High Energy Density Materials Research Articles

Time for mixing: Mixed dicationic energetic salts based on methylene bridged 4-hydroxy-3,5-dinitropyrazole and tetrazole for tunable performance

Various types of materials have been explored in the pursuit of high energy density materials (HEDMs) that have balanced energy and stability. Among them, energetic salts show numerous advantages, such as lower vapor pressures, high physical stabilities, and the opportunity for favorable tuning by careful selection of cations/anions. Nitrogen-rich bases are generally used as cations for energetic salt formation. While the synthesis of salts with larger cations lowers the sensitivity, smaller cations aid better energetic performance. A combination of both in the same ionic moieties might help in the formation of a superior explosive. In this work, a facile route for the synthesis of mixed dicationic energetic salts based on 1-((1H-tetrazol-5-yl)methyl)-3,5-dinitro-1H-pyrazol-4-ol (compound 1) has been explored by various combinations of bigger and smaller cations (compounds 4–10). All the synthesized energetic salts showed high positive heats of formation, energetic performance comparable to TATB, excellent stability towards impact and friction, and acceptable thermal stabilities. This improved technique will provide an additional option for fine-tuning the energetic properties of HEDMs and will facilitate in exploring the role of various cations in the overall performance of the energetic compounds.

Trinitromethyl-Substituted 1H-1,2,4-Triazole Bridging Nitropyrazole: A Strategy of Utterly Manipulable Nitration Achieving High-Energy Density Material.

Nitro groups have been demonstrated to play a decisive role in the development of the most powerful known energetic materials. Two trinitromethyl-substituted 1H-1,2,4-triazole bridging nitropyrazoles were first synthesized by straightforward routes and were characterized by chemical (MS, NMR, IR spectroscopy, and single-crystal X-ray diffraction) and experimental analysis (sensitivity toward friction, impact, and differential scanning calorimetry-thermogravimetric analysis test). Their detonation properties (detonation pressure, detonation velocity, etc.) were predicted by the EXPLO5 package based on the crystal density and calculated heat of formation with Gaussian 09. These new trinitromethyl triazoles were found to show suitable sensitivities, high density, and highly positive heat of formation. The combination of exceedingly high performances superior to those of HMX (1,3,5,7-tetranitrotetraazacyclooctane), and its straightforward preparation highlights compound 8 as a promising high-energy density material (HEDM). This work supports the effectivity of utterly manipulable nitration and provides a generalizable design synthesis strategy for developing new HEDMs.

Theoretical investigation on heats of formation, detonation properties and sensitivities of TANPy based energetic materials

A series of 2,4,6-triamino-3,5-dinitropyridine (TANPy) based energetic compounds were designed and optimized at the B3LYP/6-311G (d,p). The results show that all the designed compounds have high positive heats of formation, and the tetrazole ring/–N3 was an beneficial combination to increase the heats of formation. The introduction of furazan-furazan/-C(NO2)3/–CH(NO2)2 combination was effective to improve the densities and detonation properties while the furazan-furazan or furazan-tetrazine rings was beneficial to improving the values of heats of detonation. Considering the detonation properties and sensitivities, compounds D2, E2, F2 were finally screened as potential high energy density materials and their physicochemical properties were fully investigated.

Construction of Adaptive Deformation Block: Rational Molecular Editing of the N-Rich Host Molecule to Remove Water from the Energetic Hydrogen-Bonded Organic Frameworks.

Energetic hydrogen-bonded organic frameworks (E-HOFs), as a type of energetic material, spark fresh vitality to the creation of high energy density materials (HEDMs). However, E-HOFs containing cations and anions face challenges such as reduced energy density due to the inclusion of crystal water. In this work, the modification of amino groups in N-rich organic units could form a smart building block of hydrogen-bonded frameworks capable of changing the volume of the void space in the molecule through adaptive deformation of E-MOF blocks, thus enabling the replacement of water. Based on the above strategy, we report an interesting example of a series of hydrogen-bonded organic frameworks (E-HOF 2a and 3a) synthesized using a facile method. The crystal structure data of all of the compounds were also obtained in this work. Anhydrous 2a and 3a exhibit higher density, good thermal stability, and low mechanical sensitivity. The strategy of covalent bond modification for the host molecules of energetic frameworks shows enormous potential in eliminating the crystalline H2O of hydration and exploring high energy density materials.

