Protonic batteries based on chemically synthesized MnO2

Synthesis temperature, during air-oxidation of manganese hydroxide, of γ-MnO₂ influences performance of the protonic solid-state battery. X-ray powder diffraction analyses reveal a high degree of De Wolff disorder in samples synthesized at 40 and 60 °C, resulting in poor battery performance. The discharge profile of cell with proton-conducting solid electrolyte and composite zinc as anode, recorded at a constant load condition, indicates proton intercalation. MnO₂ synthesized at 80 °C exhibits improved battery performance.     

Enhanced cyclability of triple-metal-doped LiMn2O4 spinel as the cathode material for rechargeable lithium batteries

To improve the cycle performance of spinel LiMn₂O₄ as the cathode of 4-V-class lithium secondary batteries, spinel phases LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) were successfully prepared using the sol–gel method. The spinel materials were characterized by powder X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Electrochemical studies were carried out using the Li|LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn₂O₄ spinel electrode in spite of a small reduction in the initial capacity. The improvement in cycling performance is attributed to the stabilization in the spinel structure by the doped metal cations.     

A novel anode-supported stable BaCe0.7Ta0.1Y0.2O3− δ membrane prepared by all-solid-state process for solid oxide fuel cells

BaCe_0.7Ta_0.1Y_0.2O_{3− δ} (BCTY) and BaCe_0.8Y_0.2O_{3− δ} (BCY) were synthesized by solid-state reaction method at 1,300 °C for 20 h. After being exposed in 3% CO₂ + 3% H₂O + 94% N₂ at 700 °C for 20 h, the BCTY exhibited adequate chemical stability against carbonations while BCY decomposed into BaCO₃ and CeO₂. The BCTY showed the similar thermal expansion behavior to BCY from room temperature to 1,000 °C in air. The BCTY displayed a conductivity of 0.007 S/cm at 700 °C in humid hydrogen, lower than that of BCY (0.009 S/cm). A fuel cell with 10-μm thick BCTY membrane prepared through an all-solid-state process exhibited 1.004 V for OCV, 330 mW/cm² for maximum output at 700 °C, respectively. Short-term test shows that the fuel cell performance does not degrade after 20 h.     

Size-dependent luminescence in Y2Si2O7 nanoparticles doped with Ce3+ ions

Powders and thin films of nanocrystalline yttrium disilicate (Y₂Si₂O₇) doped with Ce³⁺ have been prepared by a sol–gel method. Structure and morphology of the synthesised samples have been determined and spectroscopic properties compared. The triclinic α-Y₂Si₂O₇ form (space group P 1-) for the powders annealed between 1000°C and 1200°C has been found. A total conversion into a thortveitite-type monoclinic β-Y₂Si₂O₇ polymorph after annealing of powder samples at 1400°C (space group C2/m) has been observed. In the case of films even at 1300°C the basically pure triclinic α-Y₂Si₂O₇ phase was observed with luminescent spectroscopy. The influence of grain size, controlled by thermal treatment, on the structure and luminescence properties of the fabricated materials are presented and discussed.     

Prepare high efficiency Mn-doped Zn2SiO4 green phosphors in air using nano-particles

In this study, nano-scale precursors of ZnO, SiO₂, and MnO₂ powders were used to prepare mixtures with the compositions of 2ZnO+SiO₂+X mol% MnO₂ (X=MnO₂/2ZnO, abbreviated as Zn₂SiO₄-X-MnO₂), where 2≤X≤5. The mixed Zn₂SiO₄-X-MnO₂ mixtures were calcined from 900 to 1300 °C in air in order to synthesize Zn₂SiO₄:Mn²⁺ green phosphors. The X-ray diffraction patterns of Zn₂SiO₄-X-MnO₂ particles indicated that ZnO was present in the 900 °C-calcined Zn₂SiO₄-X-MnO₂ phosphors, but not in particles calcined at temperatures of 1000 °C and higher. However, the unapparent secondary phase of ZnMnO₃ was found in the 1200 and 1300 °C-calcined Zn₂SiO₄-5-MnO₂ compositions. The luminescent characteristics of Zn₂SiO₄-X-Mn²⁺ phosphors were compared with that of a commercial product (Nichia Corp., Japan). The photoluminescence (PL) intensity of 1200 °C-calcined Zn₂SiO₄-4-MnO₂ phosphors was higher and the decay times of all synthesized Zn₂SiO₄-X-MnO₂ phosphors were longer than those of the commercial product.     

