Preparation, microstructure and electrical properties of Li1.4Al0.4Ti1.6(PO4)3 nanoceramics

NASICON-type Li_1.4Al_0.4Ti_1.6(PO₄)₃ solid electrolytes were prepared by various processes, such as crystallization of glasses, spark plasma sintering (SPS) and conventional sintering process from nanosized precursor powders synthesized by a sol–gel route. The experimental results showed that grain size and relative density were the main factors determining the ionic conductivity of the bulk materials. The SPS technique produced ceramics with nearly 100% of the theoretical density. Maximum room temperature conductivities, 1.39?×?10^?3 S cm^?1 and 1.12?×?10^?3 S cm^?1 of grain boundary conductivity and total conductivity, respectively were obtained which were the highest values for Li⁺ inorganic oxide conductors as reported. Crystallization of ceramics from a glass was also certified as a favorable route to fabricate a bulk material with high conductivity.     

Inorganic cryogels for energy saving and conversion

Cryogels are usually obtained by freezing and thawing or freeze drying of gels and residues. Essential morphological features of the cryogels are bimodal pore size distribution, nanosize of the primary particles (crystallites) and their low agglomeration. Widely used for a decades in the polymer science and technology, cryogels find now a growing number of applications in the electroceramic materials. Freeze casting technique based on the freeze gelation effect is proved to be useful forming method in the production of complex-shaped SiO₂-containing electroceramics. Directed modification of the micromorphology by using solvent exchange schemes allows to obtain SiO₂ cryogel monoliths with density ≤ 0.05 g cm^?3 and specific surface area 700–800 m² g^?1 suitable for cryogenic thermal insulation of the superconducting devices. Excellent electrocatalytic activity of the macro/mesoporous PtRu/C cryogels in the methanol oxidation reaction makes them perspective anode materials of direct methanol fuel cells. Application of the cryogel-derived starting powders promoted substantial reduction of the sintering temperatures for a number of electroceramic materials. MnO₂- and V₂O₅-based cryogels are efficient cathode materials for secondary lithium batteries with specific capacity up to 300 mAh g^?1. Recent studies demonstrated also a feasibility of cryochemical approaches to the synthesis of complex oxide-based nanocrystalline electrode materials for electrochemical supercapacitors with high specific capacity at current densities up to 50 mA cm^?2.     

Electrochemical properties of TiO2 nanotube-carbon nanotube composites as anode material of lithium-ion batteries

For use as an anode material in lithium batteries, composites consisting of TiO₂ nanotubes (TNTs) and carbon nanotubes (CNTs) are prepared by combining hydrothermal reaction of rutile TiO₂ bulk particles, blending with different amounts (0–30 wt.%) of CNTs, ball-milling, and subsequent heat treatment at 300 °C. Crystalline property analysis and morphology observation of the prepared TNT-CNT powders prove that at low CNT content the composites are consisted of dominant phase of aggregated anatase TNTs. The TNT aggregates are relaxed with increased CNT content to form crosslinked networks surrounding the amorphous CNT phases that act as a dispersing matrix. As a result, the TNT-CNT composite anode with CNT (30 wt.%) is superior for application in lithium-ion batteries because it shows a saturated discharge capacity after about 20th cycle, good high-rate capability, and the lowest interfacial resistance of 1.7–2 Ω cm^?2. The superior anode properties of TNT-CNT composite with high content of CNT are mainly due to CNT’s functions to enhance electron transfer and to facilitate Li⁺ diffusion by dispersing the TNT agglomeration.     

Effects of transition metal doping and surface treatment to improve the electrochemical performance of Li2MnO3

A novel strategy to improve the electrochemical performance of Li₂MnO₃ using transition metal doping by the mechanochemical process is proposed. Li₂MnO₃ precursors are treated with transition metal containing chemicals in the mechanochemical process, followed by heat treatment. Cr containing Li₂MnO₃, with only 1 mol% Cr doping, exhibits unique electrochemical properties with a large initial discharge capacity of 234.9 mAh?g^?1, which is superior to the 205.0 mAh?g^?1 of pristine Li₂MnO₃, and all other transition-metal containing oxides. The structures of Li₂MnO₃ and Li₂MnO₃ with the transition metal element doping (TM-Li₂MnO₃) are studied by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and the electrochemical characteristics are further investigated using electrochemical impedance spectroscopy (EIS) measurements.     

