Energy Density Research Articles

Competing roles of microstructure and defects on the mechanical properties of laser-powder bed fused Ti-6Al-2Sn-4Zr-2Mo alloy

AbstractUsing different volumetric energy densities ($${E}_{\text{v}}$$ E v ), the microstructure, texture, and defect evolution in laser-powder bed fused (PBF-LB/M) Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloy is studied. PBF-LB/M Ti-6242 rods were manufactured using different $${E}_{\text{v}}$$ E v ranging from 41.67 to 66.67 J/mm3. The $${E}_{\text{v}}$$ E v is varied by setting the scan speed to 1000 mm/s, 1200 mm/s, 1400 mm/s, and 1600 mm/s. The mechanical properties (yield strength, tensile strength, and strain at fracture) were then studied under quasi-static loading conditions. It is observed that the strength of the sample printed using the lowest $${E}_{\text{v}}$$ E v is lower than the other conditions due to the formation of the lack of fusion defects. In addition, the sample printed with the highest $${E}_{\text{v}}$$ E v consists of redeposited process by-products that result in the lowest ductility. The microstructure and texture of the samples were studied using electron backscatter diffraction. The results show that microstructural features including α′ lath width, dislocation density, and lath orientation (texture) were almost identical under different $${E}_{\text{v}}$$ E v . Therefore, the variations in mechanical properties may not controlled completely by the microstructure. The defect analysis is conducted employing X-ray computed tomography. The defect characteristics change from keyhole to lack of fusion by varying the $${E}_{\text{v}}$$ E v . The volume fraction of defects in the samples is in the range of 0.0005–0.007%, which seems to be negligible. However, the fractography analysis shows the dominance of defects in controlling the mechanical properties. This study proves the sensitivity of PBF-LB/M Ti-6242 to defects as the mechanical properties were defect-driven rather than microstructure-driven.

A low-cost electrode based on Mg-Co double hydroxide for high energy density structural supercapacitors in civil engineering

In the field of construction, structural supercapacitors (SSCs) have been widely noticed due to their simultaneous functions of load-bearing and energy storage. Unfortunately, the currently available electrodes for SSCs are still aimed at application scenarios such as electronics and electric vehicles, and while their performance is good, they are not applicable to the construction sector, which is massive in scale and extremely cost-sensitive industry. Herein, after trade-off between cost and electrochemical performance, a novel low-cost 3D nanomaterial was designed through a facile approach aimed at increasing the areal energy density of SSCs. By growing Mg-Co double hydroxide nanomaterials directly on nickel foam, we achieved a large areal capacitance of 2577 mF/cm2 at 5mA/cm2 (1136.7F/g at 2.2A/g). It also exhibits good cycling stability with a capacitance retention of 82.4% after 10,000 cycles. In addition, SSCs using magnesium-cobalt double hydroxides achieves a high energy density of 285.6 μWh/cm3 at a power density of 6.31mW/cm3, which is superior to previously reported structural devices. This demonstrates that Mg-Co double hydroxide electrode has good suitability with SSCs and effectively improves the areal energy density of SSCs. Our proposed method also provides a faster and more reliable pathway for low-cost electrode preparation in SSCs, which may lead to the development of a new generation of SSCs.

Practical Pouch Cell Supercapacitor Electrodes by Electrophoretic Deposition of Activated Carbon on Nickel Foam

AbstractThis study highlights for the first‐time the utilization of nickel foam coated with activated carbon (AC) via the electrophoretic deposition (EPD) method in the fabrication of A7 sized pouch cell supercapacitors. The scale‐up of electrodes via EPD from coin to pouch cells with mass loadings (10 mg cm−2) and thicknesses (>130 μm) that match industrial standards is also reported. Research investigations include: (a) comparison of a two dimensional (2D) aluminum foil current collector's performance with three dimensional (3D) microporous nickel foam current collectors, (b) impact of EPD of AC onto small (10 cm2) and large areas (50 cm2) of nickel foam, and (c) scaling‐up of coin to pouch cells along with a comparison against electrodes prepared via the standard doctor blade coating (or slurry casting) method. We demonstrate practical cell performance, including specific current loading (40 A g−1), hundred thousand of successive charge and discharge operation (150,000 cycles), power (27 kW kg−1) and energy densities (37.7 W h kg−1), capacitance (174 F g−1), capacitance retention (80 %) and coulombic efficiency (close to 100 %).

