Novel pentagonal carbon-based materials as multifunctional electrodes in lithium-sulfur batteries, a theoretical study

The commercialization process of lithium-sulfur batteries (LISBs) is hindered by several problems, including low electroconductivity, the dissolution of lithium polysulfides (LiPSs) and sluggish charging-discharging kinetics. Recently, two-dimensional (2D) penta-furrow structures have emerged as a distinct family of 2D structures with low mass densities, which are predicted to accelerate redox kinetics and enable sulfur conversion. Here, several novel pentagonal carbon-based substrates, including penta-graphene (penta-G) and penta-B2C (C2N, C2P, C2Si, and N2C), were first investigated in LISBs based on density functional theory (DFT) calculations. It is found that the penta-G, penta-C2P and penta-C2Si have excellent anchoring ability and can greatly improve conductivity during the whole S8/LiPSs insertion, which can effectively suppress the shuttle effect. More importantly, penta-G, penta-C2P and penta-C2Si can reduce the free energy of sulfur reduction reactions to 0.63–0.68 eV and lower the energy barriers of electrochemical conversions to 0.82–1.57 eV (Li2S dissociation) and 0.05–0.14 eV (Li-ion diffusion), thereby enhancing catalytic conversion efficiency in the discharging/charging processes. In addition, penta-G showed a much smaller volume expansion (34 %) than the 80 % value for elemental sulfur and a considerable sulfur loading amount (53.78 wt%). Our findings demonstrate that metallic pentagonal carbon-based materials could be a potential LISBs cathode material with high performance.