Showing papers on "Power density published in 2021"

Electroceramics for High-Energy Density Capacitors: Current Status and Future Perspectives

Abstract: Materials exhibiting high energy/power density are currently needed to meet the growing demand of portable electronics, electric vehicles and large-scale energy storage devices. The highest energy densities are achieved for fuel cells, batteries, and supercapacitors, but conventional dielectric capacitors are receiving increased attention for pulsed power applications due to their high power density and their fast charge-discharge speed. The key to high energy density in dielectric capacitors is a large maximum but small remanent (zero in the case of linear dielectrics) polarization and a high electric breakdown strength. Polymer dielectric capacitors offer high power/energy density for applications at room temperature, but above 100 °C they are unreliable and suffer from dielectric breakdown. For high-temperature applications, therefore, dielectric ceramics are the only feasible alternative. Lead-based ceramics such as La-doped lead zirconate titanate exhibit good energy storage properties, but their toxicity raises concern over their use in consumer applications, where capacitors are exclusively lead free. Lead-free compositions with superior power density are thus required. In this paper, we introduce the fundamental principles of energy storage in dielectrics. We discuss key factors to improve energy storage properties such as the control of local structure, phase assemblage, dielectric layer thickness, microstructure, conductivity, and electrical homogeneity through the choice of base systems, dopants, and alloying additions, followed by a comprehensive review of the state-of-the-art. Finally, we comment on the future requirements for new materials in high power/energy density capacitor applications.

Metallic Two-Dimensional MoS2 Composites as High-Performance Osmotic Energy Conversion Membranes.

Abstract: Molybdenum disulfide (MoS2) has shown large promise in harvesting osmotic energy. However, the current investigations generally focus on proof-of-concept nanoscale single-pore devices with a semiconductor phase structure. Exploration of the application viability of MoS2 in a more robust macroscopic-scale two-dimensional (2D) nanofluidic membrane and acquisition of fundamentals of how the phase structure influences the power generation process are highly demanded. Here, we demonstrate that robust and stable composite membranes made up of 2D metallic MoS2 can act as high-performance osmotic power generators. Both experiment and simulation reveal that the higher electron density of metallic MoS2 increases the affinity of cations to the surface, which renders the system excellent ion selectivity and high ionic flux and greatly promotes transmembrane ion diffusion. When natural river water and seawater are mixed, the power density can achieve about 6.7 W m-2. This work shows the great potential of metallic MoS2 in nanofluidic energy devices.

3D Carbon Frameworks for Ultrafast Charge/Discharge Rate Supercapacitors with High Energy-Power Density

Abstract: Carbon-based electric double layer capacitors (EDLCs) hold tremendous potentials due to their high-power performance and excellent cycle stability. However, the practical use of EDLCs is limited by the low energy density in aqueous electrolyte and sluggish diffusion kinetics in organic or/and ionic liquids electrolyte. Herein, 3D carbon frameworks (3DCFs) constructed by interconnected nanocages (10–20 nm) with an ultrathin wall of ca. 2 nm have been fabricated, which possess high specific surface area, hierarchical porosity and good conductive network. After deoxidization, the deoxidized 3DCF (3DCF-DO) exhibits a record low IR drop of 0.064 V at 100 A g−1 and ultrafast charge/discharge rate up to 10 V s−1. The related device can be charged up to 77.4% of its maximum capacitance in 0.65 s at 100 A g−1 in 6 M KOH. It has been found that the 3DCF-DO has a great affinity to EMIMBF4, resulting in a high specific capacitance of 174 F g−1 at 1 A g−1, and a high energy density of 34 Wh kg−1 at an ultrahigh power density of 150 kW kg−1 at 4 V after a fast charge in 1.11 s. This work provides a facile fabrication of novel 3D carbon frameworks for supercapacitors with ultrafast charge/discharge rate and high energy-power density.

