Effect of Al-Mo codoping on the structure and ionic conductivity of sol-gel derived Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript> ceramics

Al-Mo codoped Li₇La₃Zr₂O₁₂ ceramics with fine grain were prepared by sol-gel method. The influences of Al-Mo codoping on the structure, microstructure, and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and impedance spectroscopy. The cubic phase Li₇La₃Zr₂O₁₂ has been stabilized by partial substitution of Al for Li and Mo for Zr. Li_6.6-3yAl_yLa₃Zr_1.8Mo_0.2O₁₂ (0?≤?y?≤?0.1) has been sintered at 1040–1060 °C for 3 h. The liquid sintering facilitated its densification. The relative density of the composition with x?=?0.075 was approximately 96.4%. Results indicated that the Al-Mo codoped LLZO synthesized by sol-gel method effectively lowered its sintering temperature, accelerated densification, and improved the ionic conductivity.     

Synthesis,structural and conductive properties of Nd doped garnet-type Li7La3Zr2O12 Li-ion conductor

Garnet type solid electrolyte Li₇La₃Zr₂O₁₂ (LLZO) is the most promising candidate among solid electrolytes for all solid state Li batteries. In this work, small amount of Nd doping (5%–20%) to the garnet structure is proposed to improve its ionic conductivity. Nd doped garnet type solid electrolytes for Li-ion batteries were synthesized through a conventional solid state reaction method. The effect of Nd doping on the microstructure, morphology and ionic conductivity of the LLZO was studied by powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and Electrochemical impedance spectroscopy (EIS) methods. Instead of La whose valence is similar to that of Nd, XRD and Raman analyzes revealed that Nd takes the place of the higher valence element Zr. In order to compensate the valence difference, the ratio of Li increases in the structure. On the other side, results showed that Nd doped LLZO samples formed as a mixture of both tetragonal and cubic phases. According to EIS measurements, among the prepared samples, 5% Nd doped LLZO exhibits the highest ionic conductivity of 2.47 × 10⁻⁶ S cm⁻¹ at room temperature.     

Synthesis and characterization of substituted garnet and perovskite-based lithium-ion conducting solid electrolytes

Titanium, tantalum-substituted Li₇La₃Zr_2-xA_xO₁₂ (LLZO, A?=?Ta, Ti) garnets, and chromium-substituted La_(2/3)-xLi_3xTi_1-yCr_yO₃ (LLTO) perovskites were prepared by a conventional solid-state reaction and the Pechini processes. The desired crystal phases were obtained by varying the calcination temperature and time, as well as the substitution concentration. All samples indicated decomposition of the precursors when heated above 750 °C and formation of the desired phase after heat treatment at higher temperatures. Neutron diffraction data shows the formation of a predominant cubic phase in the case of Ta-LLZO, and monoclinic phase with minor impurity phases for Cr-LLTO. Ionic conductivity for Ti-LLZO (Li₇La₃Zr_1.4Ti_0.6O₁₂), Ta-LLZO (Li_6.03La₃Zr_1.533Ta_0.46O₁₂), and Cr-LLTO (La_(2/3)-xLi_3xTi_0.9Cr_0.1O₃) at room temperature were found to be 5.21?×?10^?6, 1.01?×?10^?6, and 1.2?×?10^?4 S cm^?1, respectively. The activation energies of the compounds were determined from the Arrhenius plot and were 0.44 eV (Ti_0.6-LLZO), 0.54 eV (Ta_0.5-LLZO), and 0.20 eV (Cr_0.1-LLTO).     

Mechanical behavior of Li-ion-conducting crystalline oxide-based solid electrolytes: a brief review

Li-ion-conducting solid electrolytes are receiving considerable attention for use in advanced batteries. These electrolytes would enable use of a Li metal anode, allowing for batteries with higher energy densities and enhanced safety compared to current Li-ion systems. One important aspect of these electrolytes that has been overlooked is their mechanical properties. Mechanical properties will play a large role in the processing, assembly, and operation of battery cells. Hence, this paper reviews the elastic, plastic, and fracture properties of crystalline oxide-based Li-ion solid electrolytes for three different crystal structures: Li_6.19Al_0.27La₃Zr₂O₁₂ (garnet) [LLZO], Li_0.33La_0.57TiO₃ (perovskite) [LLTO], and Li_1.3Al_0.3Ti_1.7(PO₄)₃ (NaSICON) [LATP]. The experimental Young’s modulus value for (1) LLTO is ~?200 GPa, (2) LLZO is ~?150 GPa, and (3) for LATP ~?115 GPa. The experimental values are in good agreement with density functional theory predictions. The fracture toughness value for all three of LLTO, LLZO, and LATP is approximately 1 MPa m^?2. This low value is expected since, they all exhibit at least some degree of covalent bonding, which limits dislocation mobility leading to brittle behavior.     

