Defect Structure and Up-conversion Luminescence Properties of ZrO<Subscript>2</Subscript>:Yb<Superscript>3+</Superscript>,Er<Superscript>3+</Superscript> Nanomaterials

The up-converting ZrO₂:Yb³⁺,Er³⁺ nanomaterials were prepared with the combustion and sol–gel methods. FT-IR spectroscopy was used for analyzing the impurities. The crystal structures were characterized with X-ray powder diffraction and the mean crystallite sizes were estimated with the Scherrer formula. Up-conversion luminescence measurements were made at room temperature with IR-laser excitation at 977 nm. The IR spectra revealed the conventional and OH⁻ impurities for the combustion synthesis products. The structure of the ZrO₂:Yb³⁺, Er³⁺ nanomaterials was cubic except for the minor monoclinic and tetragonal impurities obtained with the sol–gel method. The materials showed red (650–700 nm) and green (520–560 nm) up-conversion luminescence due to the ⁴F_9/2→⁴I_15/2 and (²H_11/2, ⁴S_3/2)→⁴I_15/2 transitions of Er³⁺, respectively. The products obtained with the combustion synthesis exhibited the most intense luminescence intensity and showed considerable afterglow.     

Phase transformation of nanostructured titanium dioxide thin films grown by sol–gel method

Nanostructured TiO₂ thin films were deposited on quartz glass at room temperature by sol–gel dip coating method. The effects of annealing temperature between 200^∘C to 1100^∘C were investigated on the structural, morphological, and optical properties of these films. The X-ray diffraction results showed that nanostructured TiO₂ thin film annealed at between 200^∘C to 600^∘C was amorphous transformed into the anatase phase at 700^∘C, and further into rutile phase at 1000^∘C. The crystallite size of TiO₂ thin films was increased with increasing annealing temperature. From atomic force microscopy images it was confirmed that the microstructure of annealed thin films changed from column to nubbly. Besides, surface roughness of the thin films increases from 1.82 to 5.20 nm, and at the same time, average grain size as well grows up from about 39 to 313 nm with increase of the annealing temperature. The transmittance of the thin films annealed at 1000 and 1100^∘C was reduced significantly in the wavelength range of about 300–700 nm due to the change of crystallite phase. Refractive index and optical high dielectric constant of the n-TiO₂ thin films were increased with increasing annealing temperature, and the film thickness and the optical band gap of nanostructured TiO₂ thin films were decreased.     

Up-Conversion Luminescence of the NaRF<Subscript>4</Subscript>-NaR′F<Subscript>4</Subscript> (R: Y,Yb, Er) Core-Shell Nanomaterials

Up-converting NaRF₄-NaR′F₄ (R: Y, Yb, Er) nanomaterials with different core-shell combinations were prepared with the co-precipitation method. The X-ray powder diffraction (XPD) measurements revealed the presence of both the cubic and hexagonal NaRF₄ phases. The crystallite sizes calculated with the Scherrer formula were 100 and 150 nm for the cubic and hexagonal phases, respectively. The FT-IR spectra showed water impurities. The up-conversion luminescence and luminescence decays were studied with NIR laser excitation at 970 nm. The up-conversion luminescence spectra showed strong red (640–685 nm) (⁴F_9/2 → ⁴I_15/2) and moderate green (515–560 nm) (²H_11/2, ⁴S_3/2 → ⁴I_15/2) Er³⁺ luminescence. The strongest up-conversion luminescence and longest red luminescence decay was obtained from the Na(Y,Yb)F₄-NaErF₄ core-shell combination.     

PEO-based composite lithium polymer electrolyte, PEO-BaTiO3-Li(C2F5SO2)2N

Polyethylene oxide (PEO) based polymer electrolytes with BaTiO₃ as filler and Li(C₂F₅SO₂)₂N as salt have been examined in lithium polymer batteries. The aluminum disolution potential in PEO-Li(C₂F₅SO₂)₂N was estimated to be 4.1 V vs. Li/Li⁺ at 80 °C, which was compared to that of 3.8 V vs. Li/Li⁺ in PEO-Li(CF₃SO₂)₂N. The electrical conductivity of the system was measured as a function of O/Li ratio. The highest conductivity was observed in O/Li=8. The conductivity was 1.65×10⁻³ S/cm at 80 °C and 1.5×10⁻⁵ S/cm at 25 °C. The interfacial resistance of Li/polymer electrolyte/Li annealed at 80 °C for 15 days was lower than 100 Ωcm². Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001.     

