Showing papers on "Power density published in 2014"

High Energy and Power Density Capacitors from Solution-Processed Ternary Ferroelectric Polymer Nanocomposites

Abstract: Concurrent improvements in dielectric constant and breakdown strength are attained in a solution-processed ternary ferroelectric polymer nanocomposite incorporated with two-dimensional boron nitride nanosheets and zero-dimensional barium titanate nanoparticles that synergistically interact to enable a remarkable energy-storage capability, including large discharged energy density, high charge-discharge efficiency, and great power density.

A Shape‐Adaptive Thin‐Film‐Based Approach for 50% High‐Efficiency Energy Generation Through Micro‐Grating Sliding Electrification

Abstract: Effectively harvesting ambient mechanical energy is the key for realizing self-powered and autonomous electronics, which addresses limitations of batteries and thus has tremendous applications in sensor networks, wireless devices, and wearable/implantable electronics, etc. Here, a thin-film-based micro-grating triboelectric nanogenerator (MG-TENG) is developed for high-efficiency power generation through conversion of mechanical energy. The shape-adaptive MG-TENG relies on sliding electrification between complementary micro-sized arrays of linear grating, which offers a unique and straightforward solution in harnessing energy from relative sliding motion between surfaces. Operating at a sliding velocity of 10 m/s, a MG-TENG of 60 cm(2) in overall area, 0.2 cm(3) in volume and 0.6 g in weight can deliver an average output power of 3 W (power density of 50 mW cm(-2) and 15 W cm(-3)) at an overall conversion efficiency of ∼ 50%, making it a sufficient power supply to regular electronics, such as light bulbs. The scalable and cost-effective MG-TENG is practically applicable in not only harvesting various mechanical motions but also possibly power generation at a large scale.

A High-Density, High-Efficiency, Isolated On-Board Vehicle Battery Charger Utilizing Silicon Carbide Power Devices

Abstract: This paper presents an isolated on-board vehicular battery charger that utilizes silicon carbide (SiC) power devices to achieve high density and high efficiency for application in electric vehicles (EVs) and plug-in hybrid EVs (PHEVs). The proposed level 2 charger has a two-stage architecture where the first stage is a bridgeless boost ac-dc converter and the second stage is a phase-shifted full-bridge isolated dc-dc converter. The operation of both topologies is presented and the specific advantages gained through the use of SiC power devices are discussed. The design of power stage components, the packaging of the multichip power module, and the system-level packaging is presented with a primary focus on system density and a secondary focus on system efficiency. In this work, a hardware prototype is developed and a peak system efficiency of 95% is measured while operating both power stages with a switching frequency of 200 kHz. A maximum output power of 6.1 kW results in a volumetric power density of 5.0 kW/L and a gravimetric power density of 3.8 kW/kg when considering the volume and mass of the system including a case.

Reversible Near-Infrared Light Directed Reflection in a Self-Organized Helical Superstructure Loaded with Upconversion Nanoparticles

Abstract: Adding external, dynamic control to self-organized superstructures with desired functionalities is an important leap necessary in leveraging the fascinating molecular systems for applications. Here, the new light-driven chiral molecular switch and upconversion nanoparticles, doped in a liquid crystal media, were able to self-organize into an optically tunable helical superstructure. The resulting nanoparticle impregnated helical superstructure was found to exhibit unprecedented reversible near-infrared (NIR) light-guided tunable behavior only by modulating the excitation power density of a continuous-wave NIR laser (980 nm). Upon irradiation by the NIR laser at the high power density, the reflection wavelength of the photonic superstructure red-shifted, whereas its reverse process occurred upon irradiation by the same laser but with the lower power density. Furthermore, reversible dynamic NIR-light-driven red, green, and blue reflections in a single thin film, achieved only by varying the power density of the NIR light, were for the first time demonstrated.

Tailoring gadolinium-doped ceria-based solid oxide fuel cells to achieve 2 W cm−2 at 550 °C

Abstract: In low-temperature solid oxide fuel cells, power losses due to large ohmic resistances and activation barriers of ion transport are a common problem. Here, Lee et al. report a gadolinium-doped ceria-based solid oxide fuel cell, which overcomes the problem and achieves a power density of 2 W cm−2.

