Scalable Solution-Grown High-Germanium-Nanoparticle-Loading Graphene Nanocomposites as High-Performance Lithium-Ion Battery Electrodes: An Example of a Graphene-Based Platform toward Practical Full-Cell Applications

Graphene in the form of graphene/nanocrystal nanocomposites can improve the electrochemical performance of nanocrystals for lithium-ion (Li-ion) battery anodes, which is especially important for high-capacity Li-alloy materials such as Si and Ge. For practical full-cell applications, graphene composite electrodes consisting of a large portion of active materials (i.e., a surface of graphene sheets evenly distributed with dense nanoparticles) are required. We have developed a facile solution-based method to synthesize subgram quantities of nanocomposites composed of reduced graphene oxide (RGO) sheets covered with a high concentration (∼80 wt %) of single-crystal 4.90(±0.80) nm diameter Ge nanoparticles. Subsequently, carbon-coated Ge nanoparticles/RGO (Ge/RGO/C) sandwich structures were formed via a carbonization process. The high-nanoparticle-loading nanocomposites exhibited superior Li-ion battery anode performance when examined with a series of comprehensive tests, such as receiving a practical capacity of Ge (1332 mAh/g) close (96.2%) to its theoretical value (1384 mAh/g) when cycled at a 0.2 C rate and having a high-rate capability over hundreds of cycles. Furthermore, the performance of the full cells assembled using a Ge/RGO/C anode and an LiCoO₂ cathode were evaluated. The cells were able to power a wide range of electronic devices, including an light-emitting-diode (LED) array consisting of over 150 bulbs, blue LED arrays, a scrolling LED marquee, and an electric fan. Thus, this study demonstrates a proof of concept of the use of graphene-based nanocomposites toward practical Li-ion battery applications

Alkanethiol-Passivated Ge Nanowires as High-Performance Anode Materials for Lithium-Ion Batteries: The Role of Chemical Surface Functionalization

We demonstrate that dodecanethiol monolayer passivation can significantly enhance the anode performance of germanium (Ge) nanowires in lithium-ion batteries. The dodecanethiol-passivated Ge nanowires exhibit an excellent electrochemical performance with a reversible specific capacity of 1130 mAh/g at 0.1 C rate after 100 cycles. The functionalized Ge nanowires show high-rate capability having charge and discharge capacities of ∼555 mAh/g at high rates of 11 C. The functionalized Ge nanowires also performed well at 55 °C, showing their thermal stability at high working temperatures. Moreover, full cells using a LiFePO₄ cathode were assembled and the electrodes still have stable capacity retention. An aluminum pouch type lithium cell was also assembled to provide larger current (∼30 mA) for uses on light-emitting-diodes (LEDs) and audio devices. Investigation of the role of organic monolayer coating showed that the wires formed a robust nanowire/PVDF network through strong C–F bonding so as to maintain structure integrity during the lithiation/delithiation process. Organic monolayer-coated Ge nanowires represent promising Ge–C anodes with controllable low carbon content (<i>ca.</i> 2–3 wt %) for high capacity, high-rate lithium-ion batteries and are readily compatible with the commercial slurry-coating process for cell fabrication

Self-Seeded Growth of Five-Fold Twinned Copper Nanowires: Mechanistic Study, Characterization, and SERS Applications