Boosting the electrochemical performance of Li-garnet based all-solid-state batteries with Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> electrode: Routes to cheap and large scale ceramic processing

All-solid-state batteries based on fast Li⁺ conducting solid electrolytes such as Li₇La₃Zr₂O₁₂ (LLZO) give perspective on safe, non-inflammable, and temperature tolerant energy storage. Despite the promise, ceramic processing of whole battery assemblies reaching close to theoretical capacities and finding optimal strategies to process large-scale and low cost battery cells remains a challenge. Here, we tackle these issues and report on a solid-state battery cell composed of Li₄Ti₅O₁₂ / c-Li_6.25Al_0.25La₃Zr₂O₁₂ / metallic Li delivering capacities around 70–75 Ah/kg with reversible cycling at a rate of 8 A/kg (for 2.5–1.0 V, 95 °C). A key aspect towards the increase in capacity and Li⁺ transfer at the solid electrolyte-electrode interface is found to be the intimate embedding of grains and their connectivity, which can be implemented by the isostatic pressing of cells during their preparation. We suggest that simple adaption of ceramic processing, such as the applied pressure during processing, strongly alters the electrochemical performance by assuring good grain contacts at the electrolyte-electrode interface. Among the garnet-type all-solid-state ceramic battery assemblies in the field, considerably improved capacities and cycling properties are demonstrated for Li₄Ti₅O₁₂ / c-Li_6.25Al_0.25La₃Zr₂O₁₂ / metallic Li pressed cells, giving new perspectives on cheap ceramic processing and up-scalable garnet-based all-solid-state batteries.     

Microelectrodes for local conductivity and degradation measurements on Al stabilized Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript> garnets

The attractiveness of Li₇La₃Zr₂O₁₂ (LLZO) cubic based garnets lies in their high ionic conductivity and the combination of thermal and electrochemical stability. However, relations between composition and conductivity as well as degradation effects are still not completely understood. In this contribution we demonstrate the applicability of microelectrodes (Ø = 20–300 μm) for electrochemical impedance spectroscopy (EIS) studies on LLZO garnets. Microelectrodes allow to obtain local information on the ionic conductivity. A comparison between the overall performance of the sample (3.3 × 10^?4 S cm^?1) and local measurements revealed differences in conductivity with a maximum of the locally measured values of 6.3 × 10^?4 S cm^?1 and a minimum of 2.6 × 10^?4 S cm^?1. One reason behind these conductivity variations is most probably a compositional gradient in the sample. In addition, microelectrodes are very sensitive to conductivity changes near to the surface. This was used to investigate the effect of moisture in ambient air on the conductivity variations of LLZO. Substantial changes of the measured Li-ion transport resistance were found, particularly for smaller microelectrodes which probe sample volumes close to the surface.     

Lead-free NKN-5LT piezoelectric materials for multilayer ceramic actuator

As a candidate for lead-free piezoelectric materials, Li₂O excess 0.95(Na_0.5K_0.5)NbO₃–0.05LiTaO₃ (NKN-5LT) ceramics were developed by conventional sintering process. Sintering temperature was lowered by adding Li₂O as a sintering aid. Abnormal grain growth in NKN-5LT ceramics was observed with varying Li₂O content. In the 1 mol% Li₂O excess NKN-5LT samples sintered at 1000°C for 4 h in air, electromechanical coupling factor and piezoelectric constant of NKN-5LT ceramics were found to reach the highest values of 0.37 and 250 pC/N, respectively. Lead-free piezoelectric ceramic, Li₂O excess NKN-5LT, multilayer ceramic actuators (MLCA) were fabricated. 10?×?10?×?1 mm³ size MLCAs were fabricated by conventional tape casting method. The displacement of Li₂O excess NKN-5LT MLCA with 3 mm thickness was ~1 μm at 150 V.     

Influence of the pH of li-rich Li1.2Mn0.54Ni0.13Co0.13O2 on the electrochemical performance by sol–gel method

Abstract

The positive electrode material of the lithium-rich layered oxide has poor capability, and its cycle stability and rate characterizations have not been satisfactory. The lithium-rich cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ with different particle sizes was obtained by adjusting the pH by sol–gel method. The results show that the electrochemical performance of the material is optimal at pH = 9.0. It initial discharge capacity of 262.5 mAh/g at 0.1 C between 2.0 and 4.8 V. The high reversible discharge capacities is still of 161.0 and 133.7 mAh/g after 100 cycles at 0.5 C and 2 C, with a high capacity retention of 80.46% and 84.14%, respectively. This excellent electrochemical performance is attributed to smaller and uniform particles     

Sintering behavioral and electrochemical performances of LSM-BSB composite cathode for IT-SOFCs

