Metallic Carbon Allotrope Research Articles

Two-dimensional monolayer C5-10-16: a metallic carbon allotrope as an anode material for high-performance sodium/potassium-ion batteries

Two-dimensional C5-10-16 as an anode material for high-performance sodium/potassium-ion batteries.

A new 3D porous metallic carbon allotrope composed of 5–7 nanoribbons as an anode material for sodium-ion batteries

Motivated by the successful synthesis of three-dimensional (3D) graphene monoliths, tremendous effort has been devoted to the design of 3D porous metallic carbon allotropes with rich topology by assembling various nanoribbons for the anode materials of metal-ion batteries in recent years. Going beyond the allotropes reported so far we propose a new 3D carbon monolith, Hex-C57, by using 5–7 nanoribbons observed in the experiment as the building block. Hex-C57 is found to be dynamically, thermally, and mechanically stable, and electronically metallic. An analysis based on the tight-binding model reveals that the metallicity originates from the pz-orbitals of the sp2-hybridized carbon atoms, forming the conducting channels along the axial direction. With the advantages of intrinsic metallicity, mechanical ductility, and ordered pores, Hex-C57 is a highly promising anode material for sodium-ion batteries (SIBs). Calculations of the electrochemical properties show that Hex-C57 possesses a high reversible gravimetric capacity (334.69 mAhg−1) and volumetric capacity (314.61 mAhcm−3), a small volume change (1.45%), very low diffusion barriers (0.046–0.070 eV), and a low average open-circuit voltage (0.18 V). This work not only expands the 3D porous carbon family with different nanoribbons as the building blocks, but also demonstrates the functionality of unconventional 5–7 carbon rings-assembled materials.

C-57 nanotube: electronic, optical, and mechanical properties by DFT calculations

Electronic, optical, and mechanical properties of single-walled C-57 carbon nanotube have been investigated within the framework of density functional theory (DFT). It was found that for the nanotube, there is a direct relationship between its radius and Young’s modulus: larger radius leads to larger Young’s modulus. Optical properties have been calculated within a NORMCONS pseudopotential type (Von Barth–Car Method) whit Perdew–Zunger (LDA) exch-correlation scalar relativistic functional type, showing that decrease in radius of the nanotube increases both static refractive index and dielectric constant is increased. Examining band structure and density of states (DOS) further reveals that this nanotube is a metallic carbon allotrope. The potential ability of lithium (Li) and sodium (Na) adsorption on single-layer C-57 nanotube has also been evaluated at vdW-DF3-OPT2, PBEsol and DFT-D3 levels of theory. Preferred Li or Na adsorption sites have accordingly been identified in terms of adsorption energy; and geometries of 1 up to 4 adsorbed Li or Na atoms on the outside of the nanotube was also studied. Results of the adsorption energy and the open circuit voltage (OCV) showed that this nanostructure could be a suitable material for lithium or sodium storage. In addition, suitable theoretical storage capacity (278.92 mAh g−1) was obtained as an anode material.

Cubic C20: An intrinsic superconducting carbon allotrope

Finding intrinsic carbon superconductors is an interesting topic. Based on density-functional first-principles calculations, we first study the phonon-mediated superconductivity in a cubic metallic carbon allotrope, namely sc-C20, which has been synthesized in an experiment. Electron–phonon coupling is accurately computed with the Wannier interpolation method. By solving the Eliashberg equations, we predict that sc-C20 is an intrinsic carbon superconductor, without introducing any guest atoms or doping, whose transition temperature is determined to be about 24 K. Our findings enrich the family of carbon-based superconductors.

THFS-carbon: a theoretical prediction of metallic carbon allotrope with half-auxeticity, planar tetracoordinate carbon, and potential application as anode for sodium-ion batteries.

Two-dimensional (2D) carbon materials integrated with planar tetracoordinate carbon (ptC) and negative Poisson's ratio (NPR) provide a cornerstone for constructing multifunctional energy-storage devices. As a typical 2D carbon material, the pristine graphene is chemically inert, hindering its application in metal-ion batteries. Introducing the ptC in graphene can break the extended conjugation of π-electrons and lead to an enhanced surface reactivity. Inspired by the unique geometry of [4.6.4.6] fenestrane skeleton with ptC, we theoretically design a ptC-containing 2D carbon allotrope, namely THFS-carbon. It is intrinsically metallic with excellent dynamical, thermal, and mechanical stabilities. The Young's modulus along the x direction (311.37 N m-1) is comparable to that of graphene. Intriguingly, THFS-carbon possesses an in-plane half-NPR distinct from most other 2D crystals. As a promising anode for sodium-ion batteries, THFS-carbon delivers an ultra-high theoretical storage capacity (2233 mA h g-1), a low diffusion energy barrier (0.03-0.05 eV), a low open-circuit voltage (0.14-0.40 V), and a good reversibility for Na insertion/extraction.

