Fabrication of all-solid-state rechargeable lithium-ion battery using mille-feuille structure of Li0.35La0.55TiO3

A mille-feuille structure, which comprises both sides of dense layer are sandwiched by porous layers, is one of the promising structures for 3-dimensional (3D) all-solid-state battery. The porous layers should have 3-dimensionally ordered macroporous structure to obtain large contact area between electrolyte and electrode. Li_0.35La_0.55TiO₃ (LLT) solid electrolyte with the mille-feuille structure was fabricated by the suspension filtration method. The dense layer was sintered well, no grain boundary was observed. The porous layers contacted well with dense layer. Thicknesses of dense and porous layers were 30 and 26 μm, respectively. To check compatibility of the mille-feuille LLT with all-solid-state Li ion battery, chronopotentiometry of symmetric cell with LiMn₂O₄/mille-feuille LLT/LiMn₂O₄ configuration was measured. Charge and discharge currents were clearly observed, indicating that the cell was successfully operated.     

Correlation between micro-structural properties and ionic conductivity of Li1.5Al0.5Ge1.5(PO4)3 ceramics

We report on the structure and lithium ion transport properties of Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP). This material is commercially available and is prepared as amorphous powders via a flame spray technique called Flash Creation Method (FCM). We crystallize and sinter the amorphous powders at different temperatures in order to alter grain size and grain boundary properties. The structure is then characterized by means of powder X-ray diffraction, atomic force microscopy, scanning electron microscopy and transmission electron microscopy with energy dispersive X-ray spectroscopy. AC impedance spectroscopy is used to study lithium ion transport. A maximum total conductivity of 2 × 10⁻⁴ S cm⁻¹ at room temperature is found for a sample sintered at 750 °C for 2 h. In order to distinguish between grain and grain boundary contributions to the impedance spectra, equivalent circuit fits are carried out. The results are analysed in the framework of the classical brick layer model and of a finite-element approach taking into account non-ideal grain contacts. Our experimental results for the grain and grain boundary resistances are in good agreement with the predications of the finite-element approach.     

Compatibility of LiCoO2 and LiMn2O4 cathode materials for Li0.55La0.35TiO3 electrolyte to fabricate all-solid-state lithium battery

In order to improve performance of all-solid-state lithium ion battery with honeycomb structure, a compatibility of two commonly used cathode materials, LiCoO₂ and LiMn₂O₄, to Li_0.55La_0.35TiO₃ (LLT) solid electrolyte was studied. LiCoO₂/honeycomb LLT and LiMn₂O₄/honeycomb LLT half cells were fabricated by the impregnation of mixture of the cathode material with its precursor sol into honeycomb holes followed by the calcination. Impurity phases were observed at interface between LiCoO₂ and honeycomb LLT, while no impurity phase was confirmed in the case of LiMn₂O₄. In half cell test, the LiMn₂O₄/honeycomb LLT cell showed about 6 times larger discharge capacity than the LiCoO₂/honeycomb LLT cell, because of high internal resistance of the LiCoO₂/honeycomb LLT cell caused by the impurity phases. It can be said that the formation of low resistance interface at active material/electrolyte is one of the most important key to improve performance of the all-solid-state battery. Using LiMn₂O₄ instead of LiCoO₂, better interface between cathode material and LLT was obtained.     

Fabrication of all solid-state lithium-ion batteries with three-dimensionally ordered composite electrode consisting of Li0.35La0.55TiO3 and LiMn2O4

A composite electrode between three-dimensionally ordered macroporous (3DOM) Li_0.35La_0.55TiO₃ (LLT) and LiMn₂O₄ was fabricated by colloidal crystal templating method and sol–gel process. A close-packed PS beads with the opal structure was prepared by filtration of a suspension containing PS beads. Li–La–Ti–O sol was injected by vacuum impregnation process into the voids between PS beads, and then was heated to form 3DOM-LLT. Three-dimensionally ordered composite material consisting of LiMn₂O₄ and LLT was prepared by sol–gel process. The prepared composite was characterized with SEM and XRD. All solid-state Li-ion battery was fabricated with the LLT–LiMn₂O₄ composite electrode as a cathode, dry polymer electrolyte and Li metal anode. The prepared all solid-state cathode exhibited a volumetric discharge capacity of 220 mAh cm⁻³.     

