Influence of sintering temperature on conductivity and mechanical behavior of the solid electrolyte LATP

To warrant long-term reliability for application of electrolytes in solid state batteries also mechanical properties have to be considered. Current work concentrates on Li_1+xAl_xTi_2-x(PO₄)₃ (LATP), which based on its conductivity is a very promising material. Effect of sintering temperature (950, 1000, 1050, 1100 °C) on mechanical properties and conductivity was tested. Impedance tests were carried out and as main focus of the work the mechanical behavior of LATP samples was determined. The impedance tests results revealed that LATP sintered at 1100 °C had the highest ion conductivity. The LATP sintered at 1100 °C revealed also the highest elastic modulus and hardness, which appeared to be related mainly to a smaller lattice parameter with additional effects of lower porosity especially when tested at higher loads. The results indicate that enhancement of both mechanical behavior and conductivity requires lowering secondary phase content and densifying the microstructure of the material.     

Crystal structure and multiferroic behavior of perovskite YFeO3

We present a study of multiferroic properties of YFeO₃ synthesized by means of high-energy ball milling assisted by annealing at low temperature. Fe₂O₃ and Y₂O₃ powders were mixed in a stoichiometric ratio, milled for 5?h, pressed and annealed at temperature from 773 to 1073?K. X-ray diffraction (XRD) analysis confirmed the formation of single-phase orthorhombic structure. Magnetic hysteresis loops, at room temperature, from vibrating sample magnetometry show the transition from ferromagnetic order to G-antiferromagnetic order, related to the transformation from amorphous to crystalline orthorhombic single phase. The value of Néel temperature of single phase YFeO₃ was obtained at 595?K, lower than previously reported. Dielectric behavior at room temperature of YFeO₃ single-phase sample shows a direct dependence with frequency of both dielectric constant and dielectric loss, in good agreement with Maxwell-Wagner effect. A fit made using Cole-Cole equation shows that the Low Temperature Dielectric Relaxation, LTDR, corresponds to a Debye-type relaxation. Finally, it was found that AC conductivity (σ_AC) increases linearly with frequency. All results show that YFeO₃ synthesized by high-energy ball milling assisted with annealing possess a multiferroic behavior.     

Ionic conduction,colossal permittivity and dielectric relaxation behavior of solid electrolyte Li3xLa2/3-xTiO3 ceramics

Perovskite-type solid electrolyte lanthanum lithium titanate (LLTO), exhibiting high intrinsic ionic conductivity, has been attracting interests because of its potential use in all solid-state lithium-ion batteries. In this work, we prepared LLTO ceramics by solid state reaction method and studied their conductivity and dielectric properties systematically. It is found that the bulk conductivity of LLTO is several orders of magnitude higher than the grain boundary conductivity. In addition, colossal permittivity was observed in LLTO ceramics in wide frequency/temperature ranges. Two non-Debye type relaxation peaks were observed in the imaginary part of permittivity, resulting from Li⁺ ions motion and accumulation near interfaces of grains/grain boundaries/electrodes. It is suggested that colossal permittivity may originate from the lithium ion dipoles inside the samples and the interfacial polarization of lithium ion accumulation near the grain boundaries. These results clarify the relations among colossal permittivity, relaxation behavior and ionic conduction in solid ion conductor ceramics.     

Effect of sintering temperature on the structural,electrical and electrochemical properties of novel Mg0.5Si2 (PO4)3 ceramic electrolytes

The objective of the present study is to investigate the effect of sintering temperature on the structural, electrical and electrochemical properties of novel Mg_0.5Si₂ (PO₄) ₃ NASICON structured compound prepared via sol gel method. X-ray diffraction was used to study the structural properties such as crystalline phase and lattice parameters of the solid electrolytes. Electrical properties of the compound were measured using impedance spectroscopy while the electrochemical stability was investigated by linear sweep voltammetry. All the sintering temperatures yielded compounds consisted of monoclinic crystalline phase with a space group of P1 2₁/c1. Lattice parameters for Mg_0.5Si₂ (PO₄) ₃ samples increased from the sintering temperature at 700–800 °C but decreased for sintering temperature at 900 °C. The sample sintered at 800 °C showed the highest total conductivity of 1.83×10⁻⁵ S cm⁻¹ and the highest value of ions mobility, µ of 6.17×10¹⁰ cm² V⁻¹ s⁻¹ which was attributed to the optimum size of migration channel indicated by its unit cell volume. Linear sweep voltammetry result showed that the Mg_0.5Si₂ (PO₄)₃ powder was electrochemically stable up to 3.21 V.     

