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

Carbonaceous materials are promising candidates as anode materials for non-lithium-ion batteries (NLIBs) due to their appealing properties such as good electrical conductivity, low cost, and high safety. However, graphene, a classic two-dimensional (2D) carbon material, is chemically inert to most metal atoms, hindering its application as an electrode material for metal-ion batteries. Inspired by the unique geometry of a four-penta unit, we explore a metallic 2D carbon allotrope C5-10-16 composed of 5-10-16 carbon rings. The C5-10-16 monolayer is free from any imaginary frequencies in the whole Brillouin zone. Due to the introduction of a non-sp2 hybridization state into C5-10-16, the extended conjugation of π-electrons is disrupted, leading to the enhanced surface activity toward metal ions. We investigate the performance of C5-10-16 as the anode for sodium/potassium-ion batteries by using first-principles calculations. The C5-10-16 sheet has high theoretical specific capacities of Na (850.84 mA h g-1) and K (743.87 mA h g-1). Besides, C5-10-16 exhibits a moderate migration barrier of 0.63 (0.32) eV for Na (K), ensuring rapid charging/discharging processes. The average open-circuit voltages of Na and K are 0.33 and 0.62 V, respectively, which are within the voltage acceptance range of anode materials. The fully sodiated (potassiated) C5-10-16 shows tiny lattice expansions of 1.4% (1.3%), suggesting the good reversibility. Moreover, bilayer C5-10-16 significantly affects both the adsorption strength and the mobility of Na or K. All these results show that C5-10-16 could be used as a promising anode material for NLIBs.

A first-principles study of the BC3N2 monolayer and a BC3N2/graphene heterostructure as promising anode materials for sodium-ion batteries.

High-performance sodium-ion batteries (SIBs) require anode materials with high capacity and fast kinetics. Based on first-principles calculations, we propose BC3N2 and BC3N2/graphene (B/G) heterostructure as potential SIB anode materials. The BC3N2 monolayer exhibits intrinsic metallic behavior. In addition, BC3N2 possesses a low Na+ diffusion barrier (0.15 eV), a high storage capacity (777 mA h g-1), a low open-circuit voltage (0.72 V), and a tiny axial expansion (0.36%). Compared with the BC3N2 monolayer, the B/G heterostructure exhibits a lower diffusion barrier of 0.027 eV, suggesting a much faster diffusion. More importantly, although the B/G heterostructure possesses heavier molar weight, its theoretical capacity (689 mA h g-1) is comparable to that of the BC3N2 monolayer. Based on the above-mentioned properties, we hope both the BC3N2 monolayer and the B/G heterostructure would be promising anodes for SIBs.

Boosting Potassium Adsorption and Diffusion Performance of Carbon Anodes for Potassium-Ion Batteries via Topology and Curvature Engineering: From KT-Graphene to KT-CNTs.

We propose a two-dimensional carbon allotrope (named KT-graphene) by incorporating kagome and tetragonal lattices consisting of trigonal, quadrilateral, octagonal, and dodecagonal rings. The introduction of non-hexagonal rings can give rise to the localized electronic states that improve the chemical reactivity toward potassium, making KT-graphene a high-performance anode material for potassium-ion batteries. It shows a high theoretical capacity (892 mAh g-1), a low diffusion barrier (0.33 eV), and a low average open-circuit voltage (0.51 V). The presence of electrolyte solvents is propitious to boost the K-ion adsorption and diffusion capabilities. Moreover, one-dimensional nanotubes (KT-CNTs), rolled up by the KT-graphene sheet, are metallic regardless of the tube diameter. As the curvature increases, KT-CNTs exhibit significantly increased surface activity, which can promote the electron-donating ability of K. Furthermore, the curvature effect greatly enhances the efficiency of K diffusion on the inner surface compared to that on the outer surface.

Two-dimensional graphene+ as an anode material for calcium-ion batteries with ultra-high capacity: a first-principles study.

Multivalent-ion batteries have garnered significant attention due to their high energy density, low cost, and superior safety. Calcium-ion batteries (CIBs) are regarded as the next-generation energy storage systems for their abundant natural resources and bivalent characteristics. However, the absence of high-performance anode materials poses a significant obstacle to the progress of battery technology. Two-dimensional (2D) Dirac materials have excellent conductivity and abundant active sites, rendering them promising candidates as anode materials. A novel 2D Dirac material known as "graphene+" has been theoretically reported, exhibiting prominent properties including good stability, exceptional ductility, and remarkable electronic conductivity. By using first-principles calculations, we systematically investigate the performance of graphene+ as an anode material for CIBs. Graphene+ exhibits an ultra-high theoretical capacity (1487.7 mA h g-1), a small diffusion barrier (0.21 eV), and a low average open-circuit voltage (0.51 V). Furthermore, we investigate the impact of the electrolyte solvation on the performance of Ca-ion adsorption and migration. Upon contact with electrolyte solvents, graphene+ exhibits strong adsorption strength and rapid migration of Ca-ions on its surface. These results demonstrate the promising potential of graphene+ as a high-performance anode material for CIBs.