Challenges regarding thin film deposition of garnet electrolytes for all-solid-state lithium batteries with high energy density

In this work, we studied the deposition of garnet electrolyte thin films in order to realize an all-solid-state battery with high energy density. Therefore, in a first step we investigated the stability of the garnet Li₅La₃Ta₂O₁₂ with the spinel LiCoMnO₄ in order to determine the temperature window for a successful thin film deposition on high-voltage spinels. A mixture of both materials showed a thermal stability up to 600 °C, so that all-solid-state batteries could be realized when the electrolyte is applied at a low deposition temperature. The second part of the work was the thin film deposition of Li₅La₃Ta₂O₁₂ by a sputter deposition process. When a stoichiometric Li₅La₃Ta₂O₁₂ sputter target was used, the surface of the target showed a depletion of lithium after several depositions, which leads to decreasing Li content in the thin films. In order to compensate the lithium loss we enriched the target with LiOH?H₂O. Depositions carried out with the lithium rich target showed the garnet structure on glass substrates after deposition at 500 °C. The garnet structure was observed on Au-coated EN 1.4767 substrates already at a substrate temperature of 400 °C, which is 300 K lower than comparable depositions of Li₇La₃Zr₂O₁₂. These results show that the combination of thin garnet-structured electrolytes and high-voltage spinels is possible.     

Identification of the Li sites in the Li ion conductor, Li6SrLa2Nb2O12, through neutron powder diffraction studies

In this paper a neutron powder diffraction structural study of the Li ion conducting garnet-related system, Li₆SrLa₂Nb₂O₁₂, is reported. The results show that this phase is cubic, space group Ia-3d, and contains Li in two partially occupied crystallographic sites. The first site, Li1, corresponds to the ideal tetrahedral site in the garnet framework and possesses an occupancy of 0.59(1). The second site, Li2, is significantly more distorted and possesses an occupancy of 0.352(3). Compared to the related Li₅La₃Nb₂O₁₂ system, the Li2 site occupancy is greatly increased, while the Li1 site occupancy is reduced. Despite these large differences in site occupancies, the reported conductivities for Li₅La₃Nb₂O₁₂ and Li₆SrLa₂Nb₂O₁₂ are similar, showing the complexities of these new garnet Li ion conductors.     

Investigation on lithium ion conductivity and structural stability of yttrium-substituted Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript>

Advanced Li-air battery architecture demands a high Li⁺ conductive solid electrolyte membrane that is electrochemically stable against metallic lithium and aqueous electrolyte. In this work, an investigation has been carried out on the microstructure, Li⁺ conduction behaviour and structural stability of Li₇La_3-x Y _x Zr₂O₁₂ (x = 0.125, 0.25 and 0.50) prepared by conventional solid-state reaction technique. The phase analysis of Li₇La_3-x Y _x Zr₂O₁₂ (x = 0.125, 0.25 and 0.50) sintered at 1200 °C by powder X-ray diffraction (PXRD) and Raman confirms the formation of high Li⁺ conductive cubic phase (\( Ia\overline{3}d \)) lithium garnets. Among the investigated lithium garnets, Li₇La_2.75Y_0.25Zr₂O₁₂ sintered at 1200 °C exhibits a maximized room temperature total (bulk + grain boundary) Li⁺ conductivity of 3.21 × 10^?4 S cm^?1 along with improved relative density of 96 %. The preliminary investigation on the structural stability of Li₇La_2.75Y_0.25Zr₂O₁₂ in the solutions of 1 M LiCl, dist. H₂O and 1 M LiOH at 30 °C/50 °C indicates that the Li₇La_2.75Y_0.25Zr₂O₁₂ is relatively stable against 1 M LiCl and dist. H₂O. Further electrochemical investigation is essential for practical application of Li₇La_2.75Y_0.25Zr₂O₁₂ as protective solid electrolyte membrane in aqueous Li-air battery.     

