Synthesis and electrochemical characteristics of Al2O3-coated LiNi1/3Co1/3Mn1/3O2 cathode materials for lithium ion batteries

LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials have been coated with Al₂O₃ nano-particles using sol-gel processing to improve its electrochemical properties. The X-ray diffraction (XRD) pattern of the as-prepared Al₂O₃ nano-particles was indexed to the cubic structure of the γ-Al₂O₃ phase and had an average size of ∼4 nm. The XRD showed that the structure of LiNi_1/3Co_1/3Mn_1/3O₂ was not affected by the Al₂O₃ coating. However, the Al₂O₃ coatings on LiNi_1/3Co_1/3Mn_1/3O₂ improved the cyclic life performance and rate capability without decreasing its initial discharge capacity. These electrochemical properties were also compared with those of LiAlO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode material. The electrochemical impedance spectroscopy (EIS) was studied to understand the enhanced electrochemical properties of the Al₂O₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ compared to uncoated LiNi_1/3Co_1/3Mn_1/3O₂.     

The influence of potential on the anodic dissolution of SIMFUEL (UO2)

The influence of potential on the anodic dissolution of SIMFUEL (doped uranium dioxide) has been characterized over the range 0-500 mV (versus SCE). Cathodic stripping voltammetry was used to determine the changes in surface reactivity of UO₂ in neutral solutions after different anodic oxidation timescales. Scanning electron microscopy (SEM) was used to view the damage to the SIMFUEL electrode surface which was minimal at E < 200 mV but present as local pits and eroded grains after oxidation at higher potentials. Long-term anodic oxidation at potentials below 200 mV suggests that local acidification can develop within surface asperities in the fuel and pores in corrosion product deposits accumulated on the electrode surface.     

Fabrication of high surface area graphitic nanoflakes on carbon nanotubes templates

Graphitic nanoflakes were fabricated on the carbon nanotubes templates for increasing the surface area utilizing bias assisted microwave plasma enhanced chemical vapor deposition (MWPECVD). The analysis of morphologies and structures were achieved by means of scanning electron microscopy and transmission electron microscopy. The surface area of graphitic nanoflakes, carbon nanotubes (CNTs) and graphitic nanoflakes/CNTs were 57.44 m²/g, 90.31 m²/g and 130.96 m²/g from BET measurement, respectively. The cyclic voltammetry was used to calculate the active area of platinum catalysts in 1 M sulfuric acid from hydrogen adsorption peak. An enhancement of activity could be observed from the calculation of CV results. This may be attributed to the small particle size and high dispersion of platinum particles coated on graphitic nanoflakes/CNTs. These high surface area materials could be used as catalysts supports or electrode for fuel cell applications.     

Preparation of NaBiO3 and the electrochemical characteristic of manganese dioxide doped with NaBiO3

NaBiO₃ crystal of high purity has been synthesized through chemical oxidization. The morphology and thermal stability of NaBiO₃ were examined with scanning electron microscope (SEM) and thermogravimetry-differential scanning calorimetry (TG-DSC). The electrochemical properties of MnO₂ electrodes with and without doping NaBiO₃ were studied through galvanostatic charge/discharge and cyclic voltammetry. The results indicate that the MnO₂ electrode doped with NaBiO₃ possesses remarkably higher discharge voltage and capacity and better reversibility than the pure MnO₂ electrode and Bi₂O₃ doping MnO₂ electrode.     

The mechanism and kinetics of the electrochemical cleavage of azo bond of 2-hydroxy-5-sulfophenyl-azo-benzoic acids

The electrochemical reduction of 2-hydroxy-5-[(4-sulfophenyl)azo]benzoic acid, 2-hydroxy-5-[(3-sulfophenyl)azo]benzoic acid, 2-hydroxy-5-[(2-sulfophenyl)azo]benzoic acid and 2-hydroxy-5-azo-benzoic acid has been carried out in aqueous solutions at glassy carbon electrode using cyclic voltammetry and chronoamperometry. The position of sulfo substituent relative to azo bridge as well as pH of the solution have significant impact on the electrochemical behavior of these compounds. It has been proposed that these compounds are reduced predominantly as hydrazone tautomers resulting in corresponding hydrazo compounds. The overall electrochemical reduction follows DISP2 mechanism, ultimately leading to the 5-amino salicylic acid and sulfanilic acid. The rate determining step is the homogenous redox reaction between intermediate hydrazo compound and 5-amino salicylic acid quinoneimine. The mechanism is proposed in which activated complex of 5-amino salicylic acid quinoneimine and intermediate hydrazo compound is formed with the simultaneous loss of one proton.     