3D sodiophilic mixed-ion-electron-conducting framework of hierarchical nanowire arrays for ultra-stable sodium-metal batteries

Sodium metal batteries (SMBs) have attracted increasing attentions as next-generation energy storage systems, regarding its high energy density and raw materials abundance. However, its practical application is impeded by the inferior reversibility of Na anode, stemmed from the non-uniform Na plating/stripping process and formation of “dead Na”. Herein, a three-dimensional (3D) mixed-ion-electron-conducting scaffold (MIECS) is in-situ established by self-assembled hierarchical Cu2S nanowire arrays, which renders enhanced sodiophilicity, high surface area, and robust architecture to the current collector, thereby promoting interfacial kinetics, homogenizing Na deposition, and ensuring “top-down” dissolution. As a result, Cu2S NWs@Cu MIECS enabled Na metal anode with exceptional Coulombic efficiency as high as 99.94 % over 1600 cycles at 4 mA cm−2, as well as steady plating/stripping profile for at least 2000 h at depth of discharge of 75 %. Impressively, full-cell SMB achieves ultra-stable cycling of 2000 cycles, exhibiting capacity retention as high as 96.3 % at high cathode loading of 14.7 mg cm−2, or that of 87.8 % at 5 C, with limited Na excess (N/P = 3). The 3D sodiophilic Cu2S NWs@Cu MIECS provides a promising route to highly reversible Na metal anode for developing high-energy-density SMBs.

Holistic Processing of Sawdust to Enable Sustainable Hybrid Li-Ion Capacitors

AbstractActivated carbon has long been recognized as a promising electrode material for energy storage devices. The extraordinarily high specific area makes it challenging to replace in supercapacitors since electrical double-layer capacitors need such surfaces but also porous networks to enable electrolyte penetration. As a raw material for synthesizing activated carbon, sawdust offers key benefits, such as its renewability, abundance, favorable physical attributes for energy storage, and a more environmentally friendly synthesis process compared to mined alternative sources. In this work, electrochemical characterization is carried out which highlights the critical role of pelletization in enhancing the capacitive performance of sawdust-derived activated carbon, in addition to the implicit handling and logistical benefits. Subsequently, a Li-ion capacitor is assembled with an organic solvent-based electrolyte, sawdust-derived activated carbon serving as the positive electrode, and an Al-based foil negative electrode, potentially combining high energy and power density materials into a hybrid device. Despite commendable electrochemical performance and the use of a sustainable waste-derived positive electrode with a commoditized negative electrode, challenges remain regarding the ability to mitigate the role of surface functional groups that are stabilized by bio-carbon thermal treatments. Nevertheless, this distinctive architecture holds promise as an alternative high-power energy storage technology for a future filled with renewable energy, electric vehicles, and portable electronic devices.

One-Dimensional Non-coplanar Nitrogen Chains in Manganese Tetranitride under High Pressure.

Transition metal nitrides have great potential applications as incompressible and high energy density materials. Various polymeric nitrogen structures significantly affect their properties, contributing to their complex bonding modes and coordination conditions. Herein, we first report a new manganese polynitride MnN4 with bifacial trans-cis [N4]n chains by treating with high-pressure and high-temperature conditions in a diamond anvil cell. Our experiments reveal that MnN4 has a P-1 symmetry and could stabilize in the pressure range of 56-127 GPa. Detailed pressure-volume data and calculations of this phase indicate that MnN4 is a potential hard (255 GPa) and high energy density (2.97 kJ/g) material. The asymmetric interactions impel N1 and N4 atoms to hybridize to sp2-3, which causes distortions of [N4]n chains. This work discovers a new polynitride material, fills the gap for the study of manganese polynitride under high pressure, and offers some new insights into the formation of polymeric nitrogen structures.

Predicted High-Energy Density MN8 Containing Anionic 18-Crown-6 Ring-Based Polynitrogen Monolayers Acting as Cryptand.

