Preparation and characterization of LiNi0.8Co0.15Al0.05O2 with high cycling stability by using AlO2- as Al source

We report the preparation of a series of LiNi_0.8Co_0.15Al_0.05O₂ materials with different reaction time (10, 20, 30 and 40 h) of precursor and their electrochemical properties as cathode material for lithium-ion batteries (LIBs). The preparation of LiNi_0.8Co_0.15Al_0.05O₂ was divided into two steps: a co-precipitation process to obtain Ni_0.8Co_0.15Al_0.05(OH)₂ precursor and a calcination step with LiOH. During the co-precipitation process, AlO₂^- was employed as Al source so as to guarantee Ni²⁺, Co²⁺ and Al³⁺ co-precipitation. The impacts of different synthesis time of the precursor on crystal structure, morphology and electrochemical performance of LiNi_0.8Co_0.15Al_0.05O₂ were systematically investigated. The samples with various synthesis time of precursor possessed spherical morphology and a layered α-NaFeO₂ structure with R-3m space group. Especially, when the reaction time of precursor was 30 h, the LiNi_0.8Co_0.15Al_0.05O₂ had the weakest degree of Li⁺/Ni²⁺ ions mixing and the best uniformity and integrity. When used as cathode materials for LIBs, the LiNi_0.8Co_0.15Al_0.05O₂ with 30 h exhibited high discharge capacity, good cycling performance and remarkable rate capability. The maximum discharge capacity was 202.3 mAh g⁻¹ at 0.1 C and the capacity retention approached 99.4% after 100 cycles at 1 C. At 10 C, the discharge capacity exceeded 140 mAh g⁻¹, suggesting a possible application in the high rate LIBs. The excellent electrochemical performance might be attributed to the uniform co-precipitation of Ni²⁺, Co²⁺ and Al³⁺ and well layered structure with less Li⁺/Ni²⁺ mixing.     

Performance and stability of Ruddlesden-Popper La2NiO4+δ oxygen electrodes under solid oxide electrolysis cell operation conditions

Ruddlesden-Popper La₂NiO_4+δ (LNO) oxygen electrodes were investigated under solid oxide electrolysis cell (SOEC) operation conditions. The electrochemical performance of LNO was measured in both solid oxide fuel cell (SOFC) and SOEC modes at 750 °C in air. The results suggest that LNO oxygen electrodes exhibit high electrochemical activity and the processes related to oxygen adsorption, dissociation and diffusion dominate the oxygen evolution reaction on the electrodes. Electrical conductivity relaxation (ECR) measurements imply that LNO shows better oxygen surface exchange performance than conventional LSM and LSCF electrodes, because of its special crystal structure with flexible non-stoichiometric oxygen. Significant performance degradation was observed during polarization at 500 mA cm⁻² and 750 °C in the SOEC mode for 48 h. XRD and XPS results confirmed that high-order Ruddlesden-Popper La₃Ni₂O₇ and La₄Ni₃O₁₀ phases have great contributions to the performance degradation of LNO oxygen electrodes related to anodic current polarization at 500 mA cm⁻² and 750 °C.     

Investigations on pure and Ag doped lithium lanthanum titanate (LLTO) nanocrystalline ceramic electrolytes for rechargeable lithium-ion batteries

The nano-crystalline Li_0.5La_0.5TiO₃ (LLTO) was prepared as an electrolyte material for lithium-ion batteries. The effect of Ag⁺ ion doping in three different concentrations were investigated: Ag_0.1Li_0.4La_0.5TiO₃, Ag_0.3Li_0.2La_0.5TiO₃, and Ag_0.5La_0.5TiO₃ along with Li_0.5La_0.5TiO₃. The prepared pure and Ag⁺ doped LLTO were subjected for structural, morphological, electrical and optical characterizations. The cubic superlattice structure of LLTO nano-powder was altered due to the Ag⁺ substitution tending towards a tetragonal phase. Increasing Ag⁺ substitution a complete tetragonal phase occurs in Ag_0.5La_0.5TiO₃. The average particle size of the prepared ceramic electrolyte ranged between 80 nm and 120 nm. The photoluminescence study reveals that the LLTO and Ag doped LLTO gives a blue emission peak. The size effect on grain and grain boundary resistance was observed and reported. With Ag⁺ substitution, the conductivity got decreased due to the impedance caused by Ag⁺ ions in the conducting path of Li⁺ ion. Among all the samples, Ag_0.5La_0.5TiO₃ shows maximum conductivity of the order of 10^?3 S cm^?1.     