In this paper, La_0.8Sr_0.2MnO₃-Ba_0.1Bi_0.9O_1.5-?? (LSM-BSB) composite cathode was prepared and characterized for intermediate temperature solid oxide fuel cells (IT-SOFCs). XRD results show that no reaction occurred between LSM and BSB at 900°C. SEM results show that the LSM-BSB composite cathode formed good contact with YSZ electrolyte after sintered at 900°C for 2 h, which significantly reduced the sintering temperature of cathode. Compared with the LSM-YSZ electrode sintered at 1200°C for 2 h, LSM-BSB electrode exhibits better electrochemical performance. At 800°C, the area specific resistance (ASR) of the LSM-BSB30 electrode is about 0.168 ??cm², which is nearly 1.5 times lower than that of LSM-YSZ composite cathode.     

Tailoring the pore structure of cathode supports for improving the electrochemical performance of solid oxide fuel cells

Two types of lanthanum doped strontium manganite (LSM)-yttria-stabilized zirconia (YSZ) composite cathodes were prepared, one with the finger-like straight open pores by the phase inversion tape casting, and the other with the randomly distributed tortuous pores by the conventional tape casting. A gas permeation flux of 42.5?×?10⁵ Lm^?2 h^?1 was measured under a trans-membrane pressure of 0.6 bar for the former while only 10.6?×?10⁵ Lm^?2 h^?1 for the latter. Fuel cells supported on the as-prepared LSM-YSZ composite cathodes were fabricated, comprising a 15 μm thick YSZ electrolyte layer and a 20 μm thick NiO-YSZ anode. The electrochemical performance of the fuel cells was measured using H₂ as fuels and air as oxidants. The cell supported on the phase-inversion derived cathode showed a maximum power density of 362 mWcm^?2 at 850 °C, while only 149 mWcm^?2 for the cell supported on the cathode formed by the conventional method. The difference in the electrochemical performance between the two cells can be attributed to the pore structure of the cathode supports. It is concluded that the phase inversion tape casting provides a simple and effective approach for tailoring the pore structure of the cathode support and thus enhancing the electrochemical performance.     

Electroless nano zinc oxide–activate carbon composite supercapacitor electrode

An electroless deposition process was used to synthesize the nanostructured zinc oxide (ZnO)–activated carbon (AC) as supercapacitor. The composite oxide was studied by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction analysis (XRD). The electrochemical performance of the nanocomposite was analyzed through cyclic voltammetry (CV) and AC impedance spectroscopy (EIS) in 0.1 M Na₂SO₄ as electrolyte. A specific capacitance 187 F g^?1 at a scan rate of 5 mV s^?1 was obtained using cyclic voltammetry (CV) and a nearly rectangular shaped CV curve was observed for the composite oxide. The supercapacitor was quite stable during charge–discharge cycling and exhibited constant capacitance during the long-term cycling. It also yielded a specific capacitance 171 F g^?1 at 5 mA cm^?2 with a high energy density of 21.9 Wh kg^?1 and 4.2 kW kg^?1 of power density. Due to unique structure of prepared ZnO–AC nanocomposite, it is a promising candidate for supercapacitor.     

Synthesis of nanostructured Li2MnSiO4/C using a microwave assisted sol–gel process with water as a base solvent

Microwave assisted sol–gel method is used to fabricate nanostructured Li₂MnSiO₄/C composites. Our process has the advantages in homogenous heating and reduced reaction time. In addition, the water is used as a base solvent while the conventional microwave-solvothermal method use the organic solvent as the base solvent, which makes our process much more safe and economical. Here, our prepared Li₂MnSiO₄/C composite exhibits an enhanced discharge capacity of 173.1 mAh g^?1, compared to the conventional processes.     

Cathode-electrolyte material interactions during manufacturing of inorganic solid-state lithium batteries

Solid-state lithium batteries comprising a ceramic electrolyte instead of a liquid one enable safer high-energy batteries. Their manufacturing usually requires a high temperature heat treatment to interconnect electrolyte, electrodes, and if applicable, further components like current collectors. Tantalum-substituted Li₇La₃Zr₂O₁₂ as electrolyte and LiCoO₂ as active material on the cathode side were chosen because of their high ionic conductivity and energy density, respectively. However, both materials react severely with each other at temperatures around 1085 °C thus leading to detrimental secondary phases. Thin-film technologies open a pathway for manufacturing compounds of electrolyte and active material at lower processing temperatures. Two of them are addressed in this work to manufacture thin electrolyte layers of the aforementioned materials at low temperatures: physical vapor deposition and coating technologies with liquid precursors. They are especially applicable for electrolyte layers since electrolytes require a high density while at the same time their thickness can be as thin as possible, provided that the separation of the electrodes is still guaranteed.     

