Volumetric Capacity Research Articles

Mechanically robust and conductive Ti5Te4/P@C composite materials as promising lithium-ion battery anodes

An urgent need has emerged to develop lithium-ion battery anodes that exhibit high reversible capacity and rate performance surpassing carbonaceous materials. Si-based composites have been investigated extensively. However, in this study, we explored another potential alloy anode consisting of Te and phosphorus without Si. Herein, we present a novel composite material, Ti5Te4/P@C, as an anode for lithium-ion batteries (LIBs). Tellurium, which exhibits good electrical conductivity and high volumetric capacity, and red phosphorus, which exhibits high theoretical capacity, were selected as potential anode materials. To overcome the common drawbacks of the two materials, including the vigorous expansion of volume, electrochemically inactive materials, such as titanium and carbon, were introduced as matrix buffers. Te, Ti, red phosphorus, and C were synthesized using a three-step high energy ball milling (HEBM) technique, that is, stepwise synthesis of (1) Ti and Te, (2) red phosphorus, and (3) carbon. The developed Ti5Te4/P@C composites revealed that the introduction of red P led to the generation of additional pure Te in the Ti5Te4/P@C composites, which was owing to the different binding interactions between Ti, Te, and red P, as confirmed by DFT calculations. Among the developed Ti5Te4/P@C anodes, Ti5Te4/P(30 wt%)@C exhibited outstanding cyclability and high rate performance (440 mAh g−1 at 300 mA g−1 after 500 cycles). To confirm the electrochemical responses and Li+ ion diffusion mechanisms, CV and GITT analyses were performed. Based on the electrochemical characteristics, the superior electrochemical performance of the Ti5Te4/P@C anodes can be ascribed to the well-defined composite structure, including the high electrical conductivity of Te, high theoretical capacity of red P, and effective buffering agents of Ti as a mechanical supporter and conductive C, which enable a pseudocapacitive response, providing better reversibility. Therefore, the Ti5Te4/P@C composite materials are viable anodes for high-performance LIBs.

Strain Self-Adaptive Iron Selenides Toward Stable Na+-Ion Batteries with Impressive Initial Coulombic Efficiency.

High tap density electrodes play a vital role in developing rechargeable batteries with high volumetric capacities, however, developing advanced electrodes with satisfied capacity, excellent structural stability, and achieving the resulted batteries with a high initial Coulombic efficiency (ICE) and good rate capability with long lifespan simultaneously, are still an intractable challenge. Herein, an ultrahigh ICE of 94.1% and stable cycling of carbon-free iron selenides anode is enabled with a high tap density of 2.57gcm-3 up to 4000 cycles at 5Ag-1 through strain-modulating by constructing a homologous heterostructure. Systematical characterization and theoretical calculation show that the self-adaptive homologous heterointerface alleviates the stress of the iron selenide anodes during cycling processes and subsequently improves the stability of the assembled batteries. Additionally, the well-formed homologous heterostructure also contributes to the rapid Na+ diffusion kinetic, increased charge transfer, and good reversibility of the transformation reactions, endowing the appealing rate capability of carbon-free iron selenides. The proposed design strategy provides new insight and inspiration to aid in the ongoing quest for advanced electrode materials with high tap densities and excellent stability.

A Computational Investigation of Lithium‐Based Metal Hydrides for Advanced Solid‐State Hydrogen Storage

