High Volume Energy Density Research Articles

Preparation and study on combustion performance of AP@ZrH2 core-shell composite energetic materials with high volume energy density

The development of composite energetic material with high volume energy density could increase the range and loading capacity of solid propellants. In this study, a series of core-shell composite energetic materials AP@ZrH2 were fabricated by decorating ZrH2 on the ammonium perchlorate (AP) through a solvent-nonsolvent method. A substantial increase in combustion heat (13373.67 J/g) and maximum burning temperature (1415.33 °C) are detected in composites in contrast to physically mixed sample (10660.46 J/g and 837.22 °C). This is due to the enhancement of the decomposition performance of AP, which provides sufficient oxidation gas atmosphere for combustion of ZrH2. In addition, the delay time (524 ms) and burning time (114 ms) of composites are significantly decreased compared to the physical mixed sample (2145 and 256 ms). The remarkable combustion performance and burning rate could be attributed to reduced mass and heat transfer distances. Finally, the improvement of combustion efficiency in the composites makes the size of the residual particles smaller.

A high-performance air-rechargeable aqueous Zn/organic battery with Zn2+ and H+ storage

Air-rechargeable aqueous zinc-ion batteries (AZIBs) as a self-powered system can solve a pressing need when there is no external power supply. To meet the demands of such harsh environments, it is necessary to develop high-performance air-rechargeable AZIBs. Herein, we constructed coin-type and flexible AZIBs using tris(1H-1,2,4-triazolyl)hexaazatriphenylenehexacarboxy triimide (TTA-HATTI) as the cathode material, where the cathode reaction involves uptake/remove of Zn2+ and H+ ions. The coin-type and flexible Zn//TTA-HATTI AZIBs exhibit a higher energy density (102.3 Wh kg−1) and a high volume energy density (8.5 mWh cm−3), respectively, and high-rate performance. Interestingly, the discharged TTA-HATTI cathode of flexible Zn//TTA-HATTI battery can be oxidized by O2 from air, due to the potential difference between them, resulting in the discharged flexible Zn//TTA-HATTI battery can be air-recharged without an external power supply. After being left in the air for 23 h, such flexible Zn//TTA-HATTI battery can exhibit a high discharge capacity (420 mA h g−1 at 0.5 A/g), a high rate-performance (178 mA h g−1 at 20 A/g), a better air-charging cycle stability (10 cycles) and operate well at chemical or/and galvanostatic charging mixed modes, showing superior reusability. This work provides guidance for developing high-performance air-rechargeable flexible AZIBs.

Biomimetic Exogenous "Tissue Batteries" as Artificial Power Sources for Implantable Bioelectronic Devices Manufacturing.

Implantable bioelectronic devices (IBDs) have gained attention for their capacity to conformably detect physiological and pathological signals and further provide internal therapy. However, traditional power sources integrated into these IBDs possess intricate limitations such as bulkiness, rigidity, and biotoxicity. Recently, artificial "tissue batteries" (ATBs) have diffusely developed as artificial power sources for IBDs manufacturing, enabling comprehensive biological-activity monitoring, diagnosis, and therapy. ATBs are on-demand and designed to accommodate the soft and confining curved placement space of organisms, minimizing interface discrepancies, and providing ample power for clinical applications. This review presents the near-term advancements in ATBs, with a focus on their miniaturization, flexibility, biodegradability, and power density. Furthermore, it delves into material-screening, structural-design, and energy density across three distinct categories of TBs, distinguished by power supply strategies. These types encompass innovative energy storage devices (chemical batteries and supercapacitors), power conversion devices that harness power from human-body (biofuel cells, thermoelectric nanogenerators, bio-potential devices, piezoelectric harvesters, and triboelectric devices), and energy transfer devices that receive and utilize external energy (radiofrequency-ultrasound energy harvesters, ultrasound-induced energy harvesters, and photovoltaic devices). Ultimately, future challenges and prospects emphasize ATBs with the indispensability of bio-safety, flexibility, and high-volume energy density as crucial components in long-term implantable bioelectronic devices.

