Silicon-swapped selenide sheets emerge as fast-charging battery anodes in simulations

Batteries of the future will need to charge in minutes, hold enormous amounts of energy, and survive tens of thousands of charge-discharge cycles without falling apart. Meeting all three demands at once has proven to be one of the toughest challenges in materials science, because the properties that boost capacity often undermine stability, and vice versa. Now, a team of computational physicists at the University of Guilan in Iran has proposed a new family of two-dimensional materials that, at least on paper, threads this needle. Writing in the journal Ionics, Shahab Rahimi Herabad, Mohammad Ali Mohebpour, and H. Rahimpour Soleimani report a systematic density functional theory study of three silicon-substituted transition-metal selenide monolayers, and their numbers suggest a promising recipe for next-generation alkali-ion battery anodes.

The materials in question, Ti2Se2Si, Zr2Se2Si, and Hf2Se2Si, belong to an emerging class of compounds known as transition-metal carbo-chalcogenides, or TMCCs. These layered structures combine features of two better-known two-dimensional families: transition-metal dichalcogenides such as MoS2, and MXenes, the conductive carbide and nitride sheets that have electrified the energy-storage community since their discovery. In a TMCC, a transition-metal layer is sandwiched between chalcogen atoms on one side and carbon on the other, producing a sheet that is simultaneously robust, metallic, and chemically versatile. What makes the new study distinctive is the substitution trick: the researchers replaced the central carbon layer with silicon, creating what they describe as a TMSiC family. Silicon is heavier than carbon but brings its own electronic character, and the team wanted to know whether this swap could tune the balance between ion storage capacity, ion mobility, and structural rigidity.

Before any anode material can be taken seriously, it has to survive the basic sanity checks of stability, and the Guilan group put their candidate sheets through a rigorous gauntlet of first-principles tests. They computed phonon spectra, the complete set of vibrational modes of the crystal lattice, and found no imaginary frequencies, the telltale signature of a structure that would spontaneously distort or disintegrate. They then ran ab initio molecular dynamics simulations at room temperature, letting the atoms jiggle under realistic thermal forces for extended periods, and observed that the lattices held together without reconstructing. Together, these results establish mechanical, dynamical, and thermal stability for all three monolayers, a crucial prerequisite since many theoretically proposed two-dimensional materials crumble the moment thermal fluctuations are introduced.

Perhaps the most important finding concerns the electronic structure. An ideal anode must conduct electrons efficiently, because every lithium, sodium, or potassium ion that enters the material during charging needs a matching electron to arrive at the same spot. Many candidate materials are semiconductors, and their band gaps throttle the rate at which charge can flow. The three silicon-substituted selenides, by contrast, are intrinsically metallic, and crucially they remain metallic even after the researchers loaded them with adsorbed lithium, sodium, or potassium atoms. This means the electronic highway stays open throughout the entire charge-discharge cycle, supporting continuous electron transport no matter how heavily the sheet is loaded with ions. For fast-charging applications, that persistence of metallic behavior is a significant design advantage.

The team then examined what actually happens when an alkali atom lands on the surface. Bader charge analysis, a computational technique that partitions electron density among atoms, revealed pronounced charge transfer from the adsorbed alkali atoms into the host lattice. In physical terms, the lithium, sodium, or potassium atoms give up their outermost electron to the sheet, becoming positive ions bound to a negatively charged surface. Strong charge transfer generally indicates strong adsorption, which is a double-edged sword: the ions must stick tightly enough to prevent clustering into metal dendrites, the needle-like growths that can short-circuit batteries, but not so tightly that they cannot move. The adsorption energies calculated in the study fell into the favorable regime, suggesting the sheets can host ions without triggering dangerous aggregation.

Ion mobility is where the study delivers some of its most encouraging numbers. Using the nudged elastic band method, a standard technique for mapping the energy landscape that an atom must traverse as it hops between binding sites, the researchers calculated migration barriers for lithium, sodium, and potassium on each surface. The barriers came out low across the board, and particularly small for lithium and sodium. Low diffusion barriers translate directly into fast surface diffusion, which in turn governs rate capability, the ability of a battery to deliver or accept charge at high current without sagging in voltage. In a practical cell, sluggish ion transport is one of the main bottlenecks that forces manufacturers to limit charging speeds, so a two-dimensional anode with intrinsically fast diffusion kinetics could be a genuine enabler of minutes-long charging.

Capacity, the sheer amount of charge a material can store per unit mass, is the headline number for any anode. Here the three siblings diverged. Ti2Se2Si, the lightest of the trio thanks to titanium’s relatively low atomic mass, delivered a maximum theoretical capacity of 571 milliampere-hours per gram for both lithium and sodium storage, based on thermally stable ion loading configurations. That figure is competitive with graphite, the workhorse anode of commercial lithium-ion batteries, while offering far better electronic conductivity. The zirconium and hafnium analogues provided more moderate capacities, because their heavier metal atoms inflate the mass denominator of the capacity formula, but they compensated with higher structural rigidity, which could pay dividends in long-term cycling stability where softer lattices tend to degrade.

The third key performance metric is operating voltage. An anode must work within a window that is low enough to deliver useful cell voltage but high enough to avoid plating metallic lithium on the surface, which causes dendrites and safety hazards. The calculated open-circuit voltages for all three materials ranged from roughly 0.2 to 1.0 volts against the alkali-metal reference electrodes, squarely within the desirable anode operating window. Combined with the metallic conductivity, the low diffusion barriers, and the verified stability, the overall profile of these monolayers reads like a checklist of what anode designers look for, adapted across three different alkali chemistries, which is notable because sodium and potassium batteries are being pursued as cheaper, more abundant alternatives to lithium.

The broader context makes the study timely. The past few years have seen an explosion of interest in two-dimensional materials beyond graphene, from borophene to covalent carbon nitride sheets, and the TMCC family sits at the frontier of this expansion, blending MXene-like conductivity with the chemical tunability of dichalcogenides. Previous computational work by the same group on Nb2Se2C monolayers and on scandium-based carbo-chalcogenides established a foundation, and other teams have explored silicon doping in titanium carbide MXenes for lithium storage. The new results extend that program in a coherent direction, identifying silicon substitution as an effective handle for balancing capacity, ion mobility, and structural stability in two-dimensional chalcogenides. Because the study is entirely computational, the usual caveats apply: real synthesis introduces defects, surface terminations, and electrolyte interactions that idealized simulations do not capture, and experimentalists will need to actually grow these sheets before any commercial claim can be made. But as a design blueprint, the work offers something valuable, a specific atomic substitution strategy that materials chemists can pursue, and a quantitative map of which member of the family, titanium for capacity, zirconium and hafnium for rigidity, best suits a given battery chemistry. If the laboratory can catch up with the supercomputer, silicon-substituted selenide sheets may earn a place in the fast-charging batteries of the coming decade.

Subject of Research: First-principles evaluation of silicon-substituted transition-metal selenide monolayers as anode materials for alkali-ion batteries

Article Title: Silicon-substituted Ti/Zr/Hf selenide monolayers as metallic anodes for Li/Na/K-ion batteries: a DFT study

Article References: Herabad, S. R., Mohebpour, M. A., & Soleimani, H. R. (2026). Silicon-substituted Ti/Zr/Hf selenide monolayers as metallic anodes for Li/Na/K-ion batteries: a DFT study. Ionics. https://doi.org/10.1007/s11581-026-07554-4

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07554-4

Keywords: alkali-ion batteries, anode materials, two-dimensional materials, transition-metal chalcogenides, silicon substitution, density functional theory, ion diffusion, lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, MXenes, energy storage