Two-dimensional AlB4/Al2B2: high-performance Dirac anode materials for sodium-ion batteries.

Sodium-ion batteries (SIBs) have attracted much attention due to their abundant earth-reserves and low cost. Two-dimensional (2D) Dirac materials show great application prospects as anodes for SIBs because of their excellent electronic conductivity. We explore the performances of AlB4 (Al2B2) monolayers and bilayers as anodes for SIBs by using first-principles calculations. The AlB4 (Al2B2) monolayer exhibits a high theoretical storage capacity of 954.15 (709.17) mA h g-1 and a low diffusion barrier of 0.36 (0.03) eV. The calculated average open-circuit voltage (0.68/0.18 V) falls within the acceptance range of 0.1-1.0 V for anode materials. The fully sodiated AlB4 (Al2B2) monolayer shows a tiny lattice expansion of 0.9% (2.4%), suggesting good reversibility. Furthermore, in comparison with the AlB4 (Al2B2) monolayer, the AlB4 (Al2B2) bilayer can provide stronger binding with Na on the outside surface. These results contribute to a better understanding of the AlB4 (Al2B2) monolayers and bilayers as potential high-performance anode materials for SIBs.

Penta-SiCN monolayer as a well-balanced performance anode material for Li-ion batteries.

Lithium-ion batteries (LIBs) remain irreplaceable for clean energy storage applications. The intrinsic metallic nature of penta-SiCN ensures its promising application in the electrodes of LIBs. Using first-principles calculations, we evaluate the performance of the intrinsic metallic penta-SiCN monolayer as the anode material for LIBs. Penta-SiCN exhibits a low diffusion energy barrier (0.107 eV) for Li atom migration on Si18C18N18, while the diffusion energy barrier for vacancy migration on Li17Si18C18N18 is only 0.006 eV. Additionally, penta-SiCN possesses a high theoretical capacity of 1485.98 mA h g-1, average open-circuit voltage of 0.97 V, and small volume expansion of 1%. Remarkably, penta-SiCN exhibits robust wettability towards the electrolytes (solvent molecules and metal salts) widely used in commercial LIBs, indicating the excellent compatibility in electrode applications. These intriguing theoretical findings make penta-SiCN a high performance anode material for LIBs.

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.

Two-dimensional TiCl2: a high-performance anode material for Na-ion batteries with high capacity and fast diffusion.

Na-ion batteries (NIBs) have attracted a great deal of attention for large-scale electric energy storage due to their inherent safety, natural abundant resources, and low cost. The exploration of suitable anode materials is the major challenge in advancing NIB technology. On the basis of first-principles calculations, we systematically explore the potential performance of two-dimensional (2D) TiCl2 as an electrode material for NIBs. Monolayer TiCl2 can be easily exfoliated from the bulk structure with a small exfoliation energy of 0.64 J m-2. It shows good stability, as demonstrated by its high cohesive energy, positive phonon modes, and high thermal stability. Monolayer TiCl2 has high storage capacity (451.3 mA h g-1), low diffusion energy barrier (0.02-0.14 eV), moderate average open-circuit voltage (0.81 V), and small lattice change (2.37%). Moreover, bilayer TiCl2 can significantly enhance the Na adsorption strength but reduce the Na-ion diffusion ability. These results suggest that TiCl2 is a promising anode candidate for NIBs.

Monolayer α-beryllene as an anode material for magnesium ion batteries with high capacity and low diffusion energy barrier.

High specific capacity and fast charge/discharge rate are important indicators for the development of next-generation ion batteries. Compared with conventional monovalent ion batteries like lithium-ion batteries and sodium-ion batteries, multivalent ion batteries have attracted extensive attention owing to their high energy densities. Here, we systematically explore the interactions between Mg atoms and α-beryllene monolayers by means of density functional theory calculations. Mg atoms can be adsorbed stably on α-beryllene monolayers with the adsorption energy of -0.24 eV. The low diffusion energy barriers (0.099/0.101 eV) indicate the rapid mobility of Mg during the charge/discharge process. Moreover, the α-beryllene monolayer exhibits an ultra-high theoretical specific capacity of 5956 mA h g-1 for Mg, a low average open-circuit voltage of 0.24 V, and a tiny volume change of -1.08%. Finally, the constructed h-BN/α-beryllene heterostructure shows that h-BN can serve as a protective cover to preserve pristine α-beryllene in respect of metallicity, Mg adsorption capability, and fast ionic mobility. The above mentioned outstanding results make α-beryllene a promising anode material for magnesium-ion batteries.

