Enhanced Energy Storage Performance in Na0.5Bi0.5TiO3-Based Relaxor Ferroelectric Ceramics via Compositional Tailoring.

Owing to the high power density, excellent operational stability and fast charge/discharge rate, and environmental friendliness, the lead-free Na0.5Bi0.5TiO3 (NBT)-based relaxor ferroelectrics exhibit great potential in pulsed power capacitors. Herein, novel lead-free (1-x)(0.7Na0.5Bi0.5TiO3-0.3Sr0.7Bi0.2TiO3)-xBi(Mg0.5Zr0.5)O3 (NBT-SBT-xBMZ) relaxor ferroelectric ceramics were successfully fabricated using a solid-state reaction method and designed via compositional tailoring. The microstructure, dielectric properties, ferroelectric properties, and energy storage performance were investigated. The results indicate that appropriate Bi(Mg0.5Zr0.5)O3 content can effectively enhance the relaxor ferroelectric characteristics and improve the dielectric breakdown strength by forming fine grain sizes and diminishing oxygen vacancy concentrations. Therefore, the optimal Wrec of 6.75 J/cm3 and a η of 79.44% were simultaneously obtained in NBT-SBT-0.15BMZ at 20 °C and 385 kV/cm. Meanwhile, thermal stability (20-180 °C) and frequency stability (1-200 Hz) associated with the ultrafast discharge time of ~49.1 ns were also procured in the same composition, providing a promising material system for applications in power pulse devices.

Bimodal-Structured 0.9KNbO3-0.1BaTiO3 Solid Solutions with Highly Enhanced Electrocaloric Effect at Room Temperature.

0.9KNbO3-0.1BaTiO3 ceramics, with a bimodal grain size distribution and typical tetragonal perovskite structure at room temperature, were prepared by using an induced abnormal grain growth (IAGG) method at a relatively low sintering temperature. In this bimodal grain size distribution structure, the extra-large grains (~10-50 µm) were evolved from the micron-sized filler powders, and the fine grains (~0.05-0.35 µm) were derived from the sol precursor matrix. The 0.9KNbO3-0.1BaTiO3 ceramics exhibit relaxor-like behavior with a diffused phase transition near room temperature, as confirmed by the presence of the polar nanodomain regions revealed through high resolution transmission electron microscope analyses. A large room-temperature electrocaloric effect (ECE) was observed, with an adiabatic temperature drop (ΔT) of 1.5 K, an isothermal entropy change (ΔS) of 2.48 J·kg-1·K-1, and high ECE strengths of |ΔT/ΔE| = 1.50 × 10-6 K·m·V-1 and ΔS/ΔE = 2.48 × 10-6 J·m·kg-1·K-1·V-1 (directly measured at E = 1.0 MV·m-1). These greatly enhanced ECEs demonstrate that our simple IAGG method is highly appreciated for synthesizing high-performance electrocaloric materials for efficient cooling devices.

An Ultra-Long-Life Flexible Lithium-Sulfur Battery with Lithium Cloth Anode and Polysulfone-Functionalized Separator.

Flexible and high-performance batteries are urgently required for powering flexible/wearable electronics. Lithium-sulfur batteries with a very high energy density are a promising candidate for high-energy-density flexible power source. Here, we report flexible lithium-sulfur full cells consisting of ultrastable lithium cloth anodes, polysulfone-functionalized separators, and free-standing sulfur/graphene/boron nitride nanosheet cathodes. The carbon cloth decorated with lithiophilic three-dimensional MnO2 nanosheets not only provides the lithium anodes with an excellent flexibility but also limits the growth of the lithium dendrites during cycling, as revealed by theoretical calculations. Commercial separators are functionalized with polysulfone (PSU) via a phase inversion strategy, resulting in an improved thermal stability and smaller pore size. Due to the synergistic effect of the PSU-functionalized separators and boron nitride-graphene interlayers, the shuttle of the polysulfides is significantly inhibited. Because of successful control of the shuttle effect and dendrite formation, the flexible lithium-sulfur full cells exhibit excellent mechanical flexibility and outstanding electrochemical performance, which shows a superlong lifetime of 800 cycles in the folded state and a high areal capacity of 5.13 mAh cm-2. We envision that the flexible strategy presented herein holds promise as a versatile and scalable platform for large-scale development of high-performance flexible batteries.