A comprehensive mechanistic study conducted on the formation mechanism of five-fold twinned copper nanowires by heating copper­(I) chloride with oleylamine at 170 °C is presented. Electron microscopy and UV–visible absorption spectra are used to analyze the growth mechanism of copper nanowires. High-resolution transmission electron microscopy and selected-area electron diffraction are used to investigate the detailed structure of copper nanowires and nanoparticles, and a five-twinned structure is shown to exist in the copper nanowires and nanoparticles. Additionally, experiments have been performed to indirectly confirm that oleylamine preferentially adsorbs on the {100} facets of growing crystals. On the basis of the above results, the self-seeded growth of copper nanowires is confirmed. In the initial stage of reactions, copper nanoparticles with two distinctive sizes are formed. As the reaction proceeds, larger five-twinned copper nanoparticles serve as seeds for anisotropic crystal growth. Further, copper atoms generated from an Ostwald ripening process or reduction reactions of a copper­(I) chloride–oleylamine complex continue to deposit and crystallize on the twin boundaries. Once the {110} planes are generated, oleylamine preferentially adsorbs on the newly formed {100} facets and then guides the formation of nanowires. The electrical resistivity of a single copper nanowire is measured to be 41.25 nΩ-m, which is of the same order of magnitude as the value of bulk copper (16.78 nΩ-m). Finally, an effective surface-enhanced Raman spectroscopy active substrate made of copper nanowire is used to detect the 4-mercaptobenzoic acid molecules

Solution Synthesis of Iodine-Doped Red Phosphorus Nanoparticles for Lithium-Ion Battery Anodes

Red phosphorus (RP) is a promising anode material for lithium-ion batteries due to its earth abundance and a high theoretical capacity of 2596 mA h g^–1. Although RP-based anodes for lithium-ion batteries have been reported, they were all in the form of carbon–P composites, including P–graphene, P–graphite, P–carbon nanotubes (CNTs), and P–carbon black, to improve P’s extremely low conductivity and large volume change during cycling process. Here, we report the large-scale synthesis of red phosphorus nanoparticles (RPNPs) with sizes ranging from 100 to 200 nm by reacting PI₃ with ethylene glycol in the presence of cetyltrimethylammonium bromide (CTAB) in ambient environment. Unlike the insulator behavior of commercial RP (conductivity of <10 ^–12 S m^–1), the conductivity of RPNPs is between 2.62 × 10^–3 and 1.81 × 10^–2 S m^–1, which is close to that of semiconductor germanium (1.02 × 10^–2 S m^–1), and 2 orders of magnitude higher than silicon (5.35 × 10^–4 S m^–1). Around 3–5 wt % of iodine-doping was found in RPNPs, which was speculated as the key to significantly improve the conductivity of RPNPs. The significantly improved conductivity of RPNPs and their uniform colloidal nanostructures enable them to be used solely as active materials for LIBs anodes. The RPNPs electrodes exhibit a high specific capacity of 1700 mA h g^–1 (0.2 C after 100 cycles, 1 C = 2000 mA g^–1), long cycling life (∼900 mA h g^–1 after 500 cycles at 1 C), and outstanding rate capability (175 mA h g^–1 at the charge current density of 120 A g^–1, 60 C). Moreover, as a proof-of-concept example, pouch-type full cells using RPNPs anodes and Li­(Ni_0.5Co_0.3Mn_0.2)­O₂ (NCM-532) cathodes were assembled to show their practical uses

Designed Synthesis of Solid and Hollow Cu_2–<i>x</i>Te Nanocrystals with Tunable Near-Infrared Localized Surface Plasmon Resonance

Solid and hollow structures of Cu_2–<i>x</i>Te nanocrystals are synthesized by the injection of a Te–TOP solution at different reaction times. Both types of Cu_2–<i>x</i>Te nanocrystals exhibit an intense absorption peak (localized surface plasmon resonance (LSPR)) in the near-infrared region, arising from excess holes in the valence band, and high molar extinction coefficients of 2.6 × 10⁷ M^–1 cm^–1 at 1150 nm and 8.1 × 10⁷ M^–1 cm^–1 at 1200 nm are demonstrated for the solid-type and hollow-type Cu_2–<i>x</i>Te nanocrystals, respectively. The experimentally observed extinction spectra and calculated extinction spectra based on the electrostatic approximation are studied. The LSPR responses in the near-infrared (NIR) region for both solid and hollow Cu_2–<i>x</i>Te nanocrystals are affected by the refractive index of the medium, whereas the NIR resonance shift is more obvious in the hollow-type Cu_2–<i>x</i>Te nanocrystals. Furthermore, the localized surface plasmon band of the Cu_2–<i>x</i>Te nanostructures can be tuned by post processing via oxidation and reduction methods (controlling their degree of copper deficiency)