Effect of ball milling and solid solution treatment on the microstructure and interfacial behaviors of ZrMgMo3O12p/2024Al composites

ZrMgMo₃O₁₂ is a negative expansion material, while 2024Al alloy is a positive expansion material. The difference in thermal expansion coefficients between them will cause thermal mismatch stress at the interface in ZrMgMo₃O_12p/2024Al composites. Therefore, the interface behaviors of ZrMgMo₃O₁₂–Al determine the properties of ZrMgMo₃O_12p/2024Al composites to a great extent. The effects of ball milling and solid solution treatment on the microstructure and interface behaviors of 10 vol% ZrMgMo₃O_12p/2024Al composites were studied to improve the reticular microstructure of ZrMgMo₃O₁₂ distributed at the grain boundary of the α-Al matrix. The results showed that with increasing milling energy, the microstructure of the composites changed from reticular to equiaxed, and the distribution of ZrMgMo₃O₁₂ reinforcements in the matrix was more uniform. The content and size of the primary phase Al₂Cu decreased with increasing solid solution treatment time. In addition, only ZrMgMo₃O₁₂–Al, Al₂Cu–Al₁₂Mo and Al–Al₁₂Mo interfaces can be observed, but it is difficult to observe the interfaces of ZrMgMo₃O₁₂–Al₁₂Mo in the composites milled for 12 h and solution treated for 24 h, which is related to the decomposition mechanism of ZrMgMo₃O₁₂. The decomposition mechanism is as follows: Al atoms from the α-Al matrix captured O atoms from ZrMgMo₃O₁₂ to form Al₂O₃. ZrMgMo₃O₁₂ simultaneously released Mo, Zr and Mg atoms. Mo atoms were enriched and nucleated in situ and precipitated with Al atoms to form the intermetallic compound Al₁₂Mo, while Zr and Mg atoms entered the α-Al matrix to form a solid solution.     

Effect of sintering and annealing on electrochemical and mechanical characteristics of Na3Zr2Si2PO12 solid electrolyte

NASICON (Sodium superionic conductor) type Na₃Zr₂Si₂PO₁₂ (NZSP) has received a lot of interest as the solid electrolyte for all-solid-state sodium-ion batteries (ASSIBs). The electrolyte has superior interfacial characteristics, high thermal stability, and good ionic conductivity. Because of their higher energy density, improved mechanical stability, no liquid leakage problem, and higher operating voltages, All solid-state batteries are expected to replace liquid electrolyte-based batteries in many applications. The solid electrolyte also acts as a separator, and hence additional separator is not required for cell operations. Because of its 3D open architecture and continuous diffusion channels, NZSP is considered a better solid electrolyte. The NZSP solid electrolyte has been synthesized by spark plasma sintering (SPS) followed by annealing the sintered materials. The SPS method leads the material to have higher density and ionic conductivity. Conventional sintering of the materials requires a temperature as high as 1225°C; however, the temperature required for the SPS is as low as 1050°C. Moreover, conventional sintering yields samples of relative density up to 91%, while SPSed samples have achieved a maximum density of around 98%. The ionic conductivity of solid electrolyte SPSed at 1050°C for 10 min is found to be 3.5 × 10⁻⁴ S/cm with an activation energy of 0.27 eV. The annealing of the SPSed samples improves the ionic conductivity of the SPS1050-20mins sample to roughly double the value obtained from the as-prepared SPS sample because there are fewer secondary phases and a structural change from a rhombohedral to a monoclinic system. To ascertain the samples' crystal structure, particle shape, and ionic conductivity, materials were characterized using X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopy. The samples' mechanical characteristics, for example, the hardness and fracture toughness of the samples, were also determined.     

Effects of heat treatment on the mechanical properties at elevated temperatures of plain-woven SiC/SiC composites

The effects of heat treatment on the mechanical properties of plain-woven SiC/SiC composites at 927 °C and 1200 °C in argon were evaluated through tensile tests at room temperature and at elevated temperature on the as-received and heat-treated plain-woven SiC/SiC composites, respectively. Heat treatment can improve the mechanical properties of composites at room temperature due to the release of thermal residual stress. Although heat treatment can damage the fiber, the effect of this damage on the mechanical properties of composites is generally less than the effect of thermal residual stress. Heat treatment will graphitize the pyrolytic carbon interface and reduce its shear strength. Testing temperature will affect the expansion or contraction of the components in the composites, thereby changing the stress state of the components. This study can provide guidance for the optimization of processing of ceramic matrix composites and the structural design in high-temperature environments.     