Thermophotovoltaic Efficiency of 40

Abstract: We report the fabrication and measurement of thermophotovoltaic (TPV) cells with efficiencies of >40%. The TPV cells are 2-junction devices with high-quality 1.0-1.4 eV materials that target high emitter temperatures of 1900-2400°C. These cells can be integrated into a TPV system for thermal energy grid storage (TEGS) to enable dispatchable renewable energy. With these new TPV cells, TEGS has a pathway to reach sufficiently high efficiency and sufficiently low cost to enable full decarbonization of the grid. Furthermore, the high demonstrated efficiency gives TPV the potential to compete with turbine-based heat engines for large-scale power production with respect to both cost and performance, thereby enabling possible usage in natural gas or hydrogen-fueled electricity production.

From Fundamental Understanding to Engineering Design of High-Performance Thick Electrodes for Scalable Energy-Storage Systems.

Abstract: The ever-growing needs for renewable energy demand the pursuit of batteries with higher energy/power output. A thick electrode design is considered as a promising solution for high-energy batteries due to the minimized inactive material ratio at the device level. Most of the current research focuses on pushing the electrode thickness to a maximum limit; however, very few of them thoroughly analyze the effect of electrode thickness on cell-level energy densities as well as the balance between energy and power density. Here, a realistic assessment of the combined effect of electrode thickness with other key design parameters is provided, such as active material fraction and electrode porosity, which affect the cell-level energy/power densities of lithium-LiNi0.6 Mn0.2 Co0.2 O2 (Li-NMC622) and lithium-sulfur (Li-S) cells as two model battery systems, is provided. Based on the state-of-the-art lithium batteries, key research targets are quantified to achieve 500 Wh kg-1 /800 Wh L-1 cell-level energy densities and strategies are elaborated to simultaneously enhance energy/power output. Furthermore, the remaining challenges are highlighted toward realizing scalable high-energy/power energy-storage systems.

A branched dihydrophenazine-based polymer as a cathode material to achieve dual-ion batteries with high energy and power density

Abstract: Organic electrode materials have exhibited good electrochemical performance in batteries, but their voltages and rate capabilities still require improvement to meet the increasing demand for batteries with high energy and power density. Herein, we design and synthesize a branched dihydrophenazine-based polymer (p-TPPZ) as a cathode material for dual-ion batteries (DIBs) through delicate molecular design. Compared with the linear dihydrophenazine-based polymer (p-DPPZ, with a theoretical capacity of 209 mAh g–1), p-TPPZ possessed a higher theoretical capacity of 233 mAh g–1 and lower highest occupied molecular orbital energy levels, which resulted in a high actual capacity (169.3 mAh g–1 at 0.5 C), an average discharge voltage of 3.65 V (vs. Li+/Li) and a high energy density (618.2 Wh kg–1, based on the cathode materials). The branched structure of p-TPPZ led to a larger specific surface area than that of p-DPPZ, which was beneficial for the electrolyte infiltration and fast ionic transport, contributing to the high power density. Due to the fast reaction kinetics, even at a power density of 23, 725 W kg–1 (40 C), the energy density still reached 474.5 Wh kg–1. We also made a detailed investigation of the p-TPPZ cathode's charge storage mechanism. This work will stimulate the further molecular design to develop organic batteries with both high energy and power density.

Simultaneously with large energy density and high efficiency achieved in NaNbO3-based relaxor ferroelectric ceramics

