Functionalized 2D TiB MBenes as High-performance Anodes for Lithium- and Sodium-Ion Batteries with Surface-Dominated...

Two-dimensional (2D) transition-metal borides (MBenes) hold great promise as exceptional anode materials for the next-generation lithium-ion (LIBs) and sodium-ion batteries (SIBs); however, their electrochemical performance is often compromised by the inevitable dangling bonds during the exfoliation process. Using first-principles calculations, we systematically investigated the geometrical structures, electronic, and mechanical properties of 2D functionalized TiB (TiBT, T = O, S, Se, Te, F, Cl, Br, I, Si, and P) MBenes and assessed their feasibility as advanced anode materials for LIBs/SIBs. Our comprehensive calculations of binding energy, cohesive energy, ab initio molecular dynamics simulation, mechanical property, and phonon spectrum confirm that the resulting TiBO, TiBS, TiBSe, TiBTe, TiBF, and TiBP are thermally, mechanically, and dynamically stable. In contrast, softened U-shaped phonon dispersions observed in the Brillouin zone reveal the dynamical instability of TiBCl, TiBBr, TiBI, and TiBSi. Additionally, TiBX (X = O, S, Se, Te, F, P) anodes exhibit intrinsic high electronic conductivity and low Li/Na ion diffusion barriers, which are crucial for achieving high charging-discharging rate capabilities. The robust Li (Na) adsorption strength and multilayer adsorption behavior enable TiBO, TiBS, TiBF, and TiBP anodes to deliver high storage capacities of 597.90 (575.03)-1035.05 (717.76) mAh/g, outperforming the commercial graphite anode (372 mAh/g for Li). Notably, the ion storage behavior in such ultrathin 2D MBenes is generally governed by surface-controlled pseudocapacitive kinetics. These anodes also demonstrate low average open-circuit voltages of 0.35 (0.24)-0.71 (0.43) V and minimal lattice changes of 0.87% (1.32%)-4.22% (4.85%). These encouraging findings not only underscore the potential of TiBO, TiBS, TiBF, and TiBP as appealing anode materials for LIBs/SIBs but also illustrate that the electrochemical performance of MBenes can be efficiently tailored through precise regulation of surface chemistry. Our work establishes a robust foundation for the rational design of high-performance TiB-based anode materials with surface-dominated ion-storage mechanisms.