Understanding the K+/Na+-Selectivity-Enabled Osmotic Power Generation: High Selectivity May Not Be Indispensable.

By mixing ionic solutions, considerable energy can be harvested from entropy change. Recently, we proposed a concept of potassium-permselectivity enabled osmotic power generation (PoPee-OPG) by mixing equimolar KCl and NaCl solutions via artificial potassium ion channels (APICs, Natl. Sci. Rev. 2023, 10, nwad260). However, a fundamental understanding of the relationship between the K+/Na+ selectivity and optimal performance remains unexplored. Herein, we establish a primitive molecular thermodynamic model to investigate the energy extraction process. We find PoPee-OPG differs from previous charge-selectivity-based techniques, such as the salinity gradient power generation, in two distinct ways. First, the extractable energy density and efficiency positively depend on concentration. More surprisingly, a very high potassium selectivity is not indispensable for satisfactory efficiency and energy density. An optimal K+/Na+ selectivity region of 3 to 10 is found. This somewhat counterintuitive discovery provides a renewed understanding of the emerging PoPee-OPG, and it predicts a broad applicability among existing APICs.

Effect of diameter on the stability of granulated Ca(OH)2 during thermochemical cycling in a fixed bed reactor

One solution to reduce CO2 emissions and advance climate protection in the heat sector is the utilization of thermochemical energy storages (TCES) based on the material Ca(OH)2 to store waste heat or surplus electricity. In contrast to powdered materials, the material in granular form has a lower tendency to be affected by agglomeration effects and provides higher energy density and thermal conductivity. This results in enhanced durability, stability, and efficiency of the storage, making the storage material Ca(OH)2 in granular form more suitable for TCES applications. This work investigates the performance of a chemically unmodified granular sample over 15 storage cycles in a test fixed bed reactor and evaluates whether its performance and durability are already sufficient for potential applications without further modification. In addition, different granule samples with different diameters were also cycled to determine whether the selection of certain diameter sizes can improve the stability of the granules. Furthermore, different methods were used in the pre- and post-analyses to assess the stability of the samples. The comparison of three tested granular samples with different diameters reveals that the sample with a diameter of 2–4 mm has the highest durability and reactor performance. Despite a decrease in mechanical strength, this configuration could be suitable for applications with a small number of storage cycles, such as seasonal storages.

In situ grown heterostructures based on MAX-derived TaO2F nanorod and TaC (MXene) nanosheet for high-performance hybrid supercapacitors

Two-dimensional MXene-based interface heterostructures have an undeniable position in the energy storage systems, particularly supercapacitors, due to their unique microstructure and electrochemical properties. However, the selection of materials in heterogeneous structures and the assembly strategy often have often have a significant impact on the properties of heterogeneous structures. This study proposes a in situ grown strategy for constructing TaO2F@TaC nano-heterostructures consisting of one-dimensional TaO2F nanorods combined with two-dimensional TaC nanosheets derived from the precursor MAX phase. The complex etching and growth mechanism from MAX to 1D/2D TaO2F@TaC is reasonably inferred. The construction of TaO2F@TaC nano-heterostructures effectively addresses the issue of MXene to restack and improves the poor conductivity of TaO2F. Density functional theory (DFT) calculations validated the electronic structure and charge distribution at the heterostructure interface, demonstrating its capability for electron conduction and ion transport. Moreover, the hybrid supercapacitor (HSC) based on TaO2F@TaC exhibited superior energy density (153.4 μWh cm−2 at a power density of 222.2 μW cm−2) and excellent cycle stability. The prepared quasi-solid-state supercapacitor (QSC) also shows a capacitance of 457.4 mF cm−2, and retains 99.38 % capacity after 8200 cycles. This work innovatively bypasses the multi-step process of preparing MXene heterostructures and provides a new approach for developing MXene-based electrode materials to enhance the performance of hybrid supercapacitors.