Facile synthesis of ZnCo2O4 nanowire cluster arrays on Ni foam for high-performance asymmetric supercapacitors

Abstract: ZnCo2O4 nanowire cluster arrays (NWCAs) were directly grown on Ni foam via a facile hydrothermal method. The resulting products were analyzed by using X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The ZnCo2O4 NWCAs on Ni foam were directly used as integrated electrodes for supercapacitors and exhibited a high specific capacitance of 4.05 F cm−2 at 20 mA cm−2 (1620 F g−1 at 8 A g−1) in 3 M KOH aqueous solution, and an excellent cycling ability at various current densities up to 100 mA cm−2 (40 A g−1); 90% of the initial capacitance remained after 6000 cycles. Moreover, the asymmetric supercapacitor had a high energy density of 41.00 W h kg−1 at a power density of 384 W kg−1 and 16.63 W h kg−1 at a high power density of 2561 W kg−1. Such excellent rate properties and superior cycling life suggest that ZnCo2O4 NWCAs can not only be applied in high energy density fields, but also used in high power density applications.

A vibration-based MEMS piezoelectric energy harvester and power conditioning circuit.

Abstract: This paper presents a micro-electro-mechanical system (MEMS) piezoelectric power generator array for vibration energy harvesting. A complete design flow of the vibration-based energy harvester using the finite element method (FEM) is proposed. The modal analysis is selected to calculate the resonant frequency of the harvester, and harmonic analysis is performed to investigate the influence of the geometric parameters on the output voltage. Based on simulation results, a MEMS Pb(Zr,Ti)O3 (PZT) cantilever array with an integrated large Si proof mass is designed and fabricated to improve output voltage and power. Test results show that the fabricated generator, with five cantilever beams (with unit dimensions of about 3 × 2.4 × 0.05 mm3) and an individual integrated Si mass dimension of about 8 × 12.4 × 0.5 mm3, produces a output power of 66.75 μW, or a power density of 5.19 μW∙mm-3∙g-2 with an optimal resistive load of 220 kΩ from 5 m/s2 vibration acceleration at its resonant frequency of 234.5 Hz. In view of high internal impedance characteristic of the PZT generator, an efficient autonomous power conditioning circuit, with the function of impedance matching, energy storage and voltage regulation, is then presented, finding that the efficiency of the energy storage is greatly improved and up to 64.95%. The proposed self-supplied energy generator with power conditioning circuit could provide a very promising complete power supply solution for wireless sensor node loads.

Two-dimensional heterostructures of V2O5 and reduced graphene oxide as electrodes for high energy density asymmetric supercapacitors

Abstract: In this article, we report the synthesis of electrode materials based on two-dimensional (2D) heterostructures of V2O5 nanosheets (V2O5 NS) and reduced graphene oxide (rGO) electrodes for asymmetric supercapacitor applications. Specifically, the 2D V2O5 and rGO/V2O5 nanosheet electrodes showed a specific capacitance of 253 F g−1 and 635 F g−1, respectively at a current density of 1 A g−1. The capacitance of the heterostructures is almost 2.5 times higher than the 2D V2O5 nanosheets alone. The corresponding energy density of 39 Wh kg−1 and 79.5 Wh kg−1 were achieved for the two electrodes at a power density of 900 W kg−1 in an asymmetric supercapacitor configuration. The energy and power density using the nanosheet heterostructure are, to our knowledge, higher than any of those that were previously reported for asymmetric supercapacitors using V2O5 electrodes.

Thermodynamic, Energy Efficiency, and Power Density Analysis of Reverse Electrodialysis Power Generation with Natural Salinity Gradients

Abstract: Reverse electrodialysis (RED) can harness the Gibbs free energy of mixing when fresh river water flows into the sea for sustainable power generation. In this study, we carry out a thermodynamic and energy efficiency analysis of RED power generation, and assess the membrane power density. First, we present a reversible thermodynamic model for RED and verify that the theoretical maximum extractable work in a reversible RED process is identical to the Gibbs free energy of mixing. Work extraction in an irreversible process with maximized power density using a constant-resistance load is then examined to assess the energy conversion efficiency and power density. With equal volumes of seawater and river water, energy conversion efficiency of ∼33–44% can be obtained in RED, while the rest is lost through dissipation in the internal resistance of the ion-exchange membrane stack. We show that imperfections in the selectivity of typical ion exchange membranes (namely, co-ion transport, osmosis, and electro-osmosis)...