Structural engineering design of CoTe@NixSy core-shell nanowires supported by cobalt foams and functional application in aqueous/flexible hybrid supercapacitors

CoTe@NixSy core-shell nanowires are designed and grown on cobalt foams via hydrothermal and electrodeposition method. Structural characterizations indicate the tightly coating of NixSy nanosheets around CoTe nanowires forms the novel core-shell nanowires. Benefiting from this structural engineering design, CoTe@NixSy core-shell nanowires supported by cobalt foams deliver the high areal specific capacitance of 7.56 F cm−2 at 3 mA cm−2 and retention rate of 81.3% after experiencing 5000 cycles. It needs to be specially mentioned that CoTe@NixSy core-shell nanowires were functionally applied in aqueous/flexible hybrid supercapacitors with activated carbon as the negative materials. The aqueous hybrid devices exhibit a maximum areal energy density of 0.77 mWh cm−2 at 2.52 mW cm−2 and retention rate of 81.9% after 5000 cycles. Meanwhile, the flexible hybrid devices show superior energy-storage performance, such as high volume energy density of 3.95 mWh cm−3 at 22.64 mW cm−3, improved cycle stability (82.1% after experiencing5000 cycles), and remarkable flexibility. This work not only demonstrates CoTe@NixSy core-shell nanowires as the promising candidate of energy-storage device; but also provides a novel strategy for high-performance electroactive materials.

Exploring the Chemical Kinetics of the First Oxygen Addition to Di-n-Propyl Ether Radicals at Low Temperatures.

Linear ethers are promising biomass fuels with high volume energy density and high cetane number that may be used directly as alternative fuels or fuel additives in internal combustion engines. In this work, the first O2 addition reaction of the di-n-propyl ether radical was investigated using high-level quantum chemical calculations combined with the Rice-Ramsperger-Kassel-Marcus theory to solve the master equation. The potential energy surfaces of di-n-propyl ether radicals (C6H13O) with O2 were constructed at the QCISD(T)/CBS//M062X/6-311++G(d, p) level, and the rate constants were calculated for the pressure range of 0.1-100 atm and the temperature range of 300-1500 K and fitted by a modified Arrhenius formula. The calculations show that the consumption of di-n-propyl ether peroxyl radicals (C6H13O3) via the five-membered ring or six-membered ring transition-state reaction channel is most favorable. In addition, the low-temperature oxidation experiments of di-n-propyl ether were validated based on the calculations of the current work, and the results showed that the calculations were a good predictor of the experimental results.

Ultra-foldable integrated high-performance in-plane micro-supercapacitors from laser-induced selective metallization

The popularity of flexible and wearable electronic devices has stimulated the development of flexible energy storage devices, in which micro-supercapacitor (MSCs) are the most promising. Herein, we demonstrated a novel strategy for scalable fabrication of copper-nickel-polypyrrole (Cu-Ni-PPy) MSCs devices through laser-induced selective metallization of Cu interdigitated electrode combined with electroplating Ni and electrochemical deposition active material of PPy. The prepared Cu-Ni current collector exhibit high electrical conductivity and mechanical flexibility. Moreover, the obtained Cu-Ni-PPy MSCs devices display a large areal capacitance of 126.67 mF/cm2 and a high volume energy density of 31.78 and 5.39 mWh/cm3 at the corresponding power density of 0.15 and 7.5 W/cm3, respectively. Besides, the MSCs exhibit remarkable capacity retention of 94.8% after 10,000 bending cycles and 89.3% after 10,000 cycles. The wireless charging of the MSCs device can be realized by reasonably designing the wireless charging coil (WCO) for electromagnetic conversion. It is believed that this work provides insight into the manufacture of portability and flexibility of miniaturized energy storage devices.

Interface regulation of Mg anode and redox couple conversion in cathode by copper for high-performance Mg-S battery

The Mg-S battery has great development potential benefiting from its high volume energy density and high-safety. However, it also confronts with two key issues especially when using the Mg(TFSI)2-based electrolyte. One is the poor compatibility between electrolyte and Mg anode, and the other is the poor reversibility of cathode. In this work, an artificial interphase including Zn/ZnCl2/MgZn2/MgCl2 was firstly pre-constructed by replacement reaction of ZnCl2 and Mg, which can reduce Mg plating/stripping overpotential to 0.2 V at 0.1 mA/cm2. Meanwhile, the reversibility of cathode can be improved by using copper powders as additive in sulfur/carbon composite cathode, and the improvement effect is directly related to the addition amount and particle size of copper powders. In addition, it is also revealed that the chemical reaction can occur between copper and intermediates MgS8 at the initial stage of discharge process. The reaction product of Cu2S continues to participate in the electrochemical reduction reaction to regenerate copper, which can be reoxidized to Cu2S during the charging process. The conversion of redox couple from S/S2− to Cu2S/Cu0 in cathode improves the cycling stability of the battery in comparison with the conversional Mg-S battery.

