Volume Energy Density Research Articles

An improved equalization circuit with bidirectional CUK converter for series-connected battery strings

This paper proposed an improved equalization circuit based on a bidirectional CUK converter. Compared with traditional bus equalization circuits based on CUK converter, it owns a simpler structure with fewer inductors, resulting in a smaller volume and higher energy density of the proposed equalization circuit. The operation principle and steady-state characteristic of the equalizer are analysed. The equalizer is applied to the energy balance of the series-connected battery strings, and the balance principle is designed. The proposed equalization system achieves a fast energy balance of the battery pack. Simulation results verify the effectiveness of the designed equalization circuit and balance strategy.

Black-Fe2O3 Polyhedron-Assembled 3D Film Electrode With Enhanced Conductivity and Energy Density for Aqueous Solid-State Energy Storage

Abstract The construction of advanced Fe2O3 materials with high energy density for energy storage faces challenges due to the defects of conventional widely known red-brown Fe2O3 such as poor electronic conductivity and insufficient physical/chemical stability. Unlike previous works, we successfully synthesized a novel black-Fe2O3 (B-Fe2O3) thin film electrode by adopting a simple hydrothermal strategy. Physical characterizations indicate that the as-made B-Fe2O3 product is composed of polyhedrons (mainly exhibit four to eight sides) with a micrometer grade size range. Besides, the Fe-based thin film electrode with this 3D structure has a stronger affinity and high electronic conductivity. As anode of aqueous solid-state energy storage devices, the as-synthesized B-Fe2O3 film electrode exhibits excellent volume energy density of 14.349 kWh m−3 at a power density of 1609 kW m−3, which is much higher than the best result of previous works (∼8 kWh m−3). This study may provide new insights into the development of the Fe2O3 series on developing high-efficiency Fe-based anode materials for solid-state energy storage.

Ultrafast Synthesis of Large‐Sized and Conductive Na3V2(PO4)2F3 Simultaneously Approaches High Tap Density, Rate and Cycling Capability

AbstractThe Na3V2(PO4)2F3 (NVPF) cathode material is usually nano‐sized particles exhibiting low tap density, high specific surface area, correspondingly low volume energy density, and cycle stability of the sodium‐ion batteries (SIBs). Herein, a high‐temperature shock (HTS) strategy is proposed to synthesize NVPF (HTS‐NVPF) with uniform conducting network and high tap density. During a typical HTS process (heating rate of 1100 °C s−1 for 10 s), the precursors rapidly crystallize and form large‐sized and dense particles. The tight connection between particles not only enhances their contact with carbon layers, but also reduces the specific surface area that inhibits side reactions between the interfaces and the electrolyte. Besides, ultrafast synthesis of NVPF reduces the F loss and amount of Na3V2(PO4)3 impurities, which improve cycling capability. The HTS‐NVPF demonstrates a high energy density of 413.4 Wh kg−1 and an ultra‐high specific capacity of 103.4 mAh g−1 at 10 C as well as 84.2% capacity retention after 1000 cycles. In addition, the excellent temperature adaptability of HTS‐NVPF (−45–55 °C) and remarkable electrochemical properties of NVPF||HC full cell demonstrate extreme competitiveness in commercial SIBs. Therefore, the HTS technique is considered to be a high‐efficiency strategy to synthetize NVPF and is expected to prepare other cathode materials.

Studies on fluoride ion conductivity of the mechanochemically synthesized β-KSbF4 for all-solid-state fluoride-ion batteries