Electrochemical performances of FePO<Subscript>4</Subscript>-positive active mass prepared through a new sol–gel method

This investigation is a contribution to the research on alternative cathode materials with much more promising performances for lithium batteries. It deals with the electrochemical properties of iron phosphate compound FePO₄, chemically prepared through the so-called sol–gel Pechini process, terminated by a calcination of the product precursor at temperatures (T _c) ranging between 350°C and 650°C. A crystalline phase was obtained for temperatures ≥400°C. The particle size decreased with the decrease in T _c, giving rise to a Brunauer–Emmett–Teller (BET)-specific surface area, S _BET, as high as 28 m² g⁻¹ for the sample annealed at 400°C. The electrochemical properties of FePO₄-based composite cathodes were characterized on three-electrode laboratory cells. Charge–discharge cycling determined a maximum reversible capacity of 132 mAh g⁻¹, which fell with the increase in T _c. A direct correlation was established between the activity of the material and its active surface area.     

Structural and electrochemical study on Li(Li1/3Ti5/3)O4 anode material for lithium ion batteries

Chemical and electrochemical studies have shown that various titanium oxides can incorporate lithium in different ratios. Other compounds with a spinel-type structure and corresponding to the spinel oxides LiTi₂O₄ and Li₄Ti₅O₁₂ have been evaluated in rechargeable lithium cells with promising features. The spinel Li[Li_1/3Ti_5/3]O₄ [1–5] compound is a very appealing electrode material for lithium ion batteries. The lithium insertion-deinsertion process occurs with a minimal variation of the cubic unit cell and this assures high stability which may reflect into long cyclability. In addition, the diffusion coefficient of lithium is of the order of 10⁻⁸ cm²s⁻¹ [5] and this suggests fast kinetics which may reflect in high power capabilities. In this work we report a study on the kinetics and the structural properties of the Li[Li_1/3Ti_5/3]O₄ intercalation electrode carried out by: cyclic voltammetry, galvanostatic cycling and in-situ X-ray diffraction. The electrochemical characterization shows that the Li[Li_1/3Ti_5/3]O₄ electrode cycles around 1.56 V vs. Li with a capacity of the order of 130 mAhg⁻¹ which approaches the maximum value of 175 mAhg⁻¹ corresponding to the insertion of 1 equivalent per formula unit. The delivered capacity remains constant for hundred cycles confirming the stability of the host structure upon the repeated Li insertion-deinsertion process. This high structural stability has been confirmed by in situ Energy Dispersion X-ray analysis. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Electrical and electrochemical behaviour of several LiFe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript> solid solutions as cathode materials for lithium ion batteries

Several olivine phosphates were investigated in the last years as cathode materials for secondary lithium ion batteries. Among these compounds, LiFe _x Co_1 − x PO₄ solid solutions might be interesting candidates because they should combine the high potential value of Co³⁺/Co²⁺ (higher than 4.5 V vs Li⁺/Li) with the relatively high charge–discharge rate of LiFePO₄. Solid solutions were prepared by solid-state route and characterised by X-ray powder diffraction, cyclic voltammetry, impedance spectroscopy and the Hebb–Wagner method. The results show that also low amount of iron induces high electronic conductivity in the solid solutions.     

An ab initio molecular dynamics study of ionic conductivity in hexagonal lithium lanthanum titanate oxide La0.5Li0.5TiO3

To date, the fastest lithium ion-conducting solid electrolytes known are the perovskite-type ABO₃ oxide, with A = Li, La and B = Ti, lithium lanthanum titanate (LLTO) Li_3x La_{( 2 \mathord}

Grafted natural rubber-based polymer electrolytes: ATR-FTIR and conductivity studies