Design and synthesis of 3D interconnected mesoporous NiCo2O4@CoxNi1−x(OH)2 core–shell nanosheet arrays with large areal capacitance and high rate performance for supercapacitors

Abstract: Design and fabrication of high performance pseudocapacitors from 3D hierarchical hybrid electrodes with large areal capacitance and excellent rate capability still remains a challenge. Here, 3D hierarchical hybrid mesoporous NiCo2O4@CoxNi1−x(OH)2 core–shell nanosheet arrays on Ni foam have been rationally designed and facilely synthesized via an electrodeposited routine for pseudocapacitor applications. Electrochemical measurements show that the NiCo2O4@Co0.33Ni0.67(OH)2 electrode material exhibits a large areal capacitance as high as 5.71 F cm−2 at a current density of ∼5.5 mA cm−2, as a result of our high mass loading up to ∼5.5 mg cm−2. Moreover, it exhibits an excellent rate capability (∼83.7% capacitance retention at 273 mA cm−2). Based on these excellent properties, an asymmetric supercapacitor based on 3D hierarchical hybrid mesoporous NiCo2O4@Co0.33Ni0.67(OH)2 nanosheet arrays as the positive electrode and CMK-3 as the negative electrode was successfully fabricated. The as-fabricated device achieved the maximum areal capacitance of 887.5 mF cm−2 (specific capacitance of 87.9 F g−1) at 5 mA cm−2 with a stable operational voltage of 1.6 V and a high energy density of 31.2 W h kg−1 at a power density of 396 W kg−1. Moreover, two asymmetric supercapacitors in series could power 5 mm diameter red round light-emitting diode (LED) indicators efficiently for more than 5 minutes. The present 3D hierarchical hybrid material electrode with remarkable electrochemical properties has significant potential applications in high energy density storage systems.

Vertically aligned BaTiO3 nanowire arrays for energy harvesting

Abstract: Nano-electromechanical systems (NEMS) developed using piezoelectric nanowires (NWs) have gained immense interest in energy harvesting applications as they are able to convert several different forms of mechanical energy sources into electric power and thereby function as reliable power sources for ultra-low power wireless electronics. In this work, a piezoelectric NEMS vibrational energy harvester is fabricated through the development of a synthesis process for vertically aligned barium titanate (BaTiO3) nanowire (NW) arrays directly on a conductive substrate. These poled ferroelectric NW arrays are characterized through direct vibration excitation and demonstrated to provide efficient harvesting of mechanical vibrational energy producing an average power density of ∼6.27 μW cm−3 from 1g acceleration. In order to substantiate the superior energy harvesting performance of the newly developed BaTiO3 NW arrays, a direct comparison is made with conventional ZnO NW arrays. Here, we clearly report that the ferroelectric BaTiO3 NW NEMS energy harvester has ∼16 times greater power density than the ZnO NW NEMS energy harvester from the same acceleration input.

Super-stretchy lithium-ion battery based on carbon nanotube fiber

Abstract: Super-stretchy, fiber-shaped lithium-ion batteries with a record strain of 600% are developed by winding two highly aligned carbon nanotube composite fibers. The fiber-shaped battery exhibits high specific capacity, energy density and power density that can be well-maintained under stretching.

High-Frequency PWM Buck Converters Using GaN-on-SiC HEMTs

Abstract: GaN high electron mobility transistors (HEMTs) are well suited for high-frequency operation due to their lower on resistance and device capacitance compared with traditional silicon devices. When grown on silicon carbide, GaN HEMTs can also achieve very high power density due to the enhanced power handling capabilities of the substrate. As a result, GaN-on-SiC HEMTs are increasingly popular in radio-frequency power amplifiers, and applications as switches in high-frequency power electronics are of high interest. This paper explores the use of GaN-on-SiC HEMTs in conventional pulse-width modulated switched-mode power converters targeting switching frequencies in the tens of megahertz range. Device sizing and efficiency limits of this technology are analyzed, and design principles and guidelines are given to exploit the capabilities of the devices. The results are presented for discrete-device and integrated implementations of a synchronous Buck converter, providing more than 10-W output power supplied from up to 40 V with efficiencies greater than 95% when operated at 10 MHz, and greater than 90% at switching frequencies up to 40 MHz. As a practical application of this technology, the converter is used to accurately track a 3-MHz bandwidth communication envelope signal with 92% efficiency.

