Low Energy Density Research Articles

Microstructure, hardness, and creep of Co-Fe-Ni-based high-entropy superalloy processed by laser powder-bed fusion

A Co-Fe-Ni-based high-entropy superalloy (29Co-29Fe-29Ni-4.3Al-4.3Ti-4.3 V, at.%) designed to form a γ/γ′ microstructure was fabricated via laser powder-bed fusion, utilizing a blend of elemental powders. The hardness and microstructure were compared in terms of laser processing parameters, heat treatment conditions, and fabrication methods. Lower volumetric energy density (45 J/mm³) for fusion favor the formation of swirl-shaped, partially-mixed regions. The extent of elemental enrichment and depletion varies from region to region, even within the same sample. Upon direct aging of these inhomogeneous as-built samples, γ′ precipitates form along cell boundaries, which is attributed to strong segregation of Ni and Ti elements at these boundaries. After homogenization of the as-built samples, a uniform distribution of fine γ′ precipitates is achieved through aging. The hardness of a homogenized traditionally-cast sample is lower than that of an as-built sample, owing to differences in grain size. Nevertheless, both samples aged under the same conditions exhibited a similar level of hardness, attributed to strengthening by the γ′ phase.

A Micro Battery Supercapacitor Hybrid Device with Ultrahigh Cycle Lifespan and Power Density Enabled by Bi‐Functional Coating Design

AbstractMicro energy storage devices (MESDs) have emerged as promising energy providers for micro applications due to their integrated performance. However, the limited cycle life and low power density of microbattery, and low energy density of microsupercapacitor have consistently impeded their broader practical implementation. Herein, to obtain a MESD with a long cycle life, excellent power density, and superior energy density, a novel micro battery‐supercapacitor hybrid (MBSH) device is fabricated. Two types of 3D microelectrodes are fabricated, namely, a nanowire network anode based on PEDOT‐TiON and a porous cathode based on Ni(OH)2. Benefiting from the unique hydrophobic characteristics of the PEDOT layer, high electrical conductivity of TiON, and high conductivity, and abundant ion diffusion channels of network microstructure, PEDOT‐TiON NW microelectrodes demonstrate exceptional cycling stability by retaining 70% of their capacity after 40 000 cycles. The achieved MBSH exhibits an extended voltage window ranging from 0 to 1.9 V, impressive power density of 77.5 mW cm−2, and a superior energy density of 55.6 µWh cm−2. Furthermore, it maintains a remarkable capacity retention rate of 71.6% even after undergoing 30 000 cycles. This innovative design paves the way for the developing of high‐performance microdevices with superior electrochemical properties.

Fabrication of high-quality microlens arrays on fused silica based on combined rapid evaporative ablation and precision melting polishing of CO2 lasers

Microlens arrays (MLAs) made from fused silica possess broad applications in wavefront sensing, optical focusing, beam shaping, etc. However, it is challenging to fabricate the hard-brittle silica MLAs with high accuracy and low cost by conventional manufacturing techniques efficiently. In this work, a novel two-step method, which consists of rapid evaporative ablation and precision melting polishing by CO2 lasers, is proposed to fabricate high-quality MLAs. The first step is to rapidly ablate and engrave micro-pillar arrays (MPAs) with flat groove bottom by high-energy density CO2 lasers. The second step is to precisely polish and shape the flat-topped MPAs into the dome-topped MLAs with good surface roughness (Sa) by low-energy density CO2 lasers. The whole preparation process could be achieved through a set of machining system. Firstly, the geometric dimension (period, p and height, h) of the microlens is determined by the Monte Carlo ray tracing method. Secondly, to diminish the groove depth inconsistency caused by heat accumulation, the multiple ablation compensation strategy is developed. The MPAs (p = 200–400 μm), of which maximum height error is 7.1%, are prepared in 1 s by the proposed compensation strategy. Then, the MPAs are smoothed into the MLAs by low-energy density CO2 lasers, and the average Sa is improved from 960 nm to 32.56 nm. Finally, the optical performances of the MLAs are verified from the effectiveness of imaging, focusing and homogenization. The proposed two-step processing method paves a new way to fabricate high-performance MLAs on hard-brittle fused silica with low cost and high efficiency.