AbstractHydrogen storage is a crucial step in commercializing hydrogen‐based energy production. Solid‐state hydrogen storage has gained much attention from researchers and needs extensive research. In the present study, we investigate the structural, mechanical, and optoelectronic properties of lithium‐based LiAH3 (A=Mn, Fe, Co) metal hydrides to elucidate their potential for solid‐state hydrogen storage. First, we evaluate the structure stability of LiAH3 hydrides using formation enthalpies calculations. Then, the mechanical stability is determined by elastic stiffness constants, which reveal that LiAH3 hydrides are stable mechanically as they meet the Born stability requirements. Electronic band structure calculations manifest that all LiAH3 hydrides possess a metallic character. Several optical properties have been discussed in detail. The gravimetric hydrogen storage capacities of LiMnH3, LiFeH3 and LiCoH3 hydrides are 4.65, 4.60 and 4.39 wt%, respectively, achieving the target of US‐DOE for rechargeable equipment. Additionally, we have determined the volumetric hydrogen storage capacities (Cv) for all LiAH3 hydrides. It is worth mentioning that the highest Cv values have been obtained to be 180.80, 188.18 and 177.25gH2l−1 for LiMnH3, LiFeH3 and LiCoH3 hydrides, respectively, which have achieved the US‐DOE target set for 2025. Our investigation predicts the applicability of lithium‐based hydrides as promising solid‐state hydrogen storage materials.

Analysis of the Vapor Compression Refrigeration Cycle Measures with and without Using a Heat Exchanger for Alternative Refrigerants

One of the most commonly refrigeration systems is the vapor compression refrigeration system. Since energy saving and environmental friendliness remain a challenge, researchers are working hard to find an effective solution to improve the performance of vapor compression refrigeration systems while committing to environmental standards. The main goal of this paper is to identify the best and closest alternative refrigerant to R22 among the alternative cooling fluids taken into consideration in terms of thermodynamic and mechanical properties, environmental protection, and safety of handling. This work presents an analysis and comparison of the various performance measures for a vapor compression refrigeration cycle operating without using and using a heat exchanger for environmentally friendly alternative refrigerants, namely R410A, R407A, R407C, R438, RS-44b, and R417A, and compares them with the refrigerant R22, which has direct environmental impacts on the ozone layer (ODP) and global warming (GWP). The computer simulation program Chemours Refrigerant Expert 1 was used to conduct the analyses. The performance parameters analyzed are coefficient of performance, compressor work, cooling capacity, temperature of condensation, intake and exhaust pressure, volumetric capacity, theoretical displacement, intake, exhaust, condensation and evaporation temperature without and with a heat exchanger, and super heating temperature with a heat exchanger. It was concluded from this study that the best alternative to R22 refrigerant among the alternative refrigerants taken into consideration in the study is the RS-44b refrigerant in terms of all performance measures and environmentally friendly. Keywords: Refrigerant; Vapor compression; Performance measures; Evaporation; Heat exchanger.

Soil thermal properties: influence of no-till cover crops

Soil thermal properties, which determine heat transport, can influence soil health parameters and crop productivity. The objective of this study was to evaluate the 2-year effects of no-till cover crops (CCs) and no-till no cover crop (NC) on soil thermal properties (thermal conductivity (λ), volumetric heat capacity ( CV), and thermal diffusivity ( D)). Two levels of CCs were used for this study: CC versus NC. The CCs included crimson clover ( Trifolium incarnatum L.), hairy vetch ( Vicia villosa Roth.), winter peas ( Lathyrus hirsutus L.), oats ( Avena sativa), winter wheat ( Triticum aestivum L.), triticale ( Triticale hexaploide Lart.), flax ( Linum usitassimum L.), and barley ( Hordeum vulgare L.). Soil samples were collected at 0–10, 10–20, and 20–30 cm depths and their λ, CV, and D were measured in the laboratory. Additionally, soil organic carbon, bulk density (BD), and volumetric water content (ϴ) at saturation, −33 kPa, and −100 kPa soil water pressures were measured. Results showed that BD was 18% and 14% higher under CC compared with NC management during 2021 and 2022, respectively. Furthermore, ϴ at all measured soil water pressures was slightly higher under CC compared with NC management during both years. As a result, λ and D were significantly higher under NC compared with CC management, while CV was significantly higher under CC compared with NC management, during both years and at all measured soil water pressures. Generally, soil thermal properties were directly proportional to ϴ, suggesting that ϴ may be the most important factor influencing soil thermal properties.

Expanding the Reticular Chemistry Building Block Library toward Highly Connected Nets: Ultraporous MOFs Based on 18-Connected Ternary, Trigonal Prismatic Superpolyhedra.