A Self-Healing Amalgam Interface in Metal Batteries.

Poor cyclability and safety concerns caused by the uncontrollable dendrite growth and large interfacial resistance severely restrict the practical applications of metal batteries. Herein, a facile, universal strategy to fabricate ceramic and glass phase compatible, and self-healing metal anodes is proposed. Various amalgam-metal anodes (Li, Na, Zn, Al, and Mg) show a long cycle life in symmetric cells. It has been found that liquid Li amalgam shows a complete wetting with the surface of lanthanum lithium titanate electrolyte and a glass-phase solid-state electrolyte. The interfacial compatibility between the lithium metal anode and solid-state electrolyte is dramatically improved by using an in situ regenerated amalgam interface with high electron/ion dual-conductivity, obviously decreasing the anode/electrolyte interfacial impedance. The lithium-amalgam interface between the metal anode and electrolyte undergoes a reversible isothermal phase transition between solid and liquid during the cycling process at room temperature, resulting in a self-healing surface of metal anodes.

The Effects of Aluminum-Nitride Nano-Fillers on the Mechanical, Electrical, and Thermal Properties of High Temperature Vulcanized Silicon Rubber for High-Voltage Outdoor Insulator Applications.

AlN nanoparticles were added into commercial high-temperature-vulcanized silicon rubber composites, which were designed for high-voltage outdoor insulator applications. The composites were systematically studied with respect to their mechanical, electrical, and thermal properties. The thermal conductivity was found to increase greatly (>100%) even at low fractions of the AlN fillers. The electrical breakdown strength of the composites was not considerably affected by the AlN filler, while the dielectric constants and dielectric loss were found to be increased with AlN filler ratios. At higher doping levels above 5 wt% (~2.5 vol%), electrical tracking performance was improved. The AlN filler increased the tensile strength as well as the hardness of the composites, and decreased their flexibility. The hydrophobic properties of the composites were also studied through the measurements of temperature-dependent contact angle. It was shown that at a doping level of 1 wt%, a maximum contact angle was observed around 108°. Theoretical models were used to explain and understand the measurement results. Our results show that the AlN nanofillers are helpful in improving the overall performances of silicon rubber composite insulators.

Enhanced Electrocaloric Effect in Sr2+-Modified Lead-Free BaZr xTi1- xO3 Ceramics.

Barium strontium zirconate titanate ceramics ((BaSr)(ZrTi)O3-BSZT) with Zr4+ ionic contents of 15 and 20 mol % and Sr2+ ionic contents of 15, 20, 25, and 30 mol % were prepared using a solid-state reaction approach. X-ray diffraction and scanning electron microscopy were used to characterize the lattice structure and morphologies of the ceramics. Permittivity and polarization as a function of temperature were characterized using an impedance analyzer and a Tower-Sawyer circuit. The electrocaloric effect was measured directly and calculated using the Maxwell relation (indirectly). The results indicated that the BSZT ceramics change from a normal ferroelectric to a relaxor ferroelectric with increasing Zr4+ ionic content, which can be further modified by the addition of Sr2+ ionic content. The optimized adiabatic temperature change Δ T obtained is 2.43 K in (Ba0.85Sr0.15)(Zr0.15Ti0.75)O3 ceramics, and Δ T >1.6 K over a wide temperature span of 120 °C was obtained.

Dielectric, Ferroelectric, and Magnetic Properties of Sm-Doped BiFeO3 Ceramics Prepared by a Modified Solid-State-Reaction Method.

Sm-doped BiFeO3 (BFO) material was prepared using a modified solid-state-reaction method, which used fast heating and cooling during the sintering process. The Sm doping level varied between 1 mol % to 8 mol %. Processing parameters, such as sintering temperature and annealing temperature, were optimized to obtain high-quality samples. Based on their dielectric properties, the optimum sintering and annealing temperatures were found to be 300 °C and 825 °C, respectively. Leakage-free square-shaped ferroelectric hysteresis loops were observed in all samples. The remnant polarization was maximized in the 5 mol %-doped sample (~35 µC/cm2). Furthermore, remnant magnetization was increased after the Sm doping and the 8 mol%-doped sample possessed the largest remnant magnetization of 0.007 emu/g. Our results demonstrated how the modified solid-state-reaction method proved to be an effective method for preparing high-quality BiFeO3 ceramics, as well as how the Sm dopant can efficiently improve ferroelectric and magnetic properties.

