New insights into synergistic effects of La2O3 and nitrogen doped carbon for improved redox kinetics in lithium-sulfur batteries: A computational study

The La2O3/carbon/S composite electrode shows great performance in improving cycling stability and high-rate performance of lithium-sulfur batteries. Although it has been proposed to be attributed to the synergistic effects of La2O3 and carbon material, the roles of La2O3 and carbon, and the specific manifestation of the synergy are still unclear. In the current study, the first-principles calculation was carried out to clarify these questions. The investigation reveals that only polysulfide migration and polysulfide dimer cleavage steps were carried out on the surface of La2O3. That is, only a part of rather than all of the catalytic steps occur on the surface of La2O3. By comparison, the nitrogen doped carbon, which are generally considered to have no catalytic effect, play an important role in the catalytic discharge process by realizing twice lithiation-lithium diffusion and providing a fast migration path for polysulfide dimers. Therefore, the synergistic effect is the joint participation of La2O3 and nitrogen doped carbon in the polysulfide catalytic conversion, rather than simple combination of the catalysis for La2O3 and conductivity for nitrogen doped carbon. It is hoped that the explanation of synergistic effect would help to promote the application of rare-earth oxides in high-rate long-life lithium-sulfur batteries.