Low temperature synthesis of Li5La3Nb2O12 with cubic garnet-type structure by sol–gel process

A cubic Li₅La₃Nb₂O₁₂ phase with a garnet framework was synthesized by the sol–gel process, in which lithium hydroxide, niobium oxide and acetic lanthanum were used as starting materials, while water was used as solvent. Pure garnet-like Li₅La₃Nb₂O₁₂ powders were obtained after heating the gel precursor at 700 °C for 6 h with 10 % excess lithium salt. The calcination temperature is nearly 250 °C lower than that by the solid state reaction. The phase transforms from cubic to tetragonal symmetry with loss of lithium at 717 °C, but the garnet framework remains stable to above 900 °C. A pellet annealed at 900 °C for 6 h had a room-temperature Li⁺-ion conductivity σ_Li (22 °C) = 1.0 × 10^?5 S cm^?1, a little higher than that attained by solid-state synthesis. The Li₅La₃Nb₂O₁₂ compound was chemically stable against two commonly used cathode materials, LiMn₂O₄ and LiCoO₂, up to 900 °C and against metallic lithium.     

Syntheses and Characterization of Novel Perovskite-Type LaScO3-Based Lithium Ionic Conductors

Perovskite-type lithium ionic conductors were explored in the (Li_xLa_1−x/3)ScO₃ system following their syntheses via a high-pressure solid-state reaction. Phase identification indicated that a solid solution with a perovskite-type structure was formed in the range 0 ≤ x < 0.6. When x = 0.45, (Li_0.45La_0.85)ScO₃ exhibited the highest ionic conductivity and a low activation energy. Increasing the loading of lithium as an ionic diffusion carrier expanded the unit cell volume and contributed to the higher ionic conductivity and lower activation energy. Cations with higher oxidation numbers were introduced into the A/B sites to improve the ionic conductivity. Ce⁴⁺ and Zr⁴⁺ or Nb⁵⁺ dopants partially substituted the A-site (La/Li) and B-site Sc, respectively. Although B-site doping produced a lower ionic conductivity, A-site Ce⁴⁺ doping improved the conductive properties. A perovskite-type single phase was obtained for (Li_0.45La_0.78Ce_0.05)ScO₃ upon Ce⁴⁺ doping, providing a higher ionic conductivity than (Li_0.45La_0.85)ScO₃. Compositional analysis and crystal-structure refinement of (Li_0.45La_0.85)ScO₃ and (Li_0.45La_0.78Ce_0.05)ScO₃ revealed increased lithium contents and expansion of the unit cell upon Ce⁴⁺ co-doping. The highest ionic conductivity of 1.1 × 10⁻³ S cm⁻¹ at 623 K was confirmed for (Li_0.4Ce_0.15La_0.67)ScO₃, which is more than one order of magnitude higher than that of the (Li_xLa_1−x/3)ScO₃ system.     

Effect of sintering on the ionic conductivity of garnet-related structure Li5La3Nb2O12 and In- and K-doped Li5La3Nb2O12

Garnet-structure related metal oxides with the nominal chemical composition of Li₅La₃Nb₂O₁₂, In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ and K-substituted Li_5.5La_2.75K_0.25Nb₂O₁₂ were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li₅La₃Nb₂O₁₂. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In³⁺(r_CN6: 0.79 Å) for smaller Nb⁵⁺ (r_CN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K⁺ for La³⁺ and In³⁺ for Nb⁵⁺ in Li₅La₃Nb₂O₁₂ exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ exhibits the highest bulk lithium ion conductivity of 1.8×10⁻⁴ S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10⁻¹⁰-10⁻⁷ cm²/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li₅La₃Nb₂O₁₂ was found to be unsuccessful under the investigated conditions.     