Attenuated total reflectance–Fourier transformed infrared spectroscopy measurement is employed to study the interactions between the components of 30% methyl-grafted natural rubber (MG30), lithium trifluromethanesulfonate (LiCF₃SO₃ or LiTF), and propylene carbonate (PC). Vibrational spectra data of LiTF reveals that the ν_s(SO₃) at 1,045 cm⁻¹, δ_s(CF₃) at 777 cm⁻¹, and C=O stretching mode at 1,728 cm⁻¹ for MG30 have shifted to lower wave numbers in MG30–LiTF complexes indicating that complexation has occurred between MG30 and LiTF. The solvation of lithium ion is manifested in Li⁺ ← O=C interaction as shown by the downshifting and upshifting of C=O mode at 1,788 to 1,775 cm⁻¹ and ν_as(SO₃) at 1,250 to 1258 cm⁻¹, respectively, in LiTF–PC electrolytes. There is no experimental evidence of the interaction between MG30 and PC. Competition between MG30 and PC on associating with lithium ion is studied, and the studies show that the interaction between MG30–LiTF is stronger than that of the PC–LiTF in plasticized polymer–salt complexes. The effect of PC on the ionic conductivity of the MG30–LiTF system is explained in terms of the polymer, plasticizer, and salt interactions. The temperature dependence of conductivity of the polymer films obeys the Vogel–Tamman–Fulcher relation. Values of conductivity and activation energy of the MG30-based polymer electrolyte systems are presented and discussed.     

Lithium conductivity and lithium diffusion in NASICON-type Li<Subscript>1+x</Subscript>Ti<Subscript>2–x</Subscript>Al<Subscript>x</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> (x= 0; 0.3) prepared by mechanical activation

LiTi₂(PO₄)₃ (LTP) and Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) (S. g. R-3c) have been prepared using conventional ceramic and mechanical activation (MA) methods. It has been shown that preliminary mechanical activation of initial mixtures leads to different nature and amount of dielectric admixtures in the final product after heat treatment at 800–1000 °C as compared with ceramic method. Transport properties of as prepared materials have been studied by lithium ionic conductivity at d.c. and a.c. (complex impedance method), and ⁷Li NMR spin-lattice relaxation rate T₁ ^–1 measurements. Lithium ionic conductivity of mechanochemically prepared LTP and LATP was characterized by significant reduction of grain boundary resistance, especially for LTP, while the bulk conductivity and Li ion diffusion does not noticeably change. The activation energy of bulk conductivity and Li ion diffusion, i.e. short-range motion, appeared to be almost the same for all samples and was equal to ~0.20 eV. On contrary, the activation energy of d.c.-conductivity, i.e. long-range Li ion motion decreases from ~0.6 eV for ceramic samples to ~0.4 eV for samples prepared via mechanochemical route. It was proposed that MA leads to formation of nano-particulate high-conductive grain boundaries both in LTP and LATP. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

NMR in M2Fe(CN)6 · nH2O-xLiCl systems (M = Zn, Sn, Pb)

The broadline ⁷Li and ¹H NMR spectra of the sorption products of lithium chloride on zinc, lead, and tin cyanoferrates have been analyzed. Sorption of LiCl inside the Zn₂Fe(CN)₆ · 2.5H₂O crystal structure proceeds first by the ionic exchange mechanism and then by the molecular sorption of Li⁺-Cl⁻ ionic pairs. For Sn and Pb cyanoferrates, lithium choride is adsorbed on the surface. In all products as the LiCl content increases, the hydrolysis of cyanoferrates is intensified with the increase in the number of mobile protons. Original Russian Text ? T.A. Denisova, N.A. Zhuravlev, L.G. Maksimova, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 7, pp. 1001–1003.     

Electrochemistry of WO3 based smart windows: Beliefs and facts

WO₃ is believed to be the most stable electrochromic material, particularly in organic solvents. This paper deals with the effects of prolonged cycling around and below 2 V vs Li/Li⁺ in propylene carbonate/lithium triflate electrolyte. A dramatic loss of charge capacity was observed when the sample was cycled between 4.5 V and 1.6 V vs Li/Li⁺. This was not the case when the lower limit was set to 2.0 V vs Li/Li⁺. Spectrophotometric analysis showed that the charge capacity loss was not accompanied by presence of tungsten in the electrolyte or the counter electrode. SEM pictures show some electrode damage and precipitation at the electrode surface. A corrosion mechanism is suggested. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997.     

