Preparation of the Solid Electrolytes Li4+xAlxSi1‐xO4‐yLi3PO4 and Their Ionic Conductivity

The ion conductors Li_4+xAl_xSi_1‐xO₄‐yLi₃PO₄ (x = 0 to 0.5, y = 0 to 0.6) were prepared by the Sol‐Gel method. The powder and sintered samples were characterized by DTA‐TG, XRD, SEM, and AC impedance techniques. The conductivity and sinterability increased when y increased from 0 to 0.4 in the Li_4+xAl_xSi_1‐xO₄‐yLi₃PO₄. The particle size of the powder samples is about 0.13 μm. The maximum conductivity at 20 °C is 3.128 × 10^?5s cm^?1 for Li_4.4Al_0.4Si_0.6O₄‐0.4 Li₃PO₄.     

The Ionic Conductivity of Solid Electrolytes for Li4+xMxSi1–xO4‐yLi2O (M=Al,B) Systems

The Li_4+xM_xSi_4+xO₄‐yLi₂O (M=Al, B; x = 0 to 0.6, y = 0 to 0.5) ion conductors were prepared by the Sol‐Gel method and examined in detail. The powder and sintered samples were characterized by DTA‐TG, XRD, SEM, and AC impedance techniques. The experimental results show that the conductivity and sinterability in creased with the amount of excess lithium oxide in the silicate. The Li₂O phase acts as a flux to accelerate the sintering process and to obtain high conductivity of grain boundaries. The particle size of the sintered pellets is about 0.25 μm. The maximum conductivity at 200 °C is 5.40 × 10^?3s cm^?1 for Li_4.4Al_0.4 Si_0.6O₄‐0.3Li₂O.     

Preparation of the Solid Electrolytes Li4＋xAlxSi1—xO4—yAl2O3 by the Sol—Gel Method and Study of Their Ionic Conductivity

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Preparation of Li_(4.4)Al_(0.4)Si_(0.6)O_4-xLi_3BO_3 Solid Electrolytes by Sol-Gel Method and Their Ionic Conductivity

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Li+ ion conductivity in the system Li4SiO4Li3VO4

Two ranges of solid solutions were prepared in the system Li₄SiO₄Li₃VO₄: Li_4?xSi_1?xV_xO₄, 0 < x ? 0.37 with the Li₄SiO₄ structure and Li_3+yV_1?ySi_yO₄, 0.18 ? y ? 0.53 with a γ structure. The conductivity of both solid solutions is much higher than that of the end members and passes through a maximum at ～40Li₄SiO₄ · 60Li₃VO₄ with values of ～1 × 10^?5 ohm^?1 cm^?1 at 20°C, rising to ～4 × 10^?2 ohm^?1 cm^?1 at 300°C. These conductivities are several times higher than in the corresponding Li₄SiO₄Li₃(P,As)O₄ systems, especially at room temperature. The solid solutions are easy to prepare, are stable in air, and maintain their conductivity with time. The mechanism of conduction is discussed in terms of the random-walk equation for conductivity and the significance of the term c(1 ? c) in the preexponential factor is assessed. Data for the three systems Li₄SiO₄Li₃YO₄ (Y = P, As. V) are compared.     

Enhanced electrochemical properties of a novel polyvinyl formal membrane supporting gel polymer electrolyte by Al2O3 modification

Polyvinyl formal (PVFM)‐based dense polymer membranes with nano‐Al₂O₃ doping are prepared via phase inversion method. The membranes and also their performances as gel polymer electrolytes (GPEs) for lithium ion battery are studied by field emission scanning electron microscope, X‐ray diffraction, differential scanning calorimetry, mechanical strength test, electrolyte uptake test, electrochemical impedance spectroscopy, cyclic voltammetry, and charge–discharge test. The polymer membrane with 3 wt % nano‐Al₂O₃ doping shows the improved mechanical strength of 12.16 MPa and electrolyte uptake of 431.25% compared with 10.47 MPa and 310.59% of the undoped sample, respectively. The membrane absorbs and swells liquid electrolyte to form stable GPE with ionic conductivity of 4.92 × 10^?4 S cm^?1 at room temperature, which is higher than 1.77 × 10^?4 S cm^?1 of GPE from the undoped membrane. Moreover, the Al₂O₃‐modified membrane supporting GPE exhibits wide electrochemical stability window of 1.2–4.8 V (vs. Li/Li⁺) and good compatibility with LiFePO₄ electrode, which implies Al₂O₃‐modified PVFM‐based GPE to be a promising candidate for lithium ion batteries. © 2014 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 572–577     