Nitridated mesoporous Li4Ti5O12 spheres for high-rate lithium-ion batteries anode material

Nitridated mesoporous Li₄Ti₅O₁₂ spheres were synthesized by a simple ammonia treatment of Li₄Ti₅O₁₂ derived from mesoporous TiO₂ particles and lithium acetate dihydrate via a solid state reaction in the presence of polyethylene glycol 20000. The carbonization of polyethylene glycol could effectively restrict the growth of primary particles, which was favorable for lithium ions diffusing into the nanosized TiO₂ lattice during the solid state reaction to form a pure phase Li₄Ti₅O₁₂. After a subsequent thermal nitridation treatment, a high conductive thin TiO _x N _y layer was in situ constructed on the surface of the primary nanoparticles. As a result, the nitridated mesoporous Li₄Ti₅O₁₂ structure, possessing shorter lithium-ion diffusion path and better electrical conductivity, displays significantly improved rate capability. The discharge capacity reaches 138 mAh?g^?1 at 10 C rate and 120 mAh?g^?1 at 20 C rate in the voltage range of 1–3 V.     

Magnetische Eigenschaften von Ti3−xMxO5-Phasen (M = V3+, Cr3+, Nb4+)

Magnetic Properties of Ti_3?xM_xO₅ Phases (M = V³⁺, Cr³⁺, Nb⁴⁺) The magnetic properties of Ti_3?xV_xO₅, Ti_3?xCr_xO₅, and Ti_3?xNb_xO₅ phases are reported. In the case of V³⁺ and Cr³⁺ the magnetic leaping-temperature decreases, however Nb⁴⁺ shift the phase-transition towards higher temperatures. All samples show a “memory-effect” in magnetic properties, i. e. the results of heating- and cooling-cycles are higher susceptibilities of the α-phase of Ti₃O₅. Endowed Ti₃O₅ phases show for the α- and β-Ti_3?xM_xO₅ til the leap Curie-Weiss characteristic in 1/X vs. temperature measurements. Exception is β-Ti_3?xNb_xO₅, its susceptibility is independend of the temperature up to x ? 0.3.     

Preparation and Some Properties of Lithium Vanadium Bronzes

Lithium vanadium bronzes with composition formula Li_xV₂O₅ (0.04 ≤ × ≤ 0.92) have been prepared by solid‐state reaction at 650 °C in argon atmosphere. The obtained products were characterized by X‐ray powder diffraction and IR spectroscopy. The results reveal that four phases are present in the range from x = 0.04 to 0.92, namely α, β, β′, and γ phase. The magnetic susceptibility for the investigated bronzes was measured using the conventional Gouy's method. The values of the effective magnetic moments, as calculated from experimental data, indicate the presence of V⁴⁺ ions in all bronze samples. The electrical conductivity as a function of temperature and lithium content was measured in the temperature range from room temperature to 483 K. The electrical conductivity of the bronzes is found to be affected by lithium content. The values of the electrical conductivity increase with temperature for the prepared samples and both electronic and ionic conduction are discussed.     

Structural and Electrochemical Study of Vanadium‐Doped TiO2 Ramsdellite with Superior Lithium Storage Properties for Lithium‐Ion Batteries

Titanium‐oxide‐based materials are considered attractive and safe alternatives to carbonaceous anodes in Li‐ion batteries. In particular, the ramsdellite form TiO₂(R) is known for its superior lithium‐storage ability as the bulk material when compared with other titanates. In this work, we prepared V‐doped lithium titanate ramsdellites with the formula Li_0.5Ti_1?xV_xO₂ (0≤x≤0.5) by a conventional solid‐state reaction. The lithium‐free Ti_1?xV_xO₂ compounds, in which the ramsdellite framework remains virtually unaltered, are easily obtained by a simple aqueous oxidation/ion‐extraction process. Neutron powder diffraction is used to locate the Li channel site in Li_0.5Ti_1?xV_xO₂ compounds and to follow the lithium extraction by difference‐Fourier maps. Previously delithiated Ti_1?xV_xO₂ ramsdellites are able to insert up to 0.8 Li⁺ per transition‐metal atom. The initial gravimetric capacities of 270 mAh g^?1 with good cycle stability under constant current discharge conditions are among the highest reported for bulk TiO₂‐related intercalation compounds for the threshold of one e^? per formula unit.     

