High Energy Density Materials Research Articles

Exploring the Explosive Potential: Synthesis and Characterization of Ring-Fused Oxadiazolo[3,4-b]pyrazine 1-Oxide Polymorphs with Balanced Energetic Properties.

A novel fused-ring compound, 5-azido-6-oxo-6,7-dihydro-[1,2,5]oxadiazolo[3,4-b]pyrazine 1-oxide (3a), was synthesized for the first time with simple two-step process and characterized using various spectroscopic techniques such NMR, IR, EA and HRMS. Two polymorphs (α-3a and β-3a) identified by SCXRD differ in crystal packing and noncovalent interactions, demonstrating high density, substantial heat of formation, and superior detonation properties with reduced mechanical sensitivity compared to TNT, TATB, and close to RDX, suggesting their potential as environmentally friendly high energy density materials.

Polymethylenetetrazole: Synthesis, Characterization, and Energetic Properties.

The tetrazole moiety remains one of the most interesting scaffolds in the development of new high-energy density materials (HEDMs) because of its desired characteristics, such as high nitrogen content and heat of formation (HOF). The combination of several heterocycles with high HOF seems to be a promising strategy for obtaining energetic materials with superior properties. Herein, we report the synthesis and characterization of a tetrazole polymer, polymethylenetetrazole (PMT), as a potential HEDM. The compound was characterized using NMR, IR, and Raman spectroscopy. Its weight average molecular mass was obtained by static light scattering (SLS), and its physical properties by powder XRD analysis. The density, sensitivity to friction (FS), and impact (IS) of the compound were determined as well. The results of the thermal and energetic properties of PMT suggest that this polymer could be an insensitive explosive.

Density functional theory (DFT) study on the structures and energy properties of high energy density materials based on polynitroazofurazan derivatives

In this study, inspired by the structures of the heat resistant explosives 5,5’-bis(2,4,6-trinitrophenyl)-2,2′-bi(1,3,4-oxadiazole) and 2,6-bis(picrylamino)-3,5-dinitro-pyridine, five high energy and low sensitivity energetic materials have been designed by combining the energetic fragments with the high energy azofurazan skeleton, and structure - property relationships have been investigated by means of density function theory. All compounds have excellent explosive properties (Dv: 7946–8341 m/s; P: 27.6–30.9 GPa) and high positive heats of formation (816.85–940.28 kJ/mol). Among them, compounds 3 and 4 have the best explosive properties (3: Dv: 8318 m/s P:30.7 GPa; 4: Dv: 8341 m/s P: 30.9 GPa), which are comparable to 1,3,5-trinitrohexahydro-1,3,5-triazine. The h50 values indicate that all compounds have good impact sensitivity, comparable to 1,3,5,7-tetranitro-1,3,5,7-tetrazocane and 1,3,5-trinitrohexahydro-1,3,5-triazine and superior to hexanitrohexaazaisowurtzitane. In addition, bond dissociation energies, frontier molecular orbitals, and weak interaction, etc. are calculated to further investigate the relationship between structures and properties. The calculated results show that these compounds are expected to be the next generation of high energy density materials with an excellent balance of energetic properties and stability.

Construction of carbon coated spherical Zn0.71Mn0.29Se@C for high-performance aluminum ion batteries

As a high energy density material, selenides have shown highly competitive initial capacity when applied to the positive electrode of aluminum ion batteries. However, in acidic electrolytes, the volume effect of selenides during electrochemical reactions can cause damage to the material structure. In long-term cycling tests, the performance of selenide cathode materials deteriorates rapidly, which greatly limits the application of this high-performance material in aluminum ion batteries. Here, Zn0.71Mn0.29Se@C material was synthesized for the cathode of aluminum ion batteries, which is covered by a carbon layer on the sphere shells and has good crystallinity. Zn0.71Mn0.29Se@C showed excellent performance: the capacity was maintained at 102.79 mAh/g after 2000 cycles. Attributed to the supporting effect of the carbon material, Zn0.71Mn0.29Se@C exhibits excellent structural stability. During charging and discharging, the carbon layer of the sphere shell effectively limits the volume expansion and improves the cycling performance of the battery. Meanwhile, the simulation results show that the Zn0.71Mn0.29Se@C material has a strong trapping effect for AlCl4− ions. As the main ion involved in the reaction, this strong interaction can greatly improve the reaction kinetics. On the other hand, the charge accumulation caused by the embedding of potential ions enhances the charge transfer. In conclusion, the carbon layer in the outer layer of Zn0.71Mn0.29Se@C not only supports the sphere structure, but also enhances the trapping effect for potential ions, and this novel electrode material is expected to improve the application prospect of aluminum ion batteries.

Ambient-Condition Recoverable Polymeric N10 Discovered from the Predicted Zr-N Compounds.

Polynitrogen has been widely studied recently as a rising star of high energy density materials. Here, we performed a systematic study of the Zr-N compounds in the N-rich region by the first-principles method. The high-pressure phase diagram of the Zr-N system is enriched by proposing five new compounds. ZrN10 with the infinitely extended band shaped structure is first reported. The band-like polynitrogen of ZrN10 decomposes into a more stable chain-like polynitrogen structure under the influence of temperature. Additionally, the novel honeycomb-like band-shaped N10 structure hcb-N10 has been discovered by removing the Zr atoms. The absence of the -4 oxidation state in the N10 unit prompts its further polymerization, which makes hcb-N10 possess dynamical and thermal stability in ambient conditions. hcb-N10 is a semiconductor with a bandgap of 2.97 eV due to highly localized electrons. Both chain-ZrN10 and hcb-N10 represent potential candidates for HEDMs with outstanding energy and explosive performance.