Synthesis and electrochemical properties of La-doped Li4Ti5O12 as anode material for Li-ion battery

La-doped Li₄Ti₅O₁₂ was successfully synthesized from Li₂CO₃, La₂O₃ and tetrabutyl titanate by a simple ball milling assisted modified solid-state method. The impact of La-doping on crystalline structure, particle size, morphology and electrochemical performance of Li₄Ti₅O₁₂ was investigated. The samples were characterized by XRD, SEM, galvanostatically charge–discharge and electrochemical impedance spectroscopy. The results demonstrated that the in-situ coated and ball-milling method could decrease the particle size and prevent the aggregation of Li₄Ti₅O₁₂. La-doping obviously improved the rate capability of Li₄Ti₅O₁₂ via the generation of less electrode polarization and higher electronic conductivity. Li_3.95La_0.05Ti₅O₁₂ exhibited a relatively excellent rate capability and cycling stability. At the charge–discharge rate of 0.5 C and 40 C, its discharge capacities were 176.8 mAh/g and 54.7 mAh/g. After 10 cycles, fairly stable cycling performance was achieved without obvious capacity fade at 0.5 C, 1 C, 2 C, 5 C, 10 C, 20 C and 40 C. In addition, compared to Li₄Ti₅O₁₂, Li_3.95La_0.05Ti₅O₁₂ almost did not have the initial capacity loss. It indicated that Li_3.95La_0.05Ti₅O₁₂ was a promising candidate material for anodes in Li-ion battery application.     

Microwave sintered Bi0.90La0.10Fe0.95Mn0.05O3 nanocrystalline ceramics: Impedance and modulus spectroscopy

Multiferroic Bi_0.90La_0.10Fe_0.95Mn_0.05O₃ (BLFMO) nanoceramics were synthesized by PVA sol-gel method, followed by microwave sintering. The structural, microstructural and electrical properties of BLFMO were investigated. The crystal symmetry and unit cell dimensions were determined from the experimental data using Rietveld analysis. BLFMO revealed only one electroactive region as verified from impedance and modulus spectroscopy. Overlapping large polaron tunneling transport mechanism was observed from AC conductivity analysis. Conduction below 250 °C (−30 °C≤T≤250 °C) was attributed to translational hopping while above 250 °C (250 °C≤T≤350 °C) corresponds to electron hopping between charge defects. The relative permittivity varies from 66 to 203 at 1 kHz over the measured temperature range (−150 °C≤T≤350 °C). The electrical conductivity of the microwave sintered BLFMO has been discussed based on defect reaction with Mn doping. The measured DC conductivity in the range of 10⁻¹³ S/cm at −130 °C to 10⁻⁴ S/cm at 350 °C revealed the insulating behavior of the sample. At room temperature, the DC resistivity of the sample was over ~50 MΩ cm. The stretching constant (β) obtained from KWW (Kohlrausch-Williams-Watts) equation indicates that the sample inclined towards ideal Debye behavior as the temperature increases.     

Electrical properties and energy-storage performance of (Pb0.92Ba0.05La0.02)(Zr0.68Sn0.27Ti0.05)O3 antiferroelectric thick films prepared by tape-casing method

The energy-storage performance and dielectric properties of tape-cast (Pb_0.92Ba_0.05La_0.02)(Zr_0.68Sn_0.27Ti_0.05)O₃ (PBLZST) antiferroelectric (AFE) thick films with different thicknesses were systematically studied. As the thickness of the thick films increased from 40 to 80 µm, the dielectric constant and saturation polarization (P_s) of the thick films were gradually increased, while their corresponding breakdown strength (BDS) was decreased. A maximum recoverable energy-storage density of 6.8 J/cm³, companied by an efficiency of 61.2%, was achieved in the PBLZST AFE thick film with a thickness of 40 µm at room temperature. Moreover, the energy density of the PBLZST AFE thick films also displayed good thermal stability over 25–200 °C. In addition, all the samples had a low leakage current density of ~10⁻⁶ A/cm² at room temperature. These findings demonstrated that the PBLZST thick films should be a promising candidate for applications in high energy-storage capacitors.     