The chemistry of metal-organic frameworks (MOFs) continues to expand rapidly, providing materials with diverse structures and properties. The reticular chemistry approach, where well-defined structural building blocks are combined together to form crystalline open framework solids, has greatly accelerated the discovery of new and important materials. However, its full potential toward the rational design of MOFs relies on the availability of highly connected building blocks because these greatly reduce the number of possible structures. Toward this, building blocks with connectivity greater than 12 are highly desirable but extremely rare. We report here the discovery of novel 18-connected, trigonal prismatic, ternary building blocks (tbb's) and their assembly into unique MOFs, denoted as Fe-tbb-MOF-x (x: 1, 2, 3), with hierarchical micro- and mesoporosity. The remarkable tbb is an 18-c supertrigonal prism, with three points of extension at each corner, consisting of triangular (3-c) and rectangular (4-c) carboxylate-based organic linkers and trigonal prismatic [Fe3(μ3-Ο)(-COO)6]+ clusters. The tbb's are linked together by an 18-c cluster made of 4-c ligands and a crystallographically distinct Fe3(μ3-Ο) trimer, forming overall a 3-D (3,4,4,6,6)-c five nodal net. The hierarchical, highly porous nature of Fe-tbb-MOF-x (x: 1, 2, 3) was confirmed by recording detailed sorption isotherms of Ar, CH4, and CO2 at 87, 112, and 195 K, respectively, revealing an ultrahigh BET area (4263-4847 m2 g-1) and pore volume (1.95-2.29 cm3 g-1). Because of the observed ultrahigh porosities, the H2 and CH4 storage properties of Fe-tbb-MOF-x were investigated, revealing well-balanced high gravimetric and volumetric deliverable capacities for cryoadsorptive H2 storage (11.6 wt %/41.4 g L-1, 77 K/100 bar-160 K/5 bar), as well as CH4 storage at near ambient temperatures (367 mg g-1/160 cm3 STP cm-3, 5-100 bar at 298 K), placing these materials among the top performing MOFs. The present work opens new directions to apply reticular chemistry for the construction of novel MOFs with tunable porosities based on contracted or expanded tbb analogues.

A new random walk method for simulating heat flow and temperature distribution in three-dimensional discontinuous systems

Numerical methods for analyzing diffusion phenomena involving strong discontinuities and complicated interfaces are of great scientific and technical importance. In this paper, we extend the existing step-balanced random walk, which overcomes the problem of detailed balance of a random walker in three-dimensional (3D), diffusion-tensor discontinuous systems, to particle density (ρ) discontinuous systems, and introduce volumetric heat capacity C and temperature T by considering ρ as heat density, i.e., ρ=CT, to apply it to thermal problems. Two types of thermophysical simulations are demonstrated: one is steady-state heat flow due to a temperature difference at the end surfaces on a two-phase slab model unit cell with periodic boundary conditions; the other is the time variation of temperature distribution due to heat diffusion from a point heat source in a repeated two-phase slab model with no periodic boundary conditions. We see the correct behavior of heat and temperature expected in 3D discontinuous systems composed of two phases with anisotropic thermal conductivity. The applicability to problems other than pure diffusion and the limitations of the method are also discussed.

Volume contractible Antimony bromide electrode as negative electrode for long-lasting Li-ion batteries