A biphenylene nanoribbon-based 3D metallic and ductile carbon allotrope.

Assembling two-dimensional (2D) sheets for three-dimensional (3D) functional materials is of current interest. Motivated by the recent experimental synthesis of 2D biphenylene [Science372 (2021) 852], we propose a new porous 3D metallic carbon structure, named T48-carbon, by using biphenylene nanoribbons as the building block. Based on state-of-the-art theoretical calculations, we find that T48-carbon is not only dynamically, thermally, and mechanically stable, but also energetically more favorable as compared with some other theoretically predicted carbon allotropes. Especially, T48-carbon exhibits mechanical anisotropy, ductility and intrinsic metallicity. A detailed analysis of electronic properties reveals that the metallicity mainly comes from the pz-orbital of sp2-hybridized carbon atoms. This work shows the promise of design and synthesis of 3D biphenylene-based metallic carbon materials with novel properties.

Assembling biphenylene into 3D porous metallic carbon allotrope for promising anode of lithium-ion batteries

Since the discovery of graphene, 2D carbon materials and their assembled 3D porous materials have been hotly pursued. Motivated by the recent successful synthesis of biphenylene [Science 372 (2021) 852], we design a biphenylene-nanoribbon-based 3D porous carbon allotrope. The assembled structure (named Tet-C52) possesses excellent stability, low mass density (0.86 g cm-3), and high electric conductivity due to its intrinsic metallicity. More importantly, Tet-C52 structure is found to be a promising anode material for Li-ion batteries, exhibiting a higher storage capacity (458 mAh g−1), lower diffusion energy barrier (0.09 eV), and smaller volume change (1.5%) than that of the commercialized graphite anode. For future fabrication, a possible synthesis procedure of Tet-C52 is also discussed for precursors and computed X-ray diffraction patterns.

Spiro-graphene: A two-dimensional metallic carbon allotrope of fused pentagons

Using density functional theory with the generalized gradient approximation, we explored the geometric and electronic structure of polymerized spiro [4,4]nonatetraene (spiro-graphene) as a possible two-dimensional carbon allotrope comprising sp2 and sp3 C atoms. By reflecting a shape of the hydrocarbon molecule, this two-dimensional allotrope has a covalent network of fused pentagons with nanometer-scale structural rippling. The covalent network is thermally and dynamically stable with a relatively high total energy, higher than graphene by 0.6 eV/atom. The spiro-graphene is a metal where two linear dispersion bands cross each other at the Fermi level. In addition to these linear dispersion bands, the covalent network possesses the Dirac nodal line just above the Fermi level and along the Brillouin zone boundary. Accordingly, the ribbons with zigzag edges derived from spiro-graphene possess edge states like those of graphene nanoribbons with zigzag edges.

A new 3D metallic carbon allotrope composed of penta-graphene nanoribbons as a high-performance anode material for sodium-ion batteries

We propose a new 3D metallic carbon allotrope constructed by penta-graphene nanoribbons as promising anode material for sodium-ion batteries, which expands the family of pentagon-based carbon allotropes from 2D penta-graphene to 3D metallic material.

Two-dimensional metallic carbon allotrope with multiple rings for ion batteries.

Two-dimensional (2-D) materials, especially carbon allotropes, have larger storage capacity and faster diffusion rate due to their unique structures and are usually used in ion batteries. Recently, a new stable two-dimensional carbon allotrope, namely PAI-graphene, was reported by first-principles calculations. Due to its lightweight and multiple-ring structure, great stability and excellent properties, here, we theoretically reveal the excellent performance of PAI-graphene as an anode material for Li-/Na-ion batteries. Our results show that PAI-graphene has intrinsic metallicity before and after adsorption of Li/Na, which ensures that it has good conductivity when working as an electrode material. In addition, PAI-graphene exhibits quite low open circuit voltage (0.342-0.190 V for Li, 0.339-0.233 V for Na) and diffusion barrier (0.34 eV for Li, 0.17 eV for Na), which indicates its superiority as an anode material. Most noteworthily, the Na storage capacity of PAI-graphene is up to 1674 mA h g-1, which is much higher than that of most 2-D anode materials. Thus, we believe that PAI-graphene can be an outstanding anode material with outstanding performance.