Formic acid as additive for the preparation of high-performance FePO4 materials by spray drying method

High-performance ferric phosphate (FePO₄), with well-defined ellipsoid morphology and uniform particle size distribution, is successfully fabricated via a green spray drying method with formic acid as additive. It is found that the added formic acid plays a crucial role for the formation of the well-distributed FePO₄ particles. Benefited by the outstanding structure and properties of ferric phosphate prepared above, a high performance of lithium iron phosphate (LiFePO₄) has been prepared. It exhibits high capacity, especially at high charging/discharging rate (158.4 mAh g⁻¹ at 0.2 C and 107.3 mAh g⁻¹ at 10 C), and excellent cycling stability (without capacity fading after cycling for 200cycles at 1 C). All these impressive electrochemical performance could be ascribed to the FePO₄ precursor, and further attributed to the addition of formic acid, which may play as a template, resulting in the well-defined morphology, uniform particles size distribution, hierarchical pore structure, and high surface area of the ferric phosphate.     

Effects of different chelating agents on the composition,morphology and electrochemical properties of LiV3O8 crystallites synthesized via sol–gel method

Lithium trivanadate (LiV₃O₈) crystallites have been synthesized via sol–gel processing using oxalic, tartaric, citric and malic acid as the chelating agents. The thermal decomposition process of the as-prepared LiV₃O₈ precursor was investigated by thermogravimetric (TG) and differential scanning calorimetry (DSC). The structure, morphology and electrochemical performance of the as-synthesized LiV₃O₈ samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and the galvanostatic charge–discharge test. Different chelating agents were introduced to investigate their effects on the products composition, morphology and electrochemical properties. Result show that the samples prepared with oxalic and tartaric acid are similar to show thin rod-like morphology in submicron size distribution while the samples prepared with citric and malic acid are found consisting of block-like crystallities in micron size. Further electrochemical results exhibit that the LiV₃O₈ particles with oxalic, tartaric, citric and malic acid exhibit an initial discharge capacity of 304.4 mA h/g, 296.8 mA h/g, 268.7 mA h/g and 275.3 mA h/g, respectively. After 20 cycles, they retain discharge capacity of 250.2 mA h/g, 237.6 mA h/g, 198.5 mA h/g and 206.8 mA h/g, respectively.     

Enhanced thermoelectric properties and electronic structures of p-type BiCu1−xAgxSeO ceramics

The thermoelectric properties and electronic structures were investigated on p-type BiCu_1-xAg_xSeO (x=0, 0.02, 0.05, 0.08) ceramics prepared using a two-step solid state reaction followed by inductively hot pressing. All the samples consist of single BiCuSeO phase with lamella structure and no preferential orientation exists in the crystallites. Upon replacing Cu⁺ by Ag⁺, maximum values of electrical conductivity of 36.6 S cm⁻¹ and Seebeck coefficient of 350 μV K⁻¹ are obtained in BiCu_0.98Ag_0.02SeO and BiCu_0.92Ag_0.08SeO, respectively. Nevertheless, a maximum power factor of 3.67 μW cm⁻¹K⁻² is achieved for BiCu_0.95Ag_0.05SeO at 750 K owing to the moderate electrical conductivity and Seebeck coefficient. Simultaneously, this oxyselenide exhibits a thermal conductivity as low as 0.38 W m⁻¹ K⁻¹ and a high ZT value of 0.72 at 750 K, which is nearly 1.85 times as large as that of the pristine BiCuSeO. The enhancement of thermoelectric performance is mainly attributed to the increased density of states near the Fermi level as indicated by the calculated results.     