Coral-Like Hierarchical Nanostructured ZnMn2O4/Mn2O3 Composites Synthesized by Zinc-Absent Method as a High-Performance Cathode Material for Aqueous Zinc-Ion Batteries

As one of the multivalent ion batteries, the zinc ion battery has the advantages of high-volume energy density and good safety. In this paper, coral-like and nanoparticle crosslinking hierarchical nanostructured ZnMn2O4/Mn2O3 composites were successfully synthesized as cathode materials for zinc ion batteries by a simple sol-gel combined with the zinc-absent method. ZnMn2O4/Mn2O3 composites with good properties were prepared when the zinc content was 10%. The prepared ZnMn2O4/Mn2O3 composites have the morphology of coral-like and nanoparticle crosslinking and uniform particle size distribution. Compared with pure ZnMn2O4 and Mn2O3, the composites show excellent electrochemical properties. Using 0.5 M Zn(CF3SO3)2-AN/H2O (8:2) as the electrolyte, the first discharge capacity of the material can reach 170.7 mAh·g−1 at 0.05 C. After 150 cycles, the discharge capacity remained 109 mAh·g−1. The kinetic characteristic of the electrode was studied by the galvanostatic intermittent titration technique, and the electrochemical reaction mechanism was studied by ex situ XRD. It was found that the two-phase recombination improved the diffusion rate of Zn2+. In the field of aqueous zinc ion batteries, an effective modification idea is provided for the research of spinel ZnMn2O4 cathode material with low specific capacity.

Enabling the conventional TFSI-based electrolytes for high-performance Mg/Li hybrid batteries by Mg electrode interfacial regulation

The Mg-metal batteries (MMBs) as a forceful competitor for Li-metal batteries (LMBs) have the advantages of high-safety and high-volume energy density. Whereas, the MMBs still confronts two vital issues to be addressed, including the incompatibility of conventional TFSI-based electrolytes with the Mg electrode and the poor reversibility of the cathode. In this work, to satisfyingly settle the incompatibility, an artificial interphase was first pre-constructed by high-temperature displacement reaction of CuCl2 and Mg metal, responsible for the faster charge-transfer rate and the lower Mg plating/stripping overpotential (∼0.2 V) in Mg symmetric cells. Regarding the Mg-Mo6S8 full cells, to enhance the reversibility and rate performance, Mg/Li hybrid batteries were designed. Consequently, the Mg-Mo6S8 battery can achieve excellent cycle stability and deliver a desirable capacity. Even as the current density increases to 1C, the battery still shows a desirable capacity of 92 mAh g−1 over 500 cycles.

Determination of optimum process parameters for different Ti-6Al-4V powders processed by Laser-based Powder Bed Fusion

The PBF-LB (laser-based powder bed fusion) process is subject to a large number of variables, including the characteristics of the processed powder. Since a powder with a given specification can be supplied by various powder manufacturers, the transferability of optimized parameter settings and statistical processing models is of major interest. This work therefore investigates the processing windows of two Ti-6Al-4V powders supplied by different manufacturers following the Design of Experiments (DoE) approach. The fitted regression models for porosity and roughness demonstrate a significant influence of the powder and its size distribution. Further, the powder type significantly interacts with laser power, scanning speed and hatch spacing. It is shown that an increase of the powder size distribution quantiles by less than 10 µm leads to a shift of optimum settings towards a higher volume energy density by 6.4 J/mm³ as well as to higher roughness on the top and side surfaces.

Polymers in Lithium-Sulfur Batteries.