In this study, we investigate the potential of the 18-crown-6-like two-dimensional (2D)-N8 structure to accommodate electrons from metals without compromising its covalent nitrogen network. Employing the crystal structure prediction enhanced by evolutionary algorithm and density functional theory methodology, we successfully predicted the existence of 16 layered M@2D-N8 complexes from a total of 39 MN8 systems investigated at 100 GPa (M = s-block Na-Cs, Be-Ba and d-block Ag, Au, Cd, Hg, Hf, W, and Y). Among those, there are 13 quenchable M@2D-N8 compounds that are dynamically stable at 1 atm. Orbital interactions and bonding analysis show that 2D-N8 presents a flat localized π* band that can accommodate one or two electrons without breaking the 2D covalent nitrogen network. Depending on the metal-to-polynitrogen charge transfer (formally, 1-4 electrons), these N-rich phases are semiconducting or metallic under ambient conditions. Ab initio molecular dynamics simulations show that K(I)@2D-N8 and Ca(II)@2D-N8 are thermally stable up to 600 K, while the Hf(IV)@2D-N8 compound is thermally not viable at 400 K because of the weakening of the N═N bonds due to a strong four-electron reduction. These metal 18-crown-6 ring-based polynitrogen compounds, as expected due to their high nitrogen content (eight nitrogen atoms per metal), could potentially serve as new high-energy density materials.

Microstructure and electrochemical properties of Mg/Nb/Zr co-doped LiNi0.94Mn0.04Al0.02O2 cathode materials

The increasing oil scarcity and environmental awareness have accelerated the rise of the new energy vehicle industry, but range and cost issues have hindered the rapid popularization of new energy vehicles. The Co-free Ni-rich layered cathode materials have received a wide attention due to their high energy density, low cost, and stable raw material supply. However, its structure and electrochemical stability still need to be further improved. In this study, the electrochemical properties of LiNi0·94Mn0·04Al0·02O2 (NMA), a Co-free Ni-rich layered cathode material, have been improved by co-doping of Mg, Nb, and Zr. Also, the effects of co-doping on the crystal structure, morphology and electrochemical properties of NMA cathode materials were investigated, too. The results show that the NMA material (NMA-333) with 0.9 mol% doping amount has the best electrochemical performance. The discharge-specific capacity in the first cycle at 1 C was 199.6 mAh g−1, and the capacity retention after 200 cycles reached 73.94 %, which is nearly 24 % higher than that of the original material (NMA-1.03). Meanwhile, the NMA-333 material has a relatively better rate performance, with a discharge-specific capacity of 125.2 mAh g−1 at 10 C. Moreover, the structure and morphology of the modified material were represented by SEM, TEM, XRD, and XPS. And the results showed that the co-doping modification could refine the primary particles of the NMA material, reduce the lithium-nickel mixing, and increase the lattice spacing. The XPS, SEM, and XRD of the post-cycle electrodes further showed that co-doping had stabilized the crystal structure, inhibited the generation and expansion of microcracks, and reduced the occurrence of harmful side reactions, thus improving the cycling performance of the NMA materials at high voltage. The method could be a feasible way to improve the electrochemical performance of layered high-nickel cobalt-free cathode materials.

A molecular dynamics simulation study of thermal transport in hydrazinium cyclo-pentazolate

Cyclo-pentazolate salts (CPSs) as a new type of high-energy-density materials (HEDMs) with high nitrogen content have attracted considerable research attention. In contrast to the extensive studies on their energy properties, the thermal transport process in CPSs has been less studied which relates closely to the thermal safety of this material. Concerning the hydrazinium cyclo-pentazolate (HCP), we conduct a computational study to estimate the thermal conductivity of HCP by means of the non-equilibrium molecular dynamics (NEMD) simulation. To achieve that, we have customized interaction parameters based on the default OPLS force field for the HCP, as benchmarked by its crystal structure. Our simulations have revealed surprisingly anisotropic thermal conductivity for the HCP, while the thermal conductivity becomes highest roughly in the direction perpendicular to cyclo-N 5− with its value notably higher than common high explosives. By modulating the interaction parameters within the HCP molecule, we have further captured a dominant role of the interaction between cyclo-N 5− in regulating the thermal conductivity of the HCP. The attractive Lennard–Jones (LJ) potential may restrict the relative motion between cyclo-N 5− , which forms a long-range order thus enhances thermal transport in the direction perpendicular to cyclo-N 5− . Our simulations result on the effect of (cyclo-N 5− )-(cyclo-N 5− ) interaction provide insights to engineer thermal transport in CPSs at the molecular level.