Synthesis of Na2FePO4F/C and its electrochemical performance

Using NaF as the only Na precursor, fluorophosphate Na₂FePO₄F/C materials have been synthesized via the solid-state reaction. Na₂FePO₄F starts to form at 300 °C, becomes the sole crystalline form between 400 and 600 °C, and decomposes at 650 °C. Comparing with the theoretical capacity of 124 mAh g^?1, the sample prepared at 600 °C delivered a discharge capacity of 118 mAh g^?1. The outstanding electrochemical performance is believed to result from the good crystallization and high purity of the synthesized materials. The capacity retentions at 0.5 C and 2 C are 95.8% and 89.8%, respectively, of that at 0.05 C. Furthermore, a discharge capacity of 122 mAh g^?1 is maintained under the cycling between 2.0 and 5.2 V vs. Li/Li⁺, indicating that the second Na⁺ is not extracted from the Na₂FePO₄F lattice.     

Conductivity and electrochemical performance of (Ba0.5Sr0.5)0.8La0.2CoO3−δ cathode for intermediate-temperature solid oxide fuel cell

This study reports the successful preparation of a single-phase cubic (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ perovskite by the citrate–EDTA complexing method. Its crystal structure, thermogravimetry, coefficient of thermal expansion, electric conductivity, and electrochemical performance were investigated to determine its suitability as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Its coefficient of thermal expansion shows abnormal expansion at 300 °C, which is associated with the loss of lattice oxygen. The maximum conductivity of a (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ electrode is 689 S/cm at 300 °C. Above 300 °C, the electronic conductivity of (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ decreases due to the formation of oxygen vacancies. The charge-transfer resistance and gas phase diffusion resistance of a (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ–Ce_0.8Sm_0.2O_1.9 composite cathode are 0.045 Ω cm² and 0.28 Ω cm², respectively, at 750 °C.     

La2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 as cathode materials with enhanced specific capacity and cycling stability for lithium-ion batteries

Li-rich layered oxides are the most promising cathode candidate for new generation rechargeable lithium-ion batteries. In this work, La₂O₃-coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials were fabricated via a combined method of sol-gel and wet chemical processes. The structural and morphological characterizations of the materials demonstrate that a thin layer of La₂O₃ is uniformly covered on the surface of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ particles, and the coating of La₂O₃ has no obvious effect on the crystal structure of Li-rich oxide. The electrochemical performance of La₂O₃-coated Li-rich cathodes including specific capacity, cycling stability and rate capability has been significantly improved with the coating of La₂O₃. The Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ coated with 2.5 wt% La₂O₃ exhibits the highest discharge capacity, improved cycling stability and reduced charge transfer resistance, delivering a large discharge capacity of 276.9 mAh g⁻¹ in the 1st cycle and a high capacity retention of 71% (201.4 mAh g⁻¹) after 100 cycles. The optimal rate capability of the materials is observed at the coating level of 1.5 wt% La₂O₃ such that the material exhibits the highest discharge capacity of 90.2 mAh g⁻¹ at 5 C. The surface coating of La₂O₃ can effectively facilitate Li⁺ interfacial diffusion, reduce the structural change and secondary reactions between cathode materials and electrolyte during the charge-discharge process, and thus induce the great enhancement in the electrochemical properties of the Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ materials.     

Enhanced ferroelectric properties of La-substituted BiFeO3 thin films on LaSrCoO3/Pt/TiO2/SiO2/Si (1 0 0) substrates prepared by the soft chemical method