Antimony is one of the promising anode materials for lithium-ion batteries due to its high volumetric and gravimetric capacity (theoretical specific capacity 660 mAh g-1) and stable voltage window (0.87-0.91V vs Li/Li+). However, a high-volume expansion ( ∼130%) of Sb on lithiation degrades the electrochemical performance and restricts its application. In this work, a novel strategy is explored to use antimony halide (SbBr3) instead of Sb as the starting anode material. In the first step, Li will react with SbBr3 to form LiBr and pure Sb, leading to a 78% contraction in volume, and then this pure Sb further lithiates to form Li3Sb expanding the volume (of the lithiated Sb by 130%). LiBr, which is a byproduct of the first reaction, dissolves into the solvent, leaving a porous Sb. In a nutshell, the two-step lithiation process results in a net volume-contacted porous antimony, ideal as an electrode to counter volumetric stress in subsequent charge-discharge cycles. The electrochemical performance of this electrode is much superior when compared with the pure antimony electrode, taking advantage of initial volume reduction and porous scaffold. It achieves a high specific discharge capacity of 345 mAh g-1 at a rate of 100mAg-1 even after the end of the 100th cycle and losing only 20% of its capacity. This shows that this volume contractible technique can be successfully employed for metals and metallic alloys having drastically higher Li-storing capacities than graphite.

The Thermophysical Properties of TcO2

Technetium-99 is a highly radioactive isotope with a long half-life that is common in nuclear waste. It volatizes at a low temperature, which poses a significant challenge to the clean-up and containment processes. Due to difficulties in purifying technetium compounds, their thermophysical properties have not been measured or calculated. Here, first principle methods are used along with the quasi quasi-harmonic harmonic approximation to compute the Debye temperature, volumetric thermal expansion coefficient, bulk modulus, and heat capacity of rutile TcO2 for temperatures ranging from 0 to 1500 K and applied pressures ranging from 0 to 255 GPa. The computed atomic structures agree well with the results from diffraction measurements. The computed thermophysical properties are in the neighborhood of other rutile metal oxides and, in particular, are within approximately 10–13% of rutile ReO2, which is frequently used as a substitute for TcO2 in experimental studies.

High performance all-solid-state Li–Se battery based on selenium loaded on Ti3C2 MXene cathode

Selenium has high theoretical volumetric capacity of 3253 mAh cm−3 and acceptable electronic conductivity of 1 × 10−5 S m−1, which is considered as a potential alternative to sulfur cathode for all-solid-state rechargeable batteries with high energy density. However, the development of all-solid-state Li–Se batteries (ASSLSBs) are hindered by sluggish kinetics and poor cycling life. In this work, trigonal Se nanocrystallines are homogenously distributed in the interspace and on the surface of MXene layers (denoted as Se@MXene composite) by a novel melt-diffusion method. ASSLSBs based on this Se@MXene composite cathode exhibit large specific capacity of 632 mAh g−1 at 0.05 A g−1, high-rate capability over 4 A g−1, and excellent cycling stability over 300 cycles at 1 A g−1. The ex-situ analytical techniques demonstrate that the excellent electrochemical performance of Se@MXene cathode largely arises from structural stability with the assistance of conductive MXene and reversible redox behavior between Li2Se and Se during the repeating charge/discharge process. Our study points out the potential of material design of Se cathode based on conducting 2D materials with good electrochemical behavior, which may accelerate the practicability of ASSLSBs.

Volumetric assessment of Posterior cranial fossa in a West African population

Background and Objectives: Posterior fossa pathologies can have potentially devastating outcomes. The volumetric capacity of this fossa, known to have ethnoregional variations, can thus be critical in determining outcomes and intervention measures and approaches to pathologies involving this region. This study aimed to evaluate the normal posterior fossa volumes within the West-African subpopulation. Methods: This was a descriptive study of all patients presenting for a cranial imaging study at the study location within a two-year period using a 1.5T MRI of this cranial region. Obtained data included the transverse and anteroposterior diameters, and the height of this fossa and the obtained data was analyzed. P values < 0.05 was statistically significant. Results: A total of 315 patients were recruited (165 males and 150 females). The average posterior fossa transverse diameter, anteroposterior diameter and height were 108.19 mm, 71.58 mm and 35.53 mm respectively for males, and 105.7 mm, 66.48 mm, and 34.24 mm for females respectively. The average posterior fossa volume for males (292.36 cm3) was significantly higher than for females (252.90 cm3) (p= 0.0038). The highest average posterior fossa volume was between 16-30 years for males and above 75 years for females. Conclusion: Posterior cranial fossa volumes for the West African population is significantly higher than those obtained for other regions. In addition to being beneficial in some posterior fossa space occupying lesions, this larger volume can explain the relative rarity and sexual preferences of some posterior fossa congenital abnormalities like Chiari-1 malformation amongst the West African population

Water-induced strong isotropic MXene-bridged graphene sheets for electrochemical energy storage.

