First-Principles Study of FeB₂Monolayers as High-Capacity Electrode Materials for Mg-Ion Batteries

Rechargeable Mg-ion batteries (MIBs) have attracted extensive attention due to the abundance of magnesium resources and huge superiority in energy density. But the lack of suitable electrode materials hinders the realization of MIBs. Herein, the potential of monolayer FeB 2 with two-dimensional (2D) structure as anode materials for MIBs has been comprehensively analyzed, and its performance in Li/Na/K/Ca ions batteries using first-principles calculations has been compared. The results indicate that the adatoms show different adsorption and diffusion behaviors on the B and Fe sides of FeB 2, which are subject to different electron-accepting abilities of the Fe and B layers. Besides, the FeB 2 monolayer possesses a maximum theoretical capacity of 4152 mAh g –1 for MIBs, outperforming most 2D anode materials. The ultrahigh theoretical capacity is attributed to the small lattice mismatch and the free electron gas protection that enables the stable adsorption of multilayer Mg atoms on the FeB 2 monolayers. Furthermore, the extremely low diffusion barrier and open circuit voltage demonstrate the pre-eminent electrochemical activities and performance of the FeB 2 monolayer. This work provides valuable options for the design of advanced rechargeable metal-ion batteries with high capacity and lightweight.