Correlation between Li+ adsorption capacity and the preparation conditions of spinel lithium manganese precursor

Spinel lithium manganese oxides can be used as Li⁺ adsorbent with topotactical extraction of lithium. In this paper, the solid state methods were introduced to prepare spinel lithium manganese precursors with Li₂CO₃ and LiOH·H₂O as different Li sources. The Li⁺ uptake was studied to clarify the correction between Li⁺ adsorption capacity and the preparation conditions of precursors, including different Li sources, Li/Mn mole ratios and heating time. The results indicated that the Li⁺-extracted materials prepared with LiOH·H₂O and MnCO₃ usually have higher Li⁺ adsorption capacity than Li₂CO₃ and MnCO₃, and an ascending trend was found in Li⁺ uptake with increasing Li/Mn mole ratio in the preparation of the precursor, but it is not proportional. The Mn₂O₃ impurities could be the primary reason for decreasing Li⁺ adsorption capacity. Furthermore, it is concluded that the Li⁺-extracted materials obtained from spinel manganese oxides synthesized with Li/Mn = 1.0 can serve as selective Li⁺ absorbents due to its high selectivity and large adsorption capacity.     

Synthesis of LiNi0.6Co0.2Mn0.2O2 cathode material by a carbonate co-precipitation method and its electrochemical characterization

Using Na₂CO₃ and Me(NO₃)₂ (Me = Ni, Co and Mn) as starting materials, the precursor of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material for lithium rechargeable batteries has been synthesized by carbonate co-precipitation. The precursor was mixed with Li₂CO₃ and heated in air. Thermogravimetric analysis (TG–DTA), laser particle size analysis, X-ray diffraction (XRD) and electron scanning microscopy (SEM) were employed to study the reaction process and the structures of the powders. The D₅₀ of precursor was 2.509 μm and the distribution was relatively narrow. The optimum calcination temperature was 850–900 °C. Galvanostatic cell cycling and cyclic voltammetry were also used to evaluate the electrochemical properties. The initial discharge capacity for the powders calcined at 900 °C was about 180 mA h/g at room temperature when cycled between 2.8 and 4.3 V at 0.2 C rate.     

Development of perovskite and phase transition in lead cobalt niobate modified lead zirconate titanate system

Ferroelectric lead zirconate titanate–lead cobalt niobate ceramics with the formula (1 − x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Co_1/3Nb_2/3)O₃ where x = 0.0–0.5 were fabricated using a high temperature solid-state reaction method. The formation process, the structure and homogeneity of the obtained powders have been investigated by X-ray diffraction method as well as the simultaneous thermal analysis of both differential thermal analysis (DTA) and thermogravimetry analysis (TGA). It was observed that for the binary system (1 − x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Co_1/3Nb_2/3)O₃, the change in the calcination temperature is approximately linear with respect to the PCoN content in the range x = 0.0–0.5. In addition, X-ray diffraction indicated a phase transformation from a tetragonal to a pseudo-cubic phase when the fraction of PCoN was increased. The dielectric permittivity is remarkably increased by increasing PCoN concentration. The maximum value of remnant polarization P_r (25.3 μC/cm²) was obtained for the 0.5PZT–0.5PCoN ceramic.     

Ultrafast synthesis of Li1 + αV3O8 gel precursors for lithium battery applications

A versatile route has been developed to synthesize the Li_1 + αV₃O₈ gel precursor 50 times faster than the standard path without heating by using H₂O₂ and V₂O₅ and lithium salts as precursors. Upon heat treatment it leads to stoechiometric Li_1.1V₃O₈ with an electrochemical behavior similar to the one observed from the standard material. The role of the pH and the nature of the counter ion on the structural type and the morphology of the condensed Li_1 + αV₃O_8,nH₂O compound have been investigated. pH close to the zero charge point (≈ 2) lead to intercalated Li_xV₂O₅,nH₂O type gels whereas at pH 4 condensation drives to hewettite like structures.     