Two-dimensional CSiO and CGeO: direct-band-gap semiconductors with normal/anomalous auxeticity for solar cells and alkali-metal-ion batteries.

Two-dimensional (2D) materials provide tremendous opportunities for next-generation energy storage technologies. We theoretically propose 2D group-IV oxides (α-, ß-, andγ-CXO, X = Si/Ge). Among them,α-CXO monolayers, composed of the C-O-X skeleton of silyl (germyl) methyl ether molecules, are the most stable phase.α-CXO possess robust dynamical, mechanical, and thermal stabilities. Remarkably,α-CGeO has an unusual negative Poisson's ratio (NPR). However,α-CSiO displays a bidirectional half-auxeticity, different from all the already known NPR behaviors. The intrinsic moderate direct-band-gap, high carrier mobility, and superior optical absorption ofα-CXO make them attractive for optoelectronics applications. A series ofα-CXO-based excitonic solar cells can achieve high power conversion efficiencies. Besides,α-CXO monolayers are promising anode materials for sodium- and potassium-ion batteries, exhibiting not only the high specific capacity (532-1433 mA h g-1) but also low diffusion barrier and open-circuit voltage. In particular, the specific capacity of K onα-CSiO exhibits one of the highest values ever recorded in 2D materials. The multifunctionality rendersα-CXO promising candidates for nanomechanics, nanoelectronics, and nano-optics.

Magnesene: a theoretical prediction of a metallic, fast, high-capacity, and reversible anode material for sodium-ion batteries.

Sodium-ion batteries (SIBs) have attracted great attention owing to their low cost and inherent safety. High-performance anode materials for SIBs should possess intrinsically metallic characteristic and be composed of non-toxic, earth abundant, and lightweight elements. We predict a two-dimensional Mg material (named magnesene) to be an excellent anode material, which can meet these design requirements. It is demonstrated to be stable in terms of the cohesive energy, phonon spectrum, ab initio molecular dynamics simulation, and elastic constants. The magnesene monolayer exhibits good SIB performances, including a high storage capacity of 551.3 mA h g-1, low diffusion energy barrier (0.16-0.19 eV), low open-circuit voltage (0.71-0.82 V), and small volume change (4.7%). Moreover, graphene or h-BN on top of magnesene could serve as a protective cover to preserve the performances of pristine magnesene, such as metallicity, strong Na adsorption capability, and fast ionic mobility. These intriguing theoretical findings make magnesene a promising anode material for SIBs.

Germanether: a two-dimensional auxetic semiconductor with tunable direct-band-gap and high electron mobility.

Pristine germanene is a zero-gap semi-metal, which may hinder its practical application in semiconducting devices. Here, on the basis of the structural characteristics of digermyl ether, we theoretically design a two-dimensional crystal, namely germanether. Germanether exhibits excellent dynamical and thermal stability. It possesses an indirect band gap of 1.37 eV and a high electron mobility of 2.32 × 103 cm2 V-1 s-1. The uniaxial strain and layer stacking order can trigger an indirect-to-direct band gap transition. More interestingly, germanether has remarkable in-plane negative Poisson's ratios with the largest one (∼-0.2) five times of borophenes and three times of penta-graphene. The negative Poisson's ratio arises from the interplay of Ge-O tetrahedron symmetry and Ge-4d orbitals involvement, which is different from previously reported auxetic materials. All these findings render germanether is a competitive material for the future application in nanomechanics and nanoelectronics.

Graphether: a reversible and high-capacity anode material for sodium-ion batteries with ultrafast directional Na-ion diffusion.

Sodium-ion batteries (SIBs) have been attracting great attention as the most promising alternative to lithium-ion batteries (LIBs) for large-scale energy storage. However, the absence of suitable anode materials is the main bottleneck for the commercial application of SIBs. Herein, the adsorption and diffusion behaviors of Na on graphether are predicted by first-principles density functional calculations. Our results show that Na atoms can be adsorbed on graphether forming a uniform and stable coverage on both sides. Even at low intercalated Na concentrations, the semiconducting graphether can be changed to a metallic state, ensuring good electrical conductivity. Due to the structural anisotropy of graphether, the Na+ ions show a remarkable one-dimensional diffusion with an ultralow energy barrier of 0.04 eV, suggesting ultrafast charge/discharge characteristics. The graphether monolayer has a high theoretical specific capacity of 670 mA h g-1, which is much higher than commercial graphite anode materials. Furthermore, the average voltage is 1.58 V, comparable with that of commercial TiO2 anode materials for LIBs (1.5 V). During the charge/discharge process, graphether could mostly preserve the structural integrity upon the adsorption of Na even at the maximum concentration, suggesting its good reversibility. All these results show that graphether is a promising anode material for high-performance SIBs.