Cauliflower-like Ni/NiCoP@Boron-doped diamond composite electrodes for high-performance symmetric supercapacitors

Due to the lack of electrocatalytic active sites, the supercapacitors (SCs) even based on the most stable sp3 carbon material (Boron-doped diamond) suffer from poor capacitance and low energy density. Herein, a cauliflower-like biphasic Ni/NiCoP layer has been successfully deposited on the BDD film and further applied as binder-/current collector-free SC electrodes. In a redox-active aqueous electrolyte (0.05 M Fe(CN)63−/4− + 1.0 M KOH), the Ni/NiCoP@BDD electrode with exceptional cyclic stability (∼89.0 % after 10,000 cycles) delivers a specific capacitance of 256.1 mF cm−2 at a current density of 30 mA cm−2, about 2 times higher than that in inert electrolyte. Furthermore, such a symmetric PC device provides a desired energy density of 70.0 Wh kg−1 at a high power density of 3601 W kg−1.

Toward High-Energy-Density Aqueous Zinc-Iodine Batteries: Multielectron Pathways.

Aqueous zinc-iodine batteries (ZIBs) based on the reversible conversion between various iodine species have garnered global attention due to their advantages of fast redox kinetics, good reversibility, and multielectron conversion feasibility. Although significant progress has been achieved in ZIBs with the two-electron I-/I2 pathway (2eZIBs), their relatively low energy density has hindered practical application. Recently, ZIBs with four-electron I-/I2/I+ electrochemistry (4eZIBs) have shown a significant improvement in energy density. Nonetheless, the practical use of 4eZIBs is challenged by poor redox reversibility due to polyiodide shuttling during I-/I2 conversion and I+ hydrolysis during I2/I+ conversion. In this Review, we thoroughly summarize the fundamental understanding of two ZIBs, including reaction mechanisms, limitations, and improvement strategies. Importantly, we provide an intuitive evaluation on the energy density of ZIBs to assess their practical potential and highlight the critical impacts of the Zn utilization rate. Finally, we emphasize the cost issues associated with iodine electrodes and propose potential closed-loop recycling routes for sustainable energy storage with ZIBs. These findings aim to motivate the practical application of advanced ZIBs and promote sustainable global energy storage.

N, O and P co-doped hierarchically porous carbon fiber for high performance Zinc-ion hybrid capacitors

Multi-heteroatoms co-doped hierarchically porous carbon-based electrode is an effective strategy to solve the low energy density and poor cycle stability of Zn-ion hybrid capacitors (ZHCs). Herein, N/O/P co-doped porous carbon nanofiber (N-P-PCF) was prepared, which displays fibrous network hierarchically porous structure to fast electron/ Zn2+ transport and enhance Zn2+ adsorption sites. Meanwhile, rich N (9.47 at.%), O (11.29 at.%) and P (1.29 at.%) co-doping can be beneficial for the infiltration of electrode–electrolyte interface and provide an additional pseudocapacitance. The N-P-PCF based ZHCs can yield a large specific capacitance (205 mAh g−1 at 1 A g−1), high energy density (173 Wh kg−1 at 823 W kg−1) and excenllent cycle stability for 10,000 cycles (98.6 % capacity retention), which provides a reliable multi-heteroatoms co-doped porous carbon fiber for high-performance ZHCs.