Sintering and ionic conductivity of 8YSZ and CGO10 electrolytes with small addition of Fe2O3: A comparative study

Two typical electrolytes, i.e., 8YSZ (8 mol% yttria-stabilized zirconia) and CGO10 (10 mol% Gd-doped ceria), with Si contents of ∼30 ppm and ≥500 ppm were prepared, whose grain-boundary (GB) conductivities should be controlled by intrinsic (space-charge layer) and extrinsic (resistive siliceous films) effects, respectively. 1 at% FeO_1.5 was loaded into these materials via a conventional mixed-oxide method. A comparative study was carried out to demonstrate how 1 at% Fe addition affected these materials with different levels of SiO₂ impurities with respect to sintering, GB and GI (grain interior) conductivities. FeO_1.5 was found to be a sintering promoter for both 8YSZ and CGO10 ceramics, but it is more effective to enhance the densification of ceria-based electrolytes. A reduction in sintering temperature of ∼200 °C for 1 at% Fe-doped CGO10 was achieved compared with ∼110 °C reduction for the 8YSZ with the same amount of Fe loading. The effect of FeO_1.5 loading on the electrical conduction was found to be different, depending significantly on the impurity level and the types of electrolytes. In general, the loading of FeO_1.5 is positive for ceria-based ceramics since FeO_1.5 has a scavenging effect on SiO₂ impurity with little effect on the GI conduction. Although the scavenging behavior of FeO_1.5 was also found in the impure 8YSZ, it led to a significant reduction in the GI conductivity.     

Al-doped Li7La3Zr2O12 synthesized by a polymerized complex method

Li₇La₃Zr₂O₁₂ electrolytes doped with different amounts of Al (0, 0.2, 0.7, 1.2, and 2.5 wt.%) were prepared by a polymerized complex (Pechini) method. The influence of aluminum on the structure and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X-ray diffraction (XRD), impedance spectroscopy, scanning electron microscopy (SEM), and thermal dilatometry. It was found that even a small amount of Al (e.g. 0.2 wt.%) added to Li₇La₃Zr₂O₁₂ can greatly accelerate densification during the sintering process. SEM micrographs showed the existence of a liquid phase introduced by Al additions which led to the enhanced sintering rate. The addition of Al also stabilized the higher conductivity cubic form of Li₇La₃Zr₂O₁₂ rather than the less conductive tetragonal form. The combination of these two beneficial effects of Al enabled greatly reduced sintering times for preparation of highly conductive Li₇La₃Zr₂O₁₂ electrolyte. With optimal additions of Al (e.g. 1.2 wt.%), Li₇La₃Zr₂O₁₂ electrolyte sintered at 1200 °C for only 6 h showed an ionic conductivity of 2.0 × 10⁻⁴ S cm⁻¹ at room temperature.     

Development of Ag-(BaO)0.11(Bi2O3)0.89 composite cathodes for intermediate temperature solid oxide fuel cells

The electrochemical performances of Ag-(BaO)_0.11(Bi₂O₃)_0.89 (BSB) composite cathodes on Ce_0.8Sm_0.2O_1.9 electrolytes have been investigated for intermediate temperature solid oxide fuel cells (ITSOFCs) using ac impedance spectroscopy from 500 to 700 °C. Results indicate that the electrochemical properties of these composites are quite sensitive to the composition and the microstructure of the cathode. The optimum BSB addition (50% by volume) to Ag resulted in about 20 times lower area specific resistance (ASR) at 650 °C. The ASR values for the Ag50-BSB and Ag cathodes were 0.32 and 6.5 Ω cm² at 650 °C, respectively. The high performances of Ag-BSB cathodes are determined by the high catalytic activity for oxygen dissociation and ionic conductivity of BSB, and by the excellent catalytic activity for oxygen reduction of silver. The maximum power density of the Ag50-BSB cathode was 224 mWcm⁻² at 650 °C, which classify this composite as a promising material for ITSOFC.     