Lithium–sulfur batteries (LSBs) hold great promise as one of the next‐generation power supplies for portable electronics and electric vehicles due to their ultrahigh energy density, cost effectiveness, and environmental benignity. However, their practical application has been impeded owing to the electronic insulation of sulfur and its intermediates, serious shuttle effect, large volume variation, and uncontrollable formation of lithium dendrites. Over the past decades, many pioneering strategies have been developed to address these issues via improving electrodes, electrolytes, separators and binders. Remarkably, polymers can be readily applied to all these aspects due to their structural designability, functional versatility, superior chemical stability and processability. Moreover, their lightweight and rich resource characteristics enable the production of LSBs with high‐volume energy density at low cost. Surprisingly, there have been few reviews on development of polymers in LSBs. Herein, breakthroughs and future perspectives of emerging polymers in LSBs are scrutinized. Significant attention is centered on recent implementation of polymers in each component of LSBs with an emphasis on intrinsic mechanisms underlying their specific functions. The review offers a comprehensive overview of state‐of‐the‐art polymers for LSBs, provides in‐depth insights into addressing key challenges, and affords important resources for researchers working on electrochemical energy systems.

Stable Structure and Electronic Structure for Mg(MgxVyNiz)O4 As Cathode Material for Magnesium Secondary Battery in Discharge Process Using First-Principle Calculation

1. Introduction Magnesium secondary batteries are expected to be applied as a next generation battery materials having higher volume energy density than lithium ion batteries. In our laboratory, we are conducting research and development on cathode materials for magnesium secondary batteries. In recent years, the spinel MgCo2O4 and MgCo1.5Mn0.5O4 in which part of Co is substituted with Mn have been synthesized and measured the battery characteristics of average structure1). From this previous study, it became clear that the Mg/Co cation mixing become decreasing and the first discharge capacity became increasing with the substitution of Mn atom. The first-principle calculation was also performed for the spinel MgCo2O4 and MgCo1.5Mn0.5O4 in pristine and discharge process and reported that the structure changed from a spinel structure to a rock salt structure during discharge2). From the first-principle calculation, it was found that the structure change of MgCo1.5Mn0.5O4 was remarkable because the bond between Mg and O was weakened especially by the influence of Mn. In our laboratory, we have also reported that spinel type Mg(MgxVyNiz)O4 with mixed valence vanadium ions as a host structure has better cycle characteristics than MgCo2O4 system3). However, the local structure in the charge / discharge process and the structural change when Mg is inserted have not been elucidated. The purpose of this study is to investigate the stable structure of Mg(MgxVyNiz)O4 at pristine and discharge process by using the first-principles calculation, and to clarify the mechanism of Mg insertion.2. Calculation method The stable structure of the spinel Mg(Mg0.31V1.69)O4 and Mg(Mg0.31V1.56Ni0.13)O4 inserted Mg atoms (shown as Mg1+y(Mg0.31V1.69)O4 and Mg1+y(Mg0.31V1.56Ni0.13)O4 (y = 0.125~0.75); y is equal to the amount of Mg atoms), were obtained by GGA+U method (VASP code) in discharge process. The cell size of the spinel Mg(Mg0.31V1.69)O4 and Mg(Mg0.31V1.56Ni0.13)O4 were (2×1×1).3. Results and discussion The stable structures of the spinel Mg(Mg0.31V1.69)O4 and Mg(Mg0.31V1.56Ni0.13)O4 at pristine obtained by the first-principle calculation are shown in Fig. 1. In previous study, it was reported that the 8a site was occupied by only Mg atom, and the 16d site was occupied by V, Mg and Ni atom from the average structure analysis measured by the synchrotron X-ray diffraction.3) Models are created based on the results of Rietveld analysis in this study. In both Fig. a-1) and b-1), Mg at 16d site tends to coordinate relatively close to each other in the crystal. It is found from b-1) that Ni also tends to coordinate to positions close to each other. Fig. 1.a-2) and b-2) show the stable structure at the discharge with y=0.25 of Mg inserted into the vacancy 16c site the spinel Mg(Mg0.31V1.69)O4 and Mg(Mg0.31V1.56Ni0.13)O4 at pristine, respectively. Green circles in Fig. 1 a-2) and b-2) are indicated the Mg inserted into the hole 16c site. The Mg before the structural relaxation is indicated by a black dotted circle, and the Mg moved after the structural relaxation is indicated by an arrow and a red circle in in Fig. 1 a-2) and b-2), respectively. As shown in Fig. a-2) and b-2), the structure of Mg become stable when it is inserted into the 16c site near Mg, which is mixed to the 16d site. The model in which the inserted Mg coordinated away from each other in the crystal has high total energy. In both a-2) and b-2), it is found that the Mg atoms at the 8a site near the inserted Mg have moved to the 16c site. When Mg are inserted into spinel Mg(Mg0.31V1.69)O4 and Mg(Mg0.31V1.56Ni0.13)O4, it becomes clear that the structural change to rocksalt is occurred around Mg at 16d site. This structural change during discharge is also observed in the spinel type MgCo2-xMnxO4 system. Since the distance between the nearest 8a site and 16c site is about 1.7 to 1.8 Å, it is considered that repulsion between cations occurs. On the lecture, we will show the electron density and discuss the electronic state in detail. Acknowledgement This work was partly supported by ALCA-SPRING Grant Number JPMJAL1301, Japan. We are deeply grateful for the cooperation.1) Y. Idemoto, Y. Mizutani, C. Ishibashi, N. Ishida and N. Kitamura, Electrochemistry 87, 220 (2019).2) C. Ishibashi, Y. Mizutani, N. Ishida, N. Kitamura, Y. Idemoto, Bull. Chem. Soc. Jpn. 92, 1950 (2019).3) Y. Idemoto, N. Kawakami, N. Ishida, N. Kitamura, Electrochemistry 87, 281 (2019). Figure 1