Achieving superior high-capacity K-ion batteries with the C57 carbon monolayer anode by first-principles calculations

K-ion batteries (KIBs) have attracted much attention due to their low cost, high operating voltage and fast ionic conductivity in the electrolyte. However, the development of KIBs lags because the ion size and mass of K+are larger than Li+and Na+. Benefitting from the small molar weight of carbon and its structure diversity, the two-dimensional carbon allotropes can be considered as a potential electrode material for batteries with large-radius ions. In the paper, we report a metallic carbon allotrope (C57 monolayer) as an excellent candidate for the anode material of KIBs. The low diffusion barrier and small OCV values indicate that the C57 monolayer has excellent mobility properties and a large driving force for K-ion diffusion in the charge/discharge process. Most remarkably, the maximum capacity up to 1117 mA h g−1is three times as high as the capacity of graphite-based commercial electrode. Based on our results, the C57 monolayer is ideal for an excellent anode material for KIBs.

A prediction of a new porous metallic carbon allotrope with an sp2 hybridized network: cP-C24

A new porous carbon allotrope, having 24 carbon atoms per cubic cell with a symmetry of P4132 (named as cP-C24), is theoretically predicted by first-principle calculations. Its dynamical, mechanical and thermal stabilities have been determined by phonon, elastic constants and ab initio molecular dynamics (AIMD). The mass density (2.26 g/cm3) is close to that of graphite (2.24 g/cm3). The energy of cP-C24 reveals that it is less stable than H18 carbon, diamond and graphite, but it is more stable than K6 carbon and T carbon. Furthermore, the AIMD simulations demonstrate that cP-C24 is not only thermally stable at 300 K but also at 1500 K. No band gap in the band structures demonstrates that it is metallic. Additionally, the calculated X-ray diffraction of cP-C24 has three peaks matched with the ones in previous detonated samples, indicating that the presence of cP-c24 may be produced by the detonation. Due to its porous structure, metallic property and high-temperature thermal stability, cP-C24 has potential applications for adsorption small molecules and atoms, electrode and high-temperature resistance.

CP-C20, a new metallic cubic carbon allotrope with an sp2 network

A cubic carbon phase, called cP-C20, is predicted by first-principles calculations. CP-C20 belonging to Pm-3 symmetry consists of 20 atoms in a unit cell. It has an sp2 network and possesses hollow configurations. The calculated elastic constants and phonon properties confirm mechanical and dynamical stabilities in the new carbon phase. The ab initio molecular dynamics (MD) simulations confirm its thermal stability at 300 ​K and 1000K since the configuration can also keep after MD 20 ps. Moreover, there is a zero band gap in the band structure, revealing that this new metallic carbon allotrope may act as electrodes in electronic devices.

Q-Carbon: A New Carbon Allotrope with a Low Degree of s-p Orbital Hybridization and Its Nucleation Lithiation Process in Lithium-Ion Batteries.

A novel metallic carbon allotrope, Q-carbon, was discovered using first-principles calculations. The named Q-carbon possessed a three-dimensional (3D) cage structure formed by carbon atoms with three ligands. The energy distribution of electrons in different orbitals revealed that Q-carbon has a low degree of s-p orbital hybridization. The calculated Li+ binding energies suggested Li+ aggregation inside Q-carbon during lithiation. As a result, a Li8C32 phase was formed and gradually expanded in Q-carbon, implying a typical two-phase transition. This allowed Q-carbon to have a constant theoretical voltage of 0.40 V, which effectively inhibited Li dendrite formation. A stable Li8C32/C32 two-phase interface was confirmed by stress-strain analysis, and a calculated Li+ diffusion barrier of ∼0.50 eV ensured effective Li+ diffusion along a 3D pathway. This study was of great significance for the understanding of two-phase transition of Li+ storage materials and provided a new insight into the design of new carbon materials for energy storage applications.

Spiro-Carbon: A Metallic Carbon Allotrope Predicted from First Principles Calculations.

A structurally stable microporous metallic carbon allotrope, poly(spiro[2.2]penta-1,4-diyne) or, for short, spiro-carbon, with I41 /amd (D4h ) symmetry is predicted by first-principles calculations using density functional theory (DFT). The calculations of electronic, vibrational, and structural properties show that spiro-carbon has lower relative energy than other elusive carbon allotropes such as T-Carbon and 1-diamondyne (Y-Carbon). Its structure can be pictured as a set of trans-cisoid-polyacetylene chains tangled and interconnected together by sp3 carbon atoms. Calculations reveal a metallic electronic structure arising from an "intrinsic doping" of trans-cisoid-polyacetylene chains with sp3 carbon atoms. Possible synthetic routes and various simulated spectra (XRD, NMR, and IR absorption) are provided in order to guide future efforts to synthesize this novel material.