Enhancement of ionic conductivity in the composite solid electrolyte system: TlI–Al2O3

This paper reports the heterogeneously doped alumina (Al₂O₃) on the ionic conductivity of thallium iodide. Composite materials of formula (1 − x) TlI–xAl₂O₃, x = 0–0.7 have been prepared and studied by X-ray diffraction, differential scanning calorimetry, and electrical conductivity. X-ray diffraction and differential scanning calorimetry proved the formation of composite in this binary system. The maximum enhancement observed is about three orders of magnitude with respect to the host material. The enhancement of electrical conductivity in comparison with pure thallium iodide can be interpreted with the space charge layer model. Moreover, the increased content of alumina in the system leads to the disappearance of phase transition β–α thallium iodide, which is usually observed in the pure compound. This behavior was explained by stabilizing effect of β-phase at high temperatures and suppression of α-phase at higher contents of alumina.     

Magnetic properties and Griffiths singularity in La0.45Sr0.55 Mn1−xCoxO3

The magnetic properties and the Griffiths singularity were investigated in Mn-site doped manganites of La_0.45Sr_0.55Mn_1−xCo_xO₃ (x=0, 0.05, 0.10 and 0.15) in this work. The parent sample La_0.45Sr_0.55MnO₃ undergoes a paramagnetic-ferromagnetic transition at T_C=290 K and a ferromagnetic-antiferromagnetic transition at T_N=191 K. The doping of Co ions enhances the ferromagnetism and suppresses the antiferromagnetism. The enhanced ferromagnetism results from the fact that the Co doping enhances the Mn³⁺-Mn⁴⁺ double-exchange interaction and induces the Co²⁺-Mn⁴⁺ ferromagnetic superexchange interaction. Detailed investigation on the magnetic behavior above T_C exhibits that the Griffiths singularity takes place in this series of Mn-site doped compounds. The correlated disorder induced by the Co ionic doping, together with the phase competition from the ferromagnetic and the antiferromagnetic interactions among Mn ions, is responsible for the Griffiths singularity.     

Co-precipitation synthesis and performance of multi-doped LiCrxNixMn2-2xO4-zFz cathode materials for lithium ion batteries

Multiple ion-doped lithium manganese oxides LiCr_xNi_xMn_2-2xO_4-zF_z (0 < x ≤ 0.25, z =  0.05, 0.1) with a spinel structure and space group Fd m were prepared by using the co-precipitation procedure carried out in water–alcohol solvent using adipic acid as the chelating agent. The electrochemical measurements indicated that the charge/discharge capacities of the samples prepared at 600 °C are higher than that of the treatment at 800 °C or microwave heating. The capacitance-voltage (CV) curves of LiCr_xNi_xMn_2-2xO_4-zF_z (0 < x ≤ 0.25, z = 0.05, 0.1) showed that when x ≤ 0.1, the samples had two reduction–oxidation peaks at 4.0 to 4.2-V region, whereas when x > 0.1, the samples had only one reduction–oxidation peak at 4.0- to 4.2-V region in CV measurements and could offer more stable voltage plateau in a 4-V region and also had stable electrical conductivity after 20 cycles. Another reduction–oxidation peak appeared in 4.6-4.8-V region (Ni²⁺–Ni⁴⁺ reduction–oxidation peaks); this suggests that the LiCr_xNi_xMn_2-2xO_4-zF_z (0.1 < x≤ 0.25, z = 0.05, 0.1) cathode material could offer 4.6 to 4.8-V charge/discharge plateaus, and its specific capacity increases with increasing Ni²⁺. The impedance measurements of the cell proved that the F⁻ anion doped can not only prevent Mn³⁺ from disproportion but also can prevent the passivation film from forming and can help keep stable the cell’s electrical properties. The LiCr_0.05Ni_0.05Mn_1.9O_3.9F_0.1 sintered at 600 °C shows the best cycle performance and the largest capacity in all prepared samples; its first discharge capacity is 120 mAh/g, and the discharge capacity loses only 1.78% after 20 cycles. After 100 cycles, it still remains in the spinel structure.     