Influence of Mo doping on the tribological behavior of Ti3AlC2 ceramic at different temperatures

(Ti_0·8Mo_0.2)₃AlC₂ solid solutions were successfully synthesized from Ti, Al, TiC, and Mo powders using the in situ hot-pressing sintering method. The tribological properties of (Ti_0·8Mo_0.2)₃AlC₂ and the reference Ti₃AlC₂ in the temperature range 25–800 °C were evaluated in ambient air with the counterpart of Al₂O₃ balls. The results show that (Ti_0·8Mo_0.2)₃AlC₂ has improved lubricating properties and wear resistance above 400 °C compared with Ti₃AlC₂. This can be contributed to the formation of tribo-oxidation films containing MoO₃ and MoO_3-x. Structural characterization of the tribo-oxidation films was conducted using SEM, EDS, Raman spectroscopy, and XPS to evaluate the effect of Mo doping on the wear mechanisms of Ti₃AlC₂ in detail.     

Enhanced sintering behavior of LSGM electrolyte and its performance for solid oxide fuel cells deposited by vacuum cold spray

How to obtain dense La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ (LSGM) electrolyte at low sintering temperature (<1300 °C) is a challenge to improve solid oxide fuel cell (SOFC) performance at intermediate operation temperature. In this study, a double-layer design method for vacuum cold spray (VCS) prepared-LSGM electrolyte assisted with two-step sintering at a low temperature was proposed. The sintering behavior of VCS deposited LSGM layers at 1200 °C was investigated. The LSGM layers became denser in most regions except the appearance of some cracks. Subsequently, the effect of a second LSGM layer on the sintered top layer was studied to block cracks. Results showed that the co-sintered layer with a thickness of approximately 5 μm presented a maximum open circuit voltage of ∼0.956 V at 650 °C and a maximum power density of 592 mW/cm² at 750 °C. Result indicates that the sintering assisted VCS is a promising method to prepare the LSGM electrolyte applied in intermediate temperature SOFCs.     

Structure promoted electrochemical behavior and chemical stability of AgI-doped solid electrolyte in sulfide glass system

Ion-conducting chalcogenide glass is a promising solid electrolyte with excellent conductivity and energy density for all-solid-state batteries. A suitable ionic channel for carriers in the amorphous network is urgently needed. In this work, the structural evolution of co-doped metal cations (Ge and Ga) in the glass matrix and its influence on electrochemical behavior were studied using a series of Ge_xGa_16-xSb₆₄S₁₂₈-40AgI glass samples. The macroscopic properties of samples were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Raman tests. The electrochemical behavior of samples was investigated by AC impendence spectroscopy and cyclic voltammetry (CV) measurement. Furthermore, a deliquescence experiment was applied for the chemical stability test of glass samples. The ionic conductivity of samples was developed by adding Ga components. Notably, the electrochemical window of electrolytes was remarkably wide at approximately 5 V. The resistance of samples to humidity was characterized by the decreased Raman peaks. Analysis results show that the Ga-related bonding structure evidently increased the chemical stability compared with the non-Ga sample. This work provides an insight into the effective and stable ions transport, especially in the Ge(Ga)SbS glass system. These results promote the further investigation of sulfide solid electrolytes and practical application of all-solid-state batteries.     

热处理温度对有机硅树脂结合不烧铝碳滑板性能的影响

以板状刚玉、石墨、Al粉、Si粉和B4C为主要原料,有机硅树脂作结合剂制备了不烧铝碳滑板试样。研究了在空气中先经240℃24h预处理,然后分别于400℃、600℃、800℃、1000℃、1350℃和1450℃保温3h处理后试样的烧结性能、物相组成和显微结构等变化规律。结果表明:热处理温度对有机硅树脂结合不烧铝碳滑板的性能、物相变化和显微结构影响显著。热处理温度为240~600℃时,有机硅树脂裂解产生质量损失,使试样内部结构松散,显气孔率显著增大,常温耐压强度较低;800~1000℃时,试样边缘部分B4C、Al、Si优先氧化,生成须状Al2O3和针状硼酸铝,有利于边缘骨料与基质结构紧密结合,同时,试样内部局部有柱状氮化物生成,相应的体积密度明显增加,显气孔率急剧下降,常温耐压强度达到最高值;温度>1000℃,试样中石墨大量氧化而留下很多气孔,同时Al、Si等氧化反应加剧,试样质量增加和体积膨胀明显,体积密度下降,显气孔率上升,常温耐压强度有下降趋势。     

Mechanical and electrochemical properties of cubic and tetragonal LixLa0.557TiO3 perovskite oxide electrolytes

Solid oxide electrolytes with high Li ion conductivity and mechanical stability are vital for all solid-state lithium ion batteries. The perovskite material Li_xLa_0.557TiO₃ with various initial Li (0.303 ≤ x ≤ 0.370) is synthesized by traditional solid-state reaction. The cubic and tetragonal structures are prepared with fast and slow cooling, respectively. The results reveal that the Li ion conductivity of the cubic structure is higher. In fact, the bulk conductivity of 1.65 × 10^?3 S cm^?1 is obtained at room temperature for x = 0.350. The crystal structure is not affected by the Li₂O quantity. In addition, Young's modulus, hardness, and fracture toughness are determined with indentation method for both structures. The Young's modulus increases with increasing Li₂O. However, hardness and fracture toughness keep a relatively stable value independent of Li₂O quantity.     