All-solid fluoride ion batteries (FIBs) are considered as the potential alternative to lithium-ion batteries due to their ultra-high volume energy density and high safety. Nevertheless, the major challenge for high-performance FIBs lies in the difficulty of finding a suitable solid-state electrolyte with both high ionic conductivity and easy fabrication. Herein, the air-stable β-KSbF4 with a high F− ion conductivity of 2.06×10−4 S cm−1 at 60 °C is firstly synthesized by mechanochemical synthesis combined with low-temperature annealing treatment, and the underlying mechanisms of fast ion conduction in β-KSbF4 is investigated as well. The analysis of the conductivity spectra based on Jonscher's universal power law shows that the hopping frequency changes by orders of magnitude from 30 °C (1.69×105 Hz) to 80 °C (1.67×106 Hz), and the carrier concentration is almost independent of the temperature change. The difference between the two different parameters means that the hopping process of F− ions rather than the concentration of the charge carriers determines the conductivity of β-KSbF4. Integrating β-KSbF4 with Ag cathode and Pb + PbF2 anode, a reversible cycling of conversion-type all-solid-state FIBs with a first discharge capacity of 77.4 mAh g−1 at 60 °C is achieved and can work stably for 50 cycles without considerable capacity fade. Hence, it is believed that the study on the ionic conduction characteristic of β-KSbF4 synthesized by the mechanochemical synthesis method and its successful application in all-solid-state FIBs can open a new horizon toward the development of all-solid-state FIBs.

Volume energy density and laser power: key determinants in SLS-processed PA12 mechanical properties

AbstractAdditive manufacturing (AM) represents a significant breakthrough in the field of engineering, revolutionizing the way products and components are designed and manufactured. Among the various methods used to employ polymer materials in AM, powder bed fusion (PBF) processes, specifically selective laser sintering (SLS), stand out as one of the most widely utilized approaches. This method offers substantial advantages over other AM techniques for treating polymers. However, SLS is inherently based on complex underlying physical mechanisms and phenomena and it involves a significant number of process parameters, making a comprehensive and extensive study of the process necessary. In the present article, we conduct an experimental study to examine the impact of two pivotal process parameters in SLS: volumetric energy density (VED) and nominal laser power (LP), on the mechanical properties of Polyamide 12 (PA12). The assessment of the material’s mechanical behavior was conducted by measuring its tensile, compressive, and flexural properties, adhering to the respective ASTM standards. Additionally, we employed appropriate statistical tests, including the Coefficient of Variation (CV) to estimate the process’s repeatability and consistency, and Fisher’s least significant difference (LSD) method to determine significant differences between mean property values for different process parameters. The results revealed the impact of volumetric energy density (VED) and nominal laser power (LP) on each mechanical property and mechanical index. Furthermore, the study identifies general rules and trends related to the efficiency and feasible thresholds of the process. Finally, we provide an interpretation of the results based on the fundamental physical mechanisms, also supported by the respective XRD and microscopy images.

Experimental study on the effect of titanium hydride content on the detonation performance of emulsion explosives

AbstractIn order to improve the explosion characteristics of emulsion explosives, titanium hydride was added to emulsion explosives to produce a new type of hydrogen storage emulsion explosives. Charges with different contents of titanium hydride were evaluated through underwater explosion experiments and detonation velocity tests. The tests on underwater explosion and detonation velocity reveal that compared to pure emulsion explosives, the detonation parameters of emulsion explosives containing titanium hydride showed a trend of first increasing and then decreasing. When the mass ratio of titanium hydride in the emulsion explosive is 1 % to 3 %, all detonation parameters have been improved to a certain extent. When the mass ratio of titanium hydride in the emulsion explosive is 3 % to 10 %, only part of the detonation parameters (specific impulse, specific shock energy, specific total energy and volume energy density) has been improved. The maximum increase of specific impulse, specific shock energy, specific total energy and volume energy density of emulsion explosive containing titanium hydride is 7.06 %, 8.95 %, 3.97 % and 8.22 %, respectively. Based on the analysis, it is evident that though powdered TiH2 participates in the detonation reaction process of the emulsion explosive, the majority of TiH2′s energy is released during the secondary reaction occurring after the detonation wave front. Therefore, the detonation performance of emulsion explosives can be effectively improved by adding a certain mass ratio of titanium hydride.