Solid-state synthesis of low-cost and high-energy-density sodium layered-tunnel oxide cathodes: Dynamic structural evolution, Na+/vacancy disordering, and prominent moisture stability

Manganese-based layered oxides show promise as cathode materials for sodium-ion batteries (SIBs). However, several challenges including sluggish Na+ kinetics, complex phase transitions, and poor air stability hinder their practical application. Herein, we proposed a dual-function strategy that not only precisely manipulates dynamic structural evolution from layered to tunnel structure, but also effectively suppresses Na+/vacancy and charge ordering by inhibiting electron delocalization. A series of Ti-substituted Na2/3Mn1-xTixO2 (x=0, 1/9, 2/9, 1/3) as proof of concept materials were designed to demonstrate the dual-function strategy. As a result, the optimized Na2/3Mn8/9Ti1/9O2 cathode material delivers a high specific capacity of 202.9 mAh g−1 at 0.1 C within 1.5−4.3 V, equivalent to 536.6 Wh kg−1 of energy density, and exhibits 71.0% of capacity retention after 300 cycles at 1 C. Meanwhile, a highly reversible P2/Tunnel-OP4/Tunnel phase transition process and interlocking effect between the layered and tunnel structure as well as prominent moisture stability even after soak water treatment are further confirmed by in-situ charge and discharge XRD and other advanced characterization techniques. Noting that the electrode assembled with water-solution binder still displays a high capacity retention of 85.4% after 400 cycles at 1 C. Our dual-function strategy provides valuable guidance for developing high energy density and water stable practical SIB cathode materials.

Taming cyclo-pentazolate anions with a hydrogen-bonded organic framework

Because of its high energy, aromaticity, and carbon- and hydrogen-free structure, the cyclo-pentazolate anion (c-N5-) has attracted increased attention as a potential polynitrogen structural unit for the research of next-generation high energy density materials. However, the poor thermal stability of c-N5--based compounds has become an important factor restricting their development. Here, we show that a hydrogen-bonded organic framework (HOF) self-assembles with and stabilizes c-N5-, with c-N5- situated in the pores of the resulting framework through the formation of symmetrical c-N5- hydrogen bonds as the main stabilizing factors. These factors result in an onset decomposition temperature of 153 °C for the c-N5-@HOF portion, which exceeds the thermal stabilities generally observed for c-N5--based derivatives of below 135 °C. We envisage that further c-N5--based materials with enhanced stabilities and better performance will be developed in the future.

Hierarchically Interconnected 3D Catalyst Structure of Porous Multi-Metal Oxide Nanofibers for High-Performance Li-O2 Batteries.

Non-aqueous lithium-oxygen batteries (LOBs) have emerged as a promising candidate due to their high theoretical energy density and eco-friendly cathode reaction materials. However, LOBs still suffer from high overpotential and poor cycling stability resulting from difficulties in the decomposition of discharge reaction Li2 O2 products. Here, a 3D open network catalyst structure is proposed based on highly-thin and porous multi-metal oxide nanofibers (MMONFs) developed by a facile electrospinning approach coupled with a heat treatment process. The developed hierarchically interconnected 3D porous MMONFs catalyst structure with high specific surface area and porosity shows the enhanced electrochemical reaction kinetics associated with Li2 O2 formation and decomposition on the cathode surface during the charge and discharge processes. The uniquely assembled cathode materials with MMONFs exhibit excellent electrochemical performance with energy efficiency of 82% at a current density of 50mAg-1 and a long-term cycling stability over 100 cycles at 200mAg-1 with a cut-off capacity of 500 mAhg-1 . Moreover, the optimized cathode materials exhibit a remarkable energy density of 1013Whkg-1 at the 100th discharge and charge cycle, which is nearly four times higher than that of C/NMC721, which has the highest energy density among the cathode materials currently used in electric vehicles.