A comprehensive study of LPBF parameter influence in 316L stainless steel mechanical properties, macrostructure, and printability

Additive manufacturing, particularly using Laser Powder Bed Fusion (LPBF) technologies with 316L stainless steel, has proven highly promising in biomedical engineering due to the material’s exceptional mechanical properties and biocompatibility. This study, which is a foundational step towards developing porous bone implants, focuses on assessing the influence of a broad range of parameters - spot size, scanning speed, laser power, and energy density - on the mechanical performance and structural integrity of 316L stainless steel parts across three distinct specimen geometries: fully dense parallelepipedic, fully dense cubic, and cellular (lattice) specimens. By analysing 17 different parameter sets and producing over 150 specimens, a thorough series of experimental tests were conducted, including flexural tests, compression tests, hardness tests, macroscopic evaluation of the surface of fully dense specimens, and macroscopic evaluation of the lattice structures.e in powder accumulation within the pores of cellular structures, with higher energy densities (100 J/mm3) leading to a significantly greater retention compared to lower energy densities (66 J/mm3). This underexplored phenomenon has significant implications for the selection of parameters in the fabrication of bone implants. Further research is needed to refine LPBF printing parameters and enhance the quality of porous bone implants.

Acidic "Water-in-Salt" Electrolyte Enables a High-Energy Symmetric Supercapacitor Based on Titanium Carbide MXene.

Titanium carbide MXene, Ti3C2Tx, exhibits ultrahigh capacitance in acidic electrolytes at negative potentials yet poor stability at positive potentials, resulting in low-energy densities for Ti3C2Tx-based symmetric supercapacitors. Utilizing "water-in-salt" electrolytes has successfully expanded the stable operation potential window of MXenes. However, this advancement comes at the cost of sacrificing their high capacitance in acidic electrolytes. In this work, we report an acidic "water-in-salt" (AWIS) electrolyte composed of sulfuric acid and saturated lithium halide, which effectively doubled the energy density of the Ti3C2Tx-based symmetric supercapacitor compared to those with bare acidic electrolytes. Specifically, the AWIS electrolyte successfully expanded the voltage window of the symmetric device to 1.1 V. A high specific capacitance of 112.34 F g-1 (at 10 mV s-1) was obtained due to the presence of proton redox. As a result, the symmetric device achieved a high-energy density of 19.1 Wh kg-1 and a high capacitance retention of 96.3% after 10,000 cycles. This work demonstrates the importance of designing stable and redox-active electrolytes for high-energy MXene-based symmetric supercapacitors.

Multi-objective optimization of airfoils with integral tubular high-pressure tanks for hydrogen storage

Reducing the environmental impact of air transport is one of today's most important challenges in aviation industry and research. A promising key enabler is the use of hydrogen as an alternative to fossil fuels. The development of hydrogen-powered aircraft poses new engineering challenges due to its low volumetric energy density requiring high-pressure or cryogenic storage. If the volume in the wing shall be further used for storing hydrogen under high pressure, new demands arise to airfoil design. The present work focuses on this issue by presenting a multi-objective optimization approach aiming for airfoils with both low drag and high volume for internal tubular high-pressure tanks. This allows to directly address the new design objective and to find novel airfoil shapes providing the best compromise between aerodynamic efficiency and high storage volume for pressurized hydrogen. The resulting optimization problem is solved using Evolutionary Algorithms. For an efficient aerodynamic evaluation, the open source viscous-inviscid panel method XFOIL is used. An application example, based on the flight conditions of a general aviation aircraft, demonstrates the applicability of the method. Comparisons of the resulting aerodynamic characteristics obtained by XFOIL with RANS simulations confirm the feasibility of the results.

Energy storage performance of sandwich structure dielectric composite by BNNS/TiO2 Co-doping for the high electric field capacitor

Dielectric capacitors are crucial for power systems and hybrid vehicles. However, the polymer dielectric owns low energy density and cannot meet the demands of high-power and energy storage systems. The synergistic improvement of balance between dielectric constant (εr) and breakdowon field strength (Eb), along with better energy storage performance, is a primary focus of this study. This research employs a high εr of P(VDF-TrFE-CFE) blended with linear PMMA to create a sandwich-structured composite via high-speed electrostatic spinning. Boron Nitride Nanosheets (BNNSs) for insulation and TiO2 for polarization are used as fillers, aiming to achieve polymer-based composite with large energy storage density and minimal energy loss. Results show that the sandwich-structured composite with 0.5 vol.% BNNSs in outer layer and 3 wt.% TiO2 in middle layer achieves the largest Ue of 21.8 J/cm3 at the η of 74 %. This study broadens the application of novel dielectric materials in the fields of energy.