Effects of Li2CO3 as a secondary lithium source on the LiFePO4/C composites prepared via solid-state method

Li₂CO₃ was used as the secondary lithium source for the synthesis of LiFePO₄/C composites via a solid-state reaction method by adopting Li₃PO₄ as the main lithium source. The main purpose of using Li₂CO₃ is to compensate for the partial lithium loss during the sintering while reducing the usage of excess Li₃PO₄. In this study, the effects of Li₂CO₃ amount on the phase, structural and electrochemical properties of LiFePO₄/C material were systematically investigated. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), constant-current charge–discharge test and cyclic voltammetry (CV). The results showed that by adding an appropriate amount of Li₂CO₃, the impurities, e.g. Li₃PO₄, normally appearing in the final product, could be excluded. It was found that LiFePO₄/C with Li₂CO₃ in 6% excess (vs. stoichiometric LiFePO₄) exhibited the best electrochemical performance, which delivered initial discharge capacities of 141.7, 125.2, 119.9 and 108.9 mAh g^?1, respectively, at 0.5, 1, 2 and 5C rates. The capacity was reduced to 113.4 mAh g^?1 after 50 cycles at 2C rate, with capacity retention rate of 94.6%.     

Synthesis and electrochemical characterization of M2Mn3O8 (M = Ca,Cu) compounds and derivatives

M₂Mn₃O₈ (M = Ca²⁺, Cu²⁺) compounds were synthesized and characterized in lithium cells. The M²⁺ cations, which reside in the van der Waals gaps between adjacent sheets of Mn₃O₈⁴⁻, may be replaced chemically (by ion-exchange) or electrochemically with Li. More than 7 Li⁺/Cu₂Mn₃O₈ may be inserted electrochemically, with concomitant reduction of Cu²⁺ to Cu metal, but less Li can be inserted into Ca₂Mn₃O₈. In the case of Cu²⁺, this process is partially reversible when the cell is charged above 3.5 V vs. Li, but intercalation of Cu⁺ rather than Cu²⁺ and Li⁺/Cu⁺ exchange occurs during the subsequent discharge. If the cell potential is kept below 3.4 V, the Li in excess of 4 Li⁺/Cu₂Mn₃O₈ can be cycled reversibly. The unusual mobility of + 2 cations in a layered structure has important implications both for the design of cathodes for Li batteries and for new systems that could be based on M²⁺ intercalation compounds.     

A single-crystal study of the electrochemically Li-ion intercalated spinel-type Li4Ti5O12

Single crystals of Li_4 + xTi₅O₁₂ were prepared by means of electrochemical Li-ion intercalation technique using parent Li₄Ti₅O₁₂ single crystals. The obtained Li_4 + xTi₅O₁₂ (x = 1.35) crystallizes in the cubic spinel-related type structure, space group Fd3?m, and lattice parameters of a = 8.346(2) Å and V = 581.3(5) Å³ and Z = 8. The Li-ion intercalated sites were successfully determined to be both the 8a and 16c sites by using the difference Fourier synthesis map. The structure was determined by single-crystal X-ray structure analysis and refined to the conventional value of R = 3.7% for 132 independent observed reflections. The chemical composition has been determined to be Li_5.35Ti₅O₁₂ from the result of site-population refinements. In addition, theoretical electron density distributions and total energy were calculated for three postulated compounds of “Li_4.5Ti_4.5O₁₂” and “Li_4.5 + xTi_4.5O₁₂” with x = 1.5 and 3.0.     

The electronic behaviors of visible light sensitive Nb2O5/Cr2O3/carbon clusters composite materials

Nano-sized Nb₂O₅/Cr₂O₃/carbon clusters composite material has been successfully obtained by the calcination of a Nb(HC₂O₄)₅/CrCl₃/starch complex under an argon atmosphere. The compositions of the resulting composite materials were determined using ICP, elemental analysis and surface characterization by XRD and TEM. The UV–VIS and XPS spectra of the composites were also obtained. ESR spectral examinations suggest the possibility of an electron transfer in the process of Nb₂O₅ → carbon clusters → Cr₂O₃. The reduction reaction of methylene blue with the resulting composite material has also been examined.     