Hydrothermal synthesis of LiFePO4 with small particle size and its electrochemical properties

Lithium iron phosphate (LiFePO₄) powders were prepared by hydrothermal reactions under a nitrogen atmosphere or an air atmosphere, and the microstructure and electrochemical properties of the LiFePO₄ powders were investigated. The LiFePO₄ powder prepared under the nitrogen atmosphere (LiFePO₄–N₂) had a small particle size in the range of 300–500 nm, whereas the powder prepared under the air atmosphere (LiFePO₄?air) had a large particle size in the range of 1–5 μm. Although the Fe²⁺/Fe³⁺ ratio was not significantly different in both LiFePO₄ powders, the Fe²⁺/Fe³⁺ ratio in the precursor suspension prepared under the nitrogen atmosphere was much higher than that prepared under the air atmosphere, thereby resulting in the small particle size of the LiFePO₄–N₂ powder. The discharge capacity of a LiFePO₄–N₂ electrode was 149 mAh g^?1 at a low current density of 10 mA g^?1, whereas that of a LiFePO₄?air electrode was 83 mAh g^?1. Impedance analyses indicated that the charge transfer resistances normalized to the surface area of LiFePO₄ particles for the LiFePO₄–N₂ and LiFePO₄?air electrodes were 4.6 and 4.8 Ω m², respectively. These values were not significantly different. This revealed that the factor dominating the electrochemical properties of LiFePO₄–N₂ and LiFePO₄?air powders was particle size and not crystalline lattice or Fe²⁺ concentration.     

The effect of vanadium precursors on the electrochemical performance of Li1.1V0.9O2 as an anode material for Li-ion batteries

Recently, Li_1.1V_0.9O₂ has been considered as one of the most promising anode materials for Li-ion batteries due to its high volumetric capacity at a relatively low intercalation potential. For a scalable and economical production of Li_1.1V_0.9O₂ anode material with a high electrochemical performance, however, the preparation of vanadium precursor with a good quality is of crucial importance. In this work, a high-purity V₂O₃ precursor was prepared through a thermal reduction of commercial V₂O₅ at 600 °C, which is far more cost-effective than V₂O₃. Li_1.1V_0.9O₂ was synthesized by a simple solid-state reaction of Li₂CO₃, as well as V₂O₃ at high temperature under a reducing atmosphere. In the electrochemical measurement, Li_1.1V_0.9O₂ prepared using V₂O₃ from the thermal reduction of V₂O₅ showed considerably higher specific capacity than the one using the commercial V₂O₃, maintaining a specific capacity of about 300 mAh g^?1 even after 20 cycles at 0.1 C rate, although it showed a lower coulombic efficiency for the first cycle.     

Improvement of a GDC-based composite cathode for intermediate-temperature solid oxide fuel cells

La_0.84Sr_0.16MnO_3?δ - Ce_0.8Gd_0.2O_2-δ (LSM-GDC) composite cathodes were fabricated by impregnating the LSM matrix with both LSM′ (La_0.84Sr_0.16MnO_3?δ) and GDC (or only GDC), and the ion-impregnated LSM-GDC composite cathodes showed excellent performance. At 750 °C, the value of the cathode polarization resistance (R _p ) was only 0.058 Ω cm² for an ion-impregnated LSM-GDC composite cathode which was impregnated with both LSM′ and GDC. For the performance of the single cell with the same cathode, the maximum power density was 1.1 W cm^?2 at 750 °C. The long-term test of the cell was carried out at 700 °C with a constant load of 0.3 A cm^?2 and the output voltage was stable on the whole. The results demonstrated that LSM-GDC fabricated by impregnating the LSM matrix with both LSM′ and GDC was a promising composite cathode material for the intermediate-temperature solid oxide fuel cells.     