Quantum statistical mechanics of the Sachdev-Ye-Kitaev model and charged black holes

This review is a contribution to a book dedicated to the memory of Michael E. Fisher. The first example of a quantum many body system not expected to have any quasiparticle excitations was the Wilson-Fisher conformal field theory. The absence of quasiparticles can be established in the compressible, metallic state of the Sachdev-Ye-Kitaev model of fermions with random interactions. The solvability of the latter model has enabled numerous computations of the non-quasiparticle dynamics of chaotic many-body states, such as those expected to describe quantum black holes. We review thermodynamic properties of the SYK model, and describe how they have led to an understanding of the universal structure of the low energy density of states of charged black holes without low energy supersymmetry.

A novel micro non-imaging concentrating solar module for building façade integration

Owing to the limited installation space and relative low energy density of solar radiation, how to fully utilize the solar energy potential on the building south façade is always an important issue. In this regard, this paper proposed a faced embedded solar thermal module with mini asymmetric parabolic concentrator, which could capture solar radiation within a wide range of incidence angles with relatively high thermal conversion efficiency. The optical efficiency of the proposed solar module maintains over 0.7 with the solar projection angle increasing from 0° to 90°, which covers the annual altitude angle variation of beam solar radiation incidence on the south façade. Corresponding photo-thermal model was developed and validated with 5 days continues outdoor measurement data. The predicted values were in good consistence with the experimental data with a R2 value of 0.975. Experimental results showed a daily thermal efficiency of 0.66 during the clear sky weather. The average daily thermal efficiency of the ACPC module throughout the year was 0.47 with a constant working temperature of 60 °C. The proposed device is expected to help the building integration design towards zero carbon emission building.

Effect of energy density on down surface characteristics of AlSi10Mg alloy fabricated via selective laser melting

The correlation between surface roughness and energy density in the down surface area of AlSi10Mg alloy manufactured by selective laser melting was analyzed. This study investigated the relationship between the contour melt pool shape and surface roughness in the down surface area across an energy density range of 10–150 J/mm³. As the energy density increased, the contour melt pool in the down surface area became more stable, which significantly influenced surface roughness. Low energy density resulted in the unstable formation of the contour melt pool, leading to a deterioration in surface quality, whereas high energy density promoted the stable formation of the melt pool. Sufficient energy density is essential for the complete formation of the contour melt pool on the down surface, which plays a crucial role in reducing surface roughness. However, within the energy density range where the contour melt pool is fully formed, keyhole defects may occur, and it can be anticipated that these defects may worsen at energy densities exceeding the critical threshold.

Surface-modified composites of metal–organic framework and wood-derived carbon for high-performance supercapacitors

The renewable nature, high carbon content, and unique hierarchical structure of wood-derived carbon make it an optimal self-supporting electrode for energy storage. However, the limitations in specific surface area and electrical conductivity defects pose challenges to achieving satisfactory charge storage in wood-derived carbon electrodes. Therefore, exploring diverse and effective surface strategies is crucial for enhancing the electrochemical energy storage performance. Herein, a decoration technique for enhancing aesthetic appeal involves applying a metal–organic framework (Ni/Co-MOF) containing nickel and cobalt onto the inner walls of wood tracheids. The sequential modification steps include carbonization, oxidation activation, and acid-etching. The Ni/NiO/CoO-CW-4 electrode, made by acid-etching carbonized wood (CW) doped with nickel, nickel oxide, and cobalt oxide for 4 h, has excellent surface area and pore size distribution, high graphitization degree, and exceptional conductivity. Furthermore, surface modification optimizes the surface chemistry and phase composition, resulting in a 0.8 mm thick Ni/NiO/CoO-CW-4 electrode with an exceptionally high areal capacitance of 16.76 F cm−2 at 5 mA cm−2. Meanwhile, the fabricated solid-state supercapacitor achieves an impressive energy density of 0.67 mWh cm−2 (8.38 mWh cm−3) at 2.5 mW cm−2 (31.25 mW cm−3), surpassing representative modified wood-based carbon electrodes by approximately 2–7 times. Additionally, the supercapacitor demonstrates exceptional stability, maintaining 96.21 % of capacitance even over 10,000 cycles. The parameters presented here demonstrate a significant improvement compared to those typically observed in most modified wood-derived carbon-based supercapacitors, effectively addressing common issues of low energy density and suboptimal cycling performance with wood carbon composites.