Fuel-flexible operation of a solid oxide fuel cell with Sr0.8La0.2TiO3 support

Solid oxide fuel cells with Sr_0.8La_0.2TiO₃ anode-side supports, Ni- Sm-doped ceria adhesion layer, Ni- Y₂O₃-stabilized ZrO₂ (YSZ) anode active layer, YSZ electrolyte, and La_0.8Sr_0.2MnO₃(LSM)–YSZ cathode are described. These cells are stable in simulated natural gas at current densities as low as 0.2 A cm⁻². This represents much-improved stability against coking in natural gas, compared with conventional Ni–YSZ anode-supported SOFCs which rapidly coke, even at higher current densities. Cell operation in H₂ fuel with 50–100 ppm, H₂S results in an initial decrease in cell power density, but no long-term degradation occurs and full recovery to the initial performance level is observed after dry H₂ fuel flow is restored. Degradation is not observed during or after seven redox cycles between H₂ and air.     

Mixed-metal Li3N-based systems for hydrogen storage: Li3AlN2 and Li3FeN2

The hydrogen storage systems Li₃AlN₂ and Li₃FeN₂ were synthesized mechanochemically by two different routes. In each case an intermediate material formed after milling, which transformed into Li₃MN₂ (M = Al or Fe) upon annealing. The synthesis route had a measurable effect on the hydrogen storage properties of the material: Li₃AlN₂ prepared from hydrogenous starting materials (LiNH₂ and LiAlH₄) performed better than that synthesized from non-hydrogenous materials (Li₃N and AlN). For both Li₃AlN₂ materials, the hydrogen storage capacity and the absorption kinetics improved significantly upon cycling. Ti-doped Li₃AlN₂ synthesized from LiNH₂ and LiAlH₄ showed the best hydrogen storage characteristics of all, with the best kinetics for hydrogen uptake and release, and the highest hydrogen storage capacity of 3.2 wt.%, of which about half was reversible. Meanwhile, Li₃FeN₂ synthesized from Li₃N and Fe displayed similar kinetics to that synthesized from Li₃N and Fe_xN (2 ≤ x ≤ 4), but demonstrated lower gravimetric hydrogen storage capacities. Li₃FeN₂ displayed a hydrogen uptake capacity of 2.7 wt.%, of which about 1.5 wt.% was reversible. For both Li₃AlN₂ and Li₃FeN₂, doping with TiCl₃ resulted in enhancement of hydrogen absorption kinetics. This represents the first study of a ternary lithium-transition metal nitride system for hydrogen storage.     

Advance fuel cells using Al2O3-nNaAlO2 composite as ion-conducting membrane

In present work, we reported an novel oxide-salt Al₂O₃NaAlO₂ composite, which was prepared by mixing Al₂O₃ and Na₂CO₃ two phase materials in different weight ratio, and then sintering at 1100 °C. The X-ray diffraction pattern, scanning-electron microscope and impedance spectra are applied to characterize the crystal structure, morphology and electrical properties of the Al₂O₃NaAlO₂ composite. The Al₂O₃NaAlO₂ composite as electrolyte membrane was sandwiched by two pieces of Ni_0.8Co_0.15Al_0.05Li-oxide (NCAL) electrode layer to construct advanced fuel cell. Optimizing the weight ratio of Al₂O₃ and NaAlO₂, such cell delivered an highest power density of 789 mW/cm² and an open circuit voltage (V_oc) of 1.13 V at 575 °C. The superior performance is mainly due to the excellent ion-conducting of Al₂O₃NaAlO₂ composites and the outstanding catalysis activity of the NCAL eletrodes. The EIS results revealed that the Al₂O₃NaAlO₂ composite possessed superior ionic conductivity of 0.121 S/cm at 575 °C. The interfacial effects between oxide-salt two phase including space-charge and structural misfit at the interface region dominated the ion transport for Al₂O₃NaAlO₂ composite.     

