Composition-dependent xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 bulk ceramics for high energy storage applications

This work reports the composition dependent microstructure, dielectric, ferroelectric and energy storage properties, and the phase transitions sequence of lead free xBa(Zr_0.2Ti_0.8)O₃-(1-x)(Ba_0.7Ca_0.3)TiO₃ [xBZT-(1-x)BCT] ceramics, with x?=?0.4, 0.5 and 0.6, prepared by solid state reaction method. The XRD and Raman scattering results confirm the coexistence of rhombohedral and tetragonal phases at room temperature (RT). The temperature dependence of Raman scattering spectra, dielectric permittivity and polarization points a first phase transition from ferroelectric rhombohedral phase to ferroelectric tetragonal phase at a temperature (T_R-T) of 40?°C and a second phase transition from ferroelectric tetragonal phase - paraelectric pseudocubic phase at a temperature (T_T-C) of 110?°C. The dielectric analysis suggests that the phase transition at T_T-C is of diffusive type and the BZT-BCT ceramics are a relaxor type ferroelectric materials. The composition induced variation in the temperature dependence of dielectric losses was correlated with full width half maxima (FWHM) of A₁, E(LO) Raman mode. The saturation polarization (P_s) ≈8.3?μC/cm² and coercive fields ≈2.9?kV/cm were found to be optimum at composition x?=?0.6 and is attributed to grain size effect. It is also shown that BZT-BCT ceramics exhibit a fatigue free response up to 10⁵ cycles. The effect of a.c. electric field amplitude and temperature on energy storage density and storage efficiency is also discussed. The presence of high T_T-C (110?°C), a high dielectric constant (ε_r ≈?12,285) with low dielectric loss (0.03), good polarization (P_s ≈?8.3?μC/cm²) and large recoverable energy density (W?=?121?mJ/cm³) with an energy storage efficiency (η) of 70% at an electric field of 25?kV/cm in 0.6BZT-0.4BCT ceramics make them suitable candidates for energy storage capacitor applications.     

Scalable Production of Wearable Solid-State Li-Ion Capacitors from N-Doped Hierarchical Carbon

Smart and wearable electronics have aroused substantial demand for flexible portable power sources, but it remains a large challenge to realize scalable production of wearable batteries/supercapacitors with high electrochemical performance and remarkable flexibility simultaneously. Here, a scalable approach is developed to prepare wearable solid-state lithium-ion capacitors (LICs) with superior performance enabled by synergetic engineering from materials to device architecture. Nitrogen-doped hierarchical carbon (HC) composed of 1D carbon nanofibers welded with 2D carbon nanosheets is synthesized via a unique self-propagating high-temperature synthesis (SHS) technique, which exhibits superior electrochemical performance. Subsequently, inspired by origami, here, wave-shaped LIC punch-cells based on the above materials are designed by employing a compatible and scalable post-imprint technology. Finite elemental analysis (FEA) confirms that the bending stress of the punch-cell can be offset effectively, benefiting from the wave architecture. The wearable solid-state LIC punch-cell exhibits large energy density, long cyclic stability, and superior flexibility. This study demonstrates great promise for scalable fabrication of wearable energy-storage systems.     

Flexible and transparent capacitors based on gel-type natural polymers

In this work, we study the capacitive properties of gel-type natural abundant polymers without any dopants, mainly commercial gelatin and agar in deionized water. Here, we propose a facile fabrication of flexible, transparent, and planar electrolytic capacitors using these gel-type and indium tin oxide thin films as electrodes deposited on poly(ethylene terephthalate) substrates. Through cyclic voltammetry and galvanostatic charge–discharge techniques, we found that the devices show a specific capacitance in the order of the millifarads per gram, a specific power of ~10 mW cm⁻², which is sufficient to active low-power devices, and a life cycle with nearly 100% efficiency after 1,000 cycles. We found that we do not need to add dopants that improve the ionic conductivity of the natural polyelectrolytes to obtain capacitances within the millifarads per gram. The flexibility of the capacitors was demonstrated by bending them, after which they exhibited the same electrochemical performance as the unbent devices. The optical transparency of the capacitors was measured by UV–V is spectroscopy showing a high transmittance in the visible region.     

High energy-storage density under low electric fields and improved optical transparency in novel sodium bismuth titanate-based lead-free ceramics

A novel (1-x)Na_0.5Bi_0.5TiO₃-xBaHfO₃ (abbreviated as (1-x)NBT-xBH) transparent ceramic was fabricated by the solid state reaction method. X-ray diffraction analysis showed that NBT-based transparent ceramics exhibit a cubic-like perovskite structure and the solid solubility of BH in NBT reached to 0.15. The Landau-Devonshire theory and I-E curves revealed that the transition between the antiferroelectric like phase and the ferroelectric phase deeply relies on the variation of composition and free energy. One sample (x = 0.15) was found to show a high dielectric constant (˜2418±10%) over the temperature range 57–400 °C. These ceramics also exhibited a high discharge energy density (W_d) of 2.1 J/cm³ and a high maximum polarization P_m of 34 μC/cm² under relatively low electric fields which were less than 175 kV/cm. There was also high transparency in the visible spectra (more than 0.5) when the sample thickness was 250 μm.     