Bi_0.85La_0.15FeO₃ (BLFO015) thin films were deposited by the polymeric precursor solution on La_0.5Sr_0.5CoO₃ substrates. For comparison, the films were also deposited on Pt bottom electrode. X-ray diffraction data confirmed the substitutions of La into the Bi site with the elimination of all secondary phases under a substitution ratio x = 15% at a temperature of 500 °C for 2 h. A substantial increase in the remnant polarization (P_r) with La_0.5Sr_0.5CoO₃ bottom electrode (P_r ≈ 34 μC/cm²) after a drive voltage of 9 V was observed when compared with the same film deposited on Pt substrate. The leakage current behavior at room temperature decreased from 10^?8 (Pt) to 10^?10 A/cm² on (La_0.5Sr_0.5CoO₃) electrode under a voltage of 5 V. The fatigue resistance of the Au/BLFO015/LSCO/Pt/TiO₂/SiO₂/Si (1 0 0) capacitors with a thickness of 280 nm exhibited no degradation after 1 × 10⁸ switching cycles at a frequency of 1 MHz.     

Synthesis of La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 using a polymeric method

Nanocrystalline La_0.9Sr_0.1Al_0.85Mg_0.1Co_0.05O_2.875 (LSAMC) powders were synthesized via a polymeric method using poly(vinyl alcohol) (PVA). The effect of PVA content on the synthesized powders was studied. When the ratio of positively charged valences (Mⁿ⁺) to hydroxyl groups (OH) is 1.5:1, crystalline LaAlO₃ could be obtained at such a low calcination temperature as 700 °C. While at 900 °C the ratio is of less importance, since pure LaAlO₃ perovskite could be formed for all powders after calcination at 900 °C. Thermal analysis (TG/DTA) was utilized to characterize the thermal decomposition behaviour of precursor powders. The chemical structure of the calcined powder was studied by Fourier transform infrared (FTIR) spectroscopy. The powder morphology and microstructure were examined by SEM. Dense pellets with well-developed submicron microstructures could be formed after sintering at 1450 °C for 5 h. Compared with the solid-state reaction method, the sintering temperature is substantially lower for powder prepared by the PVA method. This is due to the ultrafine and highly reactive powder produced.     

La0.6Sr0.4Co0.2Fe0.8O3-δ oxygen electrodes for solid oxide cells prepared by polymer precursor and nitrates solution infiltration into gadolinium doped ceria backbone

Infiltration is a method, which can be applied for the electrode preparation. In this paper oxygen electrode is prepared solely by the infiltration of La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐δ (LSCF) into Ce_0.8Gd_0.2O_2-δ (CGO) backbone. The use a polymer precursor as an infiltrating medium, instead of an aqueous nitrate salts solution is presented. It is shown that the polymer forms the single-phase perovskite at 600 °C, contrary to the nitrates solution. As a result, obtained area specific resistance (ASR) is lowered from 0.21 Ω cm² to 0.16 Ω cm² at 600 °C. More than 35% of LSCF in the oxygen electrode decreases the performance.     

Novel Ag2S/ZnS/carbon nanofiber ternary nanocomposite for highly efficient photocatalytic hydrogen production

Novel Ag₂S/ZnS/carbon nanofiber (CNF) ternary nanocomposite with high photocatalytic H₂ production performance was synthesized by combination of an in-situ solid-state process and a cation-exchange reaction, using organic–inorganic layered zinc hydroxide nanofibers as precursor. Moreover, the loading amount of Ag₂S nanocrystals can be readily regulated by changing the AgNO₃ concentration, and the optimized H₂ production rate was 224.9 μmol h^− 1, significantly higher than that of the reported ZnS-based composite photocatalysts. The synergistic effect of CNF and Ag₂S as water reduction and oxidation cocatalyst, respectively, can greatly suppress the charge recombination thus resulting in high photocatalytic H₂ production activity.     

The preparation and properties of La3.5Ru4O13 and La2RuO5

The stability of the La_3.5Ru₄O₁₃ and La₂RuO₅ compounds in the La–Ru–O system in various atmospheres and various temperature ranges was investigated by thermal analysis, X-ray diffraction analysis and electron microscopy. The La_3.5Ru₄O₁₃ compound is stable in oxidizing and neutral atmospheres (N₂ with 10 ppm O₂), while La₂RuO₅ is partially reduced in a neutral atmosphere to form La₂RuO_4.6. In a reducing atmosphere both compounds decompose into metallic Ru and La₂O₃. The thermal expansion coefficients of La₂RuO₅ and La_3.5Ru₄O₁₃ at 800 °C are 11.2 × 10⁻⁶ K⁻¹ and 9.3 × 10⁻⁶ K⁻¹, respectively. The specific electrical resistivity for La_3.5Ru₄O₁₃ is relatively independent of temperature and is 2 × 10⁻² Ω cm at 800 °C, while for La₂RuO₅ it decreases with increasing temperature and is 1 Ω cm at 800 °C.     