Time‐Resolved High and Low Temperature Phase Transitions of the Nanocrystalline Cubic Phase in the Y2O3‐ZrO2 and Fe2O3‐ZrO2 System

The nanocrystalline cubic Phase of zirconia was found to be thermally stabilized by the addition of 2.56 to 17.65 mol % Y₂O₃ (5.0 to 30.0 mol % Y, 95.0 to 70.0 mol % Zr cation content). The cubic phase of yttria stabilized zirconia was prepared by thermal decomposition of the hydroxides at 400°C for 1 hr. 2.56 mol % Y₂O₃‐ZrO₂ was stable up to 800°C in an argon atmosphere. The samples with 4.17 to 17.65 mol % Y₂O₃ were stable to 1200°C and higher. All samples at temperatures between 1450°C to 1700°C were cubic except the sample with 2.56 mol % Y₂O₃ which was tetragonal. The crystallite sizes observed for the cubic phase ranged from 50 to 150 Å at temperatures below 900°C and varied from 600 to 800 nm between 1450°C and 1700°C. Control of furnace atmosphere is the main factor for obtaining the cubic phase of Y‐SZ at higher temperature. Nanocrystalline cubic Fe‐SZ (Iron Stabilized Zirconia) with crystallite sizes from 70 to 137 Å was also prepared at 400°C. It transformed isothermally at temperatures above 800°C to the tetragonal Fe‐SZ and ultimately to the monoclinic phase at 900°C. The addition of up to 30 mol % Fe(III) thermally stabilized the cubic phase above 800°C in argon. Higher mol % resulted in a separation of Fe₂O₃. The nanocrystalline cubic Fe‐SZ containing a minimum 20 mol % Fe (III) was found to have the greatest thermal stability. The particle size was a primary factor in determining cubic or tetragonal formation. The oxidation state of Fe in zirconia remained Fe³⁺. Fe‐SZ lattice parameters and rate of particle growth were observed to decrease with higher iron content. The thermal stability of Fe‐SZ is comparable with that of Ca‐SZ, Mg‐SZ and Mn‐SZ prepared by this method.     

Effect of Li2O Addition on the Preparation of (Y2‐yLiy)Ti2O7‐y

A new series of (Y_2‐yLi_y)Ti₂O_7‐y having an ordered pyrochlore phase was prepared by a solid state reaction method with a solid solution range of 0.05 ≥ y ≥ 0.10. Unit cell parameters obtained by the Rietveld refinement method shows that the a‐axis decreases linearly with increasing the amount of Li ion addition, indicating the successful incorporation of the Li ion into unit cell. The average x‐fractional coordinate of the O(1) site depends on the ionic radius ratio of r(A³+)/r(Ti⁴⁺) in the A₂Ti₂O₇ with a pyrochlore phase. The Ti K‐edge XANES spectra of the (Y_2‐yLi_y)Ti₂O_7‐y show that the valence of the Ti ions is slightly less than 4 so that Ti is in the mixed valence state. Average particle size increases with increasing the amount of extra Li ion addition, which acts as a flux to lower the melting point of the materials.     

Graphitized carbon and graphene modified Fe2O3/Li4Ti5O12 as anode material for lithium ion batteries

Graphitized carbon (GC) and graphene (GE) modified Fe₂O₃/Li₄Ti₅O₁₂ (LTO) composites have been synthesized via a solid‐state reaction, respectively. The structure, morphology and electrochemical performance of the materials have also been characterized with X‐ray diffraction (XRD), scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) system, X‐ray photoelectron spectrometer (XPS), Fourier transform infrared spectroscopy (FTIR) and electrochemical measurements. The discharge capacities of Fe₂O₃/LTO, GC/Fe₂O₃/LTO and GE/Fe₂O₃/LTO are 100.2 mAh g^?1, 207.5 mAh g^?1 and 238.9 mAh g^?1 after 100 cycles at the current density of 176 mA g^?1. The cyclic stability and rate capability are in the order of GE/Fe₂O₃/LTO > GC/Fe₂O₃/LTO > Fe₂O₃/LTO because of the synergistic effect between GC (GE) and Fe₂O₃/LTO. Copyright © 2016 John Wiley & Sons, Ltd.     