Organic Bioelectronics: From Functional Materials to Next-Generation Devices and Power Sources

Conjugated polymers (CPs) possess a unique set of features setting them apart from other materials. These properties make them ideal when interfacing the biological world electronically. Their mixed electronic and ionic conductivity can be used to detect weak biological signals, deliver charged bioactive molecules, and mechanically or electrically stimulate tissues. CPs can be functionalized with various (bio)chemical moieties and blend with other functional materials, with the aim of modulating biological responses or endow specificity toward analytes of interest. They can absorb photons and generate electronic charges that are then used to stimulate cells or produce fuels. These polymers also have catalytic properties allowing them to harvest ambient energy and, along with their high capacitances, are promising materials for next-generation power sources integrated with bioelectronic devices. In this perspective, an overview of the key properties of CPs and examination of operational mechanism of electronic devices that leverage these properties for specific applications in bioelectronics is provided. In addition to discussing the chemical structure–functionality relationships of CPs applied at the biological interface, the development of new chemistries and form factors that would bring forth next-generation sensors, actuators, and their power sources, and, hence, advances in the field of organic bioelectronics is described.     

Remarkably enhanced energy storage properties of lead-free Ba0.53Sr0.47TiO3 thin films capacitors by optimizing bottom electrode thickness

The lead-free Ba_0.53Sr_0.47TiO₃ (BST) thin films buffered with La_0.67Sr_0.33MnO₃ (LSMO) bottom electrode of different thicknesses were fabricated by pulsed laser deposition method on a (001) SrTiO₃ substrate. It was found that the roughness of electrode decreases and substrate stress relaxes gradually with the increase of LSMO thickness, which is beneficial for weakening local high electric field and achieving higher E_b. Therefore, the recoverable energy density (W_rec) of BST films can be greatly improved up to 67.3 %, that is, from 30.6 J/cm³ for the LSMO thickness of 30 nm up to 51.2 J/cm³ for the LSMO thickness of 140 nm after optimizing the LSMO thickness. Furthermore, the thin film capacitor with a 140 nm LSMO bottom electrode shows an outstanding thermal stability from 20 °C to 160 °C and superior fatigue resistance after 10⁸ electrical cycles with only a slightly decrease of W_rec below 1.6 % and 3.7 %, respectively. Our work demonstrates that optimizing bottom electrodes thickness is a promising way for enhancing energy storage properties of thin-film capacitors.     

Shunt capacitor placement in radial distribution networks considering switching transients decision making approach

This paper provides a new approach in decision making process for shunt capacitor placement in distribution networks. The main core of the evaluation process is a multi-objective framework to allocate the capacitor banks. The power loss and the total harmonic distortion (THD) are the objective functions of the system under study in a long-term planning horizon. In order to select the executive plan introduced by using a multi-objective model, transient switching overvoltages have been considered. As the size and location of shunt capacitors may result in unacceptable overvoltages, the proposed technical decision making framework can be applied to avoid corresponding damages. In this paper, an iterative conventional power flow technique is introduced. This technique can be applied to evaluate THD for distribution networks as well as other power flow based objectives, such as power losses calculation and voltage stability assessment. The presented framework is a two stage one where at the first stage, a non-dominated sorting genetic algorithm (NSGA-II) augmented with a local search technique is used in order to solve the addressed multi-objective optimization problem. Then, at the second stage, a decision making support technique is applied to determine the best solution from the obtained Pareto front. In order to evaluate the effectiveness of the proposed method, two benchmarks are addressed in this paper. The first test system is a 9-bus distribution network and the second one is an 85-bus large scale distribution network. The simulation results show that the presented method is satisfactory and consistent with the expectation.     

基于电容阵列I-V测试仪的光伏STC曲线拟合研究

现有的光伏组件在标准条件(STC)下I-V曲线的拟合算法存在计算过于复杂或准确度不足的问题。为提高曲线在偏离STC环境下的拟合准度,提出了一种依据太阳电池四参数结构,通过选取曲线最大功率点(MPP)附近6个点作为拟合点,计算组件I-V数学模型从而实现曲线拟合的拟合算法。不同光伏组件的最优拟合点间隔不同,为提高拟合精度,进一步提出了自适应拟合点选取方法,同时设计了以电容阵列为负载的I-V测试仪结构并研制了一套完整仪器。该测试仪可通过增加MPP附近数据点的密度,提升拟合点的选取精度。经过MATLAB仿真与实际验证表明,模型拟合算法的拟合结果在各种测试环境下的准确度均高于多项式拟合算法;所设计的I-V测试仪性能优越,适用于工程测量之中。     

Microstructure evolution during the co-sintering of Ni/BaTiO3 multilayer ceramic capacitors modeled by discrete element simulations

Electrode discontinuities are a critical issue for manufacturing ultrathin multilayer ceramic capacitors (MLCCs). The Discrete Element Method is used to simulate, at the particle length scale, the microstructure evolution during the co-sintering of state-of-the-art nickel based-MLCCs. Electrode discontinuities are considered to originate from the heterogeneities in the initial powder packing and to grow because of the constraint imposed by adjacent dielectric layers. A parametric study demonstrates that: (i) fast heating rate leads to lower electrode discontinuity during heating, (ii) green density and thickness of the electrode should be optimized to improve the electrode connectivity, (iii) rearrangement of the nickel particles plays a significant role in electrode discontinuity, and (iv) the addition of non-sintering inclusions can improve the electrode connectivity. These findings can be generalized to other multilayer components.     

双电层电容器用中微双孔活性炭的研究进展

文章介绍了中微双孔活性炭的制备方法,综述了用作双电层电容器的最新应用研究,为中微双孔活性炭在双电层电容器中的应用提供参考。