Effect of substrate temperature on in-situ precipitation during laser powder bed fusion of Fe-TiB2 high modulus steel

ABSTRACT Fe-Ti-B high modulus steel (HMS) fabricated via laser powder bed fusion exhibits in-situ precipitation of nanostructured TiB2 particles within a ferritic Fe-matrix. However, porosity and cracking are common challenges associated with this process. This study systematically varies process parameters, specifically volume energy density and substrate temperature, to analyse macroscopic defects formation and propose methods to prevent their occurrence through detailed microstructure characterisation. For substrate temperatures of 400, 600, and 800 °C, an optimal combination of laser power and scan velocity was determined, resulting in minimised specimen porosity (< 1%). Yet, pronounced cracking occurred at 400 and 600 °C substrate temperature, most likely attributed to the presence of hard and brittle non-equilibrium microstructure constituents. Increasing the substrate temperature to 800 °C further reduces porosity and promotes the formation of the equilibrium constituents Fe-α and TiB2. These phases are desirable as they improve the stiffness-to-density ratio while reducing hardness and brittleness. By mitigating thermal gradient and resulting lower stresses, the successful fabrication of HMS samples with the desired microstructure and defect-free macrostructures becomes feasible. Potential future steps, such as incorporating in-situ heat treatments between layer depositions, are outlined and discussed as means to lower the substrate preheating temperature.

Microstructure and Properties of TiCp/GH3536 prepared by Selective Laser Melting

In this paper, TiCp/GH3536 composites were prepared by selective laser melting technology. The effects of volume energy density (VED) on the microstructure, densification, mechanical properties and thermophysical properties of TiCp/GH3536 composites were studied. The results show that the pores and nano TiC clusters in TiCp/GH3536 composites gradually disappear with the increase of VED. The interface between TiC ceramic phase and GH3536 matrix was well bonded, which was a non coherent interface, and there was no interface reactant. The optimal VED of SLM is 96.3 J/mm3, and the specific laser power, scanning rate, scanning spacing and powder layer thickness were 260W, 900 mm/s, 0.1mm and 0.03mm, respectively. The highest density of the composite is 99.96%; The maximum tensile strength and yield strength were 1137.2MPa and 900.6MPa, respectively.

Fabrication and strengthening mechanism of crack-free nano-TiC reinforced IN738LC with enhanced mechanical properties by laser powder bed fusion

IN738LC alloy has broad application potential in modern aerospace and energy industries due to its excellent high-temperature durability, excellent corrosion and fatigue resistance, however, its application has been greatly limited due to its high crack sensitivity. To address this challenge, this research proposes a method of incorporating TiC nanoparticles to mitigate cracks and enhance the strength of the nickel-based materials. The crack-free TiC-IN738LC materials were successfully fabricated using laser-powder bed fusion. The relationship between the processing parameters and processed quality was studied. The fracture morphology and mechanical properties of samples were analyzed and the strengthening mechanisms of nano-TiC particles were clarified. The results showed that volume energy density (VED) = 111.1J/mm3 is the optimal processing parameter with the laser energy 225W, scanning speed 750 mm/s, and 0.09 mm hatch distance. The effects of processing parameters were discussed in depth. Compared with the virgin IN738LC, the microhardness of TiC-IN738LC is improved by 20 %–40 %, and the tensile strength of TiC-IN738LC is enhanced by 5%–30 %, respectively, which indicates the significant strengthening effect of nano-TiC on IN738LC. The synergistic effect of fine grain strengthening, load-bearing strengthening and Orowan strengthening mechanisms was accounted for the performance enhancement. The research results provide an experimental reference for selecting the processing parameters of TiC-IN738LC.

GH3536 superalloy prepared by selective laser melting: microstructure and properties

In this paper, GH3536 superalloy was prepared by selective laser melting (SLM) using plasma rotating electrode powder as raw material. The effects of forming and heat treatment processes on the microstructure and mechanical properties of GH3536 superalloy were studied. The results show that there were obvious micro-cracks on the laser scanning plane of SLM samples, and the length of micro-cracks was between 10-100μm. The micro-cracks originated from the inside of the molten pools and penetrated the melting channels, and the heat treatment could not eliminate the cracks. With the increase of volume energy density (VED), the tensile strength and yield strength of SLM samples increased first and then decreased. The maximum values of tensile strength and yield strength reached 772.3MPa and 613.3MPa, respectively. However, with the increase of VED, the elongation of SLM samples decreased to 27.3%. After heat treatment, the tensile strength and yield strength of the material increased (up to 789MPa and 410MPa), but the elongation decreased.