Excellent Metal Phosphide Electrode for Potassium Ion Hybrid Capacitors: The Case of Carbon Nanotube-Wrapped AgP₂

Potassium-ion hybrid capacitors (PIHCs) have received extensive attention due to combining the advantages of high energy density of batteries and high power density of capacitors and are economically advantageous alternatives to lithium-ion hybrid capacitors. Metal phosphides are potential anode materials for K+-storage with high theoretical capacity, relatively low working potential, thermal stability, and metal characteristics. Nevertheless, high-performance metal phosphide materials for PIHC applications have proven to be challenging due in part to the dissatisfied electronic conductivity, irreversible deterioration of the structure, and high electron transfer resistance. In this work, we synthesize carbon nanotube (CNT)-wrapped AgP2 via a wet-ball milling (WBM) approach to prepare the electrode slurry. Simultaneously with electrode cycling, the in situ formed Ag nanocrystals increased the electrical conductivity and formed Ag-P composites that easily adsorbed more K+, the framework of CNTs effectively reduced the capacity fading caused by material refinement, and a large surface area is provided to facilitate electrolyte penetration. Owing to these advantageous merits of AgP2/CNT electrodes, the assembled PIHC exhibits a high energy/power density of 37.3 Wh kg–1/12207.3 W kg–1, respectively, and remarkable cycling life over 2000 cycles. These promising results reveal that the design interfacial engineering of the CNT-wrapped AgP2 scaffold provides a clue to propel the development of metal phosphide-based hybrid capacitors

Monodisperse Copper Nanocubes: Synthesis, Self-Assembly, and Large-Area Dense-Packed Films

In comparison to the well-characterized bottom-up synthesis of Au and Ag nanomaterials, the synthesis of Cu nanocrystals with well-defined and controllable shapes is still in need of improvement. Among the many shapes, a cube covered by six {100} facets can be regarded as a standard model to study the surface properties of {100} facets. Herein, we have prepared monodisperse Cu nanoparticles having a slightly truncated cubic shape with an average edge length of 75.7 nm and a standard deviation of 3.87% by using CuCl as the precursor, oleylamine as the reaction solvent, and trioctylphosphine and octadecylamine as shape control agents. The as-prepared Cu nanocubes tend to self-assemble on transmission electron microscopy grids or silicon substrates. Electron microscopy and small-angle X-ray scattering reveal that the Cu nanocubes prefer to self-assemble into 2D or 3D rhombohedral structures (RS). Large-area dense-packed films (1.5 cm × 2.5 cm) composed of monodisperse Cu nanocubes were fabricated by immersing a Si substrate in a dispersion of dodecanethiol-capped Cu nanocubes in toluene and evaporating the toluene at a controlled rate while holding the substrate at an angle. The electrical properties of the Cu films with various thickness and annealing temperatures were studied

Phosphorus-Rich Copper Phosphide Nanowires for Field-Effect Transistors and Lithium-Ion Batteries

Phosphorus-rich transition metal phosphide CuP₂ nanowires were synthesized with high quality and high yield (∼60%) via the supercritical fluid–liquid–solid (SFLS) growth at 410 °C and 10.2 MPa. The obtained CuP₂ nanowires have a high aspect ratio and exhibit a single crystal structure of monoclinic CuP₂ without any impurity phase. CuP₂ nanowires have progressive improvement for semiconductors and energy storages compared with bulk CuP₂. Being utilized for back-gate field effect transistor (FET) measurement, CuP₂ nanowires possess a p-type behavior intrinsically with an on/off ratio larger than 10⁴ and its single nanowire electrical transport property exhibits a hole mobility of 147 cm² V^–1 s^–1, representing the example of a CuP₂ transistor. In addition, CuP₂ nanowires can serve as an appealing anode material for a lithium-ion battery electrode. The discharge capacity remained at 945 mA h g^–1 after 100 cycles, showing a good capacity retention of 88% based on the first discharge capacity. Even at a high rate of 6 C, the electrode still exhibited an outstanding result with a capacity of ∼600 mA h g^–1. <i>Ex-situ</i> transmission electron microscopy and CV tests demonstrate that the stability of capacity retention and remarkable rate capability of the CuP₂ nanowires electrode are attributed to the role of the metal phosphide conversion-type lithium storage mechanism. Finally, CuP₂ nanowire anodes and LiFePO₄ cathodes were assembled into pouch-type lithium batteries offering a capacity over 60 mA h. The full cell shows high capacity and stable capacity retention and can be used as an energy supply to operate electronic devices such as mobile phones and mini 4WD cars

