Interlayer electronic coupling regulates the performance of FeN MXenes and Fe2B2 MBenes as high-performance Li- and Al-ion batteries

Abstract

When two-dimensional (2D) materials are stacked into van der Waals structures, interlayer electronic coupling can induce excellent properties in energy storage materials. Here, we investigate the interlayer coupling of the FeN/Fe₂B₂ heterojunction as an anode material, which is constructed using vertically planar FeN and puckered Fe₂B₂ nanosheets. These structures were searched by the CALYPSO method and computed by density functional theory calculations. The stabilities of the FeN monolayer, Fe₂B₂ monolayer, and FeN/Fe₂B₂ heterojunction were tested in terms of dynamics, mechanics, and thermodynamics, respectively. These structures have good performances as anode materials, including the capacities of the FeN (Fe₂B₂) monolayer of 9207 mA h g⁻¹ (2713 mA h g⁻¹) and 3069 mA h g⁻¹ (1005 mA h g⁻¹) for Al and Li, respectively. The stable FeN/Fe₂B₂ heterojunction shows extremely low diffusion barriers of 0.01 eV, a high Al ion capacity of 4254 mA h g⁻¹, and relatively low voltages. Hess's law revealed that the interlayer electronic coupling impacts the adsorption process of the FeN layer in the FeN/Fe₂B₂ heterojunction, which decreases the p_z orbital of the N atom for the heterojunction. The unequal distribution of electrons between the layers results in interlayer polarization; the value of interlayer polarization was quantitatively calculated to be 0.64 pC m⁻¹. The presence of adsorbed Li and Al atoms between the layers helps maintain the original structure and prevents the interlayer sliding from damaging the heterojunction. These findings offer insights for understanding the structural and electronic properties of the FeN/Fe₂B₂ heterojunction, which provides crucial information for rational design and advanced synthesis of novel electrode materials.