Optimization of processing parameters for LPBF-manufactured CoCr alloys based on laser volume energy density

In this paper, the finite element method (FEM) and experiments were adopted to optimize the processing parameters of laser powder bed fusion-manufactured cobalt-chromium (CoCr) alloys on the basis of laser volume energy density. According to simulation results, both the maximum temperature, heat-affected zone and cooling rate of molten pool increased with the enhancement of laser power and scanning speed even under the same laser volume energy density. By conducting relevant experiments, it is found that the phase transformation, microstructure and mechanical properties were also influenced by the variation of laser power and scanning speed, and the LPBF-processed CoCr alloys with excellent forming quality could be acquired when the laser power was 160 W, and the scanning speed was 750 mm/s. Therefore, it is impracticable to optimize the processing parameters only on the basis of laser volume energy density, various methods should be employed to complete the whole optimization procedure.

Modification of 316L steel powders with bronze using high energy ball milling for use as a binder component in PBF-LB/M printing of diamond-metal matrix composites

For the processing of diamond-metal matrix composites, the powder bed fusion using a laser for metals (PBF-LB/M), represents a new promising method for the additive manufacturing of diamond tools for concrete and rock machining, even with more complicated geometries. Previous research activities show a strong tendency for cracking and delamination during the construction process of the samples. This behavior is caused by thermal residual stresses associated with the embedded diamonds. To control these negative effects on the process side, the volume energy density is reduced accordingly, which, however, led to increased pore formation. This publication deals with an approach on the material side to modify a 316L stainless steel base powder with an addition of 20 wt% bronze via a high energy ball milling (HEBM) process in such a way that a homogeneous solid solution phase is created. A significantly increasing of the melting interval and a decreasing of both solidus and liquidus temperature was observed, which can reduce pore formation in the PBF-LB/M-process. In addition, XRD-diffractometry and SEM/EDS-analysis showed that the homogeneous solid solution phase of this alloyed powder segregates again into Fe- and Cu-rich phases when heated up to the melting point.

Effect of Process Parameter and Scanning Strategy on the Microstructure and Mechanical Properties of Inconel 625 Superalloy Manufactured by Laser Direct Energy Deposition

This study aimed to investigate the effect of process parameters on the microstructure and mechanical properties of Inconel 625 alloy manufactured by direct energy deposition process. The Inconel 625 samples were produced by varying the laser scanning speeds from 720 - 960 mm/min while maintaining the same the laser energy volume density. The microstructure and mechanical properties of the produced samples were evaluated, and their dimensional accuracy and mechanical properties were also analyzed in terms of the laser scanning strategy. Microstructural observations at the same energy density revealed a dendrite substructure near the laser melt pool boundaries, indicating that the dendritic microstructure was primarily formed at the beginning of the solidification of each laser bead. When the solidification further progressed into the melt pool, solidification cell substructures became dominant regardless of the laser scanning speed. The size of the solidification cell and the dendrite structure were nearly unchanged as laser scanning speed increased. This suggests that changing the laser scanning speed while maintaining the volumetric energy density does not significantly alter the solidification rates of the Inconel 625. As a consequence of the similar cell sizes, the samples produced with different laser scanning speed led to similar mechanical properties. When samples produced with two different scanning strategies, of unidirectional and 90o rotation, were compared, a better dimensional accuracy was obtained with the 90o rotation strategy, compared to that obtained with the unidirectional approach. Comparisons of mechanical properties obtained along different directions with the different laser scanning strategies revealed that the Inconel 625 produced by the laser direct energy deposition had pronounced anisotropic mechanical properties, and was the highest in strength but the lowest in maximum elongation along the laser scanning direction.