Analysis of the phase composition and homogeneity of ferrite lithium-substituted powders by the thermomagnetometry method

In the present work, the possibilities of application of the thermomagnetometry TG(M)/DTG(M) method for estimation of the phase homogeneity of end products of synthesis at different stages of ferritizing annealing are considered on the example of solid-state synthesis of Li_0.5(1?x)Fe_2.5?0.5xZn_xO₄ and Li_0.5(1 + x)Fe_2.5?1.5xTi_xO₄ (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) lithium-substituted ferrospinels. Results of thermomagnetometric analysis are compared with XRD data. It is shown that the resolution of the TG(M)/DTG(M) method on two orders exceeds capabilities of the traditional XRD method. Considerable influence of both intermediate grinding and mixing of samples and concentration of an inducted impurity on the homogeneity of the synthesized powders is confirmed.     

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.     

Synthesis of Li3Ni x V2−x (PO4)3/C cathode materials and their electrochemical performance for lithium ion batteries

Li₃Ni _x V_2?x (PO₄)₃/C (x?=?0, 0.02, 0.04 and 0.06) samples have been synthesized via an improved sol–gel method. X-ray diffraction patterns indicate that the structure of the prepared samples retains monoclinic, and the single phase has not been changed with Ni doping. From the analysis of electrochemical performance, the Li₃Ni_0.04?V_1.96(PO₄)₃/C sample exhibits the best electrochemical property. It delivers a discharge capacity of 112.1 mAh?g^?1 with capacity retention of 95.2 % over 300 cycles at 10 C rate in the range of 3.0–4.8 V; cyclic voltammetry and electrochemical impedance spectra testing further prove that the electrochemical reversibility and lithium ion diffusion behavior of Li₃V₂(PO₄)₃ have also been effectively improved through Ni doping.     

Influence of Ca2+ substitution on thermal,structural, and conductivity behavior of Bi1−xCaxFeO3−y (0.40 ≤ x ≤ 0.55)

Bi_1?xCa_xFeO_3?y (0.40 ≤ x ≤ 0.55) perovskite oxides have been synthesized by solid-state reaction method to study their properties as a cathode material for intermediate temperature solid oxide fuel cells. The as prepared samples were characterized by X-ray diffraction, differential thermal analyzer/thermogravimetry, dilatometer, and impedance spectroscopy to study their structural, thermal, and electrical properties. The Rietveld refinement results confirmed that all the samples exhibit tetragonal structure with P4mm space group. In addition to this, sample x = 0.55 exhibits Ca₂Fe₂O₅ as a secondary phase. It has been observed that lattice parameters decrease with increase in calcium content. The thermal expansion coefficient and ionic conductivity increases with increase in calcium content up to x = 0.50. The highest ionic conductivity is observed for Bi_0.5Ca_0.5FeO_3?y i.e. 1.71 × 10^?2 S cm^?1.     

Effects of phenolic resin on the electrochemical performance of Li3V2(PO4)3/C cathode materials

As a kind of lithium-ion battery cathode material, monoclinic lithium vanadium phosphate/carbon Li₃V₂(PO₄)₃/C was synthesized by adopting phenolic resin as carbon source, both for reducing agent and coating material. The crystal structure and morphology of the samples were characterized through X-ray diffraction (XRD) and scanning electron microscope (SEM). Galvanostatic charge-discharging experiments and electrochemical impedance spectrum (EIS) were utilized to determine the electrochemical insertion properties of the samples. XRD data revealed that phenolic resin does not change the crystal structure of Li₃V₂(PO₄)₃/C. Furthermore, the morphology of grains and the electronic conductivity of Li₃V₂(PO₄)₃/C were improved. Galvanostatic charge-discharging and EIS results showed that the optimal electrochemical properties and the minimum charge-transfer resistance of Li₃V₂(PO₄)₃/C can be reached when added by 5 wt.% of redundant carbon (except the carbon needed to reduce V⁵⁺ to V³⁺). The initial discharge capacity is 128.4 mAh g^?1 at 0.2 C rate and 101.2 mAh g^?1 at 5 C in the voltage range of 3.0～4.3 V.     