The presence of nanostructured Al2O3 in PMMA-based gel electrolytes

Gel polymer electrolytes (GPEs)-based on poly(methyl methacrylate) PMMA and propylene carbonate (PC) with LiClO₄ or NaClO₄ salt are prepared using either the commercial product Superacryl^® or directly from the monomer and AIBN (2,2′-azobis(isobutyronitrile)) initiator. The nanostructured aluminum oxide is added to the mentioned systems in various ratios. Solutions of liquid PC–perchlorate and polymer electrolytes are compared with focus on ionic conductivity. The ionic conductivity of polymer-based electrolytes is significantly influenced (of almost by one half order of magnitude at room temperature) by the addition of nanosized Al₂O₃. On the contrary, the conductivity of liquid electrolytes is decreased by the addition of alumina in the blend. A slight enhancement of mechanical properties is observed.     

Structural and electrical properties of (Ba1−xSrx)(Zr0.9M0.1)O3, M = Y, La, solid solutions

The aim of the work was to study the structural and electrical properties of the (Ba_1−xSr_x)(Zr_0.9Y_0.1)O₃ and (Ba_1−xSr_x)(Zr_0.9Y_0.1)O₃ solid solutions. The powders of different strontium content (x = 0, 0.03, 0.05 and 0.1) were prepared by a thermal decomposition of organo-metallic precursors containing ethylenediaminetetraacetate acid. Some parameters describing stability and transport properties of the perovskite structure, such as tolerance factor, specific free volume and global instability index, were calculated. It was found that the introduction of strontium into both solid solutions caused the increase of specific free volume and global instability index—these structures became a little less stable but, on the other hand, better ionic conductor. All samples were cubic perovskite and the substitution of strontium for barium caused the decrease of respective lattice parameters. Electrical conductivity measurements were performed by the d.c. four-probe method in controlled gas atmospheres containing Ar, air, H₂ and/or H₂O at the temperature from 300 to 800 °C. It was found that the conductivity depended on a chemical composition of the samples and the atmosphere. In general, the electrical conductivity was higher in wet atmospheres which contained oxygen, being in accordance with the model of a proton transport in the perovskite structure which assumed the presence of the oxygen vacancy. The solid solution containing 5 mol.% of strontium showed the highest conductivity and the lowest activation energy of conductivity regardless of the atmospheres.     

Electrical conductivity of the Li2SO4Li2CO3 system

With a view to improving the electrical conductivity of Li₂SO₄ at the lowest possible temperature, Li₂CO₃ was added in the ratios of 10 – 90 mol% and its conductivity was measured. The system Li₂SO₄Li₂CO₃ has its eutectic at a composition of 60:40 mol%: this composition has the maximum conductivity of the series, 2.43 × 10^?3 (ohm cm)^?1 at 723 K. The high conductivity may be due to the quasiliquid state of the mobile species within the sublattice. Further, the addition of 5 mol% of LiCl to the eutectic gave rise to an increase in the conductivity, 1.13 × 10^?3 (ohm cm)^?1 at 553 K. This may be suitable as an electrolyte for application to power sources.     

Solid oxide fuel cell cathodes prepared by infiltration of LaNi0.6Fe0.4O3 and La0.91Sr0.09Ni0.6Fe0.4O3 in porous yttria-stabilized zirconia

SOFC composite electrodes of yttria-stabilized zirconia (YSZ) and either LaNi_0.6Fe_0.4O₃ (LNF) or La_0.91Sr_0.09Ni_0.6Fe_0.4O₃ (LSNF) were prepared by infiltration to a loading of 40 wt% of the perovskite into porous YSZ using aqueous solutions of the nitrate salts. XRD measurements indicated that the perovskite structures were formed following calcination at 850 °C, at which temperature the LNF and LSNF form small particles that coat the YSZ pores. Heating to 1100 °C causes the particles to form a dense film over the YSZ but caused no solid-state reaction. Calcination of an LNF-YSZ composite to 1200 °C led to an expansion of the LNF lattice, suggesting introduction of Zr(IV) into the perovskite; further heating to 1300 °C caused the formation of La₂Zr₂O₇. For 850 °C calcination, the electrode performance of both LNF-YSZ and LSNF-YSZ composites was similar to that reported for composites of YSZ and La_0.8Sr_0.2FeO₃ (LSF), with a current-independent impedance of approximately 0.1 Ω cm² at 700 °C in air. For 1100 °C calcination, both LNF-YSZ and LSNF-YSZ composites exhibited impedances that decreased strongly under both anodic and cathodic polarization. The implications of these results for preparing electrodes based on LNF and LSNF are discussed.     