Abstract: Dielectric capacitors are in urgent need of miniaturized and lightweight products. The new lead-free NaNbO3-based ferroelectric ceramic material is a good choice owing to its high energy storage density, superior charge/discharge performance and decent frequency/temperature stability. In this work, a novel lead-free relaxor ferroelectric ceramic, (1-x)NaNbO3-xBa(Mg1/3Nb2/3)O3 [(1-x)NN-xBMN, x = 0.18, 0.20, 0.22 and 0.24], was designed and prepared via a local random field strategy. The impedance analysis demonstrates that the introduction of BMN could enhance the insulation ability and breakdown strength of the (1-x)NN-xBMN ceramic. Finally, the excellent energy storage performances with simultaneously ultrahigh energy storage density (Wst～4.04 J/cm3), recoverable energy storage density (Wrec～3.51 J/cm3), efficiency (η～87 %) and fatigue endurance (number of cycles: 5000) are obtained in the 0.78NN-0.22BMN ceramic. In addition, excellent frequency (1～100 Hz) and temperature stability (20～140 °C) can also be observed in the 0.78NN-0.22BMN ceramic. It is crucial that the ceramic shows extremely short charge-discharge time (t0.9～45 ns), tremendous current density (CD～680 A/cm2), giant power density (PD～47.6 MW/cm3) and excellent temperature stability (30～150 °C). These results indicate that 0.78NN-0.22BMN ceramic is a promising dielectric capacitor material.

Design Principles of Sodium/Potassium Protection Layer for High-Power High-Energy Sodium/Potassium-Metal Batteries in Carbonate Electrolytes: a Case Study of Na2Te/K2Te

Abstract: The sodium (potassium)-metal anodes combine low-cost, high theoretical capacity, and high energy density, demonstrating promising application in sodium (potassium)-metal batteries. However, the dendrites' growth on the surface of Na (K) has impeded their practical application. Herein, density functional theory (DFT) results predict Na2 Te/K2 Te is beneficial for Na+ /K+ transport and can effectively suppress the formation of the dendrites because of low Na+ /K+ migration energy barrier and ultrahigh Na+ /K+ diffusion coefficient of 3.7 × 10-10 cm2 s-1 /1.6 × 10-10 cm2 s-1 (300 K), respectively. Then a Na2 Te protection layer is prepared by directly painting the nanosized Te powder onto the sodium-metal surface. The Na@Na2 Te anode can last for 700 h in low-cost carbonate electrolytes (1 mA cm-2 , 1 mAh cm-2 ), and the corresponding Na3 V2 (PO4 )3 //Na@Na2 Te full cell exhibits high energy density of 223 Wh kg-1 at an unprecedented power density of 29687 W kg-1 as well as an ultrahigh capacity retention of 93% after 3000 cycles at 20 C. Besides, the K@K2 Te-based potassium-metal full battery also demonstrates high power density of 20 577 W kg-1 with energy density of 154 Wh kg-1 . This work opens up a new and promising avenue to stabilize sodium (potassium)-metal anodes with simple and low-cost interfacial layers.

High power and stable P-doped yolk-shell structured Si@C anode simultaneously enhancing conductivity and Li+ diffusion kinetics

Abstract: Silicon is a low price and high capacity anode material for lithium-ion batteries. The yolk-shell structure can effectively accommodate Si expansion to improve stability. However, the limited rate performance of Si anodes can’t meet people’s growing demand for high power density. Herein, the phosphorus-doped yolk-shell Si@C materials (P-doped Si@C) were prepared through carbon coating on P-doped Si/SiOx matrix to obtain high power and stable devices. Therefore, the as-prepared P-doped Si@C electrodes delivered a rapid increase in Coulombic efficiency from 74.4% to 99.6% after only 6 cycles, high capacity retention of ∼ 95% over 800 cycles at 4 A·g−1, and great rate capability (510 mAh·g−1 at 35 A·g−1). As a result, P-doped Si@C anodes paired with commercial activated carbon and LiFePO4 cathode to assemble lithium-ion capacitor (high power density of ∼ 61,080 W·kg−1 at 20 A·g−1) and lithium-ion full cell (good rate performance with 68.3 mAh·g−1 at 5 C), respectively. This work can provide an effective way to further improve power density and stability for energy storage devices.