Effect of B-site substitution of (Li,La)TiO3 perovskites by di-, tri-, tetra- and hexavalent metal ions on the lithium ion conductivity

We report the synthesis and lithium ion conductivity of di-, tri-, tetra- and hexavalent metal ion B-site substituted (Li,La)TiO₃(LLT) perovskites. All 5–10 mol% Mg, Al, Mn, Ge, Ru and W ion substituted LLTs crystallize in a simple cubic or tetragonal perovskite structure. Among the oxides investigated, the Al-substituted perovskite La_0.55Li_0.36□_0.09Ti_0.995Al_0.005O₃ (□=vacancy) exhibits the highest lithium ion conductivity of 1.1 × 10⁻³ S/cm at room temperature which is slightly higher than that of the undoped (Li,La)TiO₃ perovskite (8.9 × 10⁻⁴ S/cm) at the same temperature. The lithium ion conductivity of substituted LLTs does not seem to depend on the concentration of the A-site ion vacancies and unit cell volume. The high ionic conductivity of Al-substituted LLT is attributed to the increase of the B(Al)-O bond and weakening of the A(Li,La)-O bond. The conductivity behavior of the doped LLT is being described on the basis of Gibbs free energy considerations.     

Lithium conducting solid polymer electrolytes based on polyacrylonitrile copolymers: Ion solvation and transport properties

The systems poly(butadiene-co-acrylonitrile) (PBAN) - lithium salts have been studied by means of X-ray and IR spectroscopy, optical microscopy and ac- and dc-conductivity measurements. X-ray and microscopy studies have confirmed that PBAN dissolves LiClO₄ up to [CN]/[Li] ≈ 2: 1. IR spectra of the samples with LiAsF₆, LiCF₃SO₃ and LiClO₄ have indicated the coordination between Li⁺ and the polar CN groups of PBAN. So, PBAN was found to be a suitable polymer matrix for SPE. The polymer films exhibited predominant ionic conductivity. Measurements of conductivity and Li transport numbers versus temperature over a wide range of salt concentrations revealed the existence of two concentration regions (within the limits of salt solubility) corresponding to liquid-like and glass-like ion transport mechanisms. New solid polymer electrolyte with lithium single-ion conductivity of 10⁻³ S cm⁻¹ at 25 – 95 °C was obtained. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Self-assembly of boehmite nanopetals to form 3D high surface area nanoarchitectures

A flower-like boehmite nanostructure was prepared through a template-free chemical route by the self-assembly process of nanosize petals 800–1000 nm long, 200–250 nm wide, 20–50 nm thick and having an average crystallite size of about 2.21 nm. X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), DTA/TGA analyses and Brunauer–Emmet–Teller (BET-N₂) analyses were used in order to characterize the product obtained. XRD results exhibited that the obtained nanostructures composed of pure orthorhombic AlOOH phase. The effects of Cl⁻ ions and TEA on the growth of boehmite three-dimensional nanoarchitectures in the presence of NO₃^-\mathrm{NO}_{3}^{-} ions were investigated. BET analyses of as-prepared material demonstrate that this nanostructure material has a high specific surface area, as high as 123 m² g⁻¹.     

Preparation and characterization of spinel Li4Ti5O12 nanoparticles anode materials for lithium ion battery

Spinel Li₄Ti₅O₁₂ nanoparticles were prepared via a high-temperature solid-state reaction by adding the prepared cellulose to an aqueous dispersion of lithium salts and titanium dioxide. The precursors of Li₄Ti₅O₁₂ were characterized by thermogravimetry and differential scanning calorimetry. The obtained Li₄Ti₅O₁₂ nanoparticles were characterized using X-ray diffraction, transmission electron microscopy (TEM) and electrochemical measurements. The TEM revealed that the Li₄Ti₅O₁₂ prepared with cellulose is composed of nanoparticles with an average particle diameter of 20–30 nm. Galvanostatic battery testing showed that nano-sized Li₄Ti₅O₁₂ exhibit better electrochemical properties than submicro-sized Li₄Ti₅O₁₂ do especially at high current rates, which can deliver a reversible discharge capacity of 131 mAh g⁻¹ at the rate of 10 C, whereas that of the submicro-sized sample decreases to 25 mAh g⁻¹ at the same rate (10 C). Its reversible capacity is maintained at ~172.2 mAh g⁻¹ with the voltage range 1.0–3.0 V (vs. Li) at the current rate of 0.5 C for over 80 cycles.     