Electrodeposition of vanadium oxide–polyaniline composite nanowire electrodes for high energy density supercapacitors

Abstract: To meet the increasing demand for high energy density supercapacitors, it is crucial to develop positive and negative electrodes with comparable energy density. Previous studies have primarily focused on the development of positive electrodes, while negative electrodes are relatively less explored. Here we report an electro-codeposition method to synthesize a high performance negative electrode composed of a vanadium oxide (V2O5) and polyaniline (PANI) composite. Scanning electron microscopy revealed that the composite film is composed of one-dimensional polymer chains. Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) confirmed successful incorporation of V2O5 into PANI chains. Significantly, the V2O5–PANI composite nanowires exhibited a wide potential window of 1.6 V (between −0.9 and 0.7 V vs. SCE) and a maximum specific capacitance of 443 F g−1 (664.5 mF cm−2). The flexible symmetric supercapacitor assembled with this composite film yielded a maximum energy density of 69.2 W h kg−1 at a power density of 720 W kg−1, and a maximum power density of 7200 W kg−1 at an energy density of 33.0 W h kg−1. These values are substantially higher than those of other pure V2O5 or PANI based supercapacitors. Moreover, the assembled symmetric supercapacitor device showed an excellent stability with 92% capacitance retention after 5000 cycles. The capability of synthesizing high performance composite electrodes using the electro-codeposition method could open up new opportunities for high energy density supercapacitors.

Aerodynamic Fluid Bearings for Translational and Rotating Capacitors in Noncontact Capacitive Power Transfer Systems

Abstract: Wireless power transfer (WPT) is commonly accomplished with magnetic (inductive) techniques for a wide range of applications. Electrostatic or capacitive power transfer (CPT) approaches to WPT have had limited exposure primarily due to lower achievable power density when compared to inductive WPT techniques. Recently, high-frequency (in kilohertz to megahertz) power electronics have reintroduced capacitive techniques as an option for WPT over short distances ( <; 2 mm) for applications such as slip ring replacement. To further the practicality of CPT, capacitive coupling must be maximized in an effective manner, i.e., the volumetric capacitance density of rotating/translational capacitors must be significantly increased. This paper proposes the use of aerodynamic fluid bearings to maximize capacitive coupling between stationary and moving surfaces, by minimizing their separation distance, allowing for greater surface area per unit volume. The technique allows micrometers of separation distance between moving surfaces while maintaining manufacturability and mechanical robustness. Coupling capacitance is increased up to 100 times greater than rigid plate rotating and translational CPT systems. Additional benefits include the estimation of mechanical system parameters such as speed. Operational characteristics and design highlights are presented and corroborated with experimental results for general slip ring replacement applications.

Theoretical modeling and analysis of mechanical impact driven and frequency up-converted piezoelectric energy harvester for low-frequency and wide-bandwidth operation

Abstract: Vibration energy harvesters are capable of generating significant amount of power at higher frequencies rather than generating at low frequencies. Moreover, as low frequency vibrations (1–30 Hz) around the ambient environment are discursive in nature, resonance based power generators are limited to use within this low frequency range. In this paper, a mechanical impact driven and frequency up-converted wide-bandwidth piezoelectric vibration energy harvester has been proposed and demonstrated theoretically and experimentally. It converts low frequency environmental vibrations into high frequency vibration by mechanical impact. A low frequency flexible driving beam with horizontally extended tip mass, upon excitation, hits two high frequency rigid piezoelectric generating beams at the same time causing a change in the driving beam's effective stiffness that allows the device to offer approximately 180% increased −3 dB bandwidth and more than 62% of the maximum power generation within the remaining operating frequency range as well. The overall bandwidth is 7.5 Hz within 7–14.5 Hz frequency range generating a minimum peak power of 233 μW. A maximum of 378 μW peak power from one generating beam is achieved under 6 ms −2 acceleration at the resonant frequency of 14.5 Hz. Output of both generating beams connected in series produces 734 μW peak power under the same operating condition with the corresponding power density 38.8 μW cm −3 . The experimental results show some discrepancy with the theoretical results due to mechanical loss during impact and the process variations in the beam formation and assembling. The theoretical and experimental results reveal that the proposed configuration has the potential of powering small portable, handheld wireless smart devices from low frequency, specially human motion related vibrations.