Direct Measurement of Large Electrocaloric Effect in Ba(ZrxTi1-x)O3 Ceramics.

Barium zirconate titanate (BZT) (Ba(ZrxTi1-x)O3) ceramics with Zr4+ contents of x = 5, 10, 15, 20, 25, and 30 mol % were prepared using a solid-state reaction approach. The microstructures, morphologies, and electric properties were characterized using X-ray diffraction, scanning electron microscopy, and impedance analysis methods, respectively. The dielectric analyses indicate that the BZT bulk ceramics show characteristics of phase transition from a normal ferroelectric to a relaxor ferroelectric with the increasing Zr4+ ionic content. The electrocaloric effect adiabatic temperature change decreases with the increasing Zr4+ content. The highest adiabatic temperature change obtained is 2.4 K for BZT ceramics with a 5 mol % of Zr4+ ionic content.

Enhanced electrocaloric analysis and energy-storage performance of lanthanum modified lead titanate ceramics for potential solid-state refrigeration applications.

The unique properties and great variety of relaxer ferroelectrics make them highly attractive in energy-storage and solid-state refrigeration technologies. In this work, lanthanum modified lead titanate ceramics are prepared and studied. The giant electrocaloric effect in lanthanum modified lead titanate ceramics is revealed for the first time. Large refrigeration efficiency (27.4) and high adiabatic temperature change (1.67 K) are achieved by indirect analysis. Direct measurements of electrocaloric effect show that reversible adiabatic temperature change is also about 1.67 K, which exceeds many electrocaloric effect values in current direct measured electrocaloric studies. Both theoretical calculated and direct measured electrocaloric effects are in good agreements in high temperatures. Temperature and electric field related energy storage properties are also analyzed, maximum energy-storage density and energy-storage efficiency are about 0.31 J/cm3 and 91.2%, respectively.

Anode Improvement in Rechargeable Lithium-Sulfur Batteries.

Owing to their theoretical energy density of 2600 Wh kg-1 , lithium-sulfur batteries represent a promising future energy storage device to power electric vehicles. However, the practical applications of lithium-sulfur batteries suffer from poor cycle life and low Coulombic efficiency, which is attributed, in part, to the polysulfide shuttle and Li dendrite formation. Suppressing Li dendrite growth, blocking the unfavorable reaction between soluble polysulfides and Li, and improving the safety of Li-S batteries have become very important for the development of high-performance lithium sulfur batteries. A comprehensive review of various strategies is presented for enhancing the stability of the anode of lithium sulfur batteries, including inserting an interlayer, modifying the separator and electrolytes, employing artificial protection layers, and alternative anodes to replace the Li metal anode.

Large Electrocaloric Effect in Relaxor Ferroelectric and Antiferroelectric Lanthanum Doped Lead Zirconate Titanate Ceramics.

Both relaxor ferroelectric and antiferroelectric materials can individually demonstrate large electrocaloric effects (ECE). However, in order to further enhance the ECE it is crucial to find a material system, which can exhibit simultaneously both relaxor ferroelectric and antiferroelectric properties, or easily convert from one into another in terms of the compositional tailoring. Here we report on a system, in which the structure can readily change from antiferroelectric into relaxor ferroelectric and vice versa. To this end relaxor ferroelectric Pb0.89La0.11(Zr0.7Ti0.3)0.9725O3 and antiferroelectric Pb0.93La0.07(Zr0.82Ti0.18)0.9825O3 ceramics were designed near the antiferroelectric-ferroelectric phase boundary line in the La2O3-PbZrO3-PbTiO3 phase diagram. Conventional solid state reaction processing was used to prepare the two compositions. The ECE properties were deduced from Maxwell relations and Landau-Ginzburg-Devonshire (LGD) phenomenological theory, respectively, and also directly controlled by a computer and measured by thermometry. Large electrocaloric efficiencies were obtained and comparable with the results calculated via the phenomenological theory. Results show great potential in achieving large cooling power as refrigerants.