Electrification of Agricultural Machinery: One Design Case of a 4 kW Air Compressor

In response to the global pursuit of net-zero carbon emissions, the electrification of agricultural machinery is becoming a significant research and development trend. This study introduces the overall design of a 4 kW air compressor aimed at achieving a green vision for agricultural machinery. The design focuses on providing continuous and stable power and air output using a lithium-ion battery. Durability and cost-effectiveness are prioritized, with a particular emphasis on the Arduino system for integrating battery and motor systems to withstand harsh conditions and ensure ease of maintenance. A permanent magnet brushless motor was selected as the power source, paired with an optimized pulley to supply the proper torque to the air compressor. The system employs an Arduino-based feedback control sensor for air pressure regulation, ensuring energy efficiency. The primary energy source is a 48 V lithium iron phosphate battery, known for its high energy density and safety. The battery design focuses on system integration, addressing specific environmental discharge requirements. The embedded battery management system provides thermal and lifecycle parameter estimation, guaranteeing long-duration power supply and safe operation under various conditions. Unlike traditional fuel-driven systems, lithium iron phosphate batteries do not emit harmful gases, aligning with environmental standards. System integration testing demonstrated that the air pressure feedback control effectively meets the energy-saving requirements by digitally reducing power output as air accumulates in the chamber. Bench testing confirmed that the system performs as designed, achieving the desired results and advancing the goal of sustainable agricultural machinery.

Controllable construction of mesoporous hollow carbon spheres rich in micropores from waterborne benzoxazine and their application in supercapacitors

Mesoporous hollow carbon spheres (MHCSs) with mesoporous channels and nanocages structure have unique advantages in energy storage. However, this structure alone does not significantly enhance the electrochemical double layer capacitance (EDLC). Additionally, the current hydrophobic nature of polymer precursors with high char yield impedes effective binding with templates due to polarity differences. Moreover, the use of toxic organic solvents presents obstacles to further development. So, it remains a challenge to prepare MHCSs rich in micropores using polar polymers with high char yield in green solvent. In this work, we prepared MHCSs rich in micropores (MMHCSs) using waterborne benzoxazine as a carbon sources and dendritic/fibrous nano-silica as a sacrificial hard template using water as the solvent and combined with freeze-drying, curing, carbonization and an activation step. The optimal MMHCSs (MMHCSs306–1–7000.5h) has a large specific surface area (1057 m2 g−1), and has a maximum specific capacitance value near 221.45 F g−1 at 0.5 A g−1 in a three-electrode system, the specific capacitance still reaches 156.66 F g−1 at a high current density (20 A g−1) due to the full utilization of micropores in the presence of mesoporous-shell and hollow-core. When assembled into a symmetrical supercapacitor, the energy density reaches 5.91 Wh kg−1 when the power density is 137.5 W kg−1. The study provides an eco-friendly method for preparing MMHCSs, and the unique structure has potential application in supercapacitors.

Optimization of Pulsed Laser Energy Density for the Preparation of MoS2 Film and Its Device by Pulsed Laser Deposition

This article aims to explore the most optimal pulsed laser energy density when using the pulsed laser deposition (PLD) process to prepare the MoS2 films. We gradually increased the pulsed laser energy density from 70 mJ·cm−2 to 110 mJ·cm−2 and finally determined that 100 mJ·cm−2 was the best-pulsed laser energy density for MoS2 films by PLD. The surface morphology and crystallization of the MoS2 films prepared under this condition are the best. The films consist of a high-crystallized 2H-MoS2 phase with strong (002) preferential orientation, and their direct optical band gap (Eg) is 1.614 eV. At the same time, the Si/MoS2 heterojunction prepared under the optimal pulsed laser energy density shows an opening voltage of 0.61 V and a rectification ratio of 457.0.