Preparation and ionic conduction of Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte using inorganic germanium as precursor

NASION-type Li_1.5Al_0.5Ge_1.5(PO₄)₃(LAGP) is prepared by a novel sol-gel method using low cost inorganic germanium (GeO₂) as the precursor. The composition and phase transformation during the heating of the LAGP precursors are analyzed using thermogravimetric-differential scanning calorimetry (TG-DSC) and X-ray diffraction (XRD). The structures and morphologies of the LAGP are characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the LAGP annealed at 900 ℃ is partially crystallized and consists of a large number of nanoscale grains surrounded by amorphous regions. The LAGP particles present an irregular morphology with a large size distribution over a range of 0.2–1 μm. In addition, ionic conductivities of the prepared LAGP first increase and then decrease with an increase in the sintering temperature and time. A high ionic conductivity (4.18 × 10⁻⁴Scm^-1) with an activation energy of 0.30 eV are obtained for the LAGP sample sintered at 900 °C for 8 h.     

Enhancing purity and ionic conductivity of NASICON-typed Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

Increasing demand for safe energy storage and portable power sources has led to intensive investigation for all-solid state Li-ion batteries and particularly to solid electrolytes for such rechargeable batteries. One of the most promising types of solid electrolytes is NASICON-structured Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) due to its relatively high ionic conductivity and stability towards air and moisture. Here, the work is aimed on implementing the steps to hinder formation of impurity phases reported for various synthesis routes. Consequently, the applied modifications in the preparation strategies alter a crystal shape and size of prepared material. These two parameters have an enormous impact on properties of LATP. Fabrication of larger particles with a cubic shape significantly improves its ionic conductivity. As a result, LATP preparation methods such as a solution chemistry and molten flux resulted in the highest ionic conductivity samples with the value of ~10^?4 S cm^?1 at room temperature. Other LATPs obtained by solid-state reaction, sol-gel and spray drying methods depicted the ionic conductivity of ~10^?5 S cm^?1. The activation energy of lithium ion transfer in LATP varied in a range of 0.25–0.4 eV, which is in well agreement with the previously reported data.     

Preparation and electrochemical characterization of Er3+-doped ceria-chloride composite electrolyte for intermediate-temperature solid oxide fuel cells

In this study, Ce_0.8Er_0.2O_2-α was prepared via a microemulsion method. Then, Ce_0.8Er_0.2O_2-α powder was mixed with melted NaCl-KCl (1:1 mol ratio) at the weight ratio of 80%: 20% to obtain Ce_0.8Er_0.2O_2-α-KCl-NaCl at 750 °C. Ce_0.8Er_0.2O_2-α and Ce_0.8Er_0.2O_2-α-KCl-NaCl were characterized by thermogravimetry analysis and differential scanning calorimetry (TGA-DSC), Raman spectrometer, X-ray diffraction (XRD) and scanning electron microscope (SEM). The log (σT) ~ 1000 T^-1 plots and fuel cell performances of Ce_0.8Er_0.2O_2-α and Ce_0.8Er_0.2O_2-α-KCl-NaCl were tested at 400–700 °C. The maximum output power density of Ce_0.8Er_0.2O_2-α-KCl-NaCl was 187 mW cm^-2 at 700 °C which is six times greater than that of Ce_0.8Er_0.2O_2-α.     

The effect of NiO addition on the grain boundary behavior and electrochemical performance of Gd-doped ceria solid electrolyte under different sintering conditions

It has been reported that some transition metal oxides are effective aids both for the densification and the grain boundary behavior of ceria-based electrolytes. In the present work, NiO which is the most popular component of the anode of solid oxide fuel cells was added directly into the electrolyte ceramic, Ce_0.8Gd_0.2O_1.9, to investigate the effects of the presence of NiO on the properties of GDC electrolyte. All of the samples possess a single phase with cubic fluorite structure. The grain size is increased by the addition of NiO when the sintering temperature is 1400 °C. This modification in chemical composition also results in a decrease in activation energy and thus a tendency to enhance grain boundary mobility. The maximum power density of the composite electrolyte single cell is higher than that of a GDC single cell. Therefore, NiO can be used as an effective aid for ceria-based electrolytes.     

