Stacked Si2BN monolayers as ultra-high-capacity anode material for divalent Mg-ion batteries

In pursuit of developing next-generation energy storage systems, there has been increasing effort in multivalent rechargeable batteries, such as magnesium-ion batteries (MgIBs). Non-toxicity, earth abundance, and high storage capacity due to their divalent nature make MgIBs an ideal alternative to the existing lithium-ion batteries (LIBs). However, exploring efficient electrode materials capable of storing large quantities of Mg ions is one of the biggest challenges in actualizing MgIBs. Here first-principles density functional theory (DFT) simulations are employed to explore the potential of Si₂BN monolayers as a novel anode material for MgIBs. We find that under the maximum coverage effect, the stackedSi₂BN could attain a specific capacity of 359.94 mAh g−1, which further enhances to 1418.45 mAh g−1 with a defect concentration of 12 %. The open-circuit voltages fall in the ranges of 0.42–0.46 V and 0.88–0.98 V for the pristine and defected Si₂BN, respectively. Diffusion barrier calculations reveal that Mg ions diffuse 125 times faster on pristine Si₂BN than the defected one. Our simulations determine that the electronic structures, binding mechanism, equilibrium cell voltages, ionic mobilities, and thermal stabilities of stacked Si₂BN make it an excellent anode material for MgIBs.