Optimized synthesis of Cu-doped LiFePO4/C cathode material by an ethylene glycol assisted co-precipitation method

LiFePO₄/C and cupric ion doped LiFePO₄/C cathode materials were synthesized via an ethylene glycol assisted co-precipitation method. We assessed the influence of different parameters on electrochemical performance including calcination conditions, the amount of cupric ions added, doping ways, and drying methods. The microstructure of the materials was characterized by XRD, SEM, TEM, and EA. The results indicated the optimized Cu-doped LiFePO₄/C shows enhanced electrochemical performance with excellent high-rate capacity and cycle stability compared with LiFePO₄/C. The optimized Cu-doped LiFePO₄/C exhibited a high specific capacity of 148 mA h g⁻¹ at 0.1 C. Even at a rate of 10 C, it still achieved a specific capacity of 111 mA h g⁻¹ and its capacity retention ratio remained at 99.9% after 100 cycles at 1 C. These enhanced electrochemical properties were mainly due to a lesser extent of particle aggregation and more uniform carbon coating. Importantly, the synthesis process of this study is simple, fast, and economical thus it is promising to apply in industrialization.     

Electrospun ZnO–SnO2 composite nanofibers with enhanced electrochemical performance as lithium-ion anodes

ZnO–SnO₂ composite nanofibers with different structures were synthesized by a simple electrospinning approach with subsequent calcination at three different temperatures using polyacrylonitrile as the polymer precursor. The electrochemical performance of the composites for use as anode materials in lithium-ion batteries were investigated. It was found that the ZnO–SnO₂ composite nanofibers calcined at 700 °C showed excellent lithium storage properties in terms of cycling stability and rate capability, compared to those calcined at 800 and 900 °C, respectively. ZnO–SnO₂ composite nanofibers calcined at 700 °C not only delivered high initial discharge and charge capacities of 1450 and 1101 mAh g⁻¹, respectively, with a 75.9% coulombic efficiency, but also maintained a high reversible capacity of 560 mAh g⁻¹ at a current density of 0.1 A g⁻¹ after 100 cycles. Additionally, a high reversible capacity of 591 mAh g⁻¹ was obtained when the current density returned to 0.1 A g⁻¹ after 50 cycling at a high current density of 2 A g⁻¹. The superior electrochemical performance of ZnO–SnO₂ composite nanofibers can be attributed to the unique nanofibrous structure, the smaller particle size and smaller fiber diameter as well as the porous structure and synergistic effect between ZnO and SnO₂.     

Synthesis and densification of lanthanum silicate apatite electrolyte for intermediate temperature solid oxide fuel cell via co-precipitation method

Lanthanum silicate apatite (LSA, La_9.33+xSi₆O_26+1.5x, x = 0–0.67) has been widely investigated as a promising electrolyte material for intermediate temperature solid oxide fuel cell (SOFC). In this work, a facile and low-cost co-precipitation method is used to synthesize LSA precursor powders. The well dispersed nanopowders (ca. 70 nm) with pure hexagonal LSA phase are obtained by calcining the precursor at 900 °C. Impurity of La₂SiO₅, caused by the different precipitation productivities of La(NO₃)₃ and TEOS, can be eliminated through lowering the La/Si ratio in the starting mixtures. The dispersant (PEG200) plays a crucial role in co-precipitation processes, which can effectively mitigate the agglomeration and therefore significantly improve the sinterability of the nanoparticles. Dense LSA ceramic with relative density of 98% is obtained after sintering at 1550 °C, which exhibits a conductivity of 0.13 mS cm⁻¹ at 500 °C.