Structure and electrical properties of HfO<Subscript>2</Subscript> high-<Emphasis Type="Italic">k</Emphasis> films prepared by pulsed laser deposition on Si (100)

High-k gate dielectric hafnium dioxide films were grown on Si (100) substrate by pulsed laser deposition at room temperature. The as-deposited films were amorphous and that were monoclinic and orthorhombic after annealed at 500°C in air and N₂ atmosphere, respectively. After annealed, the accumulation capacitance values increase rapidly and the flat-band voltage shifts from −1.34 V to 0.449 V due to the generation of negative charges via post-annealing. The dielectric constant is in the range of 8–40 depending on the microstructure. The I–V curve indicates that the films possess of a promising low leakage current density of 4.2×10⁻⁸ A/cm² at the applied voltage of −1.5 V.     

Feasibility studies on newly identified LiCrP2O7 compound for?lithium insertion behavior

A new category of lithium intercalating cathode candidates, namely LiCrP₂O₇, was synthesized at 800°C using a citric acid assisted modified (CAM) sol–gel method and examined for possible lithium insertion behavior. The formation of a phase pure and monoclinic LiCrP₂O₇ compound with finer crystallite size was confirmed from the X-ray diffraction patterns. The presence of nano-sized particles as observed from a transmittance electron microscope image of LiCrP₂O₇ and the presence of a preferred local cation environment, evidenced from Fourier transform infra-red and ⁷Li nuclear magnetic resonance studies, are the added advantages of the present study. Further, cyclic voltametry study performed on 2016 coin cells consisting of the synthesized LiCrP₂O₇ cathode revealed an excellent cycling reversibility and structural stability. Hence, CAM sol–gel synthesized LiCrP₂O₇ is found to possess desirable physical as well as electrochemical properties, leading one to consider the same as a possible lithium intercalating cathode material.     

Enhanced electrochemical properties of LiMnPO<Subscript>4</Subscript>/C via Li-site substitution with Mg

Li_0.94Mg_0.03MnPO₄/C composite cathode materials for lithium ion battery with different carbon contents are synthesized by sol–gel method followed by heat treatment in the air. Environmental scanning electron microscopy measurements show that both firing temperature and carbon content affect the morphology of the end products. X-ray powder diffraction analysis indicates that the samples are olivine-structured. The galvanostatic charge–discharge results show that the optimal firing temperature registers 400 °C and that the electrochemical performances of Li_0.94Mg_0.03MnPO₄/C are improved by elevating its carbon amount. The sample with an initial conductive carbon content of 20 wt.% gives the best performances; when tested at the rate of 0.02C, 0.1C, and 1.0C between 2.8 and 4.4 V, its initial discharge capacity reaches 145.8, 103.0, and 72.8 mAhg⁻¹, respectively, and maintains at 100.1, 77.6, and 65.4 mAhg⁻¹, respectively, after 100 cycles.     

Synthesis and characterization of mixed vanadium oxide cathode materials for lithium-ion batteries

A family of mixed vanadium oxides LiCo_yNi_(1−y)VO₄ (x=0.2, 0.5 and 0.8) of potential use as high voltage cathode materials in lithium batteries, has been synthesized and characterized. In general the x-ray diffraction analysis showed that these compounds have an inverse spinel structure where about 85 % of the Ni²⁺ and Co²⁺ ions occupies octahedral sites and the rest tetrahedral sites along with the V⁵⁺ ions. Moreover, the annealing temperature plays a key role in determining the particle size, as demonstrated by scanning electron microscope analysis. Cycling voltammetry tests showed that the lithium insertion-extraction process in the LiCo_yNi_(1−y)VO₄ electrode materials occurs reversibly at around 4.3–4.4 V vs. Li and these results are confirmed by cycling tests. The cycling capacity is modest; however the trend of the cycling curves leads to foresee that an increase in capacity may be obtained by extending the charging process beyond 4.6 V vs. Li, once a stable electrolyte will be available. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.