C-57 carbon: A two-dimensional metallic carbon allotrope with pentagonal and heptagonal rings

By means of the first-principles calculations, we have theoretically investigated the structural stability and electronic properties of a two-dimensional planar metallic carbon allotrope named C-57 carbon which possesses the P6¯2m (D3h3) symmetry. This carbon allotrope is an all-sp2 hybridized bonding network consisting of 5–7 rings of carbon atoms. The stability of C-57 carbon is confirmed through phonon-mode analysis, total energy and elastic constants calculations, as well as first-principles molecular dynamics simulations. We conceived that the metallicity of C-57 carbon is attributed to the large states across Fermi-level contributed by py orbital due to the bond distortion, which is much different from that of graphite. This new carbon sheet can also serve as a precursor for stable one-dimensional nanotubes with metallic character. These results broaden our understanding of two-dimensional carbon allotropes and will attract more researchers to focus the research on the field of two-dimensional carbon materials. Besides, the C-57 carbon may be useful for designing of nano-electronic devices.

A new tetragonal superhard metallic carbon allotrope

A new metallic superhard carbon allotrope C5 with five carbon atoms per unit cell is theoretically predicted to be stable at ambient pressure through first-principles calculations combined with unbiased swarm structure searching techniques. This novel carbon allotrope consisting of a mixture of sp2 and sp3 carbon network exhibits excellent mechanical properties with claimed hardness of 58.5 GPa. Results from our calculated strain-stress relationship reveals that the failure mode of crystal lattice for C5 is dominated by shear type in the (010)[101] direction with shear stress magnitude of 74.3 GPa. The calculated electronic band structure of C5 suggests its metallic nature. Detailed analyses of band decomposed charge density show that the metallic nature is contributed by the sp2 carbon atoms, which form conducting pathways along the a- and b-axes.

A novel hybrid sp-sp2 metallic carbon allotrope

In this paper, we propose a novel hybrid sp-sp2 monoclinic carbon allotrope mC12. This allotrope is a promising light metallic material, the mechanical and electronic properties of which are studied based on first-principles calculations. The structure of this new mC12 is mechanically and dynamically stable at ambient pressure and has a low equilibrium density due to its large cell volume. Furthermore, calculations of the elastic constants and moduli reveal that mC12 has a rigid mechanical property. Finally, it exhibits metallic characteristics, owing to the mixture of sp-sp2 hybrid carbon atoms.

Planar metallic carbon allotrope from graphene-like nanoribbons

The net-Y, a novel two-dimensional carbon allotrope with four-, six- and eight-membered rings, is investigated by performing first-principles calculations. The calculations on structural stability unambiguously prove that net-Y is an energetically metastable, dynamically and thermally stable phase, and it can also be buckled about 0.4 Å. We find that the net-Y exhibits strong mechanical anisotropy, and the in-plane Young's modulus of net-Y along a and b directions is found smaller than graphene but comparable with that of ψ-graphene and penta-graphene. Meanwhile, the net-Y possesses intrinsic metallicity with high carrier velocities comparable to that of graphene (∼106 m/s). Excitedly, a possible synthetic route towards net-Y from graphene-like nanoribbons embedded four- and eight-membered rings is achieved by first-principles molecular dynamics simulations, indicating that the realization of net-Y is not impossible. Moreover, two three-dimensional (3D) stable close-packed net-Y carbon allotropes are also proposed. Unlike the metallic 3D planar net-Y, the 3D buckled net-Y is a superhard indirect bandgap semiconductor, which further broadens the application potential of net-Y.

Net W monolayer: A high-performance electrode material for Li-ion batteries

“Two-dimensional materials as electrodes” is believed to be one of the key solutions for the development of future battery technologies. Based on the first-principles calculations, we predict that a metallic carbon allotrope (net W), with high electrochemical performance, can be served as an anode material for Li-ion batteries (LIBs). The net W exhibits metallic conductivity, and the conductivity is excellently maintained after Li adsorption. Specifically, upon Li intercalation, only slight lattice variations (<1.5%) occur, which ensures a good cycling stability. The low diffusion barriers of 0.4 eV and the moderate average open circuit voltage of 0.42 V are in between those of the currently used anodes, graphite, and TiO2. Most remarkably, the storage capacity can be up to 1675 mA h g−1, which is about 4.5 times larger than that of the commercial graphite anode. The present findings identify that net W could be an excellent anode material for the application in LIBs.