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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 stacked Si2BN 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.