Supercritical Fluid Synthesis of LiCoPO4 Nanoparticles and Their Application to Lithium Ion Battery

In this work, LiCoPO4 nanoparticles were synthesized by supercritical fluid method using cobalt nitrate hexahydrate (Co(NO3)2 6H2O) and cobalt acetate tetrahydrate (C4H6CoO4 4H2O) as starting materials. The effect of starting materials on particle morphology, size, and the crystalline phase were investigated. The as-synthesized samples were systematically characterized by XRD, TEM, STEM, EDS, BET, and TG and charge-discharge measurements. In addition, Rietveld refinement analysis was performed. The electrochemical measurements of LiCoPO4 nanoparticles have shown differences in capacities depending on the starting materials used in the synthesis and the results have been discussed in this paper

One-Step Production of Anisotropically Etched Graphene Using Supercritical Water

We developed a one-step method for production of anisotropically etched graphene using supercritical fluid (SCF). Anisotropic etching of a graphite substrate and dispersed graphite powder with Ag nanoparticles was conducted in supercritical water (SCW). Because of the exfoliation effect of SCF, graphene was isolated from the graphite simultaneously with the anisotropic etching. High-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy revealed the production of multilayer graphene exfoliated from the anisotropically etched graphite surface

Ultrathin SnS₂ Nanoparticles on Graphene Nanosheets: Synthesis, Characterization, and Li-Ion Storage Applications

Ultrathin SnS₂ nanoparticle decorated graphene nanosheet (GNS) electrode materials with delaminated structure were prepared using stepwise chemical modification of graphene oxide (GO) nanosheets at very dilute conditions, followed by a hydrothermal treatment. The chemical modification of the graphene nanosheet surface with Sn ions enables the precipitation of ultrathin nanoparticles. The TEM analysis reveals the SnS₂ nanoparticles are homogeneously distributed on the loosely packed graphene surface in such a way that the GNS restacking was hindered. X-ray photoelectron spectroscopic analysis reveals the bonding characteristics of the SnS₂ on the GNS. The obtained nanocomposite exhibits a reversible capacity of 1002 mAh/g, which is significantly higher than its calculated theoretical capacity (584 mAh/g). Furthermore, its cycling performance is enhanced and after 50 cycles, and the charge capacity still remained 577 mAh/g, which is very close to its theoretical capacity. Due to the synergic effect, the Li-ion storage capacity observed for nanocomposites is much higher than its theoretical capacity. The ultrathin size (2 nm) and dimensional confinement of tin sulfide nanoparticles by the surrounding GNS limit the volume expansion upon lithium insertion, and the nanoporous structures serve as buffered spaces during charge/discharge and result in superior cyclic performances by facilitating the electrolyte to contact the entire nanocomposite materials and reduce lithium diffusion length in the nanocomposite

Analysis of Degradation Mechanisms in Quinone-Based Electrodes for Aqueous Electrolyte System via <i>In Situ</i> XRD Measurements

Organic materials are promising electroactive components of energy storage devices such as lithium-ion batteries and electrochemical capacitors. Among them, low-molecular-weight organics have attracted attention as higher-energy-density, environmentally friendly, and inexpensive electrode materials, but their poor cycle performance is the main drawback. Using <i>in situ</i> XRD measurement in aqueous electrolyte system, here we investigated the capacity fading mechanism of an organic electrode based on low-molecular-weight quinones. Although the capacity fading of such organic electrodes is generally attributed to their elution into the electrolyte, our structural analysis reveals that the capacity fading is also associated with the expansion of an electrochemically inactive region, which persists in the electrode but does not take part in the reversible redox reactions. Moreover, the detailed analysis of the XRD patterns suggests that the capacity fading of the electrode is accompanied by the crystal growth of organic component, which occurs through dissolution–reprecipitation processes taking place during charge–discharge cycling. The association between capacity fading and the increased size of these crystalline domains suggests that the elongated electrical/ionic conduction paths in the growing organic crystals (leading to the expansion of the electrochemically inactive region of the electrode) can be a possible capacity fading mechanism in organic electrodes

Fabrication of Liquid Scintillators Loaded with 6-Phenylhexanoic Acid-Modified ZrO2 Nanoparticles for Observation of Neutrinoless Double Beta Decay

The observation of neutrinoless double beta decay is an important issue in nuclear and particle physics. The development of organic liquid scintillators with high transparency and a high concentration of the target isotope would be very useful for neutrinoless double beta decay experiments. Therefore, we propose a liquid scintillator loaded with metal oxide nanoparticles containing the target isotope. In this work, 6-phenylhexanoic acid-modified ZrO2 nanoparticles, which contain 96Zr as the target isotope, were synthesized under sub/supercritical hydrothermal conditions. The effects of the synthesis temperature on the formation and surface modification of the nanoparticles were investigated. Performing the synthesis at 250 and 300 °C resulted in the formation of nanoparticles with smaller particle sizes and higher surface modification densities than those prepared at 350 and 400 °C. The highest modification density (3.1 ± 0.2 molecules/nm2) and Zr concentration of (0.33 ± 0.04 wt.%) were obtained at 300 °C. The surface-modified ZrO2 nanoparticles were dispersed in a toluene-based liquid scintillator. The liquid scintillator was transparent to the scintillation wavelength, and a clear scintillation peak was confirmed by X-ray-induced radioluminescence spectroscopy. In conclusion, 6-phenylhexanoic acid-modified ZrO2 nanoparticles synthesized at 300 °C are suitable for loading in liquid scintillators

Relocation of Cobalt Ions in Electrochemically Delithiated LiCoPO₄ Cathode Materials

Relocation of Cobalt Ions in Electrochemically Delithiated LiCoPO₄ Cathode Material