Exploration of the behavior and evolution features of beam-column joints with T-stub using the structural strain energy method

Based on the structural strain energy method, the work behavior of four T-stub connection joints under cyclic loading is analyzed to visualize their working behavior and failure evolution. The experimental strain data are modeled as generalized strain energy density (GSED) to characterize the structural stress state and the corresponding characteristic parameters, and the Mann-Kendall (M-K) criterion is formulated to determine the performance characteristic points (P and Q) of the joint Mj-Ej curves and to derive the starting point of structural continuity damage. Then, by analyzing the parameters of the joint working state (strain, deformation, joint energy dissipation, connection stiffness, bolt force and pry force), the trends of the joint stressing state curves before and after the critical loading are reflected. Finally, the feature point data interpolation (EDI) method is introduced to effectively expand the joint test data, visualize the change process of the strain/stress field, and deeply reveal the mechanical response mechanism and evolutionary degradation law behind it. The contribution of the above work is to quantitatively identify the P and Q characteristic points in the changing trend of the joint working state, to reveal the mechanical mechanism and the failure degradation law from the perspective of energy evolution, and to visualize the mutation of the field data before and after the P/Q using the EDI method, which is a generalized method that can be applied to the other progressive failure structures.

Probing flavor violation and baryogenesis via primordial gravitational waves

We show that observations of primordial gravitational waves of inflationary origin can shed light into the scale of flavor violation in a flavon model which also explains the mass hierarchy of fermions. The energy density stored in oscillations of the flavon field around the minimum of its potential redshifts as matter and is expected to dominate over radiation in the early universe. At the same time, the evolution of primordial gravitational waves acts as bookkeeping to understand the expansion history of the universe. Importantly, the gravitational wave spectrum is different if there is an early flavon dominated era compared to radiation domination expected from a standard cosmological model and this spectrum gets damped by the entropy released in flavon decays, determined by the mass of the flavon field mS and new scale of flavor violation ΛFV. We derive analytical expressions of the frequency above which the spectrum is damped, as-well-as the amount of damping, in terms of mS and ΛFV. We show that the damping of the gravitational wave spectrum would be detectable at BBO, DECIGO, U-DECIGO, μ−ARES, LISA, CE and ET detectors for ΛFV = 105−10 GeV and mS = OTeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O}\\left(\ extrm{TeV}\\right) $$\\end{document}. Furthermore, the flavon decays can source the baryon asymmetry of the universe. We identify the mS – ΛFV parameter space where the observed baryon asymmetry η ~ 10−10 is produced and can be tested by gravitational wave detectors like LISA and ET. We also discuss our results in the context of the recently measured stochastic gravitational background signals by NANOGrav.

2D MXene/MBene Superlattice with Narrow Bandgap as Superior Electrocatalyst for High-Performance Lithium-Oxygen Battery.

Lithium-oxygen (Li-O2) battery with large theoretical energy density (≈3500Whkg-1) is one of the most promising energy storage and conversion systems. However, the slow kinetics of oxygen electrode reactions inhibit the practical application of Li-O2 battery. Thus, designing efficient electrocatalysts is crucial to improve battery performance. Here, Ti3C2 MXene/Mo4/3B2-x MBene superlattice is fabricated its electrocatalytic activity toward oxygen redox reactions in Li-O2 battery is studied. It is found that the built-in electric field formed by a large work function difference between Ti3C2 and Mo4/3B2-x will power the charge transfer at the interface from titanium (Ti)site in Ti3C2 to molybdenum (Mo) site in Mo4/3B2-x. This charge transfer increases the electron density in 4d orbital of Mo site and decreases the d-band center of Mo site, thus optimizing the adsorption of intermediate product LiO2 at Mo site and accelerating the kinetics of oxygen electrode reactions. Meanwhile, the formed film-like discharge products (Li2O2) improve the contact with electrode and facilitate the decomposition of Li2O2. Based on the above advantages, the Ti3C2 MXene/Mo4/3B2-x MBene superlattice-based Li-O2 battery exhibits large discharge specific capacity (17167 mAhg-1), low overpotential (1.16V), and superior cycling performance (475 cycles).

Scalar induced gravitational waves in chiral scalar–tensor theory of gravity

We study the scalar induced gravitational waves (SIGWs) from a chiral scalar–tensor theory of gravity. The parity-violating (PV) Lagrangian contains the Chern–Simons (CS) term and PV scalar–tensor terms, which are built of the quadratic Riemann tensor term and first-order derivatives of a scalar field. We consider SIGWs in two cases, in which the semi-analytic expression to calculate SIGWs can be obtained. Then, we calculate the fractional energy density of SIGWs with a monochromatic power spectrum for the curvature perturbation. We find that the SIGWs in chiral scalar–tensor gravity behave differently from those in GR before and after the peak frequency, which results in a large degree of circular polarization.

