Electrochemical and solid-state NMR studies on LiCoO2 coated with Al2O3 derived from carboxylate-alumoxane

The surface of LiCoO₂ cathodes was coated with various wt.% of Al₂O₃ derived from methoxyethoxy acetate-alumoxane (MEA-alumoxane) by a mechano-thermal coating procedure, followed by calcination at 723 K in air for 10 h. The structure and morphology of the surface modified LiCoO₂ samples have been characterized with XRD, SEM, EDS, TEM, BET, XPS/ESCA and solid-state ²⁷Al magic angle spinning (MAS) NMR techniques. The Al₂O₃ coating forms a thin layer on the surface of the core material with an average thickness of 20 nm. The corresponding ²⁷Al MAS NMR spectrum basically exhibited the same characteristics as the spectrum for pristine Al₂O₃ derived from MEA-alumoxane, indicating that the local environment of aluminum atoms was not significantly changed at coating levels below 1 wt.%. This provides direct evidence that Al₂O₃ was on the surface of the core materials. The LiCoO₂ coated with 1 wt.% Al₂O₃ sustained continuous cycle stability 13 times longer than pristine LiCoO₂. A comparison of the electrochemical impedance behavior of the pristine and coated materials revealed that the failure of pristine cathode performance is associated with an increase in the particle–particle resistance upon continuous cycling. Coating improved the cathode performance by suppressing the characteristic structural phase transitions (hexagonal to monoclinic to hexagonal) that occur in pristine LiCoO₂ during the charge–discharge processes.     

Nanoscaled BaTiO3 powders with a large surface area synthesized by precipitation from aqueous solutions: Preparation,characterization and sintering

Nanosized BaTiO₃ powders with a specific surface area of 60–75 m²/g have been prepared by precipitation of a titanium ester with Ba(OH)₂ solution at temperatures less than 100 °C. The effects of the Ba(OH)₂ concentration, isopropanol mixing with water as a solvent, the Ba:Ti ratio and surface modifiers on the surface area, the particle size, the crystalline phase, the agglomeration and aggregation degree of the synthesized powders as well as dielectric properties of sintered pellets have been investigated. The properties of the obtained powders have been characterized with XRD, BET, TG-DTA, ICP-AES, HRTEM and dilatometer. A high concentration of Ba(OH)₂ can increase the agglomeration and aggregation degree of the particles while the addition of isopropanol in water is beneficial for lowering it. To obtain stoichiometrical barium titanate, the ratio of Ba:Ti should be 1.1. The leaching of barium ions during processing can be limited by washing the powder with ammonia solution at pH10.2. A BaTiO₃ ceramic (95.8% of the theoretic density) has been fabricated by sintering the powders at 1250 °C for 2 h.     

In situ synthesis of integrated dodecahedron NiO/NiCo2O4 coupled with N-doped porous hollow carbon capsule for high-performance supercapacitors

NiO and NiCo₂O₄ exhibit excellent synergistic effects and broad application prospects in electrochemical applications. However, the apparent interfacial instability between NiO and NiCo₂O₄ limits ion transport kinetics, charge/ion transfer, and electrochemical stability. In response, we developed and designed an integrated dodecahedron NiO/NiCo₂O₄ by a facile in-situ calcination method. Moreover, by utilizing the porous hollow structure of nitrogen-doped carbon capsules (N-Cc) as a conductive network, the N-Cc_x@NiO/NiCo₂O₄ heterostructures with stable interface structure, excellent electrolyte adsorption, and electron transfer pathways were carefully designed. The N-Cc_1.0@NiO/NiCo₂O₄ heterostructures are found to deliver an outstanding specific capacitance of 658.8 F g⁻¹, and a high energy density of 101.40 Wh kg⁻¹ at a power density of 775.03 W kg⁻¹, along with capacitance retention of more than 93.5% after 8000 cycles. Based on the DFT calculations and electrochemical experimental results, this work provides an effective in situ route for the construction of high-performance metal oxide heterostructure electrode materials for new energy storage devices.     

耐折高导电性银浆的制备

研究了银片粒径对折叠前后银浆电导率的影响。采用不同粒径的片状银制备了具有良好导电性能的低温固化耐折导电银浆料,将银浆网印在聚酰亚胺基板上,在140 ℃下烧结形成网印电路。用微欧姆计检测了印刷电路的电阻率,对印刷银电路折叠前后的电阻变化进行了检测,并用扫描电镜对其表面形貌进行了研究,分析了导电机理。结果表明,小片Ag作为未连接薄片之间的桥梁,在折叠后填补了空白,形成导电网络,提高了折叠后的银浆导电性能。     

Shrinkage features,microstructure evolution and properties of Gd2O3-MgO optical composite ceramics with Zr as phase stabilizer