Synthesis of Mg-Rich Mg-M-O(M = Fe, Ni, Mn) Cathode Materials Using Layered Double Hydroxide Andpositive Electrode Characteristics and Average / Local Structure

1. Introduction The Mg rechargeable battery (MRB) can be regarded as a next-generation secondary battery that replaces the Li-ion battery, since MRB is expected to have a high volume energy density due to divalent charge carrier, abundant resources, and high safety. However, the diffusion of Mg ions in solids is slower than that of Li ions, and thus there have been no reports of excellent positive electrode materials and they have not been put to practical use. As a new electrode material, we have focused on the disordered rocksalt type positive electrode materials, and tried to synthesize the material with various Mg contents by a reverse co-precipitation method 1). However, the obtained materials had lower Mg contents than expected, and it is hard to prepare a Mg-excess material. Therefore, in this study, as a new synthesis process, we used layered double hydroxide (LDH) as a precursor, and pyrolyzed them to synthesize Mg-excess new positive electrode material Mg-MO (M = Fe, Ni, Mn). For the positive electrode material, the electrode characteristics and the crystal structure were investigated in this study. 2. Experimental The precursor (layered double hydroxide) was synthesized by a coprecipitation method, and the sample was synthesized by pyrolyzing the precursor 2). As the raw materials, MgCl2 · 6H2O, MCl3 · 6H2O (M = Fe, Ni), and MnCl2 · 4H2O were dissolved in ion-exchanged water so that Mg: M became 2: 1, and then the pyrolysis was performed at 500 ° C. The obtained sample was subjected to powder X-ray diffraction measurement to identify the phase and calculate the lattice constant, and the metal composition was analyzed by ICP-AES. A three-electrode cell (manufactured by Toyo System Co., Ltd.) was utilized for a charge / discharge test at an operating temperature of 90 ° C, and the positive electrode characteristics were evaluated. In addition, synchrotron X-ray diffraction measurement (BL19B2, SPring-8) was performed, and the average structure was clarified by Rietveld analysis (RIETAN-FP). Synchrotron X-ray total scattering measurement (BL04B2, SPring-8) were also performed, and the local structure was investigated by reverse Monte Carlo analysis (RMC Profile). 3. Results As a result of X-ray diffraction measurement, the peaks could be assigned to the spinel structure (Fd-3m) in the Fe system and the rock salt structure (Fm-3m) in the Ni system. Composition analysis by ICP-AES revealed that all the samples prepared by this new process had Mg-rich composition. As a result of the charge-discharge test, a discharge capacity of Mg1.33Ni0.66O2 was only about 4.5 mAh / g although the capacity increased to about 30 mAh / g by partial substitution for Ni. On the other hand, in the Fe-based sample, the capacity was about 60 mAh / g for Mg2FeO4-δ, and excellent cycle characteristics could be confirmed. Moreover, the discharge capacity of Mg2Fe0.66Ni0.33O2 was about 170mAh / g at the 2nd discharge. Reverse Monte Carlo analysis was performed to clarify the cause of the small discharge capacity of the Ni-based samples. As a result, it was found that Ni tends to aggregate in Mg1.33Ni0.66O2 and the domain can be considered not to participate in charge / discharge. On the other hand, similar phenomenon was not observed in Mg1.33Ni0.5Mn0.16O2. From this, it can be concluded that the amount of Mg and/or synthetic process must be reexamined to improve the electrode property.This work was supported by JST ALCA-SPRING Grant Number JPMJAC1301, Japan.