Analysis of the performance, combustion and emission of Hydrogen Induction in a CRDI engine

<p style="text-align:justify; text-indent:18.0pt; margin-bottom:13px"><span style="font-size:11pt"><span style="line-height:normal"><span style="font-family:Calibri,sans-serif"><span style="font-size:10.0pt"><span style="font-family:"Times New Roman",serif">Since hydrogen gas is a plentiful element in the universe, using it as fuel for IC engines has the potential to reduce pollution while also improving the engine performance. Hydrogen gas as fuel has many advantages, including a high energy density, a rapid flame speed, clean burning, and a short quenching distance. When compared to pure diesel as fuel, alternative fuels like biodiesel (a mixture of lemon and orange peel oils) are utilised in this experiment to reduce exhaust emissions. In addition to biodiesel, hydrogen induction is used in dual fuel technology to boost the power of engine while minimising emissions and improving the fuel efficiency and fuel economy. Hydrogen gas is utilised, the engine consumes less biodiesel fuel, thereby reducing the fuel cost. According to experimental findings, a reduction in the brake-specific energy consumption of 23.48% and a rise in brake thermal efficiency of 33.4% are observed for pure diesel along with 6lpm of hydrogen gas. Therefore, hydrogen is a potential fuel to drive the internal combustion engine to produce more power and by minimizing the exhaust gas emissions. </span></span></span></span></span></p>

Development & Validation of a Packed Bed Thermal Energy Storage Model

The rapid growth of economies and population around the world have exponentially increased the demand for energy. This demand has invoked increased annual global CO2 emissions and necessitated a transition to clean energy technologies. Reliable and affordable energy storage technologies are paramount for increasing renewable energy penetration onto the grid, supporting periods with reduced or no renewable energy generation. This project is aimed at developing a Thermal Energy Storage (TES) solution that can deliver heat to a heat engine for power production or to an industrial process for prolonged periods. TES long duration energy storage (LDES) presents many potential benefits, including 1) Low Cost 2) scalability 3) high energy density 4) low carbon footprint and 5) resiliency via ability to produce synchronous power (i.e., spinning turbomachinery). The broader objective of this project is to build, test, and model the TES concept at a 2 MWh scale to determine the economic and physics-based practicality of the system. The work presented here describes the first phase objectives of the project, including benchtop scale testing, model development, and Model Validation.

Direct Fabrication of 3D Electrodes Based on Graphene and Conducting Polymers for Supercapacitor Applications

AbstractThe development of commercially viable composite conducting polymer electrodes for energy storage is limited by the requirement of multiple and complex fabrication steps, low energy density, and poor cycling stability. In this work, a straightforward, economical, single‐step method is developed for creating densely packed nanostructured PEDOT/graphene composite material demonstrating its application as an electrode for supercapacitors. The electrode achieved the highest mass loading reported so far in the literature for composite vapor phase polymerized PEDOT/rGO using aqueous FeCl3 (25.2 mg cm−2), and displayed an ultrahigh areal capacitance of 4628.3 mF cm−2 at 0.5 mA cm−2. The symmetric two‐electrode setup displayed an energy density of 169.3 µWh cm−2 and a 70% capacitance retention after 70 000 cycles, showcasing its exceptional performance and durability.

Cathode Modification of Sodium‐Ion Batteries for Improved energy Density: A Review

AbstractIn recent years, with the large‐scale commercial application of lithium‐ion batteries, the shortage of lithium resource reserves and the rising price limit its development. The sodium‐ion batteries as a new type of secondary chemical power supply, with ample resources, high safety, as well as great electrochemical performance, are expected to form complementary with Lithium‐ion batteries in the domain of extensive electrochemical energy storage and low‐velocity electric vehicles. However, due to its low energy density, it remains challenging to develop high‐performance sodium‐ion batteries. As is well‐known, the cathode material is the essential factor affecting the performance of sodium‐ion batteries. In order to solve these questions, cathode modification of sodium‐ion batteries aroused wide concern for improving the electrochemical performance. Here, the authors first discuss the challenges of sodium‐ion batteries, and review the energy storage mechanism and the causes of the low energy density. Then, recent studies on cathode modification are summarized based on the mainstream cathode materials in sodium‐ion batteries including sodium‐based transition‐metal oxides, polyanionic compounds, and Prussian blue analogues. Finally, the prospects of sodium‐ion batteries are proposed, which provides promising strategies for the development and practical application of cathode materials in the future.