Fabrication and Structural Analysis of Barium Titanate-Doped Niobium Pentoxide Ceramics for Energy Storage System

Dielectric materials are gaining attention for energy storage due to their high power density. However, their low energy density limits their applications. This paper explores dielectric materials with suitable permittivity and breakdown strength. It focuses on enhancing the energy storage capabilities of Barium Titanate-based ceramics by adding Niobium Oxide. The study investigates the effects of Nb2O5 addition on 0.98BT-0.02BMC ceramics. XRD analysis confirms a single perovskite phase for all compositions. The addition of Nb2O5 significantly improves dielectric and energy storage properties. The composition with x=4 exhibits a high dielectric constant (~2200), high energy density (1.40 J/cm³), high recoverable energy density (~1.10 J/cm³), and high efficiency (78.8%). This material shows promise for power pulse system. The Barium titanate can be used as a component in radiation detectors, such as ionization chambers and scintillation detectors. Its high density and atomic number contribute to its radiation-stopping ability

High-performance supercapacitor materials based on NiMn-LDH layered structures with MXene layers

In recent years, the environmental degradation exacerbated by extensive fossil fuel use has underscored the urgent need for cleaner and more efficient energy storage systems. This study addresses the challenges faced by hybrid supercapacitors (HSCs), which, despite their high power density and long lifespan, still suffer from low energy density and high self-discharge rates. We employ a co-precipitation method to integrate MXene with NiMn-layered double hydroxides (LDHs), optimizing the performance of HSCs. The incorporation of MXene enhances the conductivity and structural stability of NiMn-LDH, addressing issues of poor conductivity and instability during cycling. The developed NiMn-LDH@MXene electrodes demonstrate remarkable electrochemical performance, including a specific capacitance of 1530 F g⁻¹ at 2 A g⁻¹, a capacity retention rate of 90.52 % after 20,000 cycles at 10 A g⁻¹, a high energy density of 60.56 Wh kg⁻¹, and an excellent power density of 924.95 W kg⁻¹. This research not only marks a significant advancement in electrode material performance but also provides valuable insights into the development of next-generation energy storage devices with enhanced stability and efficiency.

Constructing LiF‐Enriched Solid Electrolyte Interface on Graphene Arrays with Abundant Edges on Microscale Si‐C Anodes Toward High‐Energy Lithium‐Ion Batteries

AbstractSilicon (Si) anodes offer excellent lithium storage capacity for lithium‐ion batteries but face practical limitations due to significant volume expansion and low intrinsic electrical conductivity. These issues lead to side reactions that consume the electrolyte and impede ion‐electron transport, resulting in low areal loading (<2 mg cm⁻²) and restricted energy density. To address this, a scalable method is developed using spray drying of commercial graphite flakes (s‐Gr) and nanosilicon particles (n‐Si), followed by chemical vapor deposition to create microscale Si/C anodes (s‐Gr/n‐Si/VGs). Thin vertical graphene nanosheets (VGs) are grown on the surfaces and within the internal pores, forming a robust, micron‐sized Si/C spherical composite material. The VGs construct the conductive network, allowing the electrodes to operate at high areal loadings without pulverization and promoting LiF‐enriched solid electrolyte interphase for improved cycling stability. The s‐Gr/n‐Si/VGs maintain a capacity of 641.9 mAh g⁻¹ after 1000 cycles at 11.0 mg cm⁻², retaining 95.9% capacity. In pouch cells with NCM811 cathodes, the 5.0 Ah‐level cells achieved 80.0% capacity retention after 510 cycles at 1.0 C. This research provides a feasible pathway for manufacturing high‐performance, low‐cost, and scalable Si/C anodes suitable for high‐energy‐density lithium‐ion batteries.