Power Density Optimization of 700 kHz GaN-Based Auxiliary Power Module for Electric Vehicles

Abstract: This article proposes a high-power density 1.8 kW auxiliary power module (APM) for electric vehicles (EVs) based on gallium nitride devices. A design procedure for the high-frequency phase-shift full-bridge with current-doubler rectifier using printed circuit board (PCB)-based planar magnetics is proposed. Leakage inductance analysis of the high-frequency pulsewidth-modulation converter is given to achieve both regulation and zero-voltage-switching turn- on . Then, the magnetics optimization procedure for the customized planar core is proposed with a magnetic figure-of-merit concept to meet the high-power density target. Technical considerations are detailed to meet the extreme temperature constraint imposed on the EVs components. Finally, the proposed APM is demonstrated with a switching frequency of 700 kHz and a power density of 8.1 kW/L (132.8 W/in3).

Bioinspired Hierarchical Nanofabric Electrode for Silicon Hydrovoltaic Device with Record Power Output.

Abstract: Direct electricity generation from water flow/evaporation, coined hydrovoltaic effect, has recently attracted intense interest as a facile approach to harvest green energy from ubiquitous capillary water flow or evaporation. However, the current hydrovoltaic device is inferior in output power efficiency compared to other renewable energy devices. Slow water evaporation rate and inefficient charge collection at device electrodes are two fundamental drawbacks limiting energy output efficiency. Here, we report a bioinspired hierarchical porous fabric electrode that enables high water evaporation rate, efficient charge collection, and rapid charge transport in nanostructured silicon-based hydrovoltaic devices. Such an electrode can efficiently collect charges generated in nanostructured silicon as well as induce a prompt water evaporation rate. At room temperature, the device can generate an open-circuit voltage (Voc) of 550 mV and a short-current density (Jsc) of 22 μA·cm-2. It can output a power density over 10 μW·cm-2, which is 3 orders of magnitude larger than all those reported for analogous hydrovoltaic devices. Our results could supply an effective strategy for the development of high-performance hydrovoltaic devices through optimizing electrode structures.

One Dimensional Graphene Nanoscroll -Wrapped MnO Nanoparticles for High-Performance Lithium Ion Hybrid Capacitors

Abstract: Lithium ion hybrid capacitors (LIHCs) have high power density and high energy density. One of the biggest problems in LIHCs is the kinetics mismatch of a battery-type anode and capacitive cathode due to relatively slow Li+ reaction kinetics compared to fast ion adsorption/desorption behavior. Here, to address this challenge, an efficient strategy was proposed to prepare a one dimensional (1D) graphene nanoscroll wrapped MnO nanoparticle (GNS@MnO) material by a simple freeze-drying process followed by annealing treatment. The topological end-opening architecture of the GNS and the wrapping of graphene layers facilitate fast Li+ diffusion and electron transfer. As an anode material of lithium ion batteries (LIBs), the optimized GNS@MnO-600 electrode exhibits outstanding performance for Li+ ion storage with a high specific capacity of 437 mA h g−1 even at 5.0 A g−1. The constructed LIHC based on the GNS@MnO-600 anode and 3D framework activated carbon (3DFAC) with a high specific surface area delivered a high energy density of 197 W h kg−1 at 235 W kg−1. Even at a high power density of 23.5 kW kg−1, a high energy density of 114 W h kg−1 is still maintained, as well as a long cycling life (84.8% capacity retention after 3000 cycles). We believe that this highly efficient 1D GNS wrapping strategy provides a novel design concept for the construction of fast kinetics anode materials for LIBs and LIHCs.

Graphene Nanosphere as Advanced Electrode Material to Promote High Performance Symmetrical Supercapacitor.