Enhanced Sensitivity for Hydrogen Peroxide Detection: Polydiacetylene Vesicles with Phenylboronic Acid Head Group.

It was recently reported that, besides UV irradiated polymerization, polymerization of diacetylene compounds could also been initiated by radicals generated from enzyme catalyzed hydrogen peroxide (H2O2) decomposition. A new optical sensing method for H2O2 was proposed based on this phenomenon. However, the sensitivity of this method is relatively lower than existed ones. In the present work, phenylboronic acid (PBA) functionalized 10, 12-pentacosadiynoic acid (PDA-PBA) was synthesized and its vesicles were formed successfully as colorimetric sensor for H2O2 detection. It was found that color change during the polymerization of vesicles composed of the PBA modified monomer is much stronger than that of the non-modified one. The response of PDA-PBA vesicles to H2O2 is 16 times more sensitive than that of the PDA. The absorption of PDA-PBA at 650 nm is linearly related to the concentration of H2O2 and a detection limit of ~5 µM could be achieved.

Cell morphology variations of Klebsiella pneumoniae induced by acetate stress using biomimetic vesicle assay.

Supplementation with acetate under low levels was used as a novel approach to control the morphological development of Klebsiella pneumoniae aimed to improve 1,3-propanediol (1,3-PD) production. A full range of morphological types formed from rod shape to oval shape even round shape in response to different concentrations of acetate. The cell growth and 1,3-PD productions in the shake flasks with 0.5 g/L acetate addition were improved by 9.4 and 28.37%, respectively, as compared to the control, while the cell became shorter and began to lose its original shape. The cell membrane penetration by acetate was investigated by the biomimetic vesicles, while higher concentration of acetate led to more moderate colorimetric transitions. Moreover, the percentage composition of unsaturated fatty acid (UFA) was increased as well as the increased concentrations of acetate, whereas higher UFA percentage, higher fluidity of bacterial cell membrane.

Electromechanical properties of relaxor ferroelectric P(VDF-TrFE-CFE)-P(VDF-CTFE) blends.

Electromechanical properties of the relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer blended with a small amount of poly(vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] copolymer, which possesses a much higher elastic modulus than that of the neat terpolymer, were investigated. It was observed that the presence of small amount of P(VDF-CTFE) does not affect the microstructure of the crystalline phase. However, the uniaxially stretched blended films show a slight increase in the crystallinity and increased or similar induced polarization at high electric fields compared with the neat terpolymer, likely caused by the interface effect. Consequently, for blends with P(VDF-CTFE) less than 5 wt%, the transverse strains S1 along the stretching direction for uniaxially stretched blended films are nearly the same as those of neat P(VDF-TrFE-CFE), whereas the elastic modulus along the S1-direction increases with the P(VDF-CTFE) content. As a result, the blended films exhibit a higher elastic energy density and electromechanical coupling factor k31 compared with the neat terpolymer.

Core-free rolled actuators for Braille displays using P(VDF-TrFE-CFE).

Refreshable Braille displays require many small diameter actuators to move the pins. The electrostrictive P(VDF-TrFE-CFE) terpolymer can provide the high strain and actuation force under modest electric fields that are required for this application. In this paper, we develop core-free tubular actuators and integrate them into a 3 × 2 Braille cell. The terpolymer films are solution cast, stretched to 6 µm thick, electroded, laminated into a bilayer, rolled into a 2 mm diameter tube, bonded, and provided with top and bottom contacts. Experimental testing of 17 actuators demonstrates significant strains (up to 4%) and blocking forces (1 N) at moderate electric fields (100 MV m-1). A novel Braille cell is designed and fabricated using six of these actuators.

Enhanced reducing equivalent generation for 1,3-propanediol production through cofermentation of glycerol and xylose by Klebsiella pneumoniae.