Enhanced energy storage and temperature-stable dielectric properties in (1-x)[(Na0.4K0.1Bi0.5)0.94Ba0.06TiO3]-xLa0.2Sr0.7TiO3 lead-free relaxor ceramics

With the continuous growth in sustainable and renewable technologies, ceramic capacitors are emerging as a promising energy storage device. Lead-free (1-x)[(Na0.4K0.1Bi0.5)0.94Ba0.06TiO3]-xLa0.2Sr0.7TiO3 (0 ≤ x ≤ 0.40) ceramics were prepared using the solid-state reaction technique for obtaining relaxor characteristics with improved energy storage density, efficiency, and temperature stability of dielectric permittivity. A high recoverable energy density (Wr) ∼ 2.39 J/cm3 with a good efficiency (η) of ∼ 75.21% was obtained for x = 0.30 composition under 220 kV/cm applied field. The specimen x = 0.30 exhibited excellent fatigue resistance during 105 cycles and good temperature stability of energy storage characteristics (Wr > 0.87 J/cm3, η > 74%) in the temperature range of 25–180 °C under 100 kV/cm. In addition, the temperature range in which the dielectric permittivity variation was less than ±15% was very wide (204 °C (63–267 °C) and 275 °C (39–314 °C) for x = 0.30 and 0.20 specimens, respectively). Significant improvements in material performance were attributed to A-site engineering, which resulted in a mixture of P4bm and R3c polar nano regions (PNRs), leading to reduced hysteresis loss and temperature-stable dielectric permittivity. Additionally, the size of PNRs ranged between 3 and 6 nm, with the P4bm phase dominating in the x = 0.30 specimen, leading to a large maximum polarization under an applied electric field. Therefore, (1-x)[(Na0.4K0.1Bi0.5)0.94Ba0.06TiO3]-xLa0.2Sr0.7TiO3 relaxor ceramics are promising for high energy density materials and electronic applications requiring high permittivity stability over a wide temperature range.

PO43--doped layer @ spinel @ rGO sandwich-structured lithium-rich manganese-based cathode material with enhancing rate capability and cycle stability for Li-ion battery

The Li-rich Mn-based cathode (LRM) material faces challenges like low initial coulombic efficiency (ICE) and reduced capacity retention, which limit their commercial viability in high energy density lithium-ion batteries (LIBs). These challenges primarily arise from the irreversible migration of transition metal ions (TMn+) and the escape of lattice oxygen. Herein, this study proposes a novel approach to enhance Li-rich cathodes by implementing a PO43--doped layer @ spinel @ rGO sandwich structure, which effectively addresses the aforementioned challenges. Through the synergistic effects of PO43- doping and rGO surface modification, the modified samples demonstrate remarkable electrochemical properties. These include an impressive initial coulombic efficiency (ICE) of 87.54%, and a superior capacity of 187.12 mAhg−1 and 149.44 mAhg−1 at 25°C and 45°C, respectively, following 200 cycles at 1 C. Additionally, they exhibit an outstanding rate capability of 82.3 mAhg−1 at 10 C and a minimal voltage decrease of 0.504 V after 200 cycles. The synergetic strategy presented in this work serves as an inspiring source for the exploration of high energy density and long-cycle cathode materials.

Nonbonding Electron Delocalization Stabilizes the Flexible N8 Molecular Assembly.

Electron delocalization has an important impact on the physical properties of condensed materials. However, the L-electron delocalization in inorganic, especially nitrogen, compounds needs exploitation to improve the energy efficiency, safety, and environmental sustainability of high-energy-density materials (HEDMs). This Letter presents an intriguing N8 molecule, ingeniously utilizing nitrogen's L-electron delocalization. The molecule, exhibiting a unique lollipop-shaped conformation, can fold at various angles with very low energy barriers, self-assembling into environmentally stable, all-nitrogen crystals. These crystals demonstrate unparalleled stability, high energy density, low mechanical sensitivity, and optimal electronic thermal conductivity, outperforming existing HEDMs. The remarkable properties of these designed materials are attributed to two distinct delocalized systems within nitrogen's L-shell: π- and lone pair σ-electrons, which not only stabilize the molecular structure but also facilitate interconnected 3D networks of intermolecular nonbonding interactions. This work might pave the way to the experimental synthesis of environmentally stable all-nitrogen solids.

