Two-dimensional phosphorus carbides (β-PC) as highly efficient metal-free electrocatalysts for lithium–sulfur batteries: a first-principles study†

Abstract

Li–S batteries are considered as the next-generation batteries due to their exceptional theoretical capacity. However, their practical application is hampered by the shuttling effects of lithium polysulfides (LiPSs) and the sluggish Li₂S decomposition, particularly the slow conversion from Li₂S₂ to Li₂S. Addressing these challenges, the quest for effective catalysts that can accelerate the conversion of LiPSs and enhance the performance of Li–S batteries is crucial. In this study, we explored the electrocatalytic activity of two-dimensional phosphorus carbides (β₀-PC and β₁-PC) in Li–S batteries based on first-principles calculations. Our findings reveal that these materials demonstrate optimal binding strengths (ranging from 1.09 to 1.83 eV) with long-chain LiPSs, effectively preventing them from dissolving into the electrolyte. Additionally, they show remarkable catalytic activity during the sulfur redox reaction (SRR), with ΔG being only 0.37 eV for β₀-PC and 0.13 eV for β₁-PC. The low energy barrier induced by β-PC enhances ion migration barrier and significantly expedites the charge/discharge cycles of Li–S batteries. Furthermore, we investigated the conversion dynamics of Li₂S₂ to Li₂S, employing the computational lithium electrode (CLE) model. The excellent performance in these aspects underscores the potential of these materials as electrocatalysts for Li–S batteries, paving the way for advanced high-efficiency energy storage solutions.