High-strength AlCoCrFeNi2.1 eutectic high entropy alloy skeleton with hollow brick wall structures by selective laser melting

In this work, a hollow brick wall structure was introduced into the preparation of AlCoCrFeNi2.1 EHEA to realize a skeleton structure by taking advantage of the good castability of eutectic high entropy alloys (EHEAs) and high cooling rate of selective laser melting (SLM). The effects of processing parameters on eutectic microstructure and mechanical properties of SLM-ed AlCoCrFeNi2.1 EHEA skeletons were investigated. With increasing volume energy density (VED), the microstructure along the building direction evolved from cellular structure to the coexistence of cellular and lamellar structures. The phases in the SLM-ed AlCoCrFeNi2.1 EHEA skeletons contained BCC/B2 and FCC phases. Under the VED of 137.25 J/mm3, SLM-ed skeletons with hollow brick wall structures had a compressive strength of 241.2 ± 4.2 MPa. The mechanical properties from tensile tests exhibited a yield strength of 1349.4 ± 12.4 MPa and an ultimate tensile strength of 1529.5 ± 12.8 MPa. The superior performance of the selective laser melting method was attributed to fine grain strengthening, dislocations strengthening, and heterogeneous structure of FCC and BCC/B2. This work provides possibilities for microstructure design and performance improvement of EHEAs and expands the avenue for developing advanced high-strength lightweight structural and energy-absorbing alloys.

High stability of LiCoO2 enabled by mixed conductor Li0.33La0.557Ti0.8Cr0.2O3 coating

LiCoO2 has excellent volume energy density, and is the dominant cathode materials for 3 C electronic products. However, the capacity of LiCoO2 is not fully utilized, and its cycle stability is not high enough. To preserve the structural stability of LiCoO2 at high voltage, the mixed ion-electron conductor Li0.33La0.557Ti0.8Cr0.2O3 is coated on LiCoO2 particles, and the effects of coating amount and annealing temperature on the electrochemical performances are systematically investigated. The capacity retention of the pristine LiCoO2 in the range of 2.8–4.5 V is only 51.0% after 200 cycles, which is related to the resistance increase of interface and cracks of cathode particles. The coating layer can improve the interface stability and keep the particles intact, and therefore, the capacity retention of the coated sample is significantly increased to 88.2%.

On the Biomechanical Performances of Duplex Stainless Steel Graded Scaffolds Produced by Laser Powder Bed Fusion for Tissue Engineering Applications.

This experimental study aims to extend the know-how on biomechanical performances of duplex stainless steel (DSS) for tissue engineering applications to a graded lattice geometry scaffold based on the F53 DSS (UNS S32750 according to ASTM A182) produced by laser powder bed fusion (LPBF). The same dense-out graded geometry based on rhombic dodecahedral elementary unit cells investigated in previous work on 316L stainless steel (SS) was adopted here for the manufacturing of the F53 DSS scaffold (SF53). Microstructural characterization and mechanical and biological tests were carried out on the SF53 scaffold, using the in vitro behavior of the 316L stainless steel scaffold (S316L) as a control. Results show that microstructure developed as a consequence of different volume energy density (VED) values is mainly responsible for the different mechanical behaviors of SF53 and S316L, both fabricated using the same LPBF manufacturing system. Specifically, the ultimate compressive strength (σUC) and elastic moduli (E) of SF53 are three times and seven times higher than S316L, respectively. Moreover, preliminary biological tests evidenced better cell viability in SF53 than in S316L already after seven days of culture, suggesting SF53 with dense-out graded geometry as a viable alternative to 316L SS for bone tissue engineering applications.

Development and characterization of composite materials with multi-walled carbon nanotubes and graphene nanoplatelets for powder bed fusion

