Coupled effect of TiO2-x and N defects in pyrolytic waste plastics-derived carbon on anchoring polysulfides in the electrode of Li-S batteries

Abstract

Lithium-sulfur (Li-S) batteries have the potential to provide high energy density but they suffer from shuttling phenomena that are detrimental to cyclic stability in such a way that lithium polysulfides gradually diffuse out from the cathode interface. We employed the pyrolysis residue from waste plastics for a carbon source and applied it as a cathode sulfur host for Li-S batteries to limit the shuttle effect. Annealing with the aid of KOH and the subsequent ammonia thermal treatment endowed the residue with hierarchical porosity that reached 30% mesoporosity of the total pore volume. N-defects were significantly introduced in carbon networks with edge-positioned states, which helped them chemically interact with Li moieties in the polysulfides. Furthermore, titanium sub-dioxide (TiO2-x) was formed as impurities after the thermal treatment effectively suppressed diffusion of the intermediates. Based on the coupled effect of both N-defects and TiO2-x, the prepared carbon contributed to retarding the decay rate of discharge capacity, and its decay rate decreased to 0.089% per cycle at 1 C until 500 cycles with a capacity of higher than 500 mAh g−1. This study offers a precedent for practical green design of waste plastic residues as a carbon source.