Fabrication and luminescent properties of Al2O3:Cr3 + microspheres via a microwave solvothermal route followed by heat treatment

AlOOH:Cr^3 + powders were synthesized via a microwave solvothermal route at 433 K for 30 min and were used as the precursor and template for the preparation of γ-Al₂O₃:Cr^3 + by thermal transformation at 773 K for 2 h in air. The obtained γ-Al₂O₃ based powders were microspheres with an average diameter about 1.9 μm. Photoluminescence (PL) spectra showed that the Al₂O₃:Cr^3 + particles presented a symmetric broad R band at 696 nm without appreciable splitting when excited at 462 nm. It is shown that the 0.04 mol% of doping concentration of Cr^3 + ions in γ-Al₂O₃:Cr^3 + is optimum. According to Dexter's theory, the critical distance between Cr^3 + ions for energy transfer was determined to be 47.54 Å. Based on the corresponding PL spectrum, full width at half maximum (FWHM) of Al₂O₃:Cr^3 + (0.04 mol%) was calculated to be 3.35 nm.     

Ionic conductivities of various GeS2-based oxy-sulfide amorphous materials prepared by melt-quenching and mechanical milling methods

We have previously explored the Li₂S + GeS₂ + GeO₂ system to determine the specific effect of added GeO₂ to a base 0.5Li₂S + 0.5GeS₂ glass composition. In this new study, we report the conductivities of these Li₂S + GeS₂ + GeO₂ glasses over their full glass forming range to more fully optimize the ionic conductivity. In addition to this study of bulk glasses, we have also studied the effect of creating powders of the bulk glasses and compared the conductivities of the bulk glasses to those of compacted powders. This latter study is relevant due to the fact that in most battery applications powders are the form of choice in forming battery stacks. Since we used the mechanical milling technique to produce the powders, we further extended this study to determine the extent to which the amorphous range could be expanded using the mechanical milling technique. Having access to these extended compositional range materials, we were able to extend all examinations of the role of composition, powder size, and compaction of the sample on the conductivity and we compared these results to those of the bulk glass samples.     

Experimental and simulated performance of lithium niobate 1–3 piezocomposites for 2 MHz non-destructive testing applications

Lithium niobate piezocomposites have been investigated as the active element in high temperature resistant ultrasonic transducers for non-destructive testing applications up to 400 °C. Compared to a single piece of lithium niobate crystal they demonstrate shorter pulse length by 3×, elimination of lateral modes, and resistance to cracking. In a 1–3 connectivity piezocomposite for high temperature use (200–400 °C), lithium niobate pillars are embedded in a matrix of flexible high temperature sealant or high temperature cement.In order to better understand the design principles and constraints for use of lithium niobate in piezocomposites experiments and modelling have been carried out. For this work the lithium niobate piezocomposites were investigated at room temperature so epoxy filler was used. 1–3 connectivity piezocomposite samples were prepared with z-cut lithium niobate, pillar width 0.3–0.6 mm, sample thickness 1–4 mm, pillar aspect ratio (pillar height/width) 3–6, volume fraction 30 and 45%. Operating frequency was 1–2 MHz.Experimental measurements of impedance magnitude and resonance frequency were compared with 3-D finite element modelling using PZFlex. Resonance frequencies were predicted within 0.05 MHz and impedance magnitude within 2–5% for samples with pillar aspect ratio ⩾3 for 45% volume fraction and pillar aspect ratio ⩾6 for 30% volume fraction. Laser vibrometry of pulse excitation of piezocomposite samples in air showed that the lithium niobate pillars and the epoxy filler moved in phase. Experiment and simulation showed that the thickness mode coupling coefficient k_t of the piezocomposite was maintained at the lithium niobate bulk value of approximately 0.2 down to a volume fraction of 30%, consistent with calculations using the (Smith and Auld, 1991 [1]) model for piezocomposites.     

