Unveiling atomic-scale mechanisms of tantalum-based 2D materials for high-performance Li–S batteries

Abstract

The development of effective electrocatalysts is vital for advancing lithium–sulfur (Li–S) batteries, particularly in addressing sluggish redox kinetics and the polysulfide shuttle effect. In this study, we systematically investigate the catalytic behavior of three tantalum-based two-dimensional (2D) monolayers, TaS₂, Ta₂C, and hybrid Ta₂S₂C, using first-principles calculations. All three systems exhibit excellent thermal and structural stability, confirmed by geometry optimizations and ab initio molecular dynamics (AIMD) simulations. Electronic structure analyses indicate metallic character in each case. Adsorption energy analysis reveals that TaS₂ binds strongly with Li₂S₄ (−2.60 eV), Li₂S₂ (−2.94 eV), and Li₂S (−3.93 eV), in sharp contrast to Ta₂C, which shows weak binding (e.g., +1.63 eV for Li₂S₄). Ta₂S₂C exhibits intermediate strength (−2.02 eV for Li₂S₂). Bader charge analysis further confirms significant electron redistribution during polysulfide anchoring, with up to 1.28|e| transferred on TaS₂. Importantly, free energy profiles along the sulfur reduction reaction (SRR) pathway demonstrate that the critical Li₂S₂ → Li₂S conversion step proceeds with a remarkably low barrier of 0.08 eV on TaS₂, compared to 0.70 eV on Ta₂C and 0.59 eV on Ta₂S₂C. These findings demonstrate that surface composition and coordination environments have a significant impact on catalytic performance. Overall, TaS₂ emerges as the most promising sulfur host, combining superior conductivity, strong polysulfide adsorption, and ultrafast catalytic kinetics, while Ta₂S₂C offers balanced anchoring and activity. This work provides atomic-scale insights for the rational design of advanced 2D electrocatalysts for high-performance Li–S batteries.