Enhanced dielectric performance and energy storage of PVDF‐HFP‐based composites induced by surface charged Al2O3

In order to enhance dielectric properties and energy storage density of poly(vinylidene fluoride‐hexafluoro propylene) (PVDF‐HFP), surface charged gas‐phase Al₂O₃ nanoparticles (GP‐Al₂O₃, with positive surface charges, ε’ ≈ 10) are selected as fillers to fabricate PVDF‐HFP‐based composites via simple physical blending and hot‐molding techniques. The results show that GP‐Al₂O₃ are dispersed homogeneously in the PVDF‐HFP matrix and the existence of nanoscale interface layer (matrix‐filler) is investigated by SAXS. The dielectric constant of the composites filled with 10 wt % GP‐Al₂O₃ is 100.5 at 1 Hz, which is 5.6 times higher than that of pure PVDF‐HFP. The maximum energy storage density of the composite is 4.06 J cm^?3 at an electrical field of 900 kV mm^?1 with GP‐Al₂O₃ content of 1 wt %. Experimental results show that GP‐Al₂O₃ could induce uniform fillers’ distribution and increase the concentration of electroactive β‐phase as well as enhance interfacial polarization in the matrix, which resulted in enhancements of dielectric constant and energy storage density of the PVDF‐HFP composites. This work demonstrates that surface charged inorganic‐oxide nanoparticles exhibit promising potential in fabricating ferroelectric polymer composites with relatively high dielectric constant and energy storage. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 574–583     

Ion trapping and its effect on the conductivity of LISICON and other solid electrolytes

Conductivity data for the lithium ion conducting solid electrolyte, LISICON, Li_2+2xZn_1?xGeO₄ over a particularly wide composition range, 0.15 < x < 0.85, and over the temperature range ～25 to 150°C show that both the activation energy and preexponential factor pass through maxima around x ～ 0.4 to 0.5, at which the preexponential factor exhibits anomalously high values, ～10¹³ ohm^?1 cm^?1 K. An explanation is offered which involves the trapping of mobile Li⁺ ions by the immobile sublattice at lower temperatures. This model also accounts for ageing effects observed at lower temperatures in which the conductivity decreases slowly with time. In the isostructural Li⁺ electrolytes, Li_3+xSi_xY_1?xO₄ (Y = P, As, V), the compositional dependence of both the preexponential factor and activation energy is less marked and no evidence for ion trapping effects is observed.     

Synthesis of New Lithium Ionic Conductor Thio-LISICON—Lithium Silicon Sulfides System

The new lithium ionic conductors, thio-LISICON (LIthium SuperIonic CONductor), were found in the ternary Li₂S-SiS₂-Al₂S₃ and Li₂S-SiS₂-P₂S₅ systems. Their structures of new materials, Li_4+xSi_1−xAl_xS₄ and Li_4−xSi_1−xP_xS₄ were determined by X-ray Rietveld analysis, and the electric and electrochemical properties were studied by electronic conductivity, ac conductivity and cyclic voltammogram measurements. The structure of the host material, Li₄SiS₄ is related to the γ-Li₃PO₄-type structure, and when the Li⁺ interstitials or Li⁺ vacancies were created by the partial substitutions of Al³⁺ or P⁵⁺ for Si⁴⁺, large increases in conductivity occur. The solid solution member x=0.6 in Li_4−xSi_1−xP_xS₄ showed high conductivity of 6.4×10^-4 S cm⁻¹ at 27°C with negligible electronic conductivity. The new solid solution, Li_4−xSi_1−xP_xS₄, also has high electrochemical stability up to ∼5 V vs Li at room temperature. All-solid-state lithium cells were investigated using the Li_3.4Si_0.4P_0.6S₄ electrolyte, LiCoO₂ cathode and In anode.     

