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

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/FeB heterojunction as an anode material, which is constructed using vertically planar FeN and puckered FeB nanosheets. These structures were searched by the CALYPSO method and computed by density functional theory calculations. The stabilities of the FeN monolayer, FeB monolayer, and FeN/FeB 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 (FeB) monolayer of 9207 mA h g (2713 mA h g) and 3069 mA h g (1005 mA h g) for Al and Li, respectively. The stable FeN/FeB heterojunction shows extremely low diffusion barriers of 0.01 eV, a high Al ion capacity of 4254 mA h g, and relatively low voltages. Hess's law revealed that the interlayer electronic coupling impacts the adsorption process of the FeN layer in the FeN/FeB heterojunction, which decreases the p 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. 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/FeB heterojunction, which provides crucial information for rational design and advanced synthesis of novel electrode materials.