Graphene and two-dimensional transition metal carbides and/or nitrides (MXenes) are important materials for making flexible energy storage devices because of their electrical and mechanical properties. It remains a challenge to assemble nanoplatelets of these materials at room temperature into in-plane isotropic, free-standing sheets. Using nanoconfined water-induced basal-plane alignment and covalent and π-π interplatelet bridging, we fabricated Ti3C2Tx MXene-bridged graphene sheets at room temperature with isotropic in-plane tensile strength of 1.87 gigapascals and moduli of 98.7 gigapascals. The in-plane room temperature electrical conductivity reached 1423 siemens per centimeter, and volumetric specific capacity reached 828 coulombs per cubic centimeter. This nanoconfined water-induced alignment likely provides an important approach for making other aligned macroscopic assemblies of two-dimensional nanoplatelets.

An efficient thermal lattice Boltzmann method for simulating three-dimensional liquid–vapor phase change

In this paper, a multiple-relaxation-time lattice Boltzmann (LB) approach is developed for the simulation of three-dimensional (3D) liquid–vapor phase change based on the pseudopotential model. In contrast to some existing 3D thermal LB models for liquid–vapor phase change, the present approach has two advantages: for one thing, some gradient terms, such as the gradient of volumetric heat capacity and the Laplacian term of temperature, that must be computed with finite-difference scheme in previous works is not needed for the present thermal model. For another, the current model is constructed based on the seven discrete velocities in three dimensions (D3Q7), making it more efficient and much easier to be implemented. Also, based on the scheme proposed by Zhou and He (1997), a pressure boundary condition for the D3Q19 lattice is proposed to model the multiphase flow in open systems. This model is then validated by considering the temperature distribution in a 3D saturated liquid–vapor system, the d2 law, the droplet evaporation on a heated surface and the nucleate boiling. It is observed that the numerical results fit well with the analytical solutions, and the results of the finite difference method or the experimental data. Our numerical results indicate that the present approach is reliable and efficient in dealing with the 3D liquid–vapor phase change.

An Inductive Method for Comprehensive Estimation of Temperature-Dependent Electrical and Thermal Properties of Conductive Ferromagnetic Materials

Reliable information about the properties of the processed materials has a significant impact on the effects of their processing. In induction heating processes, this also applies to information about the influence of temperature T on these properties. These are both thermal and electro-magnetic properties. Based on previous studies, a comprehensive experimental method is presented for estimating the temperature characteristics of thermal diffusivity, volumetric heat capacity and resistivity on one measurement station, with particular attention to ferromagnetic materials. The estimation process is carried out on an induction heating stand using forcing signals from an inverter generator. In a computer-controlled cycle that changes the base temperature level, basic measurements of thermal and electrical properties are carried out on a material sample in the form of a cylindrical disk. They are the results of the analysis of the temperature and electromagnetic responses of a material sample to short- and long-term step pulses of a sinusoidal excitation signal with a frequency of approximately 40 kHz. The presented estimation method can be treated as a final method or a preliminary procedure for radically narrowing the variability in decision variables inthe optimization process of simultaneous determination of the sought material characteristics.

Dibromomethane Knitted Highly Porous Hyper-Cross-Linked Polymers for Efficient High-Pressure Methane Storage.