Enhanced ionic conductivity in novel nanocomposite gel polymer electrolyte based on intercalation of PMMA into layered LiV3O8

In the present work, a novel polymer electrolyte based on poly(methyl methacrylate) (PMMA)/layered lithium trivanadate (LiV₃O₈) nanocomposite has been investigated. X-ray diffraction (XRD) study shows that d-spacing is increased from 6.3?±?0.1 Å to 12.8?±?0.1 Å upon intercalation of the polymer into the layered LiV₃O₈. Room temperature ionic conductivity of the obtained nanocomposite gel polymer electrolyte is found to be superior to that of conventional PMMA-based gel polymer electrolyte. Enhancement in ionic conductivity of the nanocomposite gel electrolyte is attributed to the formation of a two-dimensional channel as a result of decreased interaction between Li⁺ and V₃O ₈ ^? layers as confirmed by FTIR. SEM results show aggregation of nanocomposite particles resulting from extension of some of the polymer chains from interlayer to the edge providing paths for Li⁺ ion transport. Interfacial stability of nanocomposite gel electrolyte is also found to be better than that of the conventional PMMA-based gel polymer electrolyte.     

Synthesis, Phase Diagram, and Conductivity Study in a La0.5+x+yLi0.5−3xTi1−3yMn3yO3System

The stoichiometry, polymorphysm, and electrical behaviour of solid solutions of La_0.5+y+xLi_0.5−3xTi_1−3yMn_3yO₃with perovskite-type structure have been studied. Data are given in the form of a solid solution triangle, phase diagrams, XRD patterns for the three polymorphs, A,β, and C, composition-dependence of their lattice parameters, and ionic and electronic conductivity plots. Microstruture and composition were studied by SEM/EDS and electron probe microanalysis. These compounds are mixed conductors. Ionic conductivity decreases when the amount of lithium diminishes and electronic conductivity increases with manganese content.     

Effect of hydration on conductivity of Ba4La x Ca2 − x Nb2O11 + 0.5x (x = 0.5, 1, 1.5, 2) phases

Substitution of Ca by La in initial cubic double perovskite Ba₄(Ca₂Nb₂)O₁₁[VO]₁ allowed obtaining phases with a similar structure with a lower content of structural oxygen vacancies, Ba₄(La _x Ca_{2 ? x} Nb₂)O_{11 + 0.5x} [VO]_{1 ? 0.5x} (x = 0.5, 1, 1.5, 2). The impedance technique was used to measure the temperature dependences of conductivity in the atmosphere of dry and humid air. Transport numbers determined using the EMF method in an oxygen-air and water steam concentration cells point to the predominantly hole nature of conductivity in the high-temperature region (T > 600°C) and to predominance of proton conductivity in the low-temperature region. Activation energies of hole and proton conductivity were calculated. Thermogravimetric measurements were carried out under heating from 25 to 1000°C with simultaneous mass-spectrometric determination of evolved H₂O and CO₂. The properties of the studied Ba₄(La _x Ca_{2 ? x} Nb₂)O_{11 + 0.5x} (x = 0.5, 1, 1.5, 2) phases were compared with the earlier studied Ba_{4 ? x} La _x (Ca₂Nb₂)O_{11 + 0.5x} phases with similar lanthanum content.     

Lithium garnet based free-standing solid polymer composite membrane for rechargeable lithium battery

Electrolytes with high lithium-ion conductivity, better mechanical strength and large electrochemical window are essential for the realization of high-energy density lithium batteries. Polymer electrolytes are gaining interest due to their inherent flexibility and nonflammability over conventional liquid electrolytes. In this work, lithium garnet composite polymer electrolyte membrane (GCPEM) consisting of large molecular weight (W_avg ~?5?×?10⁶) polyethylene oxide (PEO) complexed with lithium perchlorate (LiClO₄) and lithium garnet oxide Li_6.28Al_0.24La₃Zr₂O₁₂ (Al-LLZO) is prepared by solution-casting method. Significant improvement in Li⁺ conductivity for Al-LLZO containing GCPEM is observed compared with the Al-LLZO free polymer membrane. Maximized room temperature (30 °C) Li⁺ conductivity of 4.40?×?10^?4 S cm^?1 and wide electrochemical window (4.5 V) is observed for PEO₈/LiClO₄?+?20 wt% Al-LLZO (GCPEM-20) membrane. The fabricated cell with LiCoO₂ as cathode, metallic lithium as anode and GCPEM-20 as electrolyte membrane delivers an initial charge/discharge capacity of 146 mAh g^?1/142 mAh g^?1 at 25 °C with 0.06 C-rate.     