1,3-Propanediol (1,3-PD) biosynthesis plays a key role in NADH consumption to regulate the intracellular reducing equivalent balance of Klebsiella pneumoniae. This study aimed to increase reducing equivalent for enhancing 1,3-PD production through cofermentation of glycerol and xylose. Adding xylose as cosubstrate resulted in more reducing equivalent generation and higher cell growth. In batch fermentation under microaerobic condition, the 1,3-PD concentration, conversion from glycerol, and biomass (OD(600)) relative to cofermentation were increased significantly by 9.1%, 20%, and 15.8%, respectively. The reducing equivalent (NADH) was increased by 1-3 mg/g (cell dry weight) compared with that from glycerol alone. Furthermore, 2,3-butannediol was also doubly produced as major byproduct. In fed-batch fermentation with xylose as cosubstrate, the final 1,3-PD concentration, conversion from glycerol, and productivity were improved evidently from 60.78 to 67.21 g/l, 0.52 to 0.63 mol/mol, and 1.64 to 1.82 g/l/h, respectively.

[Screening and breeding high 1,3-propanediol producing strains by genome shuffling].

OBJECTIVE: To improve the tolerance of main metabolites, we used genome shuffling to achieve high 1,3-propanediol producing mutants. METHODS: Based on 96 deep-well palates containing prepared ended fed-batch broth as an efficient selection method, genome shuffling has been applied in strain improvement. RESULTS: Five high producers were obtained after genome shuffling (LSG1, LSG2, LSG4, LSG5 and LSG6). During batch fermentation (3 L), the 1, 3-propanediol production of the five mutants were improved 17.0%, 19.0%, 12.9%, 23.9% and 18.0% , compared with the parent strain; the conservations from glycerol were improved 17.7%, 20.0%, 13.3%, 24.4% and 17.7%. CONCLUSION: Genome shuffling was an efficient approach for strain improvement, and 96 deep-well palates containing fed-batch broth has been demonstrated as an efficient selection approach.

Improved 1,3-propanediol production with hemicellulosic hydrolysates (corn straw) as cosubstrate: Impact of degradation products on Klebsiella pneumoniae growth and 1,3-propanediol fermentation.

To improve 1,3-propanediol (1,3-PD) production by an economic and efficient approach, hemicellulosic hydrolysates (HH) used as cosubstrate resulted in more biomass and higher reducing power for 1,3-PD production. The effects of primary degradation products such as individual sugars (xylose, glucose, mannose, arabinose and galactose) and major inhibitors (furfural, acetate and formate) on the Klebsiella pneumoiae growth and 1,3-PD production were investigated in this study. Xylose and mannose could efficiently promote the 1,3-PD production and cell growth. Furfural (0.28 g/l) and sodium acetate (1.46 g/l) in low concentration were not inhibitory to Klebsiella pneumoniae, rather they have stimulatory effect on the growth and 1,3-PD biosynthesis, especially the acetate. In fed-batch fermentation with HH as cosubstrate, the final 1,3-PD production, conversion from glycerol and productivity were 71.58 g/l, 0.65 mol/mol and 1.93 g/l/h, respectively, which were 17.8%, 25.0% and 17.7% higher than that from glycerol alone.

Multiferroic polymer composites with greatly enhanced magnetoelectric effect under a low magnetic bias.

Multiferroic laminate composites consisting of chain-end cross-linked ferroelectric polymers and magnetostrictive Metglas are reported. The composites exhibit a greatly enhanced multiferroic voltage coefficient and sensitivity relative to analogous composites. These remarkable properties are attributed to high piezoelectric and electromechanical coupling coefficients, because of the formation of larger crystalline sizes and concurrent improvement in the polarization ordering in the cross-linked polymers.

Dielectric relaxation of relaxor ferroelectric P(VDF-TrFE-CFE) terpolymer over broad frequency range.

Dielectric properties of a relaxor ferroelectric polymer, poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer, were investigated over a broad range of frequency (from 0.1 kHz to 1 GHz) and a broad range of temperature (-20 degrees C to 76 degrees C). Time-temperature superposition was used to extrapolate the dielectric constant to high frequencies (approximately 1 GHz) from low frequency data (1 MHz). The consistency between the directly measured and the extrapolated data indicate that the time-temperature superposition can be applied at temperature ranging from the glass transition to the broad ferroelectric-paraelectric transition peak of relaxor, indicating that the glass transition is still the dominating relaxation process at room temperature for the ferroelectric relaxor. Compared with the dielectric properties of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE] copolymer, the terpolymer shows a higher dielectric constant even at 1 GHz, which is considered to originate from the random defects modification converting the long-chain polar-molecular conformation to short-range molecular microstructures and enhancing the molecular motions in both polar and nonpolar nanodomains.