Over the past three decades, lithium-ion batteries (LIBs) have witnessed substantial adoption in consumer electronics [[1], [2], [3], [4], [5]]. Nonetheless, their applications have now broadened to the transportation sector driven by the rapid evolution of this technology and the imperative to mitigate the environmental impacts. The traditional LIBs confront formidable obstacles, including safety hazards, high manufacturing expanses, and the scarcity of lithium resources [[6], [7], [8]]. Conseuqnetly, these issues have motivated researchers to investigate potential substitutes for LIBs, especially the multivalent-ion batteries [[9], [10], [11], [12], [13]]. Among them, rechargeable magnesium-ion batteries (MIBs) have been recognized as a highly promising alternative due to their low cost, remarkable specific capacity (2205 mA h/g), environmental benignity and low reduction potential (−2.37 V) [14,15]. Additionally, Mg forms a smooth deposition layer during the electrodeposition, which can effectively inhibit the needle-like dendrite generation and improve the safety of batteries. In spite of these remarkable attributes, the commercialization of MIBs is severely impeded by the slow Mg migration kinetics, poor cycling efficiency, and the incompatibility between Mg metal anode and conventional electrolytes [14].

To address the aforementioned challenges, one effective approach is the fabrication of nanostructured anode materials. In recent years, 2D materials have shown considerable promise in energy storage applications owing to their distinctive chemical-physical attributes [[16], [17], [18], [19], [20], [21]]. Specifically, their layered architecture and large surface area not only facilitate rapid ion migration but also enhance the electrode-electrolyte interfacial contact area. To date, a wide diversity of 2D materials, such as borophene [22], black phosphorene [23], MXenes [24], silicene [25] and transition metal dichalcogenides [26], have been utilized as anode materials of MIBs and exhibit excellent electrochemical performance. Nevertheless, majority of them suffer from one or more inherent obstacles, including sluggish ion migration, poor cyclability, large volume expansion and low specific capacity [[27], [28], [29]]. Therefore, identifying a high-performance 2D anode material for MIBs remains a great challenge.

Recently, 2D transition metal borides (MBenes) as emerging layered materials have gained considerable attention within the field of energy storage [[30], [31], [32], [33]]. Analogous to the synthesis methodologies utilized for MXenes, the fabrication of 2D MBenes involves a chemical exfoliation from MAB phases, wherein M indicates a transition metal and A stands for Al. The inherent high electronic conductivity, excellent mechanical stability and versatile structural configurations render MBenes promising anode candidates of batteries. For example, Masood et al. conducted a theoretical investigation on the electrochemical performance of MB4 (M = Cr, Mo, W), and demonstrated that all three MBenes are appealing anode materials for MIBs with high storage capacity and low open-circuit voltage (OCV) [30]. Wang et al. reported that the CrB, FeB and MnB anodes possess high Mg storage capacities of 1707, 1608 and 1631 mA h/g, as well as low diffusion barriers of 0.58, 0.41 and 0.48 eV [31]. Despite the notable advancements achieved, the development of MIBs, particularly with regard to anode materials, remains in its nascent stages.

Herein, we conducted a comprehensive investigation into the potential of an emerging MBene, specifically TiB2 [34], as an anode material of MIBs using vdW-corrected first-principles calculations. The projected band structure calculation confirms the intrinsic metallicity of TiB2 anode, and the computed adsorption energy demonstrates a strong adsorption of Mg ions on the substrate. Moreover, the crystal orbital Hamiltonian population (COHP) analysis reveals that Mg-B bonds exhibit distinct ionic bonding characteristics and dominates the interactions between Mg ion and TiB2 anode. Furthermore, the TiB2 anode harbors a low diffusion barrier of 0.05 eV, a high storage capacity of 3085.45 mA h/g, a low average OCV of 0.39 V, and a small lattice change of 2.12 %. All these fascinating results underscore the promising potential of TiB2 monolayer as an exceptional anode material for MIBs.