Hyper-cross-linked polymers (HCPs) with ultra-high porosity, superior physicochemical stability, and excellent cost-effectiveness are attractive candidates for methane storage. However, the construction of HCPs with BET surface areas exceeding 3000 m2 g-1 remains extremely challenging. In this work, a newly developed DBM-knitting method with a slow-knitting rate is employed to increase the cross-linking degree, in which dichloromethane (DCM) is replaced by dibromomethane (DBM) as both solvent and electrophilic cross-linker, resulting in highly porous and physicochemically stable HCPs. The BET surface areas of DBM-knitted SHCPs-Br are 44%-120% higher than that of DCM-knitted SHCPs-Cl using the same building blocks. Remarkably, SHCP-3-Br exhibits an unprecedentedly high porosity (SBET = 3120m2g-1) among reported HCPs, and shows a competitive volumetric 5-100bar working methane capacity of 191 cm3 (STP) cm-3 at 273K calculated by using real packing density, which outperforms sate-of-art metal-organic framework (MOFs) at comparable conditions. This facile and versatile low-knitting-rate strategy enables effective improvement in the porosity of HCPs for porosity-desired applications.

Shallow geothermal potential and numerical modelling of the geo-exchange for a sustainable post-earthquake building reconstruction (Potenza River valley, Marche Region, Central Italy)

The southern part of the Marche Region (Italy) was hit in 2016 by dramatic seismic events that caused damages and fatalities. After these events, the national and local administrations started a development plan to improve the energy efficiency of the restored or reconstructed buildings. Shallow geothermal energy, consisting of closed-loop Borehole Heat Exchangers (BHEs) coupled with heat pumps, could represent a first-order renewable choice for indoor air conditioning (heating and cooling) systems. The feasibility and potential of the BHEs also match this technology's null visual outdoor impact which is paramount in preserving the landscape of the earthquake-affected areas. However, the exploitation, sustainability, and correct design of these systems require detailed knowledge of the ground's geological, hydrogeological, and thermophysical properties. In this framework, the present study was carried out to map and test, through the G.POT algorithm, the shallow geothermal potential and sustainability of the Potenza River valley through the publicly available data from the Italian Seismic Microzonation studies — an extensive database of geognostic drillings and other geological and geophysical surveys. This step allowed us to assign the main thermal parameters (thermal conductivity, volumetric heat capacity, specific heat extracted) to each geological layer and averaged them over the first 100 m (i.e., a typical depth for BHEs). All the data were then interpolated to produce geothermal thematic maps to visualize and compare the potential and adequacy of the territory for the installation of closed-loop BHEs. Finally, finite elements numerical models (FEFLOW® software) were developed in a balanced mode through the annual heating and cooling cycles to verify the sustainability of this renewable concerning the thermal impact induced to the ground by the BHEs during a long-term (20 years) operation.

Performance of Heat Pump Air Conditioning with R1234ze (HFO) as a Refrigerant

The study shows that refrigerants R1234ze (E) and R1234ze (Z), known for their low global warming potential, are likely to become primary choices in heat pump air conditioning for residential and commercial use. The research evaluates the thermodynamic properties of R1234ze (Z) using experimental, thermodynamic, and numerical analyses. It addresses F-gas regulation requirements and aligns with the Paris Agreement goals by exploring various refrigerants, including R227ea, R114, R236fa, R134a, R1234ze (Z), and R245fa, as potential candidates for evolving industry needs. The analysis indicates that R1234ze (Z) outperforms other working fluids in heat pump applications, with an optimized theoretical coefficient of performance (COP) at a condensation temperature 22 K lower than critical temperatures. However, actual COP deviates due to a significant pressure drop, especially with inadequate volumetric capacity. A key finding is that a substantial portion of the pressure reduction is attributed to mitigating irreversible losses, estimated at a condensation temperature of 70–75°C, emphasizing the complex relationship between pressure and performance. The study suggests that R1234ze (Z) is more suitable for high-temperature applications than traditional air conditioning systems. In a parallel assessment, the initial calculation of the coefficient of performance for R245fa evaluates the reliability of a new refrigeration industry arrangement. Test results for heat pump technology reveal that R1234ze (Z) achieves an impressive COP of up to 3.60 at a buildup temperature of 90°C with a temperature differential of 45 K. This positions R1234ze (Z) as a suitable choice for heat pump applications prioritizing simplicity in system design.