Characterization of the interface between LiCoO2 and Li7La3Zr2O12 in an all-solid-state rechargeable lithium battery

The interfacial layer formed between a lithium-ion conducting solid electrolyte, Li₇La₃Zr₂O₁₂ (LLZ), and LiCoO₂ during thin film deposition was characterized using a combination of microscopy and electrochemical measurement techniques. Cyclic voltammetry confirmed that lithium extraction occurs across the interface on the first cycle, although the nonsymmetrical redox peaks indicate poor electrochemical performance. Using analytical transmission electron microscopy, the reaction layer (∼50 nm) was analyzed. Energy dispersive X-ray spectroscopy revealed that the concentrations of some of the elements (Co, La, and Zr) varied gradually across the layer. Nano-beam electron diffraction of this layer revealed that the layer contained neither LiCoO₂ nor LLZ, but some spots corresponded to the crystal structure of La₂CoO₄. It was also demonstrated that reaction phases due to mutual diffusion are easily formed between LLZ and LiCoO₂ at the interface. The reaction layer formed during high temperature processing is likely one of the major reasons for the poor lithium insertion/extraction at LLZ/LiCoO₂ interfaces.     

Mechanism of vacuum-annealing defects and its effect on release behavior of hydrogen isotopes in Li2TiO3

Li₂TiO₃ is one of the most promising candidates among solid breeder materials. However, defects introduced into Li₂TiO₃ will act as the strong trapping sites for tritium. In the present study, mechanism of vacuum-annealing defects and its effect on release behavior of hydrogen isotopes in Li₂TiO₃ were investigated by means of X-ray diffraction, Raman spectroscopy, electron spin resonance and thermal desorption spectroscopy. The color of samples becomes dark blue and the defects were found to be introduced into Li₂TiO₃ when annealed in vacuum. This color change suggests the change from Ti⁴⁺ to Ti³⁺ due to decrease in oxygen content. The color recovers to white again after annealing in air. X-ray diffraction and Raman spectroscopy results indicate that there are no modifications on Li₂TiO₃ crystal phases, but on crystallinity. The main vacuum-annealing defects are E-centers and no other obvious types of defects were observed from electron spin resonance. Based on the experimental results, the production of defects by annealing in vacuum should be satisfied to the following conditions: (1) Li₂TiO₃ has been exposed in air more than 1 day; (2) Li₂TiO₃ must be annealed at the temperature higher than 300 °C; (3) Li₂TiO₃ should be annealed in vacuum lower than 10 Pa. E-centers formed under vacuum-annealing processes have considerable effects on release behavior of hydrogen isotopes investigated by thermal desorption spectroscopy and further should be considered in future fusion reactor. The present work gives some suggestions for future fusion reactors: (1) Li₂TiO₃ should be preserved in vacuum or kept from water vapor; (2) Li₂TiO₃ should be annealed at high temperature to remove the adsorbed water before loading into the facility, and must be finished within two days to avoid defects coming from reduction; (3) Li₂TiO₃ should be improved by adding more oxygen or other elements to refrain from defects introduced by reduction reaction.     

A novel bilayered Sr0.6La0.4TiO3/La0.8Sr0.2MnO3 interconnector for anode-supported tubular solid oxide fuel cell via slurry-brushing and co-sintering process