Improving the rate performance of LiFePO4 by Fe-site doping

LiFePO₄ doped by bivalent cation in Fe-sites show improved rate performance and cyclic stability. Under 10 C rate at room temperature, the capacities of LiFe_0.9M_0.1PO₄ (M = Ni, Co, Mg) maintain at 81.7, 90.4 and 88.7 mAh/g, respectively, in comparison with 53.7 mAh/g for undoped LiFePO₄ and 54.8 mAh/g for carbon-coated LiFePO₄ (LiFePO₄/C). The capacity retention is 95% after 100 cycles for doped samples while this value is only 70% for LiFePO₄ and LiFePO₄/C. Such a significant improvement in electrochemical performance should be partially related to the enhanced electronic conductivities (from 2.2 × 10⁻⁹ to <2.5 × 10⁻⁷ S cm⁻¹) and probably the mobility of Li⁺ ions in the doped samples.     

Electrochemical performance of nanocrystalline Li3V2(PO4)3/carbon composite material synthesized by a novel sol–gel method

A novel sol–gel method based on V₂O₅·nH₂O hydro-gel was developed to synthesize nanocrystalline Li₃V₂(PO₄)₃/carbon composite material. In this route, V₂O₅·nH₂O hydro-gel, NH₄H₂PO₄, Li₂CO₃ and high-surface-area carbon were used as starting materials to prepare precursor, and the Li₃V₂(PO₄)₃/carbon was obtained by sintering precursor at 750 °C for 4 h in flowing argon. The sol–gel synthesis ensures homogeneity of the precursors and improved reactivity. The sample was characterized by XRD, SEM and TEM. X-ray diffraction results show Li₃V₂(PO₄)₃ sample is monoclinic structure with the space group of P2₁/n. The TEM image indicates that the Li₃V₂(PO₄)₃ particles modified by conductive carbon are about 70 nm in diameter. The Li₃V₂(PO₄)₃/carbon system showed that the discharge capacities in the first and 50th cycle are about 155.3 and 143.6 mAh/g, respectively, in the range of 3.0–4.8 V. The sol–gel method is fit for the preparation of Li₃V₂(PO₄)₃/carbon composite material which may offer some favorable properties for commercial application.     

Novel poly(butylene terephthalate)/poly(vinyl butyral) blends prepared by in situ polymerization of cyclic poly(butylene terephthalate) oligomers

Blends of in situ polymerized PBT from cyclic oligomers (c-PBT) and PVB were prepared with varying compositions and compared with mechanical blends of conventional PBT and PVB. The materials were characterized by a variety of techniques including DSC, DMTA, DETA, FTIR, NMR and GPC. It was found that the in situ prepared blend of c-PBT/PVB has one glass transition temperature and shows evidence of miscibility. In contrast, the conventional blend of PBT/PVB shows incompatibility after blending. The cause of miscibility in the in situ prepared PBT/PVB blends is thought to be the formation of a graft copolymer. These results show that there are unique possibilities for in situ processing by combining polymerization of cyclic polyester oligomers with blending.     

Mechanism of hydrogen adsorption/absorption at thin Pd layers on Au(1 1 1)

Hydrogen adsorption and absorption at thin palladium deposits of 0.8-10 monolayers (ML) on Au(1 1 1) was studied in 0.1 M H₂SO₄ and HClO₄ using cyclic voltammetry, ac voltammetry, and impedance spectroscopy in the absence and in the presence of poison, crystal violet. Hydrogen adsorption on palladium is more reversible in sulfuric acid than in perchloric acid but it occurs at potentials 30 mV more positive in latter. The charge-transfer resistance exhibits a minimum at ∼0.27 V versus RHE and decreases with increasing in Pd deposit thickness in both acids. Adsorption capacitance at 0.8 ML Pd reaches maximum at the same potential. At other deposits the pseudo-capacitance starts to increase at lower overpotentials indicating the beginning of absorption, even at 2 ML Pd. The double layer capacitance is similar for all the deposits in sulfuric acid and it has a sharp maximum at 0.27 V versus RHE. In perchloric acid a broad maximum is observed. Crystal violet inhibits hydrogen adsorption but makes hydrogen absorption more reversible. The results suggest a fast direct hydrogen absorption mechanism that proceeds in parallel with slower hydrogen adsorption and indirect absorption.     

Copolymerization of trimethylene carbonate and 2,2-dimethyltrimethylene carbonate by rare earth calixarene complexes

Rare earth (Nd, Y, La) p-tert-butylcalix[n]arene (n=4, 6, and 8) complexes alone have been developed to catalyze random and block copolymerizations of trimethylene carbonate (TMC) and 2,2-dimethyltrimethylene carbonate (DTC). The random or block structure and thermal behavior of the copolymers have been characterized by SEC, NMR, DSC, XRD and PLM. Random copolymer with M_w of 14,100 and M_w/M_n of 1.36 was prepared by neodymium p-tert-butylcalix[6]arene complex under the conditions: [TMC+DTC]₀/[Nd]=400, 80 °C, 8 h. The reactivity ratios of TMC and DTC are measured to be r_TMC=4.68 and r_DTC=0.163, respectively. Random copolymerization could be well designed by the feeding ratio to prepare copolymers with controlled T_m and T_g. Only 8% TMC units in the polymer chain destroyed the crystallization of PDTC showing no T_m of the copolymer in the DSC analysis.