Phosphorus-Rich Copper Phosphide Nanowires for Field-Effect Transistors and Lithium-Ion Batteries

Phosphorus-rich transition metal phosphide CuP₂ nanowires were synthesized with high quality and high yield (∼60%) via the supercritical fluid–liquid–solid (SFLS) growth at 410 °C and 10.2 MPa. The obtained CuP₂ nanowires have a high aspect ratio and exhibit a single crystal structure of monoclinic CuP₂ without any impurity phase. CuP₂ nanowires have progressive improvement for semiconductors and energy storages compared with bulk CuP₂. Being utilized for back-gate field effect transistor (FET) measurement, CuP₂ nanowires possess a p-type behavior intrinsically with an on/off ratio larger than 10⁴ and its single nanowire electrical transport property exhibits a hole mobility of 147 cm² V^–1 s^–1, representing the example of a CuP₂ transistor. In addition, CuP₂ nanowires can serve as an appealing anode material for a lithium-ion battery electrode. The discharge capacity remained at 945 mA h g^–1 after 100 cycles, showing a good capacity retention of 88% based on the first discharge capacity. Even at a high rate of 6 C, the electrode still exhibited an outstanding result with a capacity of ∼600 mA h g^–1. <i>Ex-situ</i> transmission electron microscopy and CV tests demonstrate that the stability of capacity retention and remarkable rate capability of the CuP₂ nanowires electrode are attributed to the role of the metal phosphide conversion-type lithium storage mechanism. Finally, CuP₂ nanowire anodes and LiFePO₄ cathodes were assembled into pouch-type lithium batteries offering a capacity over 60 mA h. The full cell shows high capacity and stable capacity retention and can be used as an energy supply to operate electronic devices such as mobile phones and mini 4WD cars

Gram-Scale Synthesis of Catalytic Co₉S₈ Nanocrystal Ink as a Cathode Material for Spray-Deposited, Large-Area Dye-Sensitized Solar Cells

We report the development of Co₉S₈ nanocrystals as a cost-effective cathode material that can be readily combined with spraying techniques to fabricate large-area dye-sensitized solar cell (DSSC) devices and can be further connected with series or parallel cell architectures to obtain a relatively high output voltage or current. A gram-scale synthesis of Co₉S₈ nanocrystal is carried out <i>via</i> a noninjection reaction by mixing anhydrous CoCl₂ with trioctylphosphine (TOP), dodecanethiol and oleylamine (OLA) at 250 °C. The Co₉S₈ nanocrystals possess excellent catalytic ability with respect to I^–/I₃^– redox reactions. The Co₉S₈ nanocrystals are prepared as nanoinks to fabricate uniform, crack-free Co₉S₈ thin films on different substrates by using a spray deposition technique. These Co₉S₈ films are used as counter electrodes assembled with dye-adsorbed TiO₂ photoanodes to fabricate DSSC devices having a working area of 2 cm² and an average power conversion efficiency (PCE) of 7.02 ± 0.18% under AM 1.5 solar illumination, which is comparable with the PCE of 7.2 ± 0.12% obtained using a Pt cathode. Furthermore, six 2 cm²-sized DSSC devices connected in series output an open-circuit voltage of 4.2 V that can power a wide range of electronic devices such as LED arrays and can charge commercial lithium ion batteries