Considering that conventional lanthanum chromate (LaCrO₃) interconnector is hard to be co-sintered with green anode, we have fabricated a novel bilayered interconnector which consists of La-doped SrTiO₃ (Sr_0.6La_0.4TiO₃) and Sr-doped lanthanum manganite (La_0.8Sr_0.2MnO₃). Sr_0.6La_0.4TiO₃ is conductive and stable in reducing atmosphere, locating on the anode side; while La_0.8Sr_0.2MnO₃ is on the cathode side. A slurry-brushing and co-sintering method is applied: the Sr_0.6La_0.4TiO₃ and La_0.8Sr_0.2MnO₃ slurries are successively brushed onto green anode specimen, followed by co-firing course to form a dense bilayered Sr_0.6La_0.4TiO₃/La_0.8Sr_0.2MnO₃ interconnector. For operating with humidified hydrogen and oxygen at 900 °C, the ohmic resistances between anode and cathode/interconnector are 0.33 Ω cm² and 0.186 Ω cm², respectively. The maximum power density is 290 mW cm⁻² for a cell with interconnector, and 420 mW cm⁻² for a cell without it, which demonstrates that nearly 70% of the power output can be achieved using this bilayered Sr_0.6La_0.4TiO₃/La_0.8Sr_0.2MnO₃ interconnector.     

Order-disorder transformation and enhanced oxide-ionic conductivity of (Sm1−xDyx)2Zr2O7 ceramics

(Sm_1−xDy_x)₂Zr₂O₇ (0 ≤ x ≤ 1) ceramics are prepared by a solid state reaction process at 1973 K for 10 h in air. (Sm_1−xDy_x)₂Zr₂O₇ (0 ≤ x ≤ 0.3) ceramics exhibit a single phase of pyrochlore-type structure, while (Sm_1−xDy_x)₂Zr₂O₇ (0.5 ≤ x ≤ 1.0) possess a defective fluorite-type structure. The full width at half-maxima in the Raman spectra increases with increasing Dy content, which indicates that the degree of structural disorder increases as the Dy content increases. The ionic conductivity of (Sm_1−xDy_x)₂Zr₂O₇ ceramics is investigated by impedance spectroscopy over a frequency range of 0.2 Hz to 8 MHz in the temperature range of 873-1173 K in air and hydrogen atmospheres, respectively. The ionic conductivity has a maximum near the phase boundary between the pyrochlore- and the defective fluorite-type phases under identical temperature levels. The ionic conductivity is determined by the degree of structural disorder or unit cell free volume, which is depending on the Dy content. As the ionic conductivity in the hydrogen atmosphere is almost the same as that obtained in air, the conduction of (Sm_1−xDy_x)₂Zr₂O₇ is purely ionic with negligible electronic conduction.     

Electrical properties of Mg-doped Gd0.1Ce0.9O1.95 under different sintering conditions

Ce_0.9Gd_0.1O_1.95 with various Mg doping contents was synthesized by citric acid-nitrate low temperature combustion process and sintered under different conditions. The crystal structures, microstructures and electrical properties were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and ac impedance spectroscopy. Low solubility of Mg²⁺ in Ce_0.9Gd_0.1O_1.95 lattice was evidenced by XRD and FESEM micrographs. The samples sintered at 1300 °C exhibited the higher total conductivity than those sintered at 1100 and 1500 °C, with the maximum value of 1.48 × 10⁻² S cm⁻¹ (measured at 600 °C) at the Mg doping content of 6 mol%, corresponding to the minimum total activation energy (E_tol) of 0.84 eV (150–400 °C). The effect of Mg doping on the electrical conductivity was significant particularly at higher sintering temperatures. At the sintering temperature of 1500 °C, the addition of Mg (10 mol%) enhanced the grain boundary conductivity by over 10² times comparing with that of undoped Ce_0.9Gd_0.1O_1.95, which may be explained by the optimization of space charge layer due to the segregation of Mg²⁺ to the grain boundaries.     

Hydrogen absorption enhancement of nanocrystalline Li3N/Li2C2 composite

A nanocrystalline composite of lithium nitride and lithium carbide was synthesized through melt infiltration of lithium metal into the mesopores of carbon aerogels followed by nitrogenation with nitrogen gas. The structure, surface properties, and morphology of the prepared samples were examined by XRD, N₂ adsorption at 77 K, FE-SEM, FE-TEM, and TPD/MS. It was found that some of the lithium metal reacted with the carbon to form lithium carbide, and some of the lithium metal was transformed into lithium nitride by nitrogenation, yielding a composite of lithium nitride and lithium carbide. Relative to the bulk lithium nitride, the lithium nitride in the composite showed a significantly enhanced sequential hydrogen absorption capacity and a lowered temperature of hydrogenation/dehydrogenation.