Novel phase of the Na-N system in the N-rich region under high pressure

The study of the Na-N system in the N-rich region under high pressure enriches the structural types of polynitrogen structure: four novel structures (P1-NaN7, Cm-NaN7, C2-NaN8, and R 3‾-NaN8) are proposed. The layered structure of the Cm-NaN7 and R 3‾-NaN8 phase consisting of the N16 and N18 ring respectively are first proposed in the Na-N system under high pressure. The Cm-NaN7 and R 3‾-NaN8 phase not only can be stabilized to the ambient conditions, but also the Cm-NaN7 phase can decompose and release energy at 325 K, while the R 3‾-NaN8 phase can be stable to at least 1000 K. The research shows that the different decomposition barriers and charge transfer are important reasons for the difference of decomposition temperature. The Cm-NaN7 phase is semiconductor phase with a band gap of 0.06 eV, while the R 3‾-NaN8 phase is metal phase. Furthermore, the excellent energy density, detonation pressure, and detonation velocity of the Cm-NaN7 and R 3‾-NaN8 phase make them as potential candidates in the application of high energy density materials.

Two-dimensional medium-entropy SeSI composite cathodes with cascaded redox reactions for advanced sodium batteries

Na−S/Se/I2 batteries represent a promising rechargeable Na battery system because of high theoretical energy density and low raw material cost. However, the inherent electrical insulation and poor structural stability of S/Se/I2 cathodes result in the unsatisfactory battery performance. Here we develop a new medium-entropy Se-S-I composite cathode via a straight chemical reaction of 2xSe+yI2+CS2=2SexSIy+C, simultaneously consolidating a ternary Se-S-I compound within carbon nanocage, forming a SeSI@C core-shell structure. In the composite, SeSI has a distinctive single crystal structure with homogeneous elemental composition, while carbon shell shows a uniform annular nanoscale that can completely envelop SeSI active mass. The cathode structural design bears high electrical conductivity, fast synergistic activation and excellent structural integrity, accordingly enabling a high capacity with an ultralong cycle life in a representative Na−Se-S-I battery (425.4 mAh g−1 at 10.0 A g−1, 91.6 % retention for 2000 cycles). Notably, a tertiary cascade of Se, S, and I redox has been demonstrated for providing high capacity, and an in-situ grown carbon shell ensures electrical conductivity and structural stability through the entire cathode. This SeSI@C cathode architecture significantly alleviates issues of traditional S/Se/I2-based cathodes, and makes the Na−Se-S-I battery more promising for application.

Towards an agglomeration free Ca(OH)2/CaO thermochemical energy storage loop via nanofabricated hollow CaO microspheres with highly porous shells

The Ca(OH)₂/CaO loop offers a promising solution for seasonal thermochemical heat storage, vital for decarbonizing the heating sector thanks to its high energy density and abundant raw materials. However, cyclic hydration/dehydration of limestone-derived CaO (r-CaO) faces challenges like agglomeration and high-volume expansion, limiting its expected performances. This study focuses on fabricating hollow CaO microspheres (h-CaO) with porous shells via a facile one-pot hydrothermal synthesis method, without doping materials. These microspheres exhibit superior cyclic performance compared to r-CaO, with SEM-EDS confirming successful fabrication. Over 30 cycles in the temperature range of 400–550 °C, h-CaO achieves an average storage density of 1755 kJ/kg, peaking at 1835 kJ/kg, with kinetics twice as high as r-CaO. Most importantly, the hollow microstructure reduces dramatically the apparent volumetric expansion from 250 % to as little as 32 %, offering a potential solution to agglomeration at the reactor level and advan44cing the commercial viability of the Ca(OH)2/CaO thermochemical storage technology.

Single Step Synthesis of gem-Dinitro Methyl-1,2,4-triazole and Its Hydroxylamine Salt: An Alternative to the FOX-7 and Other Benchmark Explosives.

gem-Dinitro methyl based high-energy-density material 5-(dinitromethylene)-4,5-dihydro-1H-1,2,4-triazole (2) and its hydroxylamine salt (4) were synthesized for the first time in a single step and characterized. Further, the structure of 2 was confirmed by single-crystal X-ray diffraction (SCXRD) studies. Interestengly, both the compounds show excellent density (> 1.83 g cm-3), detonation velocity (> 8700 m s-1), pressure (> 30 GPa) and are insensitive toward mechanical stimuli such as impact and friction sensitivity. Considering their synthetic fesibility and balanced energetic performance, compounds 2 and 4 show future prospects as potential next-generation energetic materials for the replacenent of many presently used benchmark high energy density materials such as RDX, FOX-7 and highly insensitive H-FOX.

Theoretical study of a series of 1,2-diazete based trinitromethyl derivatives as potential energetic compounds.

Explosive properties of novel potential high energy density materials of a series of 1,2-diazete-based molecules with trinitromethyl functional group were investigated computationally. All the sixty seven molecules were optimised to obtain their molecular geometries and electronic structures. Electrostatic potential analysis was also carried out in the determination of different parameters. The calculations indicate that the majority of the compounds have high positive heat of formations, high density and good detonation performance greater than that of traditional energetic materials like RDX and HMX. They are also having comparable values of impact sensitivity. These features promise their potential to be used as energetic materials for future applications. Most of the designed molecules are having high positive oxygen balance values so that the study of these molecules can also be extended as potential candidates for oxidisers in solid propellants. Optimisation and vibrational frequency analysis of the studied molecules were done with density functional theory using B3LYP/aug-cc-pVDZ as the basis set to zero imaginary frequencies using Gaussian 09. Electrostatic potential analysis were carried using the Multiwfn program.

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

Activated 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.