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

Abstract

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.