Pillar-Structured Ti3 C2 Tx MXene with Engineered Interlayer Spacing for High-Performance Magnesium Batteries.

Two-dimentional (2D)Ti3 C2 Tx MXene has attracted significant attention in non-lithium-ion batteries due to its excellent electrical conductivity, high volumetric capacity, and ability to accommodate intercalants. Rechargeable magnesium batteries with Mg metal anodes are noted for their high theoretical energy density, potential safety, earth abundance, dendrite-free Mg2+ plating/stripping mechanism on the anode side, and low cost. Nevertheless, owing to the large polarity of divalent Mg2+ ions, the insertion of Mg2+ into the MXene layers suffers from sluggish kinetics, limiting the performance for storage of Mg2+ ions. Herein, a simple self-assembly strategy is demonstrated to achieve high magnesium ion storage capability with pillar-structured Ti3 C2 Tx MXene by intercalating a hyperbranched polyethylene ionomer containing quaternary ammonium ions. The ionomer intercalation/modification leads to the expansion of interlayer spacing of the MXene and, meanwhile, improves its affinity to low-polarity THF-based electrolyte.The delaminated ionomer-modified MXene shows significantly improved electrochemical performance as a cathode material for Mg batteries. It shows a promising cycling stability with a capacity retention of 86% after 400 cycles at 200mAg-1 , as well as outstanding high-rate performance with a capacity of 110mAhg-1 retained at 1,000mAg-1 relative to 213mAhg-1 at 20mAg-1 .

Small-pore hydridic frameworks store densely packed hydrogen

Nanoporous materials have attracted great attention for gas storage, but achieving high volumetric storage capacity remains a challenge. Here, by using neutron powder diffraction, volumetric gas adsorption, inelastic neutron scattering and first-principles calculations, we investigate a magnesium borohydride framework that has small pores and a partially negatively charged non-flat interior for hydrogen and nitrogen uptake. Hydrogen and nitrogen occupy distinctly different adsorption sites in the pores, with very different limiting capacities of 2.33 H2 and 0.66 N2 per Mg(BH4)2. Molecular hydrogen is packed extremely densely, with about twice the density of liquid hydrogen (144 g H2 per litre of pore volume). We found a penta-dihydrogen cluster where H2 molecules in one position have rotational freedom, whereas H2 molecules in another position have a well-defined orientation and a directional interaction with the framework. This study reveals that densely packed hydrogen can be stabilized in small-pore materials at ambient pressures.

Multiscale Micro‐Nano Hierarchical Porous Germanium with Self‐Adaptive Stress Dispersion for Highly Robust Lithium‐Ion Batteries Anode

AbstractThe manipulation of stress in high‐capacity microscale alloying anode materials, which undergo significant volumetric variation during cycling, is crucial prerequisite for improved their cycling capability. In this work, an innovative structural design strategy is proposed for scalable fabrication of a unique 3D highly porous micro structured germanium (Ge) featuring micro‐nano hierarchical architecture as viable anode for high‐performance lithium‐ion batteries (LIBs). The resultant micro‐sized Ge, consisting of interconnected nanoligaments and bicontinuous nanopores, is endowed with high activity, decreased Li+ diffusion distance and alleviated volume variation, appealing as an ideal platform for in‐depth understanding the relationship between structural design and stress evolution. Such a micro‐sized Ge being highly porous delivers a record high initial Coulombic efficiency of 92.5%, large volumetric capacity of 2,421 mAh cm−3 at 1.2 mA cm−2, exceptional rate capability (805.6 mAh g−1 at 10 Ag−1) and cycling stability (over 90% capacity retention after 1000 cycles even at 5 A g−1), largely outperforming the reported Ge‐based anodes for LIBs. Furthermore, its underlying Li storage mechanism and stress dispersion behavior are explicitly revealed by combined substantial in situ/ex situ experimental characterizations and theoretical computation. This work provides novel insights into the rational design of high‐performance and durable alloying anodes toward high‐energy LIBs.