On pseudo-𝒦-symmetric semi-Riemannian manifolds and relativistic applications

In this paper, we present a novel curvature tensor called the [Formula: see text]-curvature tensor, which is formed by combining the Weyl tensor and the [Formula: see text]-curvature tensor. It is proved that a semi-Riemannian manifold with traceless [Formula: see text]-curvature tensor is Einstein, while a [Formula: see text]-curvature flat semi-Riemannian manifold exhibits constant sectional curvature. We show that a space-time with traceless [Formula: see text]-curvature tensor or [Formula: see text]-curvature flat represents dark energy era. A semi-Riemannian manifold with divergence-free [Formula: see text]-curvature tensor is Weyl harmonic. In a space-time where the [Formula: see text]-curvature tensor is of divergence-free, both the isotropic pressure and energy density are constants. Under certain conditions, it is shown that a pseudo-[Formula: see text]-symmetric semi-Riemannian manifold reduces to a pseudo-Riemannian manifold. It is demonstrated that pseudo-[Formula: see text]-symmetric space-times can be regarded as generalized Robertson–Walker (GRW) space-times. Finally, a concrete example of pseudo-[Formula: see text]-symmetric semi-Riemannian manifolds is presented.

Reactive strontium nitride Additive: Constructing ion/electronic conductive paths for garnet-based solid-state lithium metal batteries

Solid-state lithium metal batteries (SSLMBs) using the garnet electrolyte Li6.4La3Zr1.4Ta0.6O12 (LLZTO) offer high safety and energy density compared to liquid organic electrolyte lithium-ion batteries. However, the interfacial electrochemical stabilization of Li metal anode with LLZTO leads to problems such as high interfacial resistance and Li dendrite growth, which hinders the wide application of SSLMBs. In this work, a multifunctional Li-Sr-N composite anode by mixing molten Li with Sr3N2 is constructed, in which the reactive wetting of in situ-formed Li3N achieves intimate interfacial contact, and the ionic/electronic conductive paths created by Li-Sr alloys and Li3N effectively homogenise Li deposition and suppress Li dendrites. The interfacial resistance is reduced to 40.42 Ω cm2, and the symmetric cell is stably cycled for 5500 h and 600 h at current densities of 0.1mA cm−2 and 0.4 mA cm−2, respectively, and the full cell of Li-Sr-N|LLZTO|LiFePO4 could be stably cycled for 200 cycles at 0.5C. The preparation of composite anodes using Sr3N2 as an additive may be a new strategy for producing of garnet-based SSLMBs with outstanding energy density and safety performance.

Porous carbon materials with different dimensions and their applications in supercapacitors

Abstract Supercapacitors have become attractive energy storage devices due to their high power density, good cycling stability, and fast charging and discharging speeds. Porous carbon has great specific surface area, high energy density and good conversion performance, so porous carbon as supercapacitor electrode material has been widely concerned. Carbon materials with different dimensions and sizes, such as porous carbon spheres, porous carbon nanotubes (CNTs), porous carbon nanofibers (CNFs) porous graphene (GR) and activated carbon (AC) can provide different performance advantages. At the same time, the composite of porous carbon with metal compounds, conductive polymers and particles containing N/P/O/S can further optimize electrode materials, as well as the significant effects on the increase of specific surface area and energy density are obtained. This article introduces the porous carbon materials used as electrode materials in recent years, as well as their multi-level structural materials and related composite materials. We first introduced porous carbon electrode materials with different dimensions and compared their electrochemical performance. Then, based on various research results, the factors affecting its electrochemical performance were discussed in detail. As well as, the preparation methods of porous carbon electrode materials were introduced, and the specific requirements, advantages and disadvantages of different preparation methods were briefly analyzed. The application of porous carbon electrode materials combined with other materials in supercapacitors is listed. Finally, a summary and outlook of the current research status were supplied, providing reference for the rational design of porous carbon supercapacitors in the future.