Synergistic regulation of polysulfides immobilization and conversion by MOF-derived CoP-HNC nanocages for high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have drawn intense attention in the realm of electrochemical energy storage owing to their high theoretical energy density, as well as the natural abundance of sulfur and low cost. However, the severe shutting of polysulfides and sluggish reaction kinetics hinder the practical application of Li-S batteries. To solve these problems, MOF (ZIF-67) derived in-situ N-doped carbon nanocage embedded with CoP (CoP-HNC) as an efficient sulfur host for advanced Li-S batteries is proposed here. With the abundant porosity and cavity, hollow polar heteroatom N-doped carbon architecture can effectively alleviate volume expansion, buffer electrolyte and trap polysulfides. More importantly, the embedded polar CoP nanoparticles acted as an effective electrocatalyst not only anchor polysulfide intermediates, but also promote the redox kinetics toward polysulfides conversion remarkably, which is clearly proved by experimental results and DFT calculations. Benefiting from above advantages, Li-S batteries assembled with CoP-HNC electrode achieve a significantly enhanced sulfur utilization (about 800 mAh g-1 at 5 C), improved cycling stability and ultralow capacity decay rate of 0.02% per cycle after 1000 cycles. Even at high sulfur loading of 3.0 mg cm-2, the S/CoP-HNC electrode still delivers a high initial capacity of 866 mAh g-1 at 0.5 C. This work has guiding synergistically combining desired design and electrocatalysis in sulfur cathode for Li-S batteries.

Automated summary

A novel sulfur host material CoP-HNC is proposed in this study, which can significantly improve sulfur utilization and demonstrate excellent performance in terms of cycling stability and capacity decay rate.