Two-dimensional Janus MoSSe as a potential anode material for Na/K-ion batteries: A theoretical study

First principle calculations of Janus 2D-TiSSe as an anodic electrode in batteries of lithium, sodium, and magnesium ions

CONTEXT

In recent years, rechargeable batteries have received considerable attention as a way to improve energy storage efficiency. Anodic (negative) electrodes based on Janus two-dimensional (2D) monolayers are among the most promising candidates. In this effort, the adsorption and diffusion of these Li, Na, and Mg ions on and through Janus 2D-TiSSe as anodic material was investigated by means of periodic DFT-D3 calculations. Electrochemical parameters were computed and compared. The diffusion barrier energies for migration of ions in monolayer TiSSe in three different potential directions were determined. Furthermore, the electronic properties and Mulliken charge analysis and plots of CDD were employed to investigate the interaction between ions and their surrounding surface. Our results show that the adsorption ability of TiSSe surface up to 32 metal ions falls in the following order: Li+  > Na+  > Mg2+. The maximum storage capacity is 337.37 mAh/g for Li/Na ion and 674.75 mAh/g for Mg ion. The average open-circuit voltage is 1.39, 0.93, and 0.73 V for Li, Na, and Mg ions, respectively. Lastly, the minimum diffusion barriers follow the order Li+  < Na+  < Mg2+. The structural, energetic, and thermal stability of clean Janus surface and its saturated adsorbed systems was proved by MD simulations. In addition, we compared the obtained electrochemical parameters to those reported by other researchers. This comprehensive approach demonstrates valuable insights, furthering our understanding of TiSSe's behavior and its suitability for use in MIBs.

METHODS

DFT calculations were applied with projector augmented plane waves (PAWs)/PBE functional. A two-dimensional (2D) monolayer TiSSe surface was built with a 4 × 4 supercell. The energy cutoff of plane waves was set to 400 eV. The DFT-D3 model has been used to incorporate van der Waals interactions. A geometric relaxation process was conducted using Monhkorst-Pack 8 × 8 × 1 in reciprocal space. The relaxation and electronic calculations were carried out using the Vienna Ab initio Simulation Package (VASP). Using the transition state (TS) search algorithm implemented in the Dmol3 module, linear synchronous transition and quadratic synchronous transit tools were utilized to find the minimum energy paths.

Theoretical investigation of Janus Ti2BST (T = O, Se) monolayers as anode materials for Na/K-ion batteries

The structures, stability, and electrochemical performances of Janus Ti2BST (T = O, Se) monolayers as anode materials for Na/K-ion batteries (NIBs/KIBs) are investigated by first-principles calculations. The results demonstrate that Ti2BST monolayers are mechanically, dynamically, and thermally stable. The electronic structures display good conductivity. Moreover, the low diffusion barriers of 0.107/0.039 eV (0.111/0.063 eV) for Na/K indicate that the Ti2BSO (Ti2BSSe) monolayer has excellent rate performance for NIBs/KIBs. Low average open circuit voltages (OCVs) (0.322-0.439 V) can produce a high voltage in NIBs/KIBs. Meanwhile, little structural changes during charge/discharge ensure great cycle stability. Especially, the Ti2BSO monolayer has a high theoretical capacity of 691.64/537.75 mA h g-1 for NIBs/KIBs. The outstanding performances demonstrate that the Ti2BST monolayers are potential anode materials for NIBs/KIBs.

Functionalizing Janus-structured Ti2B2 unveils exceptional capacity and performance in lithium-ion battery anodes

With the ever-growing demand for high-capacity energy storage technologies, lithium-ion batteries (LIBs) have drawn increasing attention. Ti2B2, a typical two-dimensional MBenes material, has been considered as a strong contender for anode materials of LIBs with significant performance. However, the limited Li storage capacity of MBenes has hindered its wide applications. To address this issue, we have functionalized Janus-structured MBenes, denoted as Ti2B2XaXb (Xa/Xb = N, O, S, Se). Employing first-principles simulations based on density functional theory, we have investigated the geometric characteristics and electrochemical properties of Ti2B2XaXb. Our results reveal that Ti2B2NO exhibits an exceptionally large theoretical specific capacity of 1091.17 mAh·g-1, improved by 2.4 times compared with the pristine Ti2B2 (456 mAh·g-1). Li atoms on the O side of Ti2B2NO possess a low diffusion barrier of 0.33 eV, which is conducive to the rapid charging and discharging of the battery. Moreover, the open-circuit voltage of Ti2B2NO within the safe voltage range of 0-1 V ensures the safety of battery operation. Overall, our study sheds light on understanding the underlying mechanism of surface functionalization on the Li storage properties of Janus-structured MBenes from atomic-scale, laying the groundwork for future design of high-performance anode materials.

Exploring a novel class of Janus MXenes by first principles calculations: structural, electronic and magnetic properties of Sc2CXT, X = O, F, OH; T = C, S, N

The already intriguing electronic and optical properties of the MXene Sc₂C family can be further tuned through a wide range of possible functionalizations. Here, by means of density functional theory, we show that the 36 possible elements of the Janus MXT (M: Sc₂C, X: O, F, OH, T: C, N, S) family, built by considering the four possible structural models (i) FCC, (ii) HCP, (iii) FCC + HCP, and (iv) HCP + FCC, are all potentially stable. The analysis of their mechanical properties shows the excellent mechanical flexibility of functionalized MXenes (f-MXenes) under large strain, making them more suitable for applications where stress could be an issue. Interestingly, while Sc₂C presents a metallic character, Sc₂COS, Sc₂CFN and Sc₂COHN are found to be semiconductors with bandgaps of 2.5 eV (indirect), 1.67 eV (indirect) and 1.1 eV (direct), respectively, which presents promising applications for nano- and optoelectronics. Moreover, Sc₂CFC presents a ferromagnetic ground state with the 2 × 2 × 1 supercell magnetic moment of 3.99 μ_B, while the ground state of Sc₂COHC might be antiferromagnetic with a magnetic moment of 3.98 μ_B, depending on the environment. Remarkably, the band structures of Sc₂CFC and Sc₂COHC present a half-metallic character with an HSE06 fundamental band gap of 0.60 eV and 0.48 eV, respectively. Our results confirm the extraordinary potential of the Janus MXT (M: Sc₂C, X: O, F, OH, T: C, N, S) family for novel applications in 2D nano-,opto- and spintronics.

2D phosphorus carbide as promising anode materials for Na/K-ion batteries from first-principles study

First-principles calculations based on density functional theory were used to investigate the electrochemical performance of monolayer γ-PC for Na- and K-ion batteries. Molecular dynamics simulations indicate that the monolayer γ-PC have the thermal and dynamic stability. A substantial charge transfer from the Na/K atoms to the γ-PC sheet enhances the electrical conductivity of γ-PC. The results show that the adsorption energies of Na and K are 1.53 eV and 2.04 eV, respectively, which are much higher than Na/K bulk cohesive energy and sufficiently ensure stability and safety. Additionally, the low diffusion barriers on γ-PC monolayer are 0.034 eV for Na and 0.027 eV for K, indicating excellent rate performance. The γ-PC sheet has a high theoretical capacity for both Na (519.9 mAh/g) and K (326.6 mAh/g) ion batteries, which can satisfy the requirement of energy storage devices to anode materials. Our results strongly suggest that 2D γ-PC monolayer is an exceedingly promising anode material for both NIBs and KIBs with high adsorption energies, high capacity, and low diffusion barriers.

A first-principles study of Janus monolayer TiSSe and VSSe as anode materials in alkali metal ion batteries

Anode materials play an important role in the performance of rechargeable batteries and have been attracting much research interest. In this work, we have investigated the electrochemical properties of two-dimensional (2D) Janus MSSe (M = Ti or V) for potential applications as anode materials in alkali metal ion batteries from density functional theory (DFT), following the recent successful synthesis of 2D Janus MoSSe. Our DFT calculations suggest that 2D Janus TiSSe and VSSe are stable in the 1T phase and 1H phase, respectively. It is found that alkali metal atoms X (X = Li, Na or K) can be stably adsorbed on the surfaces of Janus MSSe, and have low diffusion energy barriers. Additionally, small volume changes are observed in Janus MSSe after the adsorption of alkali metal atoms. It is predicted that the MSSe-2X systems have low open circuit voltages and high capacities. Our results suggest that 2D Janus TiSSe and VSSe are potential anode materials for alkali metal ion batteries.