Improving the applicability of wear-resistant Al–10Si–0.5 Mg alloy obtained through selective laser melting with T6 treatment in high-temperature, and high-wear environments

This study investigated the effects of T6 treatments on the microstructural evolution process and mechanical properties of Al–10Si–0.5 Mg alloy specimens fabricated through selective laser melting (SLM). The applicability of the wear-resistant alloy for high-temperature applications was evaluated. The results reveal that the volume energy density (VED) of the laser used influences the structural morphologies of the SLM-fabricated alloy components. Ultrafine crystals and residual stress formed in the SLM-fabricated alloy specimen due to the rapid cooling rate, thus causing high hardness, high strength, and extremely low elongation values. T6 heat treatment decreases the hardness and tensile strength values of the alloy specimens but improves their elongation values because the residual stress is releases and the microstructure is changes such that a large number of Si particles are present in the Al matrix. The mechanical properties are influenced by the Si particle distribution due to tensile crack initiation at hard–brittle Si particles. The mechanical properties of the as-fabricated SLM alloy are comparable to those of 4384 alloys obtained after T6 heat treatment. The SLM-fabricated specimen that presents a high VED value after T6 heat treatment exhibits good wear resistance. The as-fabricated SLM alloy specimen retained its mechanical properties according to high-temperature tensile tests. The SLM-fabricated Al alloy is a potential candidate for wear-resistance and high-temperature applications.

Blended spherical lithium iron phosphate cathodes for high energy density lithium–ion batteries

Blended spherical cathodes of lithium iron phosphate with different particle sizes were prepared using a physical mixing method. The processability and electrochemical properties of blended spherical cathodes were systematically investigated. The characterization results suggest that the blended spherical cathodes contain two different-sized particles, and smaller particles can fill in the gaps created by larger ones. This structural feature causes an increase in both the connect area of the particles and the compaction density of the blended spherical cathodes, which can enhance the processability of the materials. Increasing the difference in particle sizes between the two groups of blended spherical cathodes is beneficial to obtain an enhanced overall performance, as tested with 14,500 cylindrical batteries, such as higher compaction density, lower resistance, superior high-rate capacity, excellent cycle stability, and higher volume energy density. Therefore, lithium iron phosphate batteries fabricated using the blended spherical cathode with two particle groups that differ significantly in size have a good application prospect.

In-situ formation of Ni4Ti3 precipitate and its effect on pseudoelasticity in selective laser melting additive manufactured NiTi-based composites

Selective laser melting (SLM) additive manufacturing technology was applied to synthesize NiTi-based composites via using ball-milled Ti, Ni, and TiC mixed powder. By transmission electron microscope (TEM) characterization, it indicated that the B2 (NiTi) matrix was obtained during SLM processing. In spite of more Ti content (the Ti/Ni ratio >1), a mass of Ni-rich intermetallic compounds containing Ni4Ti3 with nanostructure features and eutectic Ni3Ti around in-situ Ti6C3.75 dendrites were precipitated. Influence of the applied laser volume energy density (VED) on the morphology and content of Ni4Ti3 precipitate was investigated. Besides, nanoindentation test of the matrix was performed in order to assess pseudoelastic recovery behavior of SLM processed NiTi-based composites. At a relatively high VED of 533 J/mm3, the maximum pseudoelastic recovery was obtained due to the lowest content of Ni4Ti3 precipitates. Furthermore, the precipitation mechanism of in-situ Ni4Ti3 was present based on the redistribution of titanium element and thermodynamics analysis, and then the relationship of Ni4Ti3 precipitate, VED and pseudoelastic recovery behavior was also revealed.