Structural and electrochemical characterization of mesoporous thin films of Nb2xV2 − 2xO5 upon lithium intercalation

Nb_2xV_2 ? 2xO₅ (0 ≤ x ≤ 1) powders were prepared by a synthetic route based on the inorganic polymerization of alkoxy-choride precursors and characterized by a combination of X-ray diffraction, ⁵¹V and ⁹³Nb NMR and Raman spectroscopy. Amorphous mesoporous thin films of similar compositions were successfully prepared by a modified Evaporation Induced Self Assembly method using polystyrene-b-polyethyleneoxide diblock copolymer as structuring agent. The electrochemical properties of the mesoporous films upon lithium insertion–deinsertion are investigated by cyclic voltammetry. This study highlights the advantages of such nanoarchitecture in terms of increased capacity to insert lithium.     

Effect of milling time on the properties of Pb(Mg1/3Nb2/3)O3 ceramics using the starting precursors PbO and MgNb2O6

Lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN) ceramics were prepared from the columbite method using calcined powders of various milling time (24–96 h). The effects on the grain size and dielectric properties of the ceramics were investigated. The results show that dielectric properties of ceramics are strongly influenced by the milling time of the starting precursors. Higher percentage of perovskite phase was found in the ceramics that was milled longer and thus the dielectric constant was found to increase when compared to the conventional 24 h milled results. Moreover, milling time also affected the particle size of the starting precursors and that of PMN powders. Therefore, milling time did not only affect the particle size of PMN powders but also the resultant grain size and the formation of perovskite phase, consequently affecting the dielectric constant of the ceramics.     

Determination of the diffusion coefficient of lithium ions in nano-Si

The diffusion coefficients of lithium ions (D_Li⁺) in nano-Si were determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). D_Li⁺ values are estimated to be ~ 10^? 12 cm² s^? 1 and exhibit a “W” type varying with the lithium concentration in silicon. Two minimum regions of D_Li⁺ (at Li_2.1 ± 0.2Si and Li_3.2 ± 0.2Si) are found, which probably result from two amorphous compositions (a-Li₇Si₃ and a-Li₁₃Si₄). Besides the two minimum regions, one maximum D_Li⁺ is observed at Li₁₅Si₄, corresponding to the crystallization of highly lithiated amorphous Li_xSi.     

Li4Ti5O12/Ag composite as electrode materials for lithium-ion battery

The Li₄Ti₅O₁₂/Ag composites were prepared by thermal decomposition of AgNO₃ added to Li₄Ti₅O₁₂ powders. The influence of the Ag contents and the mixing media on the particle size, morphology and electrochemical performance of Li₄Ti₅O₁₂/Ag composites were investigated. The highest discharge capacity of the Li₄Ti₅O₁₂/Ag composite reached at the 5 wt.% of Ag content. Compared with alcohol medium, distilled water as mixing medium presented the Li₄Ti₅O₁₂/Ag composite with higher specific capacity and better cycling performance, leading to a reversible capacity after 50 cycles of 184.2 mAh/g with a capacity degradation of 3.31% compared to the second cycle at 2 C rate.     

Lithium-ionic diffusion and electrical conduction in the Li7La3Ta2O13 compounds

The electrical properties and the mechanism of lithium ionic diffusion in the Li₇La₃Ta₂O₁₃ compounds were investigated. The bulk and total conductivity at 300 K of the Li₇La₃Ta₂O₁₃ compound are about 3.3 × 10^? 6 S/cm and 2.6 × 10^? 6 S/cm, respectively. The activation energy of bulk and total conductivity is in the range of 0.38–0.4 eV. A prominent internal friction peak in Li₇La₃Ta₂O₁₃ compounds was observed around 280 K at 0.5 Hz, which is actually composed of two subpeaks (P₁ peak at lower temperature and P₂ peak at higher temperature). From the shift of peak position with frequency, the activation energy of 1.0 eV and the pre-exponential factor of relaxation time in the order of 10^? 18–10^? 21 s were obtained if one assumes Debye relaxation processes. These values of relaxation parameters strongly suggest the existence of interaction between the relaxation species (here lithium ions or vacancies). Based on the coupling model, the relaxation activation energies are deduced as 0.45 eV and the pre-exponential factor of relaxation time as 10^? 15 s. Judging from these relaxation parameters and the similarity of structure between Li₇La₃Ta₂O₁₃ and Li₅La₃Ta₂O₁₂ compounds, the P₁ and P₂ peaks are suggested to be related with the lithium ionic diffusion between 48g?48g and 24d?48g.     

