Theoretically Evaluating Two-Dimensional Tetragonal Si2Se2 and SiSe2 Nanosheets as Cathode Catalysts for Alkali Metal–O2 Batteries

Nonaqueous alkali metal (AM)–O 2 batteries are promising next-generation energy storage devices due to their outstanding specific capacity and energy density. However, the high charge–discharge overpotential and slow electrochemical reactions limit their development. Highly active cathode catalysts can solve this problem. Based on first-principles calculations, we theoretically explore the application potential of Si 2 Se 2 and SiSe 2 nanosheets as potential cathode electrocatalysts. Different electrochemical reduction paths are proposed for understanding the discharge process. For example, for Li–O 2 battery, the main products on the electrocatalyst surface are LiO 2 and Li 2 O 2, and the charge/discharge overpotential of SiSe 2 is less than 0.46 V. The main products are NaO 2 and Na 2 O 2 for Na–O 2 battery, and the charge/discharge overpotentials are less than 0.73 V. There is only one catalytic product of K–O 2 battery, which is KO 2 . Specially, the charge/discharge overpotential of Si 2 Se 2 is significantly low, only 0.31 V for K–O 2 battery. In addition, we found that neither Si 2 Se 2 nor SiSe 2 promoted the formation of the side product Li 2 CO 3 /Na 2 CO 3 or caused the decomposition of the dimethyl sulfoxide electrolyte, suggesting that Si 2 Se 2 and SiSe 2 can effectively improve the reversible cycle life of AM–O 2 batteries.