🔬 materials science

Exploring the Potential of BY3 (Y = P, As) Monolayers as High-Capacity and Rapid-Diffusion Anodes for Sodium-Ion Batteries

This study employs first-principles DFT calculations to demonstrate that metallic BX3 (X = P, As) monolayers are promising high-performance anodes for sodium-ion batteries, offering exceptional theoretical specific capacities (up to 3875 mAh g⁻¹), ultralow Na-ion migration barriers, and stable metallic conductivity throughout the sodiation process.

Original authors: Jakkapat Seeyangnok, Joongjai Panpranot, Udomsilp Pinsook

Published 2026-07-20

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Jakkapat Seeyangnok, Joongjai Panpranot, Udomsilp Pinsook

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the world of energy storage as a bustling city where tiny messengers, called ions, zip back and forth to power our gadgets and cars. Right now, the most famous messengers are lithium ions, but they are getting expensive and hard to find, like rare gems hidden in a few specific mountains. Scientists are looking for a new, more abundant messenger: sodium. Sodium is everywhere, like salt in the ocean, making it a cheap and plentiful alternative. However, sodium ions are bigger and clumsier than their lithium cousins. When they try to squeeze into the tiny "apartments" (anodes) inside a battery, they often get stuck or cause the building to crack. To solve this, researchers are designing special, ultra-thin "apartment complexes" made of just a few layers of atoms. These 2D materials need to be strong enough to hold the heavy sodium guests without breaking, fast enough to let them move in and out quickly, and conductive enough to keep the electricity flowing smoothly. The big question is: can we find a material that acts like a super-efficient, high-capacity hotel for these sodium ions?

In this study, researchers used powerful computer simulations to explore two new candidates for this sodium-ion hotel: a single layer of atoms made of boron mixed with phosphorus (called BP3) and another made of boron mixed with arsenic (called BAs3). Think of these materials as flat, flexible sheets with a bumpy, honeycomb-like texture. The team wanted to see if these sheets could hold a massive number of sodium ions, let them zip around easily, and stay electrically active even when fully packed.

The simulations revealed that these materials are incredibly promising. First, they are structurally tough and won't fall apart. When sodium ions arrive, they don't just sit on the surface; they dive into specific "parking spots" on the sheet, specifically a hollow spot in the middle of a ring of atoms called the H3 site. The atoms hold onto the sodium with a strong, friendly grip that mixes two types of chemical bonds, making the connection very stable.

One of the most exciting findings is how much energy these sheets can store. The BP3 sheet is a true heavyweight champion, capable of holding a theoretical specific capacity of 3875 mAh g−1, while the BAs3 sheet can store 1365 mAh g−1. To put that in perspective, these numbers are much higher than many other materials scientists have looked at, suggesting these sheets could hold far more "fuel" than current options.

Speed is another superpower. For a battery to charge fast, the ions need to move quickly. The simulations showed that sodium ions can slide across these sheets with almost no resistance. The energy barrier they need to jump over is tiny—just 0.19 eV for BAs3 and 0.26 eV for BP3. This suggests that if these materials were made into real batteries, they could charge and discharge at ultra-fast speeds, perfect for devices that need a quick power boost.

The researchers also checked the "voltage," which is like the pressure pushing the energy out. They found that these materials operate at very low, stable voltages (around 0.15 V to 0.18 V), which is great for getting the most energy out of the battery without risking dangerous side effects like metal plating. Perhaps most importantly, even when the sheets are packed to their absolute limit with sodium ions, they don't turn into insulators. They stay metallic, meaning electricity can still flow through them effortlessly, ensuring the battery works efficiently from the first charge to the last.

While these results are currently just from computer models and haven't been built in a lab yet, the findings suggest that BP3 and BAs3 monolayers could be the key to building the next generation of high-energy, fast-charging sodium-ion batteries. They appear to be strong, fast, and incredibly efficient, offering a potential solution to the limitations of today's energy storage.