Electrochemical and electrical properties of Nb- and/or C-containing LiFePO4 composites

A study of LiFePO₄-based electrodes prepared through various synthesis conditions is presented. From X-Ray diffraction, high resolution transmission electron microscopy, electrochemical Li⁺ extraction/insertion and electrical conductivity data we conclude that the use of starting precursors such as Li₂CO₃, FeC₂O₄·2H₂O and/or Nb(OC₆H₅)₅ produces LiFePO₄-based composites containing significant amounts of carbon. We never succeeded in doping LiFePO₄ with Nb to yield Li_1−xNb_xFePO₄ but produced, instead, crystalline β-NbOPO₄ and/or an amorphous (Nb, Fe, C, O, P) “cobweb” around LiFePO₄ particles which is responsible for superior electrochemical activity. AC-conductivity measurements conclude to a total electrical conductivity of ∼10^− 9 S cm^− 1 at 25 °C with an activation energy of ca. 0.65 eV for pure LiFePO₄ and LiFePO₄/β-NbOPO₄ composites. C-containing LiFePO₄ samples, including those that were tentatively but unsuccessfully doped with Nb, are much more conductive (up to 1.6 · 10^− 1 S cm^− 1) with an activation energy ΔE∼0.08 eV.     

Synthesis and crystallographic studies of garnet-related lithium-ion conductors Li6CaLa2Ta2O12 and Li6BaLa2Ta2O12

High-purity specimens of Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂ have been successfully synthesized by solid-state reactions. The analytical chemical compositions of these samples were in good agreement with the nominal compositions of Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂. The Rietveld refinements verified that these compounds have the garnet-type framework structure with the lattice constants of a = 12.725(2) Å for Li₆CaLa₂Ta₂O₁₂ and a = 13.001(4) Å for Li₆BaLa₂Ta₂O₁₂. All of the diffraction peaks of X-ray powder diffraction patterns were well indexed on the basis of cubic symmetry with space group Ia-3d. To make a search for Li sites, the electron density distributions were precisely examined by using the maximum entropy method. Li⁺ ions occupy partially two types of crystallographic site in these compounds: (i) tetrahedral 24d sites, and (ii) distorted octahedral 96h sites, the latter of which are the vacant sites of the ideal garnet-type structure. The present Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂ samples exhibit the conductivity σ = 2.2 × 10^? 6 S cm^? 1 at 27 °C (E_a = 0.50 eV) and σ = 1.3 × 10^? 5 S cm^? 1 at 25 °C (E_a = 0.44 eV), respectively.     

Phase evolution and morphology of nanocrystalline BaCe0.9Er0.1O3−δ proton conducting oxide synthesised by a novel modified solution combustion route

Pure BaCeO₃ and 10 mol% Er₂O₃ doped BaCeO₃ (BCE) was synthesised by a novel modified solution combustion synthesis (MCS) route wherein the pH of the precursor solution was varied and the phase formation and morphology were compared with those obtained in conventional solution combustion synthesis (SCS). X-ray diffraction (XRD) studies confirmed the presence of the undesirable BaCO₃ phase in the calcined powders prepared using SCS route whereas the powders synthesised with the modified (MCS) route exhibited a single perovskite phase after calcination. Variation in the pH of the precursor solution resulted in a morphology change from a mix of irregular and globular at pH 4 to more spherical at pH 6 and 8. Fourier transform infrared spectroscopy (FT-IR) studies revealed that calcination time has more pronounced effect on phase formation than calcination temperature. A calcination time of 10 h at 1000 °C resulted in negligible amount of BaCO₃. Such prolonged calcination treatment resulted in substantial grain growth in the SCS sample while the MCS samples were still in the nanocrystalline form. Absence of the ceria peak (464 cm^–1) in the Raman spectra confirmed the presence of a single perovskite BaCeO₃ phase in the sintered pellets as well.