Metallic two-dimensional BP2: a high-performance electrode material for Li- and Na-ion batteries.

Searching for high-performance electrode materials is an important topic in rechargeable batteries. Using first-principles calculations, we systematically explore the potential application of a two-dimensional BP2 monolayer as a cathode material for Li-ion and Na-ion batteries. The pristine BP2 monolayer exhibits metallic characteristics, which facilitate the transportation of electrons. The Li and Na atoms bind strongly to the BP2 monolayer, indicating a good structural stability. Furthermore, the geometrical structure of BP2 is well maintained during the adsorption process. The Li and Na ions prefer to move along the zigzag direction with relatively low energy barriers. Especially, the ultralow Na diffusion barrier (0.03 eV) implies that monolayer BP2 has an excellent charge/discharge capability. The specific capacity and average electrode potential of Li (Na) are 619.45 (279.93) mA h g-1 and 2.89 (2.49) V, respectively. These results reveal that the BP2 monolayer is an appealing cathode material for alkali-metal batteries.

Two-dimensional CaFCl: ultra-wide bandgap, strong interlayer quantum confinement, and n-type doping.

Two-dimensional (2D) ultra-wide bandgap (UWBG) semiconductors have attracted tremendous attention because of their unique electronic properties and promising applications. Using first-principles calculations, monolayer (bilayer) CaFCl has a cleavage energy of 0.93 J m-2 (0.72 J m-2), suggesting that the exfoliation of monolayer and few-layer materials from the bulk phase could be feasible. The CaFCl monolayer is an UWBG semiconductor with a direct bandgap of 6.62 eV. In addition to the dynamic and thermodynamic stability, it can remain thermally stable at 2200 K, suitable for operation in high-temperature environments. The bandgap of monolayer CaFCl can be tuned by external strain and layer thickness. The decrease of the layer thickness leads to not only a bandgap increase but also an indirect-to-direct bandgap transition, suggesting a strong interlayer quantum confinement effect. Under biaxial strain, the direct bandgap can also be turned into an indirect one. The adsorption of a tetrathiafulvalene (TTF) molecule introduces deep donor states in the gap of CaFCl. Under an external electric field with direction from CaFCl to TTF, the TTF-derived donor states move closer to the conduction band edge of CaFCl and then the adsorption complex becomes effectively n-doped. Furthermore, monolayer CaFCl exhibits pronounced optical absorption in the ultraviolet range of the solar spectrum. These results render CaFCl an attractive 2D material for applications in flexible nanoelectronic and optoelectronic devices.

Theoretical prediction of silicether: a two-dimensional hyperconjugated disilicon monoxide nanosheet.

The gapless feature and air instability greatly hinder the applications of silicene in nanoelectronics. We theoretically design an oxidized derivative of silicene (named silicether) assembled by disilyl ether molecules. Silicether has an indirect band gap of 1.89 eV with a photoresponse in the ultraviolet-visible region. In addition to excellent thermodynamic stability, it is inert towards oxygen molecules. The material shows the hyperconjugation effect, leading to high performances of in-plane stiffness (107.8 N m-1) and electron mobility (6.4 × 103 cm2 V-1 s-1). Moreover, the uniaxial tensile strain can trigger an indirect-direct-indirect band gap transition. We identify Ag(100) as a potential substrate for the adsorption and dehydrogenation of disilyl ether. The moderate reaction barriers of dehydrogenation may provide a good possibility of bottom-up growth of silicether. All these outstanding properties make silicether a promising candidate for silicon-based nanoelectronic devices.

Graphether: a two-dimensional oxocarbon as a direct wide-band-gap semiconductor with high mechanical and electrical performances.

