First-principles study of a 2-dimensional C-silicyne monolayer as a promising anode in Na/K ion secondary batteries

BC6NA monolayer as an ideal anode material for high-performance sodium-ion batteries

Selecting an appropriate anode material (AM) has been considered to be a crucial initial step in advancing high-performance batteries. Within this piece of research, we examine the suitability of the BC6NA monolayer (referred to as BC6NAML) as an AM by first-principles calculations. The BC6NAML exhibits metallic behavior consistently, even with varying concentrations of Na atoms, making it an ideal choice for battery usages. Our findings revealed that the theoretical storage capacity for Na-adhered BC6NAML was 406.36 mAhg-1, surpassing graphite, TiO2, BC6NA, and numerous other 2D materials. The BC6NAML also demonstrates a diffusion barrier of 0.39 eV and favorable diffusivity of Na-ions. Although the open-circuit voltage (OCV) of BC6NAML was temperate and lower compared to the OCV of other AMs like TiO2, our results suggested that it is possible to utilize BC6NAML as one of the encouraging host materials for sodium-ion batteries (SIBs). Consequently, this investigation into the potential anodic application of BC6NAML proves valuable for future experimental studies into sodium storage for SIBs.

Two-dimensional Be2P4 as a promising thermoelectric material and anode for Na/K-ion batteries

Incredibly effective and flexible energy conversion and storage systems hold great promise for portable self-powered electronic devices. Owing to their large surface area, exceptional atomic structures, superior electrical conductivity and good mechanical flexibility, two-dimensional (2D) materials are recognized as an attractive option for energy conversion and storage application. In this work, we examined the stability, electronic, thermoelectric and electrochemical aspects of a novel 2D Be2P4 monolayer by adopting density functional theory (DFT). The Be2P4 monolayer exhibits a direct semiconductor gap of 0.9 eV (HSE06), large Young's modulus (∼198 GPa), high carrier mobility (∼104 cm2 V-1 s-1) and a low excitonic binding energy of 0.11 eV. Our calculated findings suggest that Be2P4 shows a lattice thermal conductivity of 1.02 W m K-1 at 700 K, resulting in moderate thermoelectric performance (ZT ∼ 0.7), encouraging its use in thermoelectric materials. In addition, a higher adsorption energy of -2.28 eV (-2.52 eV) and less diffusion barrier of 0.22 eV (0.17 eV) for Na(K)-ion batteries promote fast ion transport in the Be2P4 monolayer. This material also shows a high specific capacity and superior energy density of 8460 W h kg-1 (8883 W h kg-1) for Na(K)-ion batteries. Thus, our results offer insightful information for investigating potential thermoelectric and flexible anode materials based on the Be2P4 monolayer.

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.

The effect of Ge doping concentration on the electrochemical performance of silicene anode for lithium-ion batteries: a first-principles study

Two-dimensional materials have been considered as novel anode materials for LIBs because of their large surface area, small volume change, and low Li diffusion barrier. Among them, the two-dimensional material SixGey has many excellent properties as an anode. However, Ge is expensive and not suitable for mass production. Therefore, proper Ge doping is of great significance to improve performance and reduce cost. Herein, we systematically study the effect of Ge doping and its concentration on the structure and electrochemical performance of two-dimensional SixGey by density functional theory (DFT) calculations. The incorporation of low concentration Ge can improve the horizontal and vertical diffusion ability of Li atoms compared to silicene. However, excessive Ge will increase the horizontal diffusion energy barrier of Li and reduce the theoretical capacity, where Si6Ge2 has a relatively high theoretical capacity and a low diffusion energy barrier. In addition, fully lithiated 2D SixGey shows poor electrical conductivity and increasing Ge concentration seems to be effective in improving the electrical conductivity of the material. This study will provide significant theoretical guidance for the design and preparation of two-dimensional silicon-based materials.