Particle Size Polydispersity in Li-Ion Batteries

Abstract: Starting from three-dimensional X-ray tomography data of a commercial LiMn2O4 battery electrode, the effect of microstructure on the electrochemical and chemo-mechanical response of lithium-ion batteries is analyzed. Simulations show that particle size polydispersity impact the local chemical and electrical behavior of a porous electrode, while particle-particle mechanical interactions favor intercalation induced stress accumulation, resulting in a mechanically unreliable electrode microstructure. Simulations based on computer-generated electrode microstructures demonstrate that broad particle size distributions deliver up to two times higher energy density than monodisperse-sized particles based electrodes for low C-rates. However, monodisperse particle size distribution electrodes deliver the highest energy and power density for high discharge rates due to a higher surface area of reactive material per unit volume. Calculations show that the surface roughness in experimentally determined electrodes is 2.5 times higher than the one delivered by perfectly smooth spherical particles in computer generated electrodes, and provide high instantaneous power performance, but accelerate side reactions that impact negatively on power performance. The combined experimental and modeling approach demonstrates that porous electrodes with spatially uniform microstructural features improve electrochemical performance and mechanical reliability, especially for high power density applications. © 2014 The Electrochemical Society. All rights reserved.

Periodic feedwater reversal and air sparging as antifouling strategies in reverse electrodialysis

Abstract: Renewable energy can be generated using natural streams of seawater and river water in reverse electrodialysis (RED). The potential for electricity production of this technology is huge, but fouling of the membranes and the membrane stack reduces the potential for large scale applications. This research shows that, without any specific antifouling strategies, the power density decreases in the first 4 h of operation to 40% of the originally obtained power density. It slowly decreases further in the remaining 67 days of operation. Using antifouling strategies, a significantly higher power density can be maintained. Periodically switching the feedwaters (i.e., changing seawater for river water and vice versa) generates the highest power density in the first hours of operation, probably due to a removal of multivalent ions and organic foulants from the membrane when the electrical current reverses. In the long term, colloidal fouling is observed in the stack without treatment and the stack with periodic feedwater switching, and preferential channeling is observed in the latter. This decreases the power density further. This decrease in power density is partly reversible. Only a stack with periodic air sparging has a minimum of colloidal fouling, resulting in a higher power density in the long term. A combination of the discussed antifouling strategies, together with the use of monovalent selective membranes, is recommended to maintain a high power density in RED in short-term and long-term operations.

Development of high power and energy density microsphere silicon carbide–MnO2 nanoneedles and thermally oxidized activated carbon asymmetric electrochemical supercapacitors

Abstract: In order to achieve high energy and power densities, a high-voltage asymmetric electrochemical supercapacitor has been developed, with activated carbon (AC) as the negative electrode and a silicon carbide–MnO2 nanoneedle (SiC–N-MnO2) composite as the positive electrode. A neutral aqueous Na2SO4 solution was used as the electrolyte. SiC–N-MnO2 was prepared by packing growing MnO2 nanoneedle crystal species in only one direction on the silicon carbide surface. AC was oxidized by thermal treatment in order to introduce oxygen-containing functional groups. Owing to the high capacitance and excellent rate performance of SiC–N-MnO2 and AC, as well as the synergistic effects of the two electrodes, a constructed asymmetric supercapacitor exhibited superior electrochemical performance. The optimized asymmetric supercapacitor could be cycled reversibly in the voltage range from 0 to 1.9 V, and it exhibited a specific capacitance of 59.9 F g−1 at a scan rate of 2 mV s−1 and excellent energy density and power density (30.06 W h kg−1 and 113.92 W kg−1, respectively) with a specific capacitance loss of less than 3.1% after 1000 charge–discharge cycles, indicating excellent electrochemical stability. These encouraging results show great potential in terms of developing energy storage devices with high energy and power densities for practical applications.

Design of segmented thermoelectric generator based on cost-effective and light-weight thermoelectric alloys

Abstract: A segmented thermoelectric (TE) generator was designed with higher temperature segments composed of n-type Mg 2 Si and p-type higher manganese silicide (HMS) and lower temperature segments composed of n- and p-type Bi–Te based compounds. Since magnesium and silicon based TE alloys have low densities, they produce a TE module with a high specific power density that is suitable for airborne applications. A two-pair segmented π-shaped TE generator was assembled with low contact resistance materials across bonding interfaces. The peak specific power density of this generator was measured at 42.9 W/kg under a 498 °C temperature difference, which has a good agreement with analytical predictions.