Preparation of Li4Ti5O12 Yolk–Shell Powders by Spray Pyrolysis and their Electrochemical Properties

We have reported for the first time the preparation of yolk–shell‐structured Li₄Ti₅O₁₂ powders for use as anode materials in lithium‐ion batteries. One Li₄Ti₅O₁₂ yolk–shell‐particle powder is directly formed from each droplet containing lithium, titanium, and carbon components inside the hot wall reactor maintained at 900 °C. The precursor Li₄Ti₅O₁₂ yolk–shell‐particle powders, which are directly prepared by spray pyrolysis, have initial discharge and charge capacities of 155 and 122 mA h g^?1, respectively, at a current density of 175 mA g^?1. Post‐treatment of the yolk–shell‐particle powders at temperatures of 700 and 800 °C improves the initial discharge and charge capacities. The initial discharge capacities of the Li₄Ti₅O₁₂ powders with a yolk–shell structure and a dense structure post‐treated at 800 °C are 189 and 168 mA h g^?1, respectively. After 100 cycles, the corresponding capacities are 172 and 152 mA h g^?1, respectively (retentions of 91 and 90 %).     

Einkristalle von Y3F[Si3O10] im Thalenit-Typ

Single Crystals of Y₃F[Si₃O₁₀] with Thalenite-Type Structure Colourless, diamond-shaped single crystals of Y₃F[Si₃O₁₀] (monoclinic, P2₁/n; a = 730.38(5), b = 1112.47(8), c = 1037.14(7) pm, β = 97.235(6)°, Z = 4) with thalenite-type structure are obtained upon the reaction of YF₃ with Y₂O₃ and SiO₂ (1 : 4 : 9 molar ratio) in evacuated silica tubes at 700 °C in the presence of CsCl as flux within seven days. The crystal structure consists of triangular [FY₃]⁸⁺ cations and catena-trisilicate anions [Si₃O₁₀]^8–, which exhibit a horseshoe-shape resulting from two vertex-shared terminal [SiO₄] tetrahedra with both staggered and eclipsed conformation relative to the central one. The Y³⁺ cations have coordination numbers of seven plus one (Y1) or seven (Y2 and Y3), but only one F^– anion belongs to each and vice versa, the remainder ligands being oxygen members of [Si₃O₁₀]^8– anions.     

Improvement of electrochemical performance for Li-rich spherical Li1.3[Ni0.35Mn0.65]O2+x modified by Al2O3

The Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x microspheres are firstly prepared and subsequently transferred into the Al₂O₃-coated Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x microspheres by a simple deposition method. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. The results reveal that the Al₂O₃-coated Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x sample has a typical α-NaFeO₂ layered structure with the existence of Li₂MnO₃-type integrated component, and the Al₂O₃ layer is uniformly coated on the surface of the spherical Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x particles with a thickness of about 4 nm. Importantly, the Al₂O₃-coated Li-rich sample exhibits obviously improved electrochemical performance compared with the pristine one, especially the 2 wt.% Al₂O₃-coated sample shows the best electrochemical properties, which delivers an initial discharge capacity of 228 mAh g^?1 at a rate of 0.1 C in the voltage of 2.0–4.6 V, and the first coulombic efficiency is up to 90 %. Furthermore, the 2 wt.% Al₂O₃-coated sample represents excellent cycling stability with capacity retention of 90.9 % at 0.33 C after 100 cycles, much higher than that of the pristine one (62.2 %). Particularly, herein, the typical inferior rate capability of Li-rich layered cathode is apparently improved, and the 2 wt.% Al₂O₃-coated sample also shows a high rate capability, which can deliver a capacity of 101 mAh g^?1 even at 10 C. Besides, the thin Al₂O₃ layer can reduce the charge transfer resistance and stabilize the surface structure of active material during cycling, which is responsible for the improvement of electrochemical performance of the Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x .     

Valence Distributions of Iron and Manganese in Pure,Manganese‐doped and Calcium‐doped Yttrium Orthoferrite

The valence distributions of Fe and Mn in yttrium orthoferrite (YFeO,), YFe_0.6Mn0.4O3 and Y_0.9Ca_0.1Fe_0.6Mn_0.4O_3.8 were studied by the measurement of thermal power. Pure YFeO₃ shows the n‐type electrical conductivity associated with small polaron hopping between Fe²⁺ and Fe³⁺. Both YFe_0.4Mn_0.4‐O₃ and Y_0–9Ca_0–1.Fe_0–6Mn_0–4O_3–8 show n‐type and p‐type conductivities at high and low temperatures respectively associated with small polaron hopping between Mn³⁺ and Mn⁴⁺, iron has only oxidation state of Fe³⁺ and does not have contribution to the electrical conductivity.     

