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.

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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.

Colloidal iron pyrite nanocrystals (or FeS 2 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, FeS 2 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 FeS 2 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, farinfrared spectroscopy, and Raman spectroscopy techniques. Through this study, a hypothesis has been verified that solvothermal syntheses can also produce FeS 2 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 FeS 2 from iron diethyldithiocarbamate.

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.

The synthesis of colloidal nanocrystals (NCs) of lithiated group 14 elements (Z=Si, Ge, and Sn) is reported, which are Li4.4Si, Li3.75Si, Li4.4Ge, and Li4.4Sn. LixZ 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 LixZ 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 LixZ NCs. This ball‐milling‐assisted surface protection method may be generalized to similar systems, such as NaxZ and KxZ. Moreover, Li4.4Si and Li4.4Ge NCs were conformally encapsulated in carbon fibers, providing great opportunities for studying the potential of using LixZ to mitigate the volume‐fluctuation‐induced poor cyclability problem confronted by Z anodes in lithium‐ion batteries.

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.