Electrochemical corrosion behavior of carbon-based thin films in chloride ions containing electrolytes

Commercially available carbon-based thin films consisting of single layers of amorphous diamond-like carbon or multilayers of crystalline TiAlN or CrN with diamond-like carbon top coatings were evaluated in relation to their electrochemical corrosion behavior in chloride ions containing electrolytes. The hardened working steel (an alloy of 0.9% C, 4.1% Cr, 4.9% Mo, 1.8% V, 6.4% W) was used as a substrate material.The potentiodynamic corrosion behavior of coated samples was tested in 3.5 wt.% NaCl solution and Hank's balanced body solution, HBBS (0.89 wt.% NaCl, further chlorides, sulfates, carbonates and phosphates). The multi-layers TiAlN + a-C:H:W and CrN + a-C:H:W exhibited only a minor improvement in corrosion resistance. Single layers of amorphous diamond-like carbon coating without hydrogen (a-C) spall off during the corrosion tests in chloride containing media. A minor improvement of the corrosion resistance is possible. The a-C:H and the a-C:H:Si, which contain hydrogen, showed the best corrosion resistance with a 100 times lower corrosion current density.     

The effects of bismuth intercalation on structure and thermal conductivity of TiS2

The structure and thermal conductivity of the bismuth (Bi) intercalated compounds Bi_xTiS₂ (0 ≤ x ≤ 0.25) were investigated by using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermal conductivity measurements. The results indicated that besides lattice expansion and distortion, bismuth intercalation caused structural transition of Bi_xTiS₂ from stage-1 to stage-2 as x ≥ ∼0.1, which led to the appearance of D₄ and A₂ modes in Raman spectra. The enhancement of relative intensities of D₄ and A₂ peaks with increasing Bi content reflected increase of the concentration of stage-2 phase in the samples. The red shift of mode E_g as well as D₄ and A₂ would reflect weakening of intra-layer bonds, while the blue shift of A_1g after intercalation suggested the enhancement of chemical binding in the van der Waals gaps due to charge transfer. In addition, the weakening of A_1g intensity can be explained by the lattice distortion produced by bismuth intercalation. Remarkable reduction in (lattice) thermal conductivity of titanium disulfide (TiS₂) through Bi intercalation was realized, which could be attributed to the phonon scattering by “rattling” of the intercalated bismuth atoms in the van der Waals gaps of TiS₂.     

Direct intercalation of alkali metal ions in FeOCl

The direct intercalation of Li⁺, Na⁺, K⁺ and their crown ether complexes has been observed when FeOCl reacts with the respective methoxide salts of these ions. The lattice parameters of the compounds formed are reported. The intercalation process is interpreted in terms of oxidation of the methoxide ion accompanied by a partial reduction of the Fe(III) in the FeOCl, with the intercalation of the alkali metal ion in the lattice for charge compensaion.     

Periclase solid solutions containing Li+1 and R+3 ions

Recent work on phase equilibria diagrams has shown that periclase can take R⁺³ (Cr⁺³, Al⁺³, and Fe⁺³) in solid solution at elevated temperatures. In order to retain electrical neutrality, 2R⁺³ and a vacancy replaces 3Mg⁺² in the periclase lattices. When Li⁺¹ is added to MgO/R₂O₃ compositions, one Li⁺¹ and one R⁺³ replaces 2 Mg⁺² to form a solid solution which is stable at room temperature. These periclase solid solutions are more stable under conditions of temperature fluctuations and hydration than periclase/R₂O₃ solid solutions without lithia.     

The effect of Li intercalation on different sized TiO2 nanoparticles and the performance of dye-sensitized solar cells

The effect of Li⁺ insertion into different sized TiO₂ nanoparticles and their influences on the photoconversion efficiency of dye-sensitized solar cells (DSSC) were investigated. TiO₂ nanoparticles with different particle sizes (22 nm, 14 nm and 6 nm) doped with Li⁺ were employed to form thin film electrodes and their properties were characterized by X-ray diffraction (XRD) and electrochemical impedance spectroscopy analysis. XRD evidenced the presence of anatase as the main phase. From the XRD analysis, it was observed that the Li⁺ ions could be inserted into both the surface and bulk of the TiO₂ nanoparticles. In the larger particle size, the Li⁺ ions are inserted into the bulk anatase where as Li⁺ ions bounded on the TiO₂ surface for the smaller crystallite size. The photovoltaic properties were measured by a current-voltage meter under AM1.5 simulated light radiation. It exhibited that the overall photoconversion efficiency of DSSC was decreased in the larger particles while it was enhanced in the smaller nanoparticles when Li⁺ was doped into the TiO₂ nanoparticles. A nearly 40% decrease in the efficiency (η) of DSSC was observed upon intercalation of Li⁺ ions into 22 nm sized TiO₂ nanoparticles (P25). The 14 nm sized TiO₂ nanoparticles (P90) showed slightly less efficiency (η) upon Li⁺ doping than that of the undoped sample. However, the smallest sized TiO₂ nanoparticles (6 nm) showed higher efficiency than that of the undoped one. This phenomenon is explained based on electron trapping and charge recombination due to lithium doping.     