Preparation of dense La<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>Ga<Subscript>0.8</Subscript>Mg<Subscript>0.2</Subscript>O<Subscript>3-δ</Subscript> with high ionic conductivity by solid-state synthesis

The results of a systematic investigation on the effects of processing steps, via solid-state reactions, on structural phase characteristics and ionic conductivity of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ solid electrolyte are reported. The main purpose of this work is to establish an optimized route for obtaining good densification and high ionic conductivity of this solid electrolyte. Processing routes with three successive calcinations at 1250 °C followed by attrition milling (R1), and with two sequences of calcination at 1350 °C with intermediary attrition milling (R2) give rise to near full density at 1450 °C sintering temperature. The rate of grain growth is fast when the relative density reaches 95%. Elemental mapping reveals uniform distribution of the constituents in the matrix along with La₄Ga₂O₉, LaSrGa₃O₇ and sub-micrometer MgO grains at grain boundaries. The ionic conductivity of grains remains unchanged with the processing route and sintering profile. The blocking effect of charge carriers at grain boundaries decreases with increasing the dwell temperature.     

The effect of Ca2+ in Li0.24+xLa0.59−xCaxTiO3-LaPO4 system

Li_0.2375+xLa_0.5875−xCa_xTiO₃-LaPO₄ fast ionic conductor was synthesized by high temperature solid-state reaction. A.C. impedance measurements show that the compositions of system have better conductivities in low doping content of Ca²⁺, but the conductivity goes down from 1.039·10⁻⁴ Scm⁻¹ to 1.173·10⁻⁵ Scm⁻¹ with increasing the content of Ca²⁺. The activation energy is about 20 kJ·mol⁻¹ in the temperature range of 25–400 °C. X-ray powder diffraction shows that the doping Ca²⁺ would not affect the structure of compositions in the system. The main phase is β-Li_0.24+xLa_0.59−xCa_xTiO₃ perovskite solid solution, LaPO₄ as a second phase also can be found. With the increasing content of Ca²⁺ (x>0.05), another phase CaTiO₃ appears obviously. IR measurement also indicates that the structure of compositions in the system would not be affected by Ca²⁺ doping. The decomposition voltage of Li_0.24+xLa_0.59−xCa_xTiO₃-LaPO₄ keeps on 1.6 V.     

Effect of molybdenum on Li<Subscript>2</Subscript>Mn<Subscript>4</Subscript>O<Subscript>9</Subscript> for rechargeable lithium ion batteries

Li₂Mn₄O₉ and molybdenum-doped Li₂Mn₄O₉ have been prepared by simple solid-state method. Molybdenum is used as a dopant since it is resistant to both corrosion and high-temperature creep deformation. The structural, morphological, and electrical performances of the samples have been analyzed. The material exhibits a cubic structure with the fd3m space group. Using EDAX, the chemical compositions of the samples have been identified. The dc electrical conductivity of the Mo-doped (LM2) sample is found to be increased to 7.44?×?10^?6 S cm^?1 at 393 K. The enhanced electrical property of the molybdenum-doped Li₂Mn₄O₉ reveals it as a feasible cathode material for rechargeable Li-ion batteries.     

Lithium garnet oxide dispersed polymer composite membrane for rechargeable lithium batteries

Free-standing composite polymer membranes comprising of high molecular weight poly (ethylene oxide) (PEO) complexed with lithium perchlorate (LiClO₄) and Li₆La₂BaTa₂O₁₂ (LLBTO) garnet oxide as filler were developed via standard solution-casting method. The as-synthesized composite membranes were investigated through powder x-ray diffraction (PXRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and impedance spectroscopy techniques for their phase, thermal, morphological, and electrical properties, respectively. The lithium ion conductivity of polymer composite membranes consisting of PEO₈/LiClO₄ with various weight percents (5, 10, 15, 20, 25, and 30) of LLBTO were evaluated. We demonstrated a significant enhancement in Li⁺ conductivity with the addition of LLBTO to the polymer-lithium salt complex. Among the investigated membranes, the composite containing 20 LLBTO wt% garnet oxide exhibits maximized room temperature (30 °C) Li⁺ conductivity of 2.03 × 10^?4 S cm^?1 and electrochemical stability greater than 4.5 V.     

Thermal properties and ionic conductivity of Li<Subscript>1,3</Subscript>Ti<Subscript>1,7</Subscript>Al<Subscript>0,3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> solid electrolytes sintered by field-assisted sintering

Li_1,3Ti_0,7Al_0,3(PO₄)₃ (LATP) powder was obtained by a conventional melt-quenching method and consolidated by field-assisted sintering technology (FAST) at different temperatures. Using this technique, the samples could be sintered to relative densities in the range of 93 to 99 % depending on the sintering conditions. Ionic and thermal conductivity were measured and the results are discussed under consideration of XRD and SEM analyses. Thermal conductivity values of 2 W/mK and ionic conductivities of 4?×?10^?4 Scm^?1 at room temperature were obtained using relatively large particles and a sintering temperature of 1000 °C at an applied uniaxial pressure of 50 MPa.     