Qualitative identification of nitrate nitrogen in compound fertilizers by infrared spectroscopy

ABSTRACT

In this study, NPK compound fertilizers containing nitrate nitrogen were tested by Fourier transform infrared spectroscopy (FTIR), and the relative contents of nitrate nitrogen and qualitative comparison were qualitatively identified. The raw materials of compound fertilizers: agricultural ammonium nitrate (AN), potassium nitrate (KNO₃) and ammonium phosphate (NH₄)₂HPO₄ were analyzed by infrared spectroscopy respectively. The results showed that the absorption peaks of nitrate (NO₃^?1) in solid agricultural fertilizers were 1384 cm^?1, 825 cm^?1. Furthermore, the NPK compound fertilizer with 4%, 5.5%, 6% and 9.5% nitrate nitrogen content were respectively tested by infrared spectroscopy. The results showed that with the increase of nitrate nitrogen content in the compound fertilizers, the relative intensity of the infrared absorption peaks of nitrate increased as well. Moreover, the relative intensity of the absorption peaks at 1384 cm^?1 and 825 cm^?1 are proportional to the content of nitrate in the nitro-compound fertilizer-containing ammonium nitrogen and nitrate nitrogen.     

Ion transport studies on Al–Zn ferrite dispersed nano-composite polymer electrolyte

A ferrite dispersed PEO based nano-composite polymer electrolyte has been developed in the present work. Formation of nano-composites, change in the structural and microscopic properties of the system have been investigated by X-ray diffraction, optical microscopy and SEM imaging. Existence of spinodal decomposition structure indicates formation of nano sized composite polymer electrolyte. Increase in formation of crystalline domain has been evidenced in thermal studies upon dispersal of nano-sized filler particles in pristine electrolyte matrix. The ionic transport studies through impedance spectroscopy exhibit highest electrical conductivity for the composition [93PEO-7NH₄SCN]:2 wt% Al–Zn ferrite, viz. is 1.22?×?10^?4 S/cm at room temperature with ionic transference number in excess of 0.9. Arrhenius type thermally activated conduction process is reflected during temperature dependent conductivity studies on these electrolytes.     

Evaluation of La<Subscript>2</Subscript>CoTi<Subscript>0.7</Subscript>Mg<Subscript>0.3</Subscript>O<Subscript>6</Subscript> as an electrode material for a symmetrical SOFC

La₂CoTi_0.7Mg_0.3O₆ (LCTM) material has been prepared at 1473 K for 24 h in air. X-ray powder diffraction study has revealed that it contains two orthorhombic perovskite phases (in a ratio ~1:4) with close unit cell parameters. Annealing of LCTM in reducing (Ar/H₂, 8%) atmosphere at 1173 K for 12 h has resulted in the preparation of a single-phase material containing the GdFeO₃-type perovskite phase with the unit cell parameters of a?=?5.5631(3) Å, b?=?5.5462(3) Å, c?=?7.8522(5) Å. LCTM material exhibits a reversible transformation of a mixture of two perovskite phases with close cation content in air and a single perovskite phase in a reducing atmosphere. Both as-prepared and reduced LCTM samples have been studied by thermogravimetric analysis and dilatometry in air and Ar/H₂ (8%). No chemical interaction between the as-prepared LCTM and standard electrolyte materials for SOFC like GDC and YSZ has been observed up to 1273 K. High-temperature electrical conductivity of the as-prepared LCTM at variable oxygen partial pressure (10^?4-0.21 atm) showed weak dependence over pO₂ with E_a?=?0.48?±?0.01 eV. AC impedance study of the symmetrical cells LCTM/GDC/LCTM has revealed ASR value at 1173 K of ~8.1?±?0.1 Ω?cm² in air and 0.24?±?0.05 Ω?cm² in a reducing atmosphere. These results allow to consider LCTM as a promising electrode material for a symmetrical SOFC.     

Application of GDC-YDB bilayer and LSM-YDB cathode for intermediate temperature solid oxide fuel cells

Yttria-doped bismuth (YDB) and gadolinia-doped ceria (GDC) are investigated as a bilayer electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). LSM-YDB is used as a cathode material in order to improve the poor ionic conduction of LSM and the compatibility with the YDB electrolyte. The performance of the bilayer cell was measured under humidified H₂ (3 % H₂O) atmosphere and an operating temperature between 500 °C and 650 °C. The polarization resistance and ohmic resistance of the GDC-YDB bilayer cell were 0.189 Ωcm² and 0.227 Ωcm² at 650 °C, respectively. The bilayer cell showed 0.527 Wcm^?2 in the maximum power density at 650 °C, which is about two times higher than the single-layer cell of 0.21 Wcm^?2. The OCV of the bilayer cell was 0.89 V at 650 °C, suggesting that the electronic conduction caused by the reduction of ceria was successfully suppressed by the YDB layer. The introduction of an YDB-GDC bilayer cell with LSM-YDB cathode thus appears to be a promising method for improving the performance of GDC-based SOFCs and reducing operating temperature.