Novel core/shell CoSe2@PPy nanoflowers for high-performance fiber asymmetric supercapacitors

A novel type of fiber asymmetric supercapacitor was fabricated by assembling a CoSe2@PPy core/shell nanoflower positive electrode and an EACF negative electrode. Full cells show good flexibility, high-rate capacity, outstanding volume specific capacitance, high volume energy density and are used to power mini-scale photodetectors.

Elastic Sandwich‐Type rGO–VS2/S Composites with High Tap Density: Structural and Chemical Cooperativity Enabling Lithium–Sulfur Batteries with High Energy Density

AbstractDriven by increasing demand for high‐energy‐density batteries for consumer electronics and electric vehicles, substantial progress is achieved in the development of long‐life lithium–sulfur (Li–S) batteries. Less attention is given to Li–S batteries with high volume energy density, which is crucial for applications in compact space. Here, a series of elastic sandwich‐structured cathode materials consisting of alternating VS2‐attached reduced graphene oxide (rGO) sheets and active sulfur layers are reported. Due to the high polarity and conductivity of VS2, a small amount of VS2 can suppress the shuttle effect of polysulfides and improve the redox kinetics of sulfur species in the whole sulfur layer. Sandwich‐structured rGO–VS2/S composites exhibit significantly improved electrochemical performance, with high discharge capacities, low polarization, and excellent cycling stability compared with their bare rGO/S counterparts. Impressively, the tap density of rGO–VS2/S with 89 wt% sulfur loading is 1.84 g cm−3, which is almost three times higher than that of rGO/S with the same sulfur content (0.63 g cm−3), and the volumetric specific capacity of the whole cell is as high as 1182.1 mA h cm−3, comparable with the state‐of‐the‐art reported for energy storage devices, demonstrating the potential for application of these composites in long‐life and high‐energy‐density Li–S batteries.

Flexible Asymmetric Threadlike Supercapacitors Based on NiCo2 Se4 Nanosheet and NiCo2 O4 /Polypyrrole Electrodes.

Flexible threadlike supercapacitors with improved performance are needed for many wearable electronics applications. Here, we report a high performance flexible asymmetric all-solid-state threadlike supercapacitor with a NiCo2 Se4 positive electrode and a NiCo2 O4 @PPy (PPy: polypyrrole) negative electrode. The as-prepared electrodes display outstanding volume specific capacitance (14.2 F cm-3 ) and excellent cycling performance (94 % retention after 5000 cycles at 0.6 mA) owing to their nanosheet and nanosphere structures. The asymmetric all-solid-state threadlike supercapacitor expanded the stability voltage window from 0-1.0 V to 0-1.7 V and exhibits high volume energy density (5.18 mWh cm-3 ) and superior flexibility under different bending conditions. This study provides a scalable method for fabricating high performance flexible supercapacitors from easily available materials for use in wearable and portable electronics.

Investigation of crystal growth mechanism during selective laser melting and mechanical property characterization of 316L stainless steel parts

A fundamental investigation of the development of grain structure of 316L stainless steel fabricated by selective laser melting (SLM) was conducted. Finite element analysis (FEA) was carried out in order to reveal the growth mechanism of grains under rapid solidification conditions. From this analysis, the crystal growth patterns were determined as a function of the temperature gradient along grain development orientation. A detailed discussion of preferred crystal orientation of dendrites was performed by geometrical analysis in conjunction with experimental findings. In addition, the dendrite spacings were measured, and the variation in spacings as a function of scan speed was studied. It was found that, the rapid solidification induced by high-speed laser scanning brought about sub-micron grains within the final solidified microstructure and a high volume energy density ω could cause the increase of primary dendrite spacing. Furthermore, the result also indicated that both grain size and densification level dependent on ω could affect the mechanical properties significantly. As the ω was settled at the optimal value of 125.00J/mm3, a high Vicker hardness of 281.6HV0.1, a large tensile strength of 590MPa and an attendant elongation rate of 21.1% were obtained.