Intercalation processes influence the structure and electrophysical properties of lithium-conducting compounds having defect perovskite structure

The structural features and electrophysical properties of lithium-conducting compounds having defect perovskite structure based on Li_0.5La_0.5Nb₂O₆ and Li_0.5La_0.5TiO₃ were studied using X-ray diffraction and synchrotron analyses, potentiometry, and complex impedance spectroscopy. Intercalated lithium was found to differently influence ion conductance in titanium- and niobium-containing materials. This difference was found to arise from the structural features of the materials. The systems studied have high chemical diffusion coefficients of lithium (D _Li⁺ = 1 × 10⁻⁶ cm²/s for Li_0.5La_0.5Nb₂O₆ and D _Li⁺ = 3.3 × 10⁻⁷ cm²/s for Li_0.5La_0.5TiO₃).     

Effect of vanadium doping on electrochemical performance of LiMnPO4 for lithium-ion batteries

A series of LiMn_1-x V _x PO₄ samples have been synthesized successfully via a conventional solid-state reaction method. The active materials are characterized by x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy. The electrochemical performances of the samples are tested using cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge measurement techniques. It is confirmed that the samples are in single phase when the content of vanadium (x) is lower than 0.05. If that content is higher than 0.1, the samples are shown to contain an additional conductive phase of Li₃V₂(PO₄)₃. The vanadium doping significantly enhances the electrochemical properties of LiMnPO₄. It is underlined that the optimal ratio for a low-vanadium doping with the best electrochemical performance is 0.1 and this material exhibits a corresponding initial charge and discharge capacity of 98.9 and 98.1 mAh g^?1 at 0.1 C under 50 °C. The capacity retention is higher than 99 % after 30 cycles. The dramatic electrochemical improvement of the LiMnPO₄ samples is ascribed to the strengthened ability of lithium-ion diffusion and enhanced electronic conductivity for the V-doped samples.     

Preparation and characterization of NASICON type Li+ ionic conductors

The new scandium/aluminium co-doped NASICON phases Li_1?+?x Al _y Sc _x???y Ti_2???x (PO₄)₃ (x?=?0.3, y?=?0,0.1,0.2,0.3) were prepared by mechanical milling followed by annealing of the mixtures at 950 °C. X-ray diffraction of all samples showed the formation of NASICON structure with space group R-3c along with a minor impurity. Rietveld refinement of the X-ray data was performed to identify the structural variation. Doping with Sc³⁺ caused elongation of a- and c- axes for all the compounds when compared with undoped LiTi₂(PO₄)₃. The compound Li_1.3Sc_0.3Ti_1.7(PO₄)₃ showed a maximum of a?=?8.5504(7), c?=?20.986(3) Å at room temperature and exhibited highest coefficient of thermal expansion. The highest ionic conductivity (σ), 7.28×10^?4 S cm^?1 was observed for Li_1.3Sc_0.3Ti_1.7(PO₄)₃, two orders of magnitude higher than for the undoped phase.     

Structural characterization and physical properties of the system La1.33LixCrxTi2−xO6

New phases which arise from partial substitution of Ti⁴⁺ by Cr³⁺ and Li⁺ of the compound La_2/3TiO₃ have been obtained, giving rise to the series La_1.33Li_xCr_xTi_2−xO₆ (x=0.66, 0.55 and 0.44). These phases adopt a perovskite-type structure as deduced from their structural characterization. Rietveld's analyses of neutron diffraction data show that it is orthorhombic (S.G. Pbnm) with ordered domains. Conductivity has been examined by complex impedance spectroscopy and it increases with increasing lithium and chromium content. These materials behave as mixed conductors with low activation energies. Magnetic susceptibility variation with temperature shows antiferromagnetic interactions at the lowest temperatures.