Two-Dimensional ABS₄ (A and B = Zr, Hf, and Ti) as Promising Anode for Li and Na-Ion Batteries

Metal ion intercalation into van der Waals gaps of layered materials is vital for large-scale electrochemical energy storage. Transition-metal sulfides, ABS₄ (where A and B represent Zr, Hf, and Ti as monolayers as anodes), are examined as lithium and sodium ion storage. Our study reveals that these monolayers offer exceptional performance for ion storage. The low diffusion barriers enable efficient lithium bonding and rapid separation while all ABS₄ phases remain semiconducting before lithiation and transition to metallic states, ensuring excellent electrical conductivity. Notably, the monolayers demonstrate impressive ion capacities: 1639, 1202, and 1119 mAh/g for Li-ions, and 1093, 801, and 671 mAh/g for Na-ions in ZrTiS₄, HfTiS₄, and HfZrS₄, respectively. Average voltages are 1.16 V, 0.9 V, and 0.94 V for Li-ions and 1.17 V, 1.02 V, and 0.94 V for Na-ions across these materials. Additionally, low migration energy barriers of 0.231 eV, 0.233 eV, and 0.238 eV for Li and 0.135 eV, 0.136 eV, and 0.147 eV for Na make ABS₄ monolayers highly attractive for battery applications. These findings underscore the potential of monolayer ABS₄ as a superior electrode material, combining high adsorption energy, low diffusion barriers, low voltage, high specific capacity, and outstanding electrical conductivity.