Effect of substrate temperature on electrical and magnetic properties of epitaxial La1−x Pb x MnO3 films

Epitaxial La_1−x Pb _x MnO₃ (LPMO) thin films, grown on (100) SrTiO₃ substrates by laser ablation technique at different temperatures between 600 and 850°C, have been characterized for electrical and magnetic properties. The temperature dependence of resistivity showed that the metal-insulator transition temperature (T _MI) decreases with increasing substrate temperature, which has been attributed to decrease in Pb content in the filsm. The YBa₂Cu₃O _x /La_1−x MnO₃ heterostructures, exhibiting both superconductivity and ferromagnetism, have been fabricated.     

Ni-MH battery based on plasticized alkaline solid polymer electrolytes

Solid-state nickel metal hydride cells were fabricated using plasticized alkaline solid polymer electrolytes (ASPE) prepared from polyvinyl alcohol (PVA), potassium hydroxide (KOH), alumina (α-Al₂O₃), and propylene carbonate (PC). The ASPE film with PVA/KOH/α-Al₂O₃/PC/H₂O weight ratio of 1.00:0.67:0.09:2.64:1.32 and conductivity of (6.6 ± 1.7) × 10⁻⁴ S cm⁻¹ was used in fabrication of the electrochemical cells. To investigate the electrochemical properties of the plasticized ASPE, cells with the configuration Mg₂Ni/plasticized ASPE/Ni(OH)₂ were fabricated. At the eighth cycle with a current drain of 0.1 mA and plateau voltage of ∼1.1 V, the discharge lasted for 14 h before the cell was considered to have failed. The failure mode of the cell was due to the formation of thin Mg(OH)₂ insulating layers.     

Effect of synthesis conditions on the morphology of MnO2 (α-, β-, γ-) synthesized by the hydrothermal-electrochemical method

The morphology and particle size of various MnO₂ compounds synthesized by the hydrothermal-electrochemical method is presented. Individual crystals as well as bundles of fibers were obtained, with diameters ranging from several tens of nanometers to several microns. The effects of the solution pH, synthesis temperature and the applied current density are discussed. Two very different morphologies were found for α-MnO₂ synthesized under different conditions. Various morphologies were also found for γ-MnO₂ and γ/β-MnO₂ compounds. The relationship between the synthesis parameters, γ-MnO₂ structural parameters and the morphology is discussed. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Electrical conductivity and chemical stability of perovskite-type BaCe0.8-xTixY0.2O3-δ

Here we report the synthesis, chemical stability, and electrical conductivity of Ti-doped perovskite-type BaCe_0.8-x Ti _x Y_0.2O_3-δ (x = 0.05, 0.1, 0.2, and 0.3; BCTY). Samples were synthesized by conventional solid state (ceramic) reaction from corresponding metal salts and oxides at elevated temperature of 1,300–1,500 °C in air. The powder X-ray diffraction confirmed the formation of a simple cubic perovskite-type structure with a lattice constant of a = 4.374(1), 4.377(1), and 4.332(1) ? for x = 0.05, 0.1, and 0.2 members of BCTY, respectively. Like BaCe_0.8Y_0.2O_3-δ (BCY), Ti substituted BCTY was found to be chemically not stable in 100% CO₂ and form BaCO₃ at elevated temperature. The bulk electrical conductivity of BCTY decreased with increasing Ti content and the x = 0.05 member exhibited the highest conductivity of 2.3 × 10⁻³ S cm⁻¹ at 650 °C in air, while a slight increase in the conductivity, especially at low temperatures (below 600 °C), was observed in humidified atmospheres.     

