Theoretically evaluating two-dimensional tetragonal Si 2 Se 2 and SiSe 2 nanosheets as anode materials for alkali metal-ion batteries.

In this work, based on first-principles calculations, we theoretically predict two kinds of two-dimensional tetragonal Si-Se compounds, Si 2 Se 2 and SiSe 2 , as the anode materials for alkali metal-ion batteries. The results show that Si 2 Se 2 and SiSe 2 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 Si 2 Se 2 , and 0.45 eV, 0.43 eV and 0.30 eV on the surface of SiSe 2 , respectively, which indicate excellent rate capability. Most remarkably, Si 2 Se 2 and SiSe 2 can deliver high specific capacities. The predicted specific capacities of Si 2 Se 2 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 SiSe 2 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 Si 2 Se 2 , and 1.13 V vs. Li + /Li, 1.09 V vs. Na + /Na and 1.01 V vs. K + /K for SiSe 2 , which are beneficial for achieving the high discharge voltage in full cells. Considering these advantages, Si 2 Se 2 and SiSe 2 monolayers can be competitive candidates as anode materials for alkali metal-ion batteries.