Abstract: To get carbon electrode with both excellent gravimetric and volumetric capacitances at high mass loadings is critical to supercapacitors. Herein, cracked defective graphene nanospheres (GNS) well meet above requirements. The morphology and structure of the GNS are controlled by polystyrene sphere template/glucose ratio, microwave heating time, and Fe content. The typical GNS with specific surface area of 2794 m2 g-1 , pore volume of 1.48 cm3 g-1 , and packing density of 0.74 g cm-3 performs high gravimetric and volumetric capacitances of 529 F g-1 and 392 F cm-3 at 1A g-1 with a capacitance retention of 62.5% at 100 A g-1 in a three-electrode system in 6 mol L-1 KOH aqueous electrolyte. In a two-electrode system, the GNS possesses energy density of 18.6 Wh kg-1 (13.8 Wh L-1 ) at the power density of 504 W kg-1 , which is higher than all reported pure carbon materials in gravimetric energy density and higher than all reported heteroatom-doped carbon materials in volumetric energy density, in aqueous solution, as far as it is known. A structural feature of carbon materials that possess both high energy density and high power density is pointed out here.

Ultrafast Li/Fluorinated Graphene Primary Batteries with High Energy Density and Power Density

Abstract: Lithium/fluorinated carbon (Li/CFx) primary batteries have essential applications in consumer electronics and medical and high-power military devices. However, their application is limited due to the difficulty in achieving simultaneous high power density and high energy density in the CFx cathode. The tradeoff between conductivity and fluorine content is the decisive factor. Herein, by rational design, 3D porous fluorinated graphene microspheres (FGS-x) with both high conductivity and a high F/C ratio are successfully synthesized for the first time. FGS-x possesses an F/C ratio as high as 1.03, a nanosheet structure with hierarchical pores, abundant C═C bonds, few inactive C-F2 bonds, and electrochemically active C-F bonds. The beneficial features that can increase discharge capacity, shorten the diffusion length for both ions and electrons, enhance the Li+ intercalation kinetics, and accommodate the volume change are demonstrated. The Li/FGS-1.03 coin cell delivers an unprecedented power density of 71,180.9 W/kg at an ultrahigh rate of 50 C (43.25 A/g), coupled with a high energy density of 830.7 Wh/kg. Remarkably, the Li/FGS-1.03 pouch cell exhibits a record cell-level power density of 12,451.2 W/kg at 20 C. The in-depth investigation by the ex situ method on structural evolution at different discharge depths reveals that the excellent performance benefits from the structural stability and the uniform formation of LiF. The FGS-1.03 cathode also has excellent performance in extreme operating temperatures (0 to 100 °C) and high active material mass loading (4.3 mg/cm2). These results indicate that the engineered fluorinated graphene developed here has great potential in applications requiring both high power density and high energy density.

Minimization of ion transport resistance: diblock copolymer micelle derived nitrogen-doped hierarchically porous carbon spheres for superior rate and power Zn-ion capacitors

Abstract: Although tremendous progress has been made in exploring high-energy-density aqueous Zn-ion capacitors (ZICs) recently, their rate capability and power density still remain great challenges. Herein, diblock copolymer micelle derived nitrogen-doped hierarchically porous carbon spheres (N-HPCSs) were fabricated for high energy aqueous ZICs with superior rate performance and power density. It was found that the reasonable pore size distribution and nitrogen-doping of N-HPCSs are favorable for mass transportation by smoothing and reducing the diffusion routes, leading to efficient and fast Zn-ion storage. Consequently, the as-assembled aqueous N-HPCS ZIC yielded a high capacity of 180.4 mA h g−1 at 0.5 A g−1, superior rate performance of maintaining 58.3 mA h g−1 even at an extremely high current density of 100 A g−1, a high energy density of 144.3 W h kg−1, and an excellent power density of 79.9 kW kg−1 with an ultrafast charge time of 2.1 seconds. Moreover, the aqueous N-HPCS ZIC displayed an exciting capacity retention of 98.2% after an ultra-long stability test of 50 000 cycles. This work proposes an efficient strategy to design high-performance electrodes for ZICs with ultrafast Zn-ion storage.