Although many graphene derivatives have sizable band gaps, their electrical or mechanical properties are significantly degraded due to the low degree of π-conjugation. Besides the π-π conjugation, there exist hyperconjugative interactions arising from the delocalization of σ electrons. Inspired by the structural characteristics of a hyperconjugated molecule, dimethyl ether, we design a two-dimensional oxocarbon (named graphether) by the assembly of dimethyl ether molecules. Our first-principles calculations reveal the following findings: (1) monolayer graphether possesses excellent dynamic and thermal stabilities as demonstrated by its favourable cohesive energy, the absence of soft phonon modes, and high melting point. (2) It has a direct wide-band-gap energy of 2.39 eV, indicating its potential applications in ultraviolet optoelectronic devices. Interestingly, the direct band gap feature is rather robust against the external strains (-10% to 10%) and stacking configurations. (3) Due to the hyperconjugative effect, graphether has the high intrinsic electron mobility. More importantly, its in-plane stiffness (459.8 N m-1) is even larger than that of graphene. (4) The Pt(100) surface exhibits high catalytic activity for the dehydrogenation of dimethyl ether. The electrostatic repulsion serves as a driving force for the rotation and coalescence of two dehydrogenated precursors, which is favourable for the bottom-up growth of graphether. (5) Replacement of the C-C bond with an isoelectronic B-N bond can generate a stable Pmn21-BNO monolayer. Compared with monolayer hexagonal boron nitride, Pmn21-BNO has a moderate direct band gap energy (3.32 eV) and better mechanical property along the armchair direction.

[Effects of CSN4 knockdown on proliferation and apoptosis of breast cancer MDA-MB-231 cells].

Breast cancer is one of the most common malignant tumors endangering women. It has been found that the subunits of the COP9 complex are closely related to the occurrence and development of malignant tumors, and the CSN4 subunit plays an important role in regulating the whole complex. In the breast cancer cell line MDA-MB-231, we successfully established a lentivirus-mediated CSN4-knockdown cell line. CCK8 cell proliferation assays and colony formation experiments confirmed that CSN4 knockdown significantly decreased the cellular proliferation rate. Cell cycle analysis showed that CSN4 knockdown increased sub-G1 population and induced apoptosis. In addition, Western blotting assays confirmed that CSN4 regulates the expression of CDK6 and Caspase3, suggesting that CSN4 modulates the proliferation and apoptosis of breast cancer cells by regulating the expression of CDK6 and Caspase3 genes and thereby tumorigenesis. This study has deepened our understanding of the molecular mechanism of apoptosis and cell growth in breast cancers, and further revealed the role and mechanism of CSN4 in cancer biology.

Monolayer CS as a metal-free photocatalyst with high carrier mobility and tunable band structure: a first-principles study.

Producing hydrogen fuel using suitable photocatalysts from water splitting is a feasible method to harvest solar energy. A desired photocatalyst is expected to have suitable band gap, moderate band edge position, and high carrier mobility. By employing first-principles calculations, we explore a α-CS monolayer as a metal-free efficient photocatalyst. The α-CS monolayer shows good energetic, dynamic, and thermal stabilities and is insoluble in water, suggesting its experimental practicability. Monolayer and bilayer α-CS present not only appropriate band gaps for visible and ultraviolet light absorption but also moderate band alignments with water redox potentials in pH neutral water. Remarkably, the α-CS monolayer exhibits high (up to 8453.19 cm2 V-1s-1 for hole) and anisotropic carrier mobility, which is favorable to the migration and separation of photogenerated carriers. In addition, monolayer α-CS experiences an interesting semiconductor-metal transition by applying uniaxial strain and external electric field. Moreover, α-CS under certain strain and electric field is still dynamically stable with the absence of imaginary frequencies. Furthermore, we demonstrate that the graphite (0 0 1) surface is a potential substrate for the α-CS growth with the intrinsic properties of α-CS maintaining. Therefore, our results could pave the way for the application of α-CS as a promising photocatalyst.

Prediction of a new BeC monolayer with perfectly planar tetracoordinate carbons.

Recently, there has been a growing interest in exploring planar hypercoordinate carbons in two-dimensional nanostructures. However, atomic monolayers with ideal planar hypercoordinate carbon are quite rare due to the challenge in stabilizing the exotic motifs. We predicted a global minimum two-dimensional BeC monolayer using the global particle-swarm optimization method. Each carbon binds peripheral four atoms in the same plane, forming a perfectly planar tetracoordinate carbon moiety. The cohesive energy, phonon-spectrum and mechanical stability criteria confirm the stability of monolayer BeC. In addition, the BeC monolayer has a large in-plane stiffness (145.54 N m-1) and thermo-dynamical stability (up to 2000 K). Furthermore, BeC is an indirect semiconductor with a band gap of 1.01 eV and possesses exceptionally high carrier mobilities (∼104 cm2 V-1 s-1), rendering it suitable for application in electronics and photoelectronics.