XRD,XPS, SEM/EDX and broadband impedance spectroscopy study of pyrophosphate (LiFeP2O7 and Li0.9Fe0.9Ti0.1P2O7) ceramics

LiFeP₂O₇ and Li_0.9Fe_0.9Ti_0.1P₂O₇ were synthesised by solid-state reaction and ceramics were sintered. The structure of compounds was studied in the temperature range 300–700 K by X-ray diffraction. Ceramics’ surfaces were investigated by scanning electron microscope. Binding energies of Fe 2p, P 2p and O 1s core levels at ceramics’ surfaces have been determined by X-ray photoelectron spectroscopy and different valence states of Fe and P were detected. Elemental compositions of the compounds were studied by energy dispersive X-ray spectrometer. Impedance spectroscopy was performed in the frequency range 10 Hz–3 GHz and in the temperature interval 400–700 K. The changes of the activation energy of ionic conductivity at 528 and 550 K for LiFeP₂O₇ and Li_0.9Fe_0.9Ti_0.1P₂O₇, respectively, were found. The phenomena can be related to disordering in the unit cells of the compounds.     

Crystal structure analysis of Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> powder prepared by wet chemical reaction and solid-state reaction by using X-ray diffraction (XRD)

Lithium phosphate (Li₃PO₄) is one of the promising solid electrolyte materials for lithium-ion battery because of its high ionic conductivity. A crystalline form of Li₃PO₄ had been prepared by two different methods. The first method was wet chemical reaction between LiOH and H₃PO₄, and the second method was solid-state reaction between Li₂O and P₂O₅. Crystal structure of Li₃PO₄ white powder had been investigated by using an X-ray diffraction (XRD) analysis. The results show that Li₃PO₄ prepared by wet chemical reaction belongs to orthorhombic unit cell of β-Li₃PO₄ with space group Pmn2₁. Meanwhile, Li₃PO₄ powder prepared by solid-state reaction belongs to orthorhombic unit cell of γ-Li₃PO₄ with space group Pmnb and another unknown phase of Li₄P₂O₇. The impurity of Li₄P₂O₇ was due to phase transformation in solid state reaction during quenching of molten mixture from high temperature. Ionic conductivity of Li₃PO₄ prepared by solid-state reaction was ～3.10^?7 S/cm, which was higher than Li₃PO₄ prepared by wet chemical reaction ～4.10^?8 S/cm. This increasing ionic conductivity may due to mixed crystal structures that increased Li-ion mobility in Li₃PO₄.     

Sol-gel synthesis of the lithium-ion conducting perovskite La0.57Li0.3TiO3 effect of synthesis and thermal treatments on the structure and conducting properties

The lithium ionic conducting perovskite La_0.57Li_0.3TiO₃ has been synthesised via a sol-gel method at a temperature of 700 °C. The crystallinity of the product can be greatly increased by further heat treatment at 1000 °C. In this paper the product of the sol-gel synthesis is compared with the product of conventional solid-state synthesis, and the influence of the synthesis method as well as of quenching on the crystal structure and ionic conductivity has been studied. AC-impedance measurements show two contributions to the ionic conductivity, which can be adscribed to intergranular and intragranular effects, respectively. A lower intergranular resistivity is observed for sol-gel samples, while quenching mainly affects the materials prepared by solid-state reaction. The crystal structure of the material prepared by the sol-gel method is identical to that of the material prepared by the solid state reaction, although the synthesis temperature is nearly 600 °C lower. A tetragonal superstructure is observed when either type of material is slowly cooled from 1300 °C. Quenching from the same temperature results in the suppression of that superstructure. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Swift heavy ion irradiation-induced modifications in structural and electrical properties of Y3+-substituted yttrium iron garnet

The consequences of 50 MeV Li³⁺ ion irradiation (fluence: 5×10¹³ ions/cm²) on the structural and electrical properties of the Y_3+xFe_5?xO₁₂ (x=0.0, 0.2, 0.4 and 0.6) garnet system have been investigated over the temperature range of 300–673 K. It is found that the percentage formation of an additional yttrium orthoferrite phase observed along with the bcc garnet phase considerably reduces for x=0.4 and 0.6 compositions after swift heavy ion (SHI) irradiation. The nature of thermal variation of DC resistivity curves for x=0.0 and 0.2 compositions is different from that for x=0.4 and 0.6 compositions. The SHI irradiation influences the magnitude of DC resistivity and conduction mechanism for the single-phase compositions while for mixed-phase compositions they remain unaffected. The results have been explained in the light of replacement of magnetic (5μ_B), smaller (0.64 Å), Fe³⁺ ion by nonmagnetic (0μ_B), larger (0.89 Å), Y³⁺ ion, the presence of the yttrium orthoferrite phase and swift heavy ion irradiation-induced paramagnetic centers in the system.     

