (NCs) of lithiated group 14 elements (Z=Si, Ge, and Sn) is reported, which are Li4.4 Si, Li3.75 Si, Li4.4 Ge, and Li4.4 Sn. Lix Z compounds are highly reactive and cannot be synthesized by existing methods. The success relied on separating the surface protection from the crystal formation and using a unique passivating ligand. Bare Lix Z crystals were first produced by milling elemental Li and Z in an argon-filled jar. Then, under the assistance of additional milling, hexyllithium was added to passivate the freshly generated Lix Z NCs. This ball-milling-assisted surface protection method may be generalized to similar systems, such as Nax Z and Kx Z. Moreover, Li4.4 Si and Li4.4 Ge NCs were conformally encapsulated in carbon fibers, providing great opportunities for studying the potential of using Lix Z to mitigate the volume-fluctuation-induced poor cyclability problem confronted by Z anodes in lithium-ion batteries.

Lithium silicide (LixSi) is the lithiated form of silicon, one of the most promising anode materials for the next generation of lithium-ion batteries (LIBs). In contrast to silicon, LixSi has not been well studied. Herein we report a facile high-energy ball-milling-based synthesis of four phase-pure LixSi (x = 4.4, 3.75, 3.25, and 2.33), using hexane as the lubricant. Surprisingly, the obtained Li3.75Si phase shows significant downward shifts in all X-ray diffraction peak positions, compared with the standard. Our interpretation is that the high-energy ball-mill-synthesized Li3.75Si presents smaller internal pressures and larger lattice constants. The chemical-stability study reveals that only surface reactions occur after Li4.4Si and Li3.75Si are immersed in several battery-assembly-related chemicals. The thermal-stability study shows that Li4.4Si is stable up to 350 °C and Li3.75Si is stable up to 200 °C. This remarkable thermal stability of Li3.75Si is in stark contrast to the long-observed metastability for electrochemically synthesized Li3.75Si. The carbon encapsulation of Li4.4Si has also been studied for its potential applications in LIBs.

A simple and generic approach--alternating voltage induced electrochemical synthesis (AVIES)--has been reported for synthesizing highly dispersed colloidal metal (Au, Pt, Sn, and Pt-Pd) and metal oxide (ZnO and TiO2) nanocrystals. The respective nanocrystals are produced when a zero-offset alternating voltage at 60 Hz is applied to a pair of identical metal wires, which are inserted in an electrolyte solution containing capping ligands. In the case of Au, the obtained nanocrystals are highly crystalline nano-icosahedra of 14 ± 2 nm in diameter, the smallest Au icosahedra synthesized in aqueous solutions via green chemistry. Their catalytic activity has been demonstrated through facilitating the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride. This AVIES approach is an environmentally benign process and can be adopted by any research lab.

Alternating voltage-induced electrochemical synthesis (AVIES) produces well-dispersed, size-controlled, single-crystalline, colloidal palladium nanocrystals (Pd-NCs). An alternating voltage is applied to two Pd wires inserted in an electrolyte solution containing capping ligands. Pd-NCs are directly ejected from the Pd electrodes through cathodic reduction of the PdO intermediates. The obtained Pd-NCs are soluble in either polar or non-polar solvents, depending on the selected capping ligands. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

A simple method of alternating voltage-induced electrochemical synthesis has been developed to synthesize highly dispersed colloidal Au nanoicosahedra of 14 ± 3 nm in size. This simple and effective method uses a common transformer to apply a zero-offset alternating voltage to a pair of identical Au electrodes that are immersed in an electrolyte solution containing ligands. The obtained Au nanoicosahedra in this work are among the smallest Au icosahedra synthesized in aqueous solutions. A series of experimental conditions have been studied, such as voltage, the electrolyte identity and concentration, stabilizer identity and concentration, and reaction temperature. The mechanistic study indicates that Au nanoicosahedra are produced on electrode surfaces through an intermediate state of AuO x . The kinetic rate constant of these Au icosahedra in catalyzing the reduction of 4-nitrophenol with sodium borohydride is found much larger than the literature values of similar Au nanocrystals. In addition, the synthesis of Au–Pd-alloyed NCs has also been attempted.