Mechanical and electrochemical behavior of novel electrolytes based on partially stabilized zirconia for solid oxide fuel cells

In this study, 3 mol% yttria stabilized zirconia (3YSZ) is investigated as a SOFC electrolyte alternative to 8 mol% yttria stabilized zirconia (8YSZ). The mechanical and electrochemical properties of both materials are compared. The mechanical tests indicate that the thickness of 3YSZ can be reduced to half without sacrificing the strength compared to 8YSZ. By reducing the thickness of 3YSZ from 150 µm to 75 µm, the peak power density is shown to increase by around 80%. The performance is further enhanced by around 22% by designing of novel electrode structure with regular cut-off patterns previously optimized. However, the cell with novel designed 3YSZ electrolyte exhibits 30% lower maximum power density than that of the cell with 150 µm-thick standard 8YSZ electrolyte. Nevertheless, the loss in the performance may be tolerated by decreasing the fabrication cost revealing that 3YSZ electrolyte with cut-off patterns can be employed as SOFC electrolyte alternative to 8YSZ.     

Microstructure and EMW absorbing properties of SiCnw/SiBCN-Si3N4 ceramics annealed at different temperatures

SiC nanowire/siliconboron carbonitride-Silicon nitride (SiC_nw/SiBCN-Si₃N₄) ceramics were prepared via a low-pressure chemical vapor deposition and infiltration (LPCVD/CVI) technique. The as-prepared ceramics were annealed at varying temperatures (1200–1600 °C) in a N₂ atmosphere, and their crystallization mechanism and absorbing properties were subsequently studied. The absorbing properties of the SiC_nw/SiBCN-Si₃N₄ ceramics improved with the annealing temperature up to a certain value and decreased thereafter. Among the samples tested, the SiC_nw/SiBCN-Si₃N₄ ceramics annealed at 1300 °C showed the highest permittivity (real and imaginary parts) and dielectric loss values in the X-band (ca. 5.34, 2.55, and 0.47 respectively), and this could be attributed to the precipitation of carbon and SiC nanocrystals. The sample treated at 1300 °C decreased its minimum reflection coefficient (RC) from −12.0 to −59.68 dB (compared with the as-received SiC_nw/SiBCN-Si₃N₄ ceramics) and the effective RC (below -10 dB) in the whole X-band could be achieved when the thickness was set to 3–3.5 mm. These results revealed that the absorbing performance was significantly improved after the heat treatment at 1300 °C.     

Effects of the surface treatment of the Al2O3 filler on the lithium electrode/solid polymer electrolyte interface properties

The lithium deposition-dissolution process in solid polymer electrolytes containing Al₂O₃ filler treated under different conditions has been investigated comparing with the ionic conduction behavior of the electrolyte. The composite electrolytes were prepared from poly(ethylene oxide) (PEO), LiBF₄ and α-Al₂O₃ filler by using a dry process, where the surface of α-Al₂O₃ was beforehand modified by a wet process. The exchange current densities, i₀, of the lithium electrode process in P(EO)₂₀LiBF₄ with and without Al₂O₃ filler were determined by a micro-polarization method. The temperature dependence of i₀ provided similar values for activation energy, ca. 25 and 70 kJ mol⁻¹ in both temperature regions above and below 60 °C, respectively. The effect of the surface treatment of the filler on the lithium electrode process gave a different tendency from that on the ionic conductivity. The Al₂O₃ surface treated by alkali solution enhanced the electrode process to the largest extent among the fillers used here, while it led to rather poor cycling stability in voltammetry. The enhanced reaction rate at the lithium electrode/solid polymer electrolyte interface has probably resulted in the improved ion dissociation by the surface groups of the Al₂O₃ filler.     

碳纤维在不同电解质体系下的电化学表面改性

使用电化学氧化法对PAN基碳纤维进行表面改性,通过扫描电子显微镜（SEM）、Raman光谱和X射线光电子能谱仪（XPS）表征了碳纤维表面物理化学结构,同时结合力学性能分析,评价了碳酸氢铵、硫酸铵和复合铵盐溶液3种电解质体系的改性效果。实验结果表明,碳酸氢铵溶液下的电化学改性有利于界面粘结强度的提高,而硫酸铵溶液下的电化学改性有利于降低抗拉伸强度的损失,当采用复合溶液改性时,则可以同时提高碳纤维的抗拉伸强度和其复合材料的抗层间剪切强度。