Effect of V5+ in the complex Li3xLa2/3−xTiO3-LaPO4 system

Lithium fast ion conductors of the composition Li_0.3La_2/3Ti_0.7P_0.3−xV_xO_3.3 (LTV) based on mixtures of Li_3xLa_2/3−xTiO₃ and LaPO₄ were prepared by solid state reaction at high temperature (≈ 1300 °C). AC impedance measurements indicate total conductivities of about 1 × 10⁻⁴ Scm⁻¹ for compositions of x=0∼0.3 at room temperature with an activation energy of ≈18 kJ·mol⁻¹ in the temperature range from 30 to 400 °C. X-ray powder diffraction patterns showed that the LTV system is composed of Li_3xLa_2/3−xTiO₃ perovskite solid solution and LaP_1−xV_xO₄ solid solution.     

High-rate Li4Ti5O12/C composites as anode for lithium-ion batteries

The Li₄Ti₅O₁₂/C composites were synthesized by a simple solid-state reaction at 800 °C for 12 h by using Super P® conductive carbon black as carbon source. X-ray diffraction analysis shows that the Li₄Ti₅O₁₂ with 0, 5, 7.5, and 10 wt% carbon shows similar patterns with cubic spinel structure. Scanning electron microscope shows that Li₄Ti₅O₁₂ aggregated seriously, but the aggregation was inhibited by the addition of Super P® carbon. The results indicate that the addition of 5 wt% carbon during sintering and a further 5 wt% carbon during slurry preparation shows the best rate capability of 110 mAh/g when the cells were charge/discharged at 10 C rate. The comparison of the charge–discharge curves shows that the higher rate improvement should further decrease the particle size of LTO or improve the conductivity of LTO itself.     

Effect of lanthanum ions on magnetic properties of Y3Fe5O12 nanoparticles

Lanthanum ion (La³⁺)-substituted garnet nanoparticles Y_3?x La _x Fe₅O₁₂ (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) were fabricated by a sol–gel method. Their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectrum. The XRD results show that samples of Y_3?x La _x Fe₅O₁₂ (0.0 ≤ x ≤ 0.8) are all single phase and the sizes of particles range from 32 to 65 nm. Those of Y₂LaFe₅O₁₂ consisted of peaks from garnet and LaFeO₃ structures. Compared to pure YIG, the saturation magnetization is larger when the La concentration x = 0.2. However, with increasing La concentration (x), it decreases obviously. Meanwhile, may be due to the enhancement of the surface spin effects, the saturation magnetization rises as the particle size is increased. Different from the pure YIG, the Mössbauer spectra of Y_2.8La_0.2Fe₅O₁₂ and Y_2.2La_0.8Fe₅O₁₂ are composed of four sets of six-line hyperfine patterns. The results tell us that the substitution of La³⁺ ions with large ionic radius (1.061 Å) will give rise to a microscopic structure distortion of the a- and d-sites to different degrees, and the Zeeman sextets from a- and d-sites begin to split into two sub-sextets, which is helpful to explain the phenomenon observed in the study of the magnetic property.     

Chloride spinels: A new group of solid lithium electrolytes

The chloride spinels Li₂MCl₄ with M = Mg, Mn, Fe and Cd show very high lithium ionic conductivity in the solid state. The ionic conductivity in the compounds under investigation was established with the help of emf measurements. The specific conductivities measured by both frequency response analysis and the four probe ac method are 1.3 Ω^?1 · cm^?1 for Li₂CdCl₄, and about 0.9Ω^?1 · cm^?1 for Li₂MnCl₄, Li₂MgCl₄, and Li₂FeCl₄ at 773 K. There are several indications that the ternary chlorides become highly disordered at elevated temperatures. Thus the Arrhenius plots, i.e. In σ · T vs 1/T-curves, exhibit significant bends, the slopes below the transition temperature being considerably higher than those above.