Corrosion properties of plasma-polymerized methylcyclohexane films using electrochemical methods

Three types of methylcyclohexane (MCH) coating were deposited as interlayer dielectrics on copper using plasma-enhanced chemical vapor deposition (PECVD) at three different RF plasma power levels. The coating performance was then evaluated by an electrochemical im pedance spectroscopy (EIS) and a potentiodynamic polarization test in 3.5 wt.% NaCl solution. An atomic force microscopy (AFM) and Fourier transform infrared reflection (FT-IR) spectroscopy were also conducted to analyze the coatings. The MCH coatings showed a lower corrosion rate than the copper substrate in the potentiodynamic tests. The EIS results showed that the corrosion resistance of the coatings increased with an increasing plasma power. Thus, the MCH films with an increasing plasma power improved the corrosion resistance due to the formation of a low-porosity coating, the enhanced formation of C−H, C−C, and C≡C stretching configurations, and the improved smooth surfaces.

Lithium ion mobility in poly(vinyl alcohol) based polymer electrolytes as determined by 7Li NMR spectroscopy

Solvent-free polymer electrolytes based on poly(vinyl alcohol) (PVA) and LiCF₃SO₃ have shown relatively high conductivities (10⁻⁸-10⁻⁴ S cm⁻¹), with Arrhenius temperature dependence below the differential scanning calorimeter (DSC) glass transition temperature (343 K). This behaviour is in stark contrast to traditional polymer electrolytes in which the conductivity reflects VTF behaviour. ⁷Li nuclear magnetic resonance (NMR) spectroscopy has been employed to develop a better understanding of the conduction mechanism. Variable temperature NMR has indicated that, unlike traditional polymer electrolytes where the linewidth reaches a rigid lattice limit near T_g, the lithium linewidths show an exponential decrease with increasing temperature between 260 and 360 K. The rigid lattice limit appears to be below 260 K. Consequently, the mechanism for ion conduction appears to be decoupled from the main segmental motions of the PVA. Possible mechanisms include ion hopping, proton conduction or ionic motion assisted by secondary polymer relaxations.

NMR studies of modified nasicon-like, lithium conducting solid electrolytes*1

²⁷Al, ³¹P and ⁷Li NMR measurements have been performed on lithium conducting ceramics based on the LiTi₂(PO₄)₃ structure with Al, V and Nb metal ions substituted for either Ti or P within the framework NASICON structure. The ²⁷Al magic angle spinning NMR measurements have revealed that, although Al is intended to substitute for octahedral Ti sites, additional substitution into tetrahedral environments (presumably phosphorous sites) occurs with increasing amount of Al addition. This tetrahedral substitution appears to occur more readily in the presence of vanadium, in Li_1+xAl_xTi_2−x(PO₄)_2.9(VO₄)_0.1, whereas similar niobium additions (in place of vanadium) appear to stifle tetrahedral substitution. ⁷Li static NMR spectra reveal quadrupolar structure with C_q approximately 42 kHz, largely independent of substitution. Measurement of the ⁷Li central transition linewidth at room temperature reveals a relatively mobile lithium species (300–900 Hz) with linewidth tending to decrease with Al substitution and increase with increasing V or Nb. This new structural information is discussed in the context of ionic conduction in these ceramics.

Potential of 129Xe NMR spectroscopy of adsorbed xenon for testing the chemical state of the surface of mesoporous carbon materials illustrated by the example of aggregates of diamond and onion-like carbon nanoparticles

The chemical shift in the 129Xe NMR spectrum of adsorbed xenon is very sensitive to the presence of oxygen-containing functional groups on the surface of mesoporous carbon materials. Well-characterized, structurally similar nanodiamond and onion-like carbon samples are considered here as model objects.

Synthesis of single-crystalline LiFePO4 with rhombus-like morphology

In this investigation, carbon-coated LiFePO4 cathode materials were synthesized with a facile hydrothermal method. The structure and electrochemical properties of the materials were investigated by X-ray diffraction (XRD), Roman, transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS), and electrochemical impedance spectroscopy (EIS). By adjusting the mixing concentration of starting materials, a single-crystalline LiFePO4 with an anisotropic rhombus morphology (Space Group: Pmnb No. 62) were successfully synthesized. In addition, the carbon coated on the surface of LiFePO4 material prepared has a lower ID/IG (0.80), which indicates an optimized carbon structure with an increased amount of sp2-type carbon. Electrochemical performance test shows that the carbon-coated LiFePO4 cathode materials have an initial discharge capacity of 146 mAh g−1 at 0.2C.

Synthesis of a porous sheet-like V₂O₅-CNT nanocomposite using an ice-templating 'bricks-and-mortar' assembly approach as a high-capacity, long cyclelife cathode material for lithium-ion batteries

Tailoring the nanostructures of electrode materials is an effective way to enhance their electrochemical performance for energy storage. Herein, an ice-templating "bricks-and-mortar" assembly approach is reported to make ribbon-like V2O5 nanoparticles and CNTs integrated into a two-dimensional (2D) porous sheet-like V2O5-CNT nanocomposite. The obtained sheet-like V2O5-CNT nanocomposite possesses unique structural characteristics, including a hierarchical porous structure, 2D morphology, large specific surface area and internal conducting networks, which lead to superior electrochemical performances in terms of long-term cyclability and significantly enhanced rate capability when used as a cathode material for LIBs. The sheet-like V2O5-CNT nanocomposite can charge/discharge at high rates of 5C, 10C and 20C, with discharge capacities of approximately 240 mA h g-1, 180 mA h g-1, and 160 mA h g-1, respectively. It also retains 71% of the initial discharge capacity after 300 cycles at a high rate of 5C, with only 0.097% capacity loss per cycle. The rate capability and cycling performance of the sheet-like V2O5-CNT nanocomposite are significantly better than those of commercial V2O5 and most of the reported V2O5 nanocomposite.