A novel composite ceramic, composed of equal-volumetric Zr-stabilized Gd₂O₃ and MgO phases, was prepared to be transparent in mid-wave infrared range. Zr stabilized Gd₂O₃ is proved to have a lower lattice parameter (10.7516 Å) using XRD refinement. Pressureless sintering behavior of Gd₂O₃-MgO with/without 2 at% Zr-doping (naming ZGM and GM) was studied via the real-time observation technique. The shrinkage of ZGM green body proceeds steadily up to 1400 °C while that of the undoped one shrinks sharply at 1250 °C due to Gd₂O₃ phase transition. The segregation of Zr element along the grain boundaries of Zr-Gd₂O₃ creates a synergized effect on the grain refinement with pinning effect. Dense ZGM ceramics exhibit superior transmittance of 78.3 %‐85.6 % at 3–5 µm, which show good consistency with the calculated values. The refractive index of Zr- Gd₂O₃ varies from 1.87 at 3 µm to 1.80 at 5 µm, which is smaller than those of monoclinic Gd₂O₃.     

Mn/Cu nanoclusters-grafted N-doped carbon nanotubes: Robust oxygen electrode catalysts for Zn-air batteries

Developing efficient nonprecious electrocatalysts that can drive the oxygen electrode reactions in zinc-air batteries (ZABs) is important but remains challenging. In this work, novel materials comprising Mn/Cu nanoclusters-grafted N-doped carbon nanotubes are synthesized by preparing and then pyrolyzing Mn/Cu polyphthalocyanine-encapsulated carbon nanotubes (CNTs), followed by treating the products with acidic solution. The materials are named CNTs@(Mn,Cu)PPc-T, where T denotes the pyrolysis temperature in °C, and they are demonstrated to serve as efficient oxygen electrode catalysts for zinc-air batteries (ZABs). Among them, the one synthesized at 900 °C, CNTs@(Mn,Cu)PPc-900, requires more positive onset and half-wave potentials for reduction of oxygen and a low overpotential for the evolution of oxygen. A rechargeable ZAB assembled with CNTs@(Mn,Cu)PPc-900 electrocatalyst delivers a high power density (158.5 mW cm⁻²) and displays an excellent stability in 200 cycles of charge/discharge (in over 33 h). Such performance is even superior to that of a ZAB containing the benchmark Pt/C + RuO₂ catalyst as an air cathode under identical testing condition.     

Design of a CaAlSiN3:Eu/glass composite film: Facile synthesis,high saturation-threshold and application in high-power laser lighting

Even though CaAlSiN₃:Eu²⁺ (CASN) is, in many regards, a highly suitable red phosphor that can be used in white light-emitting diodes, it can hardly be used in high-power laser-lighting because of its low saturation-threshold. By using CASN-based composite ceramics, it is possible to increase the threshold but new difficulties appear. These include complex and expensive synthesis, while the saturation-threshold still has room for improvement. In this study, we prepare a CASN/glass composite film, using an industry-friendly blade-coating method. The film has a high internal quantum efficiency of 79%, which suggests low conversion loss. Under 1.17 W blue laser excitation, a high luminous efficacy of 21.0 lm/W can be obtained. More importantly, the composite film shows a record-high saturation-threshold of more than 12.7 W (∼320 W/cm²) blue laser excitation. With these outstanding properties, CASN/glass composite films may open doors towards commercially viable red color converters for high-power laser-lighting applications.     

Single crystal structure determination and infrared fluorescence of the system (K3Sr1−xNdx) (Nd1−xSr1+x) Nb10O30

The μ-pulling down technique has permitted to grow single crystal fibers, of the gross chemical formula K₃Sr₂NdNb₁₀O₃₀, having a sufficient optical quality to carry out spectroscopic studies. The crystal structure has been determined and refined to reliability factors: (i) R₁ = 0.0384 (wR₂ = 0.0665) at room temperature; (ii) R₁ = 0.0334 (wR₂ = 0.0638) at 120 K. Difference in the cationic distribution over the 15- and 12-fold sites was noticed. IR fluorescence spectra investigated under different laser excitation wavelength at 300 K and 77 K show strong emissions at 0.9 and 1.06 μm. Low temperature fluorescence behavior is compatible with Nd³⁺ ions located in both Sr²⁺ and K⁺ sites with 15- and 12-fold coordination, respectively.     

Separation of CNF agglomerates from a ceramic suspension by spray drying technique

Aqueous silicon nitride based composite suspensions with the addition of 3.1 wt% of carbon nano-fibers (CNFs) were dried using two different drying techniques: spray drying and freeze drying. The paper deals with optimisation of parameters of the spray drying processwith the aim of maximising the yield and improve the quality of the granulate. Freeze drying was selected as a reference drying method, because no powder separation can occur in the course of the process. Prepared suspensions were spray dried at 4 different temperatures: 80, 110, 140 and 180 °C. After each run, two types of granules were obtained: from the separation flask and from the product vessel. Thermo-gravimetric analysis together with SEM examination show that spray drying results in separation of CNFs agglomerates. The granules from separation flask are always enriched by CNFs agglomerates whilst the granules from product vessel have reduced content of CNFs agglomerates. Sintering of spray-dried granules from the product vessel resulted in the composite with uniform microstructure, low amount of CNFs agglomerates and high relative density.