Theoretically evaluating two-dimensional tetragonal Si₂Se₂ and SiSe₂ nanosheets as anode materials for alkali...

In this work, based on first-principles calculations, we theoretically predict two kinds of two-dimensional tetragonal Si-Se compounds, Si₂Se₂ and SiSe₂, as the anode materials for alkali metal-ion batteries. The results show that Si₂Se₂ and SiSe₂ are thermally and dynamically stable and have good electronic conductivity. The diffusion barriers of Li, Na and K atoms are 0.07 eV, 0.17 eV and 0.17 eV on the surface of Si₂Se₂, and 0.45 eV, 0.43 eV and 0.30 eV on the surface of SiSe₂, respectively, which indicate excellent rate capability. Most remarkably, Si₂Se₂ and SiSe₂ can deliver high specific capacities. The predicted specific capacities of Si₂Se₂ are 1252 mA h g^-1, 501 mA h g^-1 and 250 mA h g^-1 for Li, Na and K storage, respectively, and the corresponding specific capacities of SiSe₂ are 1441 mA h g^-1, 865 mA h g^-1 and 180 mA h g^-1. In addition, the highest plateaus of open-circuit voltages are 0.50 V vs. Li⁺/Li, 0.60 V vs. Na⁺/Na and 1.01 V vs. K⁺/K for Si₂Se₂, and 1.13 V vs. Li⁺/Li, 1.09 V vs. Na⁺/Na and 1.01 V vs. K⁺/K for SiSe₂, which are beneficial for achieving the high discharge voltage in full cells. Considering these advantages, Si₂Se₂ and SiSe₂ monolayers can be competitive candidates as anode materials for alkali metal-ion batteries.