Synthesis and characterization of Bi-doped zirconia for solid electrolyte

(100-x)ZrO₂(x)Bi₂O₃ (x = 5, 10, 15) system has been synthesized by solid-state reaction technique. Tetragonal Bi_7.38Zr_0.62O_12.31 phase has formed in all the samples after sintering at 850 °C for 24 h. Apart from this, ZrO₂ and Bi₂O₃ are also identified as minority phases. The volume fraction of Bi_7.38Zr_0.62O_12.31 phase increases with increasing concentration of Bi₂O₃. The AC conductivity plots exhibit phase transition at 570 °C and 460 °C for x = 10 and x = 15 samples, respectively. The maximum conductivity is observed (1.60 mS/cm) in x = 15 sample. These results are correlated and supported with microstructural and thermal analysis.     

Influence of cobalt ions on the electrochemical properties of lamellar manganese oxides

Evaluation of Co-doping on the electrochemical properties of the sol-gel birnessite and the new lithiated manganese oxide Li_0.45MnO_2+δ is reported. For both compounds the synthesis of Co-doped materials via a solution technique is described. We demonstrate the interest of Co-doped structures with the selected content of 0.15 Co per mole of oxide as the optimum composition. In the case of Li_0.45Mn_1−yCo_yO_2+δ. prepared at 300 °C, a mixture of a lamellar phase and a cubic one is identified while the Co-doped birnessite appears as a single phase. A probable substitution of Mn by Co ions explains the better specific capacity of 185 mAh/g found and the excellent stability observed over 40 cycles in the voltage range 4.2−2.0 V. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Thermo-electric method for nearly complete oxidization of highly iron-doped lithium niobate crystals

A new method is presented, allowing the nearly complete oxidization of lithium niobate crystals (LiNbO₃), doped with large amounts of iron oxide (0.05–3 wt. % Fe₂O₃) utilizing annealing at 700 °C in the presence of externally applied electric fields. The treatment results in a concentration ratio of Fe²⁺ and Fe³⁺ ions of less than 2×10^-3. Strong oxidization of iron in LiNbO₃ reduces the photorefractive effect and is therefore of particular interest for nonlinear-optical applications. PACS 42.65.-k; 66.30.Hs; 71.55.-i     

Identification of the 109Xe and 105Te α-decay chain

The α-decay chain ¹⁰⁹Xe → ¹⁰⁵Te → ¹⁰¹Sn was identified at the Holifield Radioactive Ion Beam Facility. Advances in digital electronics have made possible the identification of both alpha emitters in the same experiment despite the disparate half-lives of 13 ±2 ms and 620 ±70 ns for ¹⁰⁹Xe and ¹⁰⁵Te, respectively. Two α-decay transitions were observed from ¹⁰⁹Xe with Q_α values of 4067 ±10 and 4217 ±8 keV. One transition between the ground states of ¹⁰⁵Te and ¹⁰¹Sn was observed with a Q_α value of 4889 ±6 keV. Using the measured half-lives, branching ratios, and Q_α values the reduced α-decay widths, δ², were determined. Comparison of the δ² value for ¹⁰⁵Te with ²¹³Po indicates a “superallowed" character in the α emission of ¹⁰⁵Te.     

Preparation, characterization and electrochemical performance of γ-MnO2 and LiMn2O4 as cathodes for lithium batteries

The spinel LiMn₂O₄ is a very promising cathode material with economical and environmental advantages. LiMn₂O₄ materials have been synthesized by solid state method using γ-MnO₂ as manganese source, and Li₂CO₃ or LiNO₃ as Li sources. γ-MnO₂ is a commercial battery grade electrolytic manganese dioxide (TOSOH-Hellas GH-S) and LiMn₂O₄ samples were synthesized at a calcinations temperature up to 800 °C. γ-MnO₂ and LiMn₂O₄ samples were characterized by X-ray diffraction, thermal and electrochemical measurements. X-ray powder diffraction of as prepared LiMn₂O₄ showed a well-defined highly pure spinel single phase. The electrochemical performance of LiMn₂O₄ and its starting material γ-MnO₂ was evaluated through cyclic voltammetry, galvanostatic (constant current charge-discharge cycling) The electrochemical properties in terms of cycle performance were also discussed. γ-MnO₂ showed fairly high initial capacity of about 200 mAhg⁻¹ but poor cycle performance. LiMn₂O₄ samples showed fairly low initial capacity but good cycle performance.     