PurposeWith the technological progress, high-performance materials are emerging in the market of additive manufacturing to comply with the advanced requirements demanded for technical applications. In selective laser sintering (SLS), innovative powder materials integrating conductive reinforcements are attracting much interest within academic and industrial communities as promising alternatives to common engineering thermoplastics. However, the practical implementation of functional materials is limited by the extensive list of conditions required for a successful laser-sintering process, related to the morphology, powder size and shape, heat resistance, melt viscosity and others. The purpose of this study is to explore composite materials of polyamide 12 (PA12) incorporating multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GNP), aiming to understand their suitability for advanced SLS applications.Design/methodology/approachPA12-MWCNT and PA12-GNP materials were blended through a pre-optimized process of mechanical mixing with various percentages of reinforcement between 0.50 wt.% and 3.00 wt.% and processed by SLS with appropriate volume energy density. Several test specimens were produced and characterized with regard to processability, thermal, mechanical, electrical and morphological properties. Finally, a comparative analysis of the performance of both carbon-based materials was performed.FindingsThe results of this research demonstrated easier processability and higher tensile strength and impact resistance for composites incorporating MWCNT but higher tensile elastic modulus, compressive strength and microstructural homogeneity for GNP-based materials. Despite the decrease in mechanical properties, valuable results of electrical conductivity were obtained with both carbon solutions until 10–6 S/cm.Originality/valueThe carbon-based composites developed in this research allow for the expansion of the applicability of laser-sintered parts to advanced fields, including electronics-related industries that require functional materials capable of protecting sensitive devices against electrostatic discharge.

The dynamical analysis of a parameterized dark energy cosmological model in the f(R,G) gravity

In this paper, we investigate the dynamical behavior of the universe with a flat FLRW model in [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] both signify the Ricci scalar and Gauss–Bonnet invariant. Furthermore, in order to determine the model’s behavior, it must have the late-time universe’s behavior, which involves both an accelerated expansion as well as ending in a big rip. We present a model that begins with a point-type singularity, i.e. a point with zero volume and infinite energy density, by using parametrization of the scale factor [Formula: see text]. The model’s actions are accelerating and expanding at the moment, and [Formula: see text]CDM in late times. Our extensive analysis encompasses the energy conditions, dynamics of certain model solutions and additional cosmological tests through a dominant model. Finally, the proposed framework acts exactly like a quintessence dark energy model in the current time and is reliable with standard cosmology [Formula: see text]CDM in late times.

Stochastic homogenisation of free-discontinuity functionals in randomly perforated domains

Abstract In this paper, we study the asymptotic behaviour of a family of random free-discontinuity energies E ε {E_{\varepsilon}} defined in a randomly perforated domain, as ε goes to zero. The functionals E ε {E_{\varepsilon}} model the energy associated to displacements of porous random materials that can develop cracks. To gain compactness for sequences of displacements with bounded energies, we need to overcome the lack of equi-coerciveness of the functionals. We do so by means of an extension result, under the assumption that the random perforations cannot come too close to one another. The limit energy is then obtained in two steps. As a first step, we apply a general result of stochastic convergence of free-discontinuity functionals to a modified, coercive version of E ε {E_{\varepsilon}} . Then the effective volume and surface energy densities are identified by means of a careful limit procedure.

Experimental investigation on a thermochemical seasonal sorption energy storage battery utilizing MgSO4-H2O.

Thermochemical sorption energy storage (TSES) is the most recent thermal energy storage technology and has been proposed as a promising solution to reduce the mismatch between the energy supply and demand by storing energy for months in form of chemical bonds and restore it in form of synthesis chemical reaction. Compared with sensible/latent thermal energy processes, TSES system has major advantages, including a high energy storage capacity/density and the possibility of long-term energy retention with negligible heat loss. Therefore, a solid-gas thermochemical sorption battery is established and investigated utilizing a composite working pair of MgSO4-H2O based on room temperature expanded graphite (RTEG), treated with sulfuric acid (H2SO4) and ammonium persulfate ((NH4)2S2O8) as a porous additive. The experimental results showed that energy storage density and sorption efficiency increase with the increment of charging temperature or decreasing of discharging temperature at a certain ambient temperature. Under experimental conditions, energy density ranged from 31.7 to 908.8 kJ/kg (corresponding to volume energy density from 11.7 to 335.8 MJ/m3), while sorption energy efficiency ranged from 28.3 to 79.1%. The highest values were obtained when charging, condensation, and discharging temperatures were 95, 20, and 15 °C, respectively. The maximum thermal efficiency was 21.1% at charging/discharging temperature of 95/15 °C with sensible to sorption heat ratio of 3:1.