Stilbene-incorporated platinum(II) di-yne electrocatalysts for generating hydrogen from acetic acid

Molecular hydrogen (H2) is a potential alternative to fossil fuels since it is a green energy source with high energy density and non-polluting combustion materials. We present herein the electrochemical properties and hydrogen evolution reaction (HER) ability of two Pt(II) diynes (Pt-Sb-Pt & Sb-Pt-Sb) bearing stilbene unit. Both complexes catalyzed the HER in acidic media. In addition, density functional theory (DFT) calculation was carried out at B3LYP/LANL2DZ level of theory in gas phases as well as in the solvent (DMF) to delineate the possible mechanism of HER. We demonstrated that the studied Pt(II) electrocatalysts shift the reduction potential noticeably. However, no apparent role of photo-switchable stilbene fragment on electrolysis was observed and the presence of ethynyl moiety was necessary for stabilization of the metal center. To the best of our knowledge, this is the first study highlighting the electrocatalytic HER by platina-ynes.

High Li-ion diffusion coefficient in LiMn1.5Ni0.5O4 thin films for all-solid Li-ion battery applications

Among various choices of high-performance cathode materials, Ni substituted LiMn2O4 spinel LiMn1.5Ni0.5O4 (LMNO) has proved to be one of the solutions to yield a high-performance and high-energy density material, which can operate at a higher potential window. This study explores the high diffusion coefficient and electrochemical performance at wide current rates of LMNO thin films with less than 50 nm thickness, fabricated on SrTiO3 and SS substrates by the pulsed laser deposition method. The LMNO film with less thickness and the performance without binder and conducting carbon widen the Li-ion path and decrease diffusion length, resulting a higher diffusion coefficient on the order of 10−5 to 10−6 cm2/s, which is several orders higher than the previously obtained reports for bulk counterpart. The cycling stability and rate capability at different current densities of LMNO thin film electrodes are further investigated. Charge–discharge profile at varying current rates of 5, 10, 15, 20, 25, 50, 75, 100, and 125 mA/cm2 is obtained for 500 cycles. The as fabricated film shows a stable profile for 500 cycles with 1.3 and 2.3 μA h/cm2 areal discharge capacity at 25 and 5 mA current rates, respectively. Electrode interfacial properties of LMNO film (before and after cycles) are analyzed using impedance technique. This study indicates that the LMNO thin films can be employed as a cathode layer for fabricating the all-solid thin film batteries for energy applications.

DFT investigation on detonation properties and sensitivities of bridged triazolo[4,5‐d]pyridazine based energetic materials

AbstractA series of bridged triazolo[4,5‐d]pyridazine based energetic materials were optimized at B3LYP/6‐311G(d, p) level of density functional theory (DFT), and their detonation properties and sensitivities were calculated. The results show that the NN bridge/N3 group were beneficial to improve values of heats of formation while NN bridge/C(NO2)3 group can improve detonation properties remarkably. In view of the sensitivities, compound F2 possesses the minimum values of impact sensitivity which reveals that NHNH bridge/C(NO2)3 group will decrease the stability of the designed compounds. Take both of detonation properties and sensitivities into consideration, compounds C8, E7, E8, F8 were screened as candidates of potential energetic materials since these compounds possess similar detonation properties and sensitivities values to those of RDX. All the calculated results were except to shine lights on the design and synthesis of novel high energy density materials.

Nitroiminotriazole (NIT) based potential solid propellants: synthesis, characterization, and applications.

Nitroimino (R = N-NO2) energetic material is a unique class of high energy density materials (HEDM). Synthesis and characterization of insensitive nitroimino compounds are a major challenge. Here triazole-based nitroimino compounds and their high-nitrogen green energetic salts in excellent yields are described. These materials exhibit high positive heats of formation (7.84 to 735.29 kJ mol-1), good densities (1.66 to 1.98 g cm-3), suitable detonation properties (P = 22.02 to 31.88 GPa; D = 7472 to 8936 ms-1) and high ballistic properties (Isp 205.66 to 295.35 s; C* = 1065 to 1832 ms-1) with good thermal (Td = 136-378 °C) and mechanical stabilities (IS = 10-40 J and FS = 120-360 N).