Binder-Free, Thin-Film Ceramic-Coated Separators for Improved Safety of Lithium-Ion Batteries.

Separators play a crucial role in ensuring the safety of lithium-ion batteries (LIBs). Commercial polyolefin-based separators such as polyethylene (PE) still possess serious safety risks under abuse conditions because of their poor thermal stability. In this work, a novel type of binder-free, thin ceramic-coated separators with superior safety characteristics is demonstrated. A thin layer of alumina (Al2O3) is coated on commercial PE separators using the electron-beam physical vapor deposition (EB-PVD) technique. Scanning electron microscopy (SEM), contact angle, impedance spectroscopy, and adhesion test techniques were employed to evaluate structure-property correlations. When compared to commercial slurry-coated separators, the EB-PVD-coated separators display (i) higher thermal stability, (ii) stronger ceramic-polymer adhesion, and (iii) competitive electrochemical performance of full LIB cells. Thermal stability, in terms of improved shutdown and breakdown characteristics of the separator, was studied using the in situ impedance technique up to 190 °C. In addition, the improved adhesion of the ceramic layer deposited on the PE separator was studied following the tape adhesion strength test. We prove that the thin (binder-free) ceramic layer coated by EB-PVD is far more effective in improving separator safety than those made using the conventional thick slurry coating.

Ferroelectric BaTiO3/SrTiO3 multilayered thin films for room-temperature tunable microwave elements.

Ferroelectric BaTiO3/SrTiO3 with optimized c-axis-oriented multilayered thin films were epitaxially fabricated on (001) MgO substrates. The microstructural studies indicate that the in-plane interface relationships between the films as well as the substrate are determined to be (001)SrTiO3//(001)BaTiO3//(001)MgO and [100]SrTiO3//[100]BaTiO3//[100]MgO. The microwave (5 to 18 GHz) dielectric measurements reveal that the multilayered thin films have excellent dielectric properties with large dielectric constant, low dielectric loss, and high dielectric tunability, which suggests that the as-grown ferroelectric multilayered thin films can be developed for room-temperature tunable microwave elements and related device applications.

Linearity and temperature dependence of large-area processed high-q barium strontium titanate thin-film varactors.

Ba(0.6)Sr(0.4)TiO(3) (BST) thin-films with large dielectric tunability as high as 4:1 were obtained using a large-area pulsed laser deposition process, with low loss-tangents below 0.01 at zero-bias and 10 GHz. This paper summarizes experimental results obtained on large-area processed BST thin films on 100-mm-diameter sapphire substrates characterized using a varactor shunt switch test structure. Varactors with 0.25-mumthick BST films exhibited large dielectric tunability, the relative dielectric permittivity at zero bias of 990 tuned to 250 at an electric field of 320 kV/cm. The leakage current through the BST film was below 2 nA up to 6 V dc bias. The quality factor (Q) exceeded 300 at relatively low 6 V dc bias for the BST varactors at 1 GHz. These results confirm that large-area processed BST thin films are ready to compete with semiconductor varactors for commercial applications at RF, microwave, and millimeterwave frequencies.

Capacitance of thin-film ferroelectrics under different drive signals.

Thin-film ferroelectric capacitance can be obtained by 2 different methods. Capacitance obtained using the derivative of its hysteresis loop is related to large applied signals and can be called the large-signal capacitance. Capacitance measured directly with a small, applied ac signal together with a slow changing dc bias is called the small-signal capacitance. This paper investigated the voltage dependence of the large- and small-signal capacitances. Measurements show that the large-signal C-V curve of thin-film ferroelectrics has much sharper peaks and higher peak values than the small-signal C-V curve. Analyses based on the Landau-Khalatnikov model shows that practical small-signal capacitance is closer to the ideal capacitance. However, its C-V curve has clearance areas around the coercive voltage, and the polarization switching is not reflected in the small-signal capacitance. This causes the peaks of small-signal C-V curves to be lower than that of large-signal C-V curves.

Highly efficient quantum-dot light-emitting diodes with DNA-CTMA as a combined hole-transporting and electron-blocking layer.

Owing to their narrow bright emission band, broad size-tunable emission wavelength, superior photostability, and excellent flexible-substrate compatibility, light-emitting diodes based on quantum dots (QD-LEDs) are currently under intensive research and development for multiple consumer applications including flat-panel displays and flat lighting. However, their commercialization is still precluded by the slow development to date of efficient QD-LEDs as even the highest reported efficiency of 2.0% cannot favorably compete with their organic counterparts. Here, we report QD-LEDs with a record high efficiency (approximately 4%), high brightness (approximately 6580 cd/m(2)), low turn-on voltage (approximately 2.6 V), and significantly improved color purity by simply using deoxyribonucleic acid (DNA) complexed with cetyltrimetylammonium (CTMA) (DNA-CTMA) as a combined hole transporting and electron-blocking layer (HTL/EBL). This, together with controlled thermal decomposition of ligand molecules from the QD shell, represents a novel combined, but simple and very effective, approach toward the development of highly efficient QD-LEDs with a high color purity.