Preparation and intercalation chemistry of magnesium-iron(III) layered double hydroxides containing exchangeable interlayer chloride and nitrate ions

Layered double hydroxides (LDHs) with Mg²⁺ and Fe³⁺ cations in the brucite-like layers and having chloride or nitrate ions in the interlayer region have been prepared and characterized by powder X-ray diffraction (PXRD), elemental analysis and thermal analysis. Thermal decomposition of the LDH-nitrate occurs in two steps, with loss of water followed by simultaneous dehydroxylation of the layers and loss of NO_x/O₂ arising from the nitrate anions. Thermal decomposition of the LDH-chloride involves an additional step, with chloride ions becoming grafted to the layers, prior to loss of HCl. The interlayer anions may be readily replaced by sulfate, thiosulfate, tartrate and vinylbenzenesulfonate ions suggesting that these materials may be useful precursors to Mg-Fe(III) LDHs intercalated with a variety of inorganic and organic anions.     

低In电解液电沉积制备CuInSe2吸收层

通过线性电位扫描分析了低In电解液中的阴极电化学反应,结果表明柠檬酸钠可以降低Cu2+的活性,而H2SeO3的加入可导致阴极上Se元素与Cu+和In3+发生复杂的协同反应.低In电解液中恒电位沉积的薄膜与CIS的化学计量比相差较大,分段电位的恒电位沉积得到的薄膜更接近于CuInSe2(CIS)化学计量比.薄膜在N2气氛上退火处理,得到了黄铜矿结构CIS薄膜,禁带宽度为1.06eV.     

Low temperature specific heat of intercalation compounds M x TiS2 (M = 3d transition metals)

Specific heats of intercalation compounds Fe_x TiS₂ (x = 0–1/3) and M_1/4 TiS₂ (M = Mn, Fe, Co and Ni) have been measured in the temperature range 0.35–5 K using an ac calorimetry method. The temperature dependence of the specific heats for these materials is written as the sum of electronic, lattice and anomalous terms. The anomalous specific heats show a Schottky type behavior, which is due to a very small amount of localized 3d atoms with crystal-field splittings, but the remaining majority of the intercalated guest 3d atoms are regarded as having itinerant electron character that contributes to the enhancement of the density of states at the Fermi energy or of electronic specific heat coefficient.     

Modeling mechanical stress and exfoliation damage in carbon fiber electrodes subjected to cyclic intercalation/deintercalation of lithium ions

Gradients in lithium ion concentration distribution in carbon fiber are accompanied by non-uniform fiber swelling leading to development of mechanical stresses. During lithium deintercalation these stresses may lead to initiation and growth of radial cracks in the fiber. The subsequent cycle of intercalation may result in arc-shaped cracks deviating from the tip of the radial cracks. These phenomena decrease the mechanical properties of fibers if used in structural batteries and reduce the charging properties of the battery by decreased diffusivity of lithium ions and by exfoliating layers on the fiber surface. The crack propagation and possible damage evolution scenarios are analyzed using linear elastic fracture mechanics. The crack geometry dependent ion concentration distributions and the elastic stress distributions were found using finite element software ANSYS.     

Effect of magnetic field on the specific heats of intercalation compounds Mx TiS2 (M=3d transition metals)

Specific heats of single crystals of intercalation compounds M_xTiS₂ (M=Mn, Fe, Co, and Ni) have been measured using ac calorimetric method over the temperature range T = 0.38–14 K under magnetic fields up to 4.5 T. Considering the lattice dynamical properties of these intercalates, we have analyzed the observed specific heat data C, which can be expressed by the sum of electronic, lattice, magnetic, and anomalous terms, C = T + T³ + C_mag + C_a, where C_a is of a Schottky type. The temperature and magnetic field dependences of and C_mag are discussed from various viewpoints, such as existing spin fluctuation model, which reveals that the itinerant electron picture is appropriate to understand the electronic and magnetic properties of this material system.     

Conversion of graphite intercalation compounds to carbon materials containing polymetallic nanoparticles

We report the formation of ternary graphite intercalation compounds (GICs) with FeCl₃ and PtCl₄ via reaction between hexachloroplatinic acid and a binary GIC with iron(III) chloride. Mössbauer spectroscopy and X-ray microanalysis results show that ternary GICs form only when the interlayer spaces in the parent binary GIC are incompletely occupied (stage III or lower). The coexistence of different chloride molecules in the ternary GIC leads to the formation of intermetallic nanoparticles when the material is reduced. The yield of the intermetallic phase increases with decreasing graphite particle size.     