Theoretical prediction and characterization of novel two-dimensional ternary tetradymite compounds La2X2Y (X = I, Br, Cl; Y = Ge, Te) as anode materials for metal-ion batteries

Tetradymite compounds, such as Bi2Te3, crystallizing in rhombohedral structures have triggered tremendous research interest from the scientific community because of their intriguing properties. Herein, using the state-of-the-art first-principles calculations, we identify that La2X2Y (X = I, Br, Cl; Y = Ge, Te) nanosheets exhibit a ternary tetradymite-type structure with extraordinary electrical and electrochemical properties. It is first demonstrated that the layered La2X2Y compounds exhibit weak interlayer coupling with cleavage energies in the range of ∼0.28-0.38 J m-2, allowing the ready separation of monolayers that can be synthesized by mechanical exfoliation from their bulk counterparts. Next, we predict that La2X2Ge nanosheets exhibit a semiconducting nature, and upon physical realistic strain, a Dirac cone can be realized. These findings can be exploited in the transport properties. Furthermore, we comprehensively investigated the electrochemical properties of the predicted systems to evaluate their potential use in metal-ion (Li/Na) batteries. Our detailed analyses reveal that the Li (Na) adatoms are sufficiently mobile on the surface of the studied systems. For instance, the binding energy for the Li (Na) adatom on La2I2Ge is -2.24(-1.79) eV with a diffusion barrier of as small as ∼0.31(0.20) eV. Subsequently, the maximum theoretical specific capacity for Li (Na) reaches as high as 887(1064) mA h g-1, which can be attributed to a much higher storage capacity compared to previously identified 2D anode materials. These findings substantiate that the predicted nanosheets could be synthesized to explore their potential applications in future metal-ion batteries.

Prediction of a planar BxP monolayer with inherent metallicity and its potential as an anode material for Na and K-ion batteries: a first-principles study

Borophene, the lightest two-dimensional material, exhibits exceptional storage capacity as an anode material for sodium-ion batteries (NIBs) and potassium-ion batteries (PIBs). However, the pronounced surface activity gives rise to strong interfacial bonding between borophene and the metal substrate it grows on. Incorporation of heterogeneous atoms capable of forming strong bonds with boron to increase borophene stability while preserving its intrinsic metallic conductivity and high theoretical capacity remains a great challenge. In this study, a particle swarm optimization (PSO) method was employed to determine several new two-dimensional monolayer boron phosphides (BxP, x = 3-6) with rich boron components. The obtained BxP has great potential to be used as an anode material for sodium-ion batteries/potassium-ion batteries (SIBs/PIBs), according to DFT calculations. BxP demonstrates remarkable stability compared with borophene which ensures their feasibility of experimental synthesis. Moreover, B5P and B6P exhibit high electronic conductivity and ionic conductivity, with migration energy barriers of 0.20 and 0.21 eV for Na ions and 0.07 eV for K ions. Moreover, the average open circuit voltage falls within a favorable range of 0.25-0.73 V, which results in a high storage capacity of 1119-2103 mA h g-1 for SIBs and 631-839 mA h g-1 for PIBs. This study paves the way for exploring boron-rich 2D electrode materials for energy applications and provides valuable insights into the functionalization and stabilization of borophene.

First-principles study of two-dimensional C-silicyne nanosheet as a promising anode material for rechargeable Li-ion batteries

Li-ion batteries are one of the sustainable alternatives to meet the growing energy demands of an increasing population. However, finding a suitable negative electrode is key for improving battery performance. In the present work, first principles-based investigations are carried out to explore the capability of a planar 2D C-silicyne nanosheet - which is a Si analogue of α-graphyne having -CC- substitution - as an anode for improving the performance of Li-ion batteries. Thermally and dynamically stable C-silicyne sheets exhibit a metallic nature as inferred from the density of states studies. The average adsorption energies for sequential adsorption of the Li atom over the monolayer range from -1.35 to -0.46 eV, implying favourable interactions between the monolayer and the Li atom which indicate that during the lithiation process, clustering amongst the metal atoms is not preferred. The energy barrier for the migration of Li-ions is 0.21 eV, indicating an active charge/discharge process. A high storage capacity of 836.07 mA h g^-1 and a working potential of 0.60 V is obtained. A negligible amount of volume change of the C-silicyne monolayer after full lithiation is observed which implies good cyclability. All these outcomes imply that C-silicyne nanosheets are a potential anode material for next-generation LIBs.

Si doped T-graphene: a 2D lattice as an anode electrode in Na ion secondary batteries

Heteroatom doping into 2-dimensional lattices of materials such as graphene brings revolutionary reform in the field of materials endowing the parent material with remarkable properties.