Preparation of two–dimensional gradient fillers reinforced polymer nanocomposites for high–performance energy storage of dielectric capacitors

The serious interfacial issue between the inorganic filler and the organic matrix in the dielectric nanocomposite results in a low electric field breakdown strength (Eb) and low energy density (Ue). In this work, novel KxNa1–xNbO3@ZrO2 (KNN@ZO) nanosheets (NSs) were prepared by coating highly insulated ZO on the ferroelectric two–dimensional (2D) KNN NSs via a chemical precipitation method. As fillers, the KNN@ZO significantly improved the energy storage performances of poly (vinylidene fluoride) (PVDF)–polymethyl methacrylate (PMMA) blends. The highly insulated ZO shell restricts the carrier migration at the filler/polymer interface, thereby reducing the local electric field distortion. By sandwich structural design, a high Ue of 19.8 J/cm3, with a large difference of electrical displacement (8.5 μC/cm2), is measured in KNN@ZO/PVDF–PMMA with 5 % filler content at 528 MV/m. According to the finite element simulation, the 2D morphology and gradient structure can enhance the electric field distribution, and therefore effectively increase the Eb of nanocomposites. The results indicate that the 2D core–shell NSs fillers with gradient dielectric constant represent an effective approach to improve energy storage performance of the polymer–based nanocomposites.

Ferroelectric BaTiO3 Freestanding Sheets for an Ultra-High-Speed Light-Driven Actuator.

Light-driven actuators convert optical energy into physical motion. Organic materials, commonly used in light-driven actuators thus far, suffer from two limitations: slow repetitive operation and the requirement of two different light sources. Herein, we report a high-speed, light-driven actuator that can be operated by a single light source with low-energy density. We achieved this breakthrough by utilizing a freestanding epitaxial sheet of ferroelectric BaTiO3. One repetitive operation takes only 120 μs, which is 104 times faster than that of organic-based counterparts. The high-speed operation is derived from the light-induced nonthermal deformation provided by the excellent ferroelectricity (remnant polarization of 23 μC/cm2) and piezoelectricity (d33 of 600 pm/V) of the sheet. The displacement-to-length ratio is achieved to be 3.7% with a relatively low laser power density (10-200 mW/cm2) compared to previously reports (150-109 mW/cm2). Furthermore, the actuator was operable even in water, demonstrating its potential in various applications.

Prevention of solidification cracking in alloy 718 additive manufacturing by laser metal deposition method based on control guidelines for weld solidification cracking

The chemical composition of alloy 718 powder was optimized to suppress a solidification cracking in the additive manufactured part by the laser metal deposition method. The relationship between the condition of additive manufacturing and defects was evaluated. A lack of fusion was observed on the low heat input (low energy density), and the solidification cracking occurred on the high heat input (high energy density). The powder composition of alloy 718 was attempted to be optimized from a theoretical approach of the solidification cracking susceptibility. It was found that Si and B had a significant influence on the solidification cracking, therefore a preventive powder with reduced Si and B was developed. The effects of Si and B on solidification cracking were compared by reproducing the solidification conditions during additive manufacturing and evaluating the solidification brittle temperature range (BTR) using the Varestraint test. It was found that the BTR of the preventive material was smaller, and the solidification cracking susceptibility was improved. In addition, the solidification cracking did not occur in additive manufacturing using the preventive powder. In other words, it is suggested that the countermeasure for weld solidification cracking leads to the prevention of solidification cracking in additive manufacturing directly, and the effectiveness of the optimization of powder composition was verified.