Influence of space-charge on hysteresis loop characteristics of ferroelectric thin films.

Hysteresis loops of Pb(Zr, Ti)O3 (PZT) thin films obtained by using a Sawyer-Tower (ST) circuit are affected by many factors. This paper investigated the influence of space charge on the hysteresis loop of thin-film ferroelectrics, based on the model that polarization consists of two parts: linear and switching polarization. It is found that the space charge affects both the shape and offset of the ideal hysteresis loop. Further investigation shows that the practical hysteresis loop has a close relationship with the equivalent ST circuit parameters: the leakage resistance of the FE film, the equivalent input impedance of the measurement equipment, the signal source, and other similar parameters. The normally assumed symmetric hysteresis loop without any offset is obtained with an ST circuit when the output becomes stable. The hysteresis loop obtained at the initial stage of applied signal depends on the initial status of the FE film, and remnant polarization causes an initial offset that gradually disappears.

Performance of thin-film ferroelectric capacitors for EMC decoupling.

This paper studied the effects of thin-film ferroelectrics as decoupling capacitors for electromagnetic compatibility applications. The impedance and insertion loss of PZT capacitors were measured and compared with the results from commercial off-the-shelf capacitors. An equivalent circuit model was extracted from the experimental results, and a considerable series resistance was found to exist in ferroelectric capacitors. This resistance gives rise to the observed performance difference around series resonance between ferroelectric PZT capacitors and normal capacitors. Measurements on paraelectric (Ba,Sr)TiO(3)-based integrated varactors do not show this significant resistance. Some analyses were made to investigate the mechanisms, and it was found that it can be due to the hysteresis in the ferroelectric thin films.

Microwave characterization of nanostructured ferroelectric Ba(0.6)Sr(0.4)TiO(3) thin films fabricated by pulsed laser deposition.

A series of nanostructured ferroelectric thin films of barium strontium titanate were fabricated using a pulsed laser deposition system with real-time in situ process control. Pulsed laser deposition parameters were controlled during the growth of nanostructured thin films for use in the development of high frequency tunable microwave devices. The thin films were all grown at the same substrate temperature and laser beam energy density, but the chamber oxygen partial pressure (COPP) was varied systematically from 19 mTorr through 1000 Torr. Structural and electromagnetic characterization was performed using atomic force microscopy and evanescent microwave microscopy, respectively. Atomic force microscopy showed a linear increase in grain size with increases in the ambient oxygen pressure from 38 to 150 mTorr and from 300 mTorr to 1000 Torr. The correlation of the microwave properties with the epitaxial film microstructure can be attributed to stresses and polarizability in the film. Microwave characterization showed that a COPP of 75 mTorr yielded the most desirable film in terms of tunability and loss tangent over a wide frequency range.

Rapid bioenabled formation of ferroelectric BaTiO3 at room temperature from an aqueous salt solution at near neutral pH.

A 12-mer peptide, identified through phage display biopanning, has been used for the first time to induce the rapid formation of ferroelectric (tetragonal) nanocrystalline BaTiO3 at room temperature from an aqueous salt precursor solution at near neutral pH. BaTiO3 is widely used in capacitors, thermistors, displays, and sensors owing to its attractive dielectric, ferroelectric, pyroelectric, optical, and electrochemical properties. Two 12-mer peptides (BT1 and BT2) were selected from a phage-displayed peptide library via binding to tetragonal BaTiO3 powder. While these peptides possessed various types of amino acids, 8 of the 12 amino acids were common to both peptides. Each of these peptides induced the formation of faceted nanoparticles (50-100 nm diameter) from an aqueous precursor solution. X-ray diffraction and selected area electron diffraction patterns obtained from these faceted nanoparticles were consistent with the BaTiO3 compound. Rietveld analyses of the X-ray diffraction patterns yielded good fits to tetragonal crystal structures, with the BaTiO3 formed in the presence of the BT2 peptide exhibiting the most tetragonal character. A coating of the latter BaTiO3 nanoparticles exhibited polarization hysteresis (a well-known characteristic of ferroelectric materials) at room temperature and a relative permittivity of 2200. Such rapid, peptide-induced precipitation at room temperature provides new opportunities for direct BaTiO3 formation on low-melting or reactive materials (e.g., plastics, cloths, bio-organics) and the low temperature integration of BaTiO3 into electronic devices (e.g., on silicon or flexible polymer substrates).