γ-MnO2/polyaniline composites: Preparation, characterization, and applications in microwave absorption

MnO₂/doped polyaniline (PANI) is prepared by an in situ polymerization method using γ-MnO₂ as the addition agent and hydrochloric acid as the doping agent. Products are characterized by FT-IR, UV-vis, XRD, and TEM. Conductivity, electromagnetic properties, and microwave absorption properties are first discussed on the basis of structural characterization. The as-prepared products of MnO₂/PANI are partially crystalline in nature and spherical in pattern with grain sizes of 50-70 nm. MnO₂ particles are successfully decorated with doped PANI. MnO₂/PANI displays moderate electric conduction, excellent dielectric losses, and microwave absorption capabilities. Compared to pure MnO₂, the dielectric and reflection loss properties of MnO₂/PANI composites exhibit significant improvements, with an effective absorption band at 5 GHz under −10 dB and maximum reflection loss of −21 dB at 13.56 GHz. Pure MnO₂ shows an effective absorption band of 3 GHz under −10 dB and a maximum reflection loss of −14.20 dB at 11.5 GHz. Thus, MnO₂/PANI composites are found to be a promising microwave absorption material.     

Ultrafine layered LiCoO2 obtained from citrate precursors

A new method for the preparation of ultrafine LiCoO₂ with a layered crystal structure was developed, which consists in thermal pyrolysis of homogeneous lithium-cobalt-citrate precursors. Atomic scale mixing of Li and Co is achieved by citric acid acting as a chelating agent. Electron spectroscopy of concentrated Li-Co-citrate solutions with Li:Co:Cit=1:1:1 and Li:Co:Cit=1:1:2 reveals that the predominant species at pH=7 are [Co(C₆H₅O₇)]⁻ and [Co(C₆H₅O₇)₂]⁴⁻ complexes. Freeze-drying of the two types of solutions leads to the formation of LiCo(C₆H₅O₇).nH₂O and (NH₄)₃LiCo(C₆H₅O₇)₂.nH₂O precursors, where Co²⁺ ions are complexed by one and two triionized citrate ions, respectively, and Li⁺ ions serve as counter ions. Between 400–600 °C, the thermal decomposition of these metal-citrate precursors yields LiCoO₂ with layered and pseudo-spinel structure, the proportion between them being depending on: (i) the Co/citrate ratio; (ii) the concentration of the freeze-dried solution; (iii) the heating rate. At 400 °C, the most defectless layered LiCoO₂, consisting of hexagonal individual particles with dimensions of 120–170 nm, is a product of the bis-citrate decomposition with a slow heating rate. For this sample, heating up to 600 °C does not affect the crystal size dimensions. For ultrafine layered LiCoO₂ and LiCoO₂ obtained by solid state reaction at high-temperatures (850 °C), the deintercalation and intercalation reactions proceed in the 3.95 – 3.99 and 3.86 – 3.88 voltage intervals, respectively. For defect trigonal LiCoO₂, additional oxidation and reduction peaks at 3.7 – 3.8 and 3.4 – 3.5 V were observed. We did not succeed in preparing monophase LiCoO₂ with pseudo-spinel structure. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Sept. 14–21, 1996     

Synthesis of MnO2 nanoparticles from sonochemical reduction of MnO4− in water under different pH conditions

MnO₂ was synthesized by sonochemical reduction of MnO₄⁻ in water under Ar atmosphere at 20 °C, where the effects of solution pH on the reduction of MnO₄⁻ were investigated. The obtained XRD results showed that poor crystallinity δ-MnO₂ was formed at pH 2.2, 6.0 and 9.3. When solution pH was increased from 2.2 to 9.3, the morphologies of δ-MnO₂ changed from aggregated sheet-like or needle-like structures to spherical nanoparticles and finally to cubic or polyhedron nanoparticles. After further irradiation, MnO₂ was readily reduced to Mn²⁺. It was confirmed that H₂O₂ and H atoms formed in the sonolysis of water acted as reductants for both reduction for MnO₄⁻ to MnO₂ and MnO₂ to Mn²⁺. The optimum irradiation time for the effective synthesis of MnO₂ was 13 min at pH 2.2, 9 min at pH 6.0, 8 min at pH 9.3, respectively.