Specific heat measurements of intercalation compounds M x TiS2 (M=3d transition metals) using ac calorimetry technique

Specific heats of 3d transition metal intercalates of 1T-CdI₂-type TiS₂, M _x TiS₂ (M=V, Cr, Mn, Fe, Co, and Ni; 0x1), have been measured in the temperature range 1.6–300 K using an ac calorimetry technique. The electronic specific heat coefficient (2–100 mJ/mole K²) and the Debye temperature _D (240–430 K) are found to depend on the guest 3d metals and their concentrations. All the intercalates show anomalous specific heat at low temperatures following an – lnT dependence ( and are constants), as found in dilute alloys.     

碳纳米管用于锂离子电池负极材料的嵌锂机理研究

研究了将纳米碳管用于锂离子电池负极材料的嵌锂机理,包括纳米碳管的充放电容量、充放电前后碳纳米管的IR光谱、循环伏安曲线和充放电过程中的XRD图谱研究。研究结果表明,纳米碳管具有比较高的放电容量,首次放电比容量为649.4mA·h/g,循环20次后充放电效率仍可达94.1%。IR光谱研究表明纳米碳管的充放电过程中在电极界面存在SEI膜;循环伏安法研究表明碳纳米管负极随着循环次数增加,不可逆容量减少,锂离子的嵌入与脱出更加可逆;XRD分析则说明在充放电过程中d002增大,有越层反应发生。     

表面包覆技术对微晶石墨嵌锂行为的影响

鉴于天然微晶石墨资源丰富,嵌锂容量较高的特点,对天然微晶石墨进行了粉体分级和表面包覆处理,以提高微晶石墨用作锂离子电池负极材料的首次循环效率、可逆容量和使用寿命。实验表明,微晶石墨经过颗粒分级和表面包覆碳膜的处理后,其首次循环效率提高至90%,循环稳定性也得到了明显改善。     

Li absorption and intercalation in single layer graphene and few layer graphene by first principles

We present an exhaustive first-principles investigation of Li absorption and intercalation in single layer graphene and few layer graphene, as compared to bulk graphite. For single layer graphene, the cluster expansion method is used to systemically search for the lowest energy ionic configuration as a function of absorbed Li content. It is predicted that there exists no Li arrangement that stabilizes Li absorption on the surface of single layer graphene unless that surface includes defects. From this result follows that defect-poor single layer graphene exhibits significantly inferior capacity compared to bulk graphite. For few layer graphene, we calibrate a semiempirical potential to include the effect of van der Waals interactions, which is essential to account for the contribution of empty (no Li) gallery to the total energy. We identify and analyze the Li intercalation mechanisms in few layer graphene and map out the sequence in stable phases as we move from single layer graphene, through few layer, to bulk graphite.     

Lithium intercalation and deintercalation processes in Li4Ti5O12 and LiFePO4

We have studied the kinetics of electrochemical lithium intercalation and deintercalation processes at different currents in lithium iron phosphate and lithium titanate based composite materials containing fine carbon particles. The results demonstrate that lithium intercalation and deintercalation processes in the electrode materials are characterized by an overvoltage: 4 and 2 mV, respectively, for a cell with a lithium titanate based electrode and 4 and 24 mV for a lithium iron phosphate based cell. Li₄Ti₅O₁₂ solubility in Li₇Ti₅O₁₂ is 1.1% (the limit of the solid solution at Li_4.03Ti₅O₁₂), and Li₇Ti₅O₁₂ solubility in Li₄Ti₅O₁₂ is 2.5% (the limit of the solid solution at Li_6.93Ti₅O₁₂). The conductivity of the phosphate and titanate solid solutions involved in the lithium intercalation and deintercalation processes has been determined.     

Enhanced near-infrared quantum cutting in CaMoO4:Yb phosphors induced by doping with Li ions for improving solar cells efficiency

The near-infrared (NIR) quantum cutting (QC) CaMoO₄:Yb³⁺ phosphors co-doped with Li⁺ ions were synthesized by the sol–gel methods. The dependence of the structure, morphology, photoluminescence (PL) and downconversion (DC) quantum efficiency on the Li⁺ doping concentration have been investigated in details. It was demonstrated that the CaMoO₄:Yb³⁺ phosphors with appropriate concentration of the Li⁺ ions show improved crystallinity and remarkable increase of the NIR emission from the Yb³⁺ ions, if compared with the Li⁺-free samples. The enhancement of the NIR emission and DC quantum efficiency was suggested to be a consequence of the improved crystallinity and stronger absorption of the host due to the [MoO₄] tetrahedra distortion induced by the Li⁺ ions. Cooperative energy transfer (CET) from the host to the Yb³⁺ ions is discussed as a possible mechanism for the NIR emission enhancement. Excellent luminescence properties of the Li⁺ doped CaMoO₄:Yb³⁺ phosphor demonstrate its potential application as a better QC layer to increase the energy conversion efficiency of the Si-based solar cells.