Solid vitreous inorganic electrolytes in Li<Subscript>2</Subscript>O-LiF-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system for rechargeable lithium power sources: Ionic conductivity and activation energy

The effect of chemical composition to ionic conductivity and activation energy of vitreous solid electrolytes (SE) based on Li₂O-P₂O₅-LiF system (Li₂O ≥ 45.4 mol %) was detected. The temperature effect to conductivity and activation energy was studied. An original technology was designed to prepare vitreous SEs in Li₂O-P₂O₅-LiF system containing up to 20 mol % LiF and characterized with ionic conductivity up to 4.4 × 10^?7 S cm^?1 (24°C) and activation energy about 0.567 eV. The synthesized materials are characterized with high X-ray amorphism and technological performance.     

Synthese von Y2O2(CN2) und Leuchtstoffeigenschaften von Y2O2(CN2):Eu

Synthesis of Y₂O₂(CN₂) and Luminescence Properties of Y₂O₂(CN₂):Eu Crystalline powders of the new compound Y₂O₂(CN₂) were prepared by solid state reactions from different mixtures of YCl₃/YOCl/Y₂O₃ and Li₂(CN₂) at temperatures between 620 °C and 650 °C. Structure refinements based on X‐ray powder diffraction revealed that trigonal Y₂O₂(CN₂) crystallizes with a structure that is closely related to that of Y₂O₂S, whereas linear N‐C‐N units replace sulphur atoms in Y₂O₂S. In addition, a hexagonal polytype of Y₂O₂(CN₂) was obtained in which a different stacking sequence of yttrium atoms creates a doubling of the c‐axis. Europium‐doped samples of Y₂O₂(CN₂) were prepared and the luminescence properties of Y₂O₂(CN₂):Eu are presented.     

Synthesis of garnet structured Li7+x La3Y x Zr2-x O12 (x = 0–0.4) by modified sol–gel method

Preparation of lithium garnet Li₇La₃Zr₂O₁₂ (LLZ) in cubic phase by solid state method requires high temperature sintering around 1,200 °C for 36 h in Al₂O₃ crucible with intermittent grinding. Synthesis of LLZ in cubic phase at lower temperatures by wet chemical methods was reported earlier, however that decompose at high temperature around 850 °C. In this work we report the systematic studies on synthesis of garnet structured electrolytes by modified sol–gel method by the simultaneous substitution of Li⁺ and Y³⁺ for Zr⁴⁺ according to the formulae Li_7+x La₃Y _x Zr_2-x O₁₂ (x = 0, 0.1, 0.2, 0.3 and 0.4). The present investigation revealed that the cubic garnet phase is obtained at much lower temperature for Li₇La₃Zr₂O₁₂ and the simultaneous increase of both Li⁺ and Y³⁺ in Li_7+x La₃Y _x Zr_2-x O₁₂ requires slightly higher sintering temperatures for the formation of cubic garnet phase. SEM micrographs of the Li_7+x La₃Y _x Zr_2-x O₁₂ (x = 0, 0.1, 0.2, 0.3 and 0.4) annealed at minimum sintering temperature required for the formation of cubic garnet phase revealed the increase in grain size and relatively dense structure with increase of x in Li_7+x La₃Y _x Zr_2-x O₁₂.     

The influence of the method of addition of Al2O3 to 3YSZ material on its thermal and electrical properties

The properties of tetragonal yttria-stabilized zirconia composites with the small addition of alumina (Al₂O₃?Y₂O₃?ZrO₂ composite) obtained on two ways of synthesis were studied in terms of usability for anode materials in solid oxide fuel cell. Both methods were based on citric synthesis: in the first one, Al₂O₃ was coprecipitated with the tetragonal ZrO₂ in the form of citrate by citric acid, while in the second Al₂O₃ was impregnated in the form of aluminium nitrate precursor on tetragonal ZrO₂ matrix. The obtained materials were analysed by X-ray diffraction, dilatometry and impedance spectroscopy. The results of measurements show that regardless of synthesis method, the addition of Al₂O₃ influences the conductivity of samples by increasing their grain boundaries conductivity as an effect of removing of SiO₂ and decreasing of conductivity activation energy. The impregnation of Al₂O₃ on tetragonal ZrO₂ and sintering of this material above shrinking temperature cause, however, radical decrease of porosity of materials, which disqualifies these samples as anode materials. In the case of samples obtained by coprecipitation the significant decrease of porosity is not observed.