Transition metal embedded C2N with efficient polysulfide immobilization and catalytic oxidation for advanced lithium-sulfur batteries: A first principles study

Developing highly efficient host materials to suppress the lithium polysulfides (LiPSs) shuttling and accelerate the Li2S conversion is essential for advanced lithium-sulfur (Li-S) batteries. In this work, based on first principles computations, we explored transition metal embedded C2N monolayers (M@C2N, M = Mn, Fe, Co, Ni, Cu) as host materials and catalysts for Li-S batteries. Our results show that M@C2N monolayers could prevent the LiPSs shuttling with strong adsorption energies towards LiPSs, due to the synergistic effect of M-S and Li-N bonds. Moreover, the presence of transition metal atoms in the C2N could improve its electric conductivity. On the whole lithiation process, all the adsorbed systems are still conductive, which is helpful to boost the sulfur utilization. Importantly, M@C2N monolayers could promote the Li2S decomposition and thus enhance the oxidation kinetics of Li2S back to sulfur. Among them, Co@C2N monolayer is the best host material, which possesses the largest adsorption energies with LiPSs and the lowest decomposition energy of Li2S. This work opens a new avenue for the development of host materials with excellent catalytic activity towards LiPSs, and also sheds light on M@C2N as superior cathode materials.