Technical Summary: Exploring the Potential of BY3 (Y = P, As) Monolayers as High-Capacity and Rapid-Diffusion Anodes for Sodium-Ion Batteries

Problem Statement
The global demand for large-scale energy storage has exposed critical limitations in Lithium-ion battery (LIB) technology, including resource scarcity, rising costs, and safety hazards related to thermal runaway. While Sodium-ion batteries (SIBs) offer a promising, cost-effective alternative due to the abundance of sodium, their practical realization is hindered by the lack of anode materials that can simultaneously accommodate the larger ionic radius of Na+, maintain structural integrity, ensure rapid ion diffusion, and preserve electrical conductivity. Traditional bulk anodes often suffer from sluggish kinetics and severe volume expansion. Consequently, there is a need to identify robust two-dimensional (2D) materials capable of delivering high specific capacities and fast charging rates for next-generation SIBs.

Methodology
This study employs first-principles density functional theory (DFT) calculations using the QUANTUM ESPRESSO package to systematically evaluate two-dimensional BX3 (X = P, As) monolayers as potential anode candidates. The computational approach includes:

Structural and Thermodynamic Stability: Calculations of total formation energies ( $E_f$ ) and average adsorption energies ( $E_{ab}$ ) across a range of sodium concentrations to construct convex hulls and identify stable intermediate phases.
Electrochemical Performance: Derivation of open-circuit voltage (OCV) profiles from the gradient of formation energy and calculation of theoretical specific capacities based on fully sodiated ground-state configurations ( $Na_{72}B_8X_{24}$ ).
Diffusion Kinetics: Investigation of sodium-ion migration barriers using the climbing image nudged elastic band (CI-NEB) method to determine minimum energy pathways (MEPs).
Electronic and Bonding Analysis: Utilization of projected density of states (PDOS), charge density difference (CDD), Bader charge analysis, and projected Crystal Orbital Hamilton Population (pCOHP) to elucidate charge transfer mechanisms, bonding character (ionic vs. covalent), and the preservation of metallic conductivity during sodiation.

Key Contributions and Results

Stability and Metallic Character: Both BAs3 and BP3 monolayers exhibit excellent mechanical and dynamical stability. Crucially, they possess an intrinsic metallic character that is preserved even at maximum theoretical sodiation limits, ensuring continuous electron transport.
Adsorption Mechanism and Site Preference: The materials demonstrate a strong thermodynamic affinity for sodium adsorption. The H3 hollow site is identified as the most favorable binding configuration for both systems. This preference is driven by a synergistic mechanism involving substantial ionic charge transfer (approximately 0.83–0.88 $e$ from Na to the host) and deep covalent orbital hybridization. pCOHP analysis confirms that the H3 site offers significantly stronger covalent bonding ( $I_{pCOHP}$ of -0.58 eV for Na–As and -0.52 eV for Na–P) compared to other sites, outweighing minor differences in ionic charge transfer.
Electrochemical Metrics:
- Specific Capacity: The monolayers achieve ultrahigh theoretical specific capacities of 3875 mAh g⁻¹ for BP3 and 1365 mAh g⁻¹ for BAs3. These values significantly outperform contemporary 2D SIB anodes, including MXenes, transition metal dichalcogenides, and previously studied boron-phosphorus networks.
- Voltage Profiles: The materials exhibit low, stable average open-circuit voltages of 0.18 V for BP3 and 0.15 V for BAs3. The voltage profiles remain strictly positive throughout the sodiation process, effectively suppressing the thermodynamic driving force for hazardous sodium metal plating and dendrite formation.
Diffusion Kinetics: The study identifies ultralow optimal migration barriers for Na-ion diffusion along the direct pathway (Path 1): 0.19 eV for BAs3 and 0.26 eV for BP3. These low barriers suggest the potential for ultra-fast charge and discharge kinetics, a critical requirement for high-power applications.

Significance
The paper establishes that BX3 (X = P, As) monolayers are structurally resilient and highly conductive candidates for next-generation, high-energy-density sodium-ion batteries. By combining ultrahigh theoretical capacities with low operating voltages and rapid ion diffusion kinetics, these materials address the primary bottlenecks of current SIB anode technology. The preservation of metallic conductivity throughout the electrochemical cycle further ensures efficient electron transport, making these frameworks theoretically viable for high-performance energy storage systems. The findings provide a rigorous theoretical foundation for the future development